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HABILITATION THESIS

RESEARCHES ON POSSIBILITIES TO IMPROVE

ENGINES FUELLING

Assoc. Prof. Ph.D. Florin Emil MARIA IU Technical University of Cluj-Napoca

Faculty of Mechanics

Automotive Engineering and Transports Department

2015

Habilitation thesis – F. Mariasiu 1

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SUMMARY

PAGE

Acknowledgments!!!!!!!!!!!!!!!!!!!!!!!!!!!! 2

Abstract!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.. 3

Nomenclature!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 5

1. CONTEXT OF HABILITATION!!!!!!!!!!!!!!!!!!!!!. 9

2. RESEARCH DIRECTIONS AND COMPETENCES!!!!!!!!!!!!.. 11

3. RESEARCH ACTIVITIES AND RESULTS!!!!!!!!!!!!!!!!. 14

4. CONTEXT OF RESEARCH WORK!!!!!!!!!!!!!!!!!!!. 18

4.1. NECCESITY AND CONTEMPORARY CONTEXT OF RESEARCH ACTIVITIES!!!!!!!!!!!!!!!!!!!!!!!!!!!..

18

4.2. POSSIBILITIES TO INCRESE BIOFUEL’S POTENTIAL USED IN

INTERNAL COMBUSTION ENGINES FUELLING!!!!!!!!!!!

20

4.2.1. Effects of biofuel characteristics on injection process!!!!... 20

4.2.2. Effects of external energy (ultrasonic) application on biofuel use performances!!!!!!!!!!!!!!!!!!!!!!..

39

4.2.3. Possibilities to improve cold-start process of engines fuelled with biofuels!!!!!!!!!!!!!!!!!!!!!!!!!

55

4.2.4. Possibilities to reduce engine’s friction losses at cold-start!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

61

5. CONCLUSIONS!!!!!!!!!!!!!!!!!!!!!!!!!!!.. 75

6. CAREER DEVELOPMENT PLAN. !!!!!!!!!!!!!!!!!!! 77

References!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!. 79

Researches on possibilities to improve biofuel’s use in internal combustion engines fuelling 2

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Acknowledgments

Reaching a new level of development and professional training by supporting

habilitation thesis would not have been possible without the continued support of

those around me.

Without the unconditionally help of my family, confidence of department

leadership and collegiate collaboration with members of Automotive Engineering and

Transports Department, this would not be possible.

Therefore, now, all my thanks and good thoughts are turning to them.

Assoc. Prof. Florin Emil MARIASIU, PhD


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Abstract

The habilitation thesis in mechanical engineering domain of candidate (assoc.prof.

Florin Emil MARIASIU, PhD) represents the synthesis of educational and research activities

conducted at the Technical University of Cluj-Napoca, Department of Automotive and

Transportation.

Research directions addressed by the candidate are refers to investigate the

possibility of increasing the efficient use of biofuels in internal combustion engines fuelling.

As a result of research conducted, were identified contemporary issues which this topic

facing and using original and unconventional methods, were able to manage the issuance of

applicative and relevant solutions and conclusions presented through scientific articles and

books published.

The context in which candidate’s need to follow habilitation process is analyzed and

justified is found in the thesis’ first chapter (CONTEXT OF HABILITATION).

In the second chapter of habilitation thesis "RESEARCH DIRECTIONS AND

COMPETENCES", are presented the research directions followed by the candidate and skills

held by it, as a direct results of professional and academic development.

Chapter 3 entitled "RESEARCH ACTIVITIES AND RESULTS" reviews the scientific

results obtained through research activities. Are presented scientific articles, published books

in the field of biofuels and internal combustion engines, the experience in managing and

conducting research projects, awards and distinctions, patent applications, national and

international collaborations with academia.

The widely development and detailing of research activity in biofuels is being

conducted under Chapter 4 "CONTEXT OF RESEARCH WORK". Based on the summary of

the main articles published in important scientific journals, are presented research directions

and results. Were discussed issues related to the investigation of possibilities: to increase

the efficiency of biofuels use in internal combustion engines fuelling, to optimize engine cold

start process and to reduce engine friction losses. Solutions presented have an original and

unconventional approach on investigated topics (subjects), and also a applicative character

by issuing two patent applications based on the results of this research.

Opinion issued on this basis is found in a succinct (summary) form in the fifth chapter

of the habilitation thesis "CONCLUSIONS". It presents new research directions opened by

the results already obtained.

In the last chapter (Chapter 6 "CAREER DEVELOPMENT PLAN") are highlighted

current and future directions (on short- and long-term) in academic and research career and

directions to be followed by the candidate.


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Rezumat

Teza de abilitare în domeniul ingineriei mecanice a candidatului, conf.dr.ing. Florin

Emil MARIA!IU, reprezint" sinteza activit"#ii educa#ionale $i de cercetare desf"$urate în

cadrul Universit"#ii Tehnice din Cluj-Napoca, departamentul Autovehicule Rutiere $i

Transporturi.

Direc#iile de cercetare abordate de c"tre candidat se refer" la investigarea posibilit"#ilor de

cre$tere a eficien#ei utiliz"ri biocombustibililor în alimentarea motoarelor cu ardere intern".

În urma activit"#ii de cercetare desfa$urate, s-au identificat problemele contemporane

cu care se confrunt" subiectul tratat, iar prin utilizarea unor metode originale $i

neconven#ionale s-a reu$it emiterea de concluzii $i solutii aplicative pertinente, prezentate

prin intermediul articolelor $tiin#ifice $i a c"rtilor de specialitate publicate.

Contextul în care necesitatea abilit"rii în $tiin#" a candidatului este analizat" $i

justificat", se regase$te în primul capitol al tezei (CONTEXT OF HABILITATION).

În al doilea capitol al tezei de abilitare “RESEARCH DIRECTIONS AND

COMPETENCES”, se prezint" direc#iile de cercetare urmate de candidat $i competen#ele

de#inute de c"tre acesta ca urmare a dezvolt"rii profesionale $i academice.

Capitolul 3 intitulat “RESEARCH ACTIVITIES AND RESULTS”, trece în revist"

rezultatele $tiin#ifice ob#inute prin desf"$urarea activit"#ilor de cercetare. Sunt prezentate

articolele $tiin#ifice publicate, c"r#ile din domeniu, experien#a în managementul $i derularea

proiectelor de cercetare, premiile $i distinc#iile ob#inute, cererile de brevet de inven#ie,

colabor"rile na#ionale $i interna#ionale cu mediul academic.

Dezvoltarea pe larg a activitâ#ii de cercetare în domeniul biocombustibililor este

realizat" în cadrul capitolului 4 “CONTEXT OF RESEARCH WORK”. Pe baza sintezei

principalelor articole publicate în reviste (jurnale) $tiin#ifice importante, sunt prezentate

direc#iile $i rezultatele cercet"riilor efectuate. Au fost abordate subiecte ce #in de investigarea

posibilit"#ilor: de cre$tere a eficien#ei utiliz"rii biocombustibililor în motoarele cu ardere

intern", de optimizare a procesului de pornire la rece a motoarelor $i reducerea pierderilor

prin frecare. Solu#iile oferite prezint" caracterul original $i neconven#ional al abord"rii temelor

(subiectelor) investigate, dar $i caracterul aplicativ prin emiterea a dou" cereri de inven#ie

bazate pe rezultatele acestor cercet"ri.

Concluziile emise pe baza celor prezentate anterior, se reg"sesc într-o form"

succint" în cadrul capitolului al cincilea al tezei de abilitare “CONCLUSIONS”. Se prezint" $i

noile direc#ii de cercetare deschise de rezultatele deja ob#inute.

În cadrul ultimului capitol al tezei ( capitolul 6 “CAREER DEVELOPMENT PLAN”)

sunt reliefate direc#iile prezente $i viitoare (pe termen scurt $i lung) ale carierei universitare $i

ale direc#iilor de cercetare ce vor fi urmate de c"tre candidat.


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Nomenclature

%, &, ' - Bohac model constants

!’ - isentropic bulk modulus

( - density of the sample

)* - surface strain

)U - ultimate strain rate

+ - shape factor

, - corresponding stress

,' - yield stress for the injector material

,max - maximum stress allowed for injector material.

µ - oil dynamic viscosity

µref - oil dynamic viscosity, at 40 °C

A, B, and C - constants depending on the material (Antoine equation)

Bp - bore

BMEP - brake mean effective pressure

BSFC - brake specific fuel consumption

BXXUs_irr - abbreviation where XX represents the volumetric percentage of methyl ester in

the blends with the diesel fuel.

CI - compression ignition

CN - cavitation number

CFD - computational fluid dynamics

Ccb - coefficient of the hydrodynamic losses in main bearings

Ccs - coefficient of friction losses in main bearings seals


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Cp - proportionality constant (related to surface roughness)

Cpb - coefficient for connecting rod bearing hydrodynamics

Cps - coefficient for skirt-cylinder wall hydrodynamics

Cpr - coefficient for piston ring-cylinder wall

Cvb - coefficient for camshaft bearing hydrodynamic

Cvf - flat cam follower constant

Cvh - oscillating hydrodynamic lubrication constant

Cvm - oscillating mixed lubrication constant

Cvs - boundary lubrication constant due to the camshaft bearing seals

Db - bearing diameter

Eus - ultrasonic energy

FAMEs - fatty acid methyl esters

FMEP - friction mean effective power

Fmeppiston - piston group friction mean effective pressure

Fmepaux - auxiliary losses

Fmepcam - friction losses of camshaft

Fmepcrankshaft - crankshaft friction mean effective pressure

Fmepvalvetrain - friction mean effective pressure in the valve train

IC – internal combustion

IMEP - indicated mean effective pressure

K -factor dependent on the injector nozzle material

l - thickness of the hardened layer

L - maximum thickness of the hardened layer

Lb - bearing length


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Lv - maximum valve lift

MDPR - Mean Depth of Penetration Rate (erosion estimation rate)

n - oil lubrication viscosity index

nb - number of bearings

nc - number of cylinders

nss - stress–strain relation exponent

nv - number of valves

N - engine speed

Ni - impacts per unit area

NOx – oxides if nitrogen

OHV – overhead valvetrain

pinj -pressure at the inlet of the nozzle

pout - pressure at the outlet of the nozzle

pvap - vapor pressure

pvap_i - vapor pressure of the ith pure of xi FAME component

pvap_mix - total vapor pressure of the mixtures

Pus - ultrasonic power

RME - rapeseed methyl ester

R-PVO - rapeseed pure vegetable oil

s - speed of sound in fluid

S - stroke

Si - size of the impact loads

t - time

T – temperature

Vp - piston average speed


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VBD - volume of irradiated biofuel (biodiesel)

VOF - volume-of-fluid

u - speed of sound

W – energy

WD- wheel drive


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1. CONTEXT OF HABILITATION

The process of habilitation is based on modern and contemporary need to improve

processes that characterizing higher (academic) education, through the educational,

research and institutional components, at the level of each staff member (or functional

entities) of higher education institution structure.

Details of the educational and research route (path) provide necessary information to

identify existing competences and skills, with potentially in determining individual

complementarity of candidates with academic environment.

Habilitation process provides a snapshot of academic career by nominating and

outlining past, current and future directions in candidate’s professional activities; and further,

help to correlate these activities, with the overall institutional development directions of the

department and/or the university.

Obtaining the certificate of habilitation will be for each member of the academic

community (committed and connected requirements contemporary academia), in a defining

manner, a tool to be used, constantly updated and adapted to modern trends and

requirements of science education, research activity and economy.

Realization and completion of all these activities should be viewed in terms of

increasing the efficiency of teaching (and transmission) to PhD student of the mandatory and

specific competences and skills require by research’s activity and management.

Beside those mentioned above, the context and necessity of habilitation is strongly

conditioned by following issues:

• Mandatory conditions imposed by Technical University of Cluj-Napoca’s internal

methodology to obtain the title of professor


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• Necessity and willingness to transfer the accumulated knowledge in scientific

research and also the knowhow in management of research activities to younger

researchers

• Demands from former students to continue at PhD level the developing of ideas,

problems and researches studied already for bachelor and/or master thesis.


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2. RESEARCH DIRECTIONS AND COMPETENCES

The characterization of candidate’s research activity is a multi- trans- and inter-

disciplinary one, with the main goal of investigating the limitations of biofuels use in internal

combustion engines and to offer proper (and also applicative) solutions to improve their use.

The complexity of research activity is given by the numerous factors of influence

responsible of possibilities to optimize the internal combustion engines when biofuels are

used. The influences of biofuels physico-chemical characteristics were studied in aim to

improve engine’s performance in terms of: energetic efficiency, pollutant emission (especially

NOx pollutants) and friction losses (Figure 1). Each research was finalized by offering a

proper and/or applied solution (patent application).

Figure 1. Major direction of researches


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The approaches on this particularly issues need to use complex a combined

knowledge from different domains:

• Thermodynamics, Physics - the analysis of combustion processes inside the

combustion chamber of an internal combustion engine;

• Chemistry - determining mechanisms and formation influence factors of pollutants

classes in exhaust gases emitted into the atmosphere by internal combustion engines;

characterization of biofuels properties.

• Mechanical - establishing optimal operating points considering the ratio effective

power / emissions level, in the operation of internal combustion engines

• Tribology and Wear – identifying the magnitude of friction and the possibilities to

reduce the engine’s mechanisms wear, to increase overall the engine efficiency.

• Mathematics, Statistics and Computer Simulation - setting theory and mathematical

structure of the models; determine the dependency relations; analyses of experimental

data.

• Management - management of the research projects (and related activities)

• Experimental techniques - use of modern equipment and instrumentation to identify

the parameters that govern the important processes in the formation and emission of

toxic and carcinogenic pollutants

• Environmental issues – modern experimental techniques for investigating pollutant

emissions

• Human healthcare – assessments on pollutant emissions effects on humans.

Those necessary multidisciplinary competences, skills and knowledge were developed

by candidate since PhD graduation (2003) and used in candidate’s research activity, trough a

permanent training and education.

The competences and skills of candidate can be summarized as follow:

1. Professional

a) Advanced knowledge and skill in IC engines functional processes

b) Advanced knowledge and skills in IC engine simulation

c) Capacities and abilities of identification, definition and solving of specific

problem in IC engines processes in general and in pollutant emissions


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processes in particularly

d) Advanced skills in modern research methods and methodology for optimal

design, modelling, analysis and experimental testing of IC engines

2. Educational

a) Information and knowledge transfer to students

b) Implication of colleagues and students in research and educational activities

c) Analyse of students’ demands, perceptions and assessments on educational

program

d) Use of TIC and blended learning in teaching and educational activity

3. Transversal

a) Very good abilities in personal and inter-personal communication

b) Proactive approach of problems

c) Good abilities in human and material resources management


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3. RESEARCH ACTIVITIES AND RESULTS

The research topics addressed by the candidate are topics of nationally and

internationally interest, through research and studies on the possibilities of integration and

widespread use of renewable resources in energy production.

In particular, due to education, knowledge and expertise of the candidate, those

research (and educational) activities aimed further, novelty and original possibilities to

increase the energy efficiency of internal combustion engines and also the possibilities on

large-scale use of biofuels in internal combustion engines fuelling.

The major challenge in candidate research activity was the successful completion of

PN II Idei Exploratorii ID 175 project, as project manager (director). The project theme

regarded the investigation on external energy apply effects on internal combustion engines

fuelled with biofuels. The accumulated experience and new directions open in candidate’s

research activity from this project, has enabled to continue research in this field, but (perhaps

more importantly) helped to mature process of candidate as researcher.

Taking into consideration the objective demands of Romanian educational system, the

research activity is closely correlated with educational and academic activity. The

dissemination activities of research’s results were done to national and international scientific

community and also to the colleagues and students.

The results of research and educational academic activity can be summarized as:

• 4 text books as single or first author

• 4 text books as co-author

• 1 e-learning course (“The management of transport vehicles’ engines”-

DIDATEC E-learning platform)

• 41 scientific articles as single/first author and co-author of 35 scientific articles

presented at national and international conferences and symposiums and/or


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published in scientific journals (10 indexed in ISI-Thompson and ISI-

Proceedings; 28 indexed in international database (Web of Science, Scopus,

Google Schoolar, Fisita, CABI, Copernicus, EBSCO, ProQuest), 12 citations)

• 1 national research grant as director and 8 as team member

• 1 European funded project as short-term expert

• 7 articles published in mass media journals (related to the specific of biofuels

research)

• Main author of 2 patent applications (RO 127 032-A2, "Cold start device of

internal combustion engines fueled with biodiesel" and RO 128 768-A2,

"Device to reduce lubricating oil viscosity for internal combustion engines start

at low ambient temperatures ")

• Coordinator of more that 150 bachelor and master thesis

• Coordinator-professor of students participating to Rexroth/Aventics Pneumobil

Race contest (2009-2015) – air-powered prototype vehicles.

The competences, abilities and skill s accumulated by candidate trough entire period of

research activity offer opportunities to collaborate with national and foreign researchers.

Strongly contacts were made with researchers from abroad:

• Germany (prof.dr. Stefan Stolte – University of Bremen, Centre of

Environmental Research and Sustainable Technology (UFT); dr. Dana

Kralisch - Friedrich-Schiller-University Jena)

• Austria (Prof. Dipl. Hans-Georg Frantz MPBL - FH JOANNEUM, Kapfenberg)

• Norway (dr. Otto Andersen – Stiftinga Vestlandsforsking/Western Norway

Research Institute - WNRI, Sergio Manzzeti – Fjordforsk A.S.)

• Slovakia (Dr Pavol Hvizdos - Institute of Materials Research\Slovakia

Academy of Science)

• Slovenia (Dr. Ema Zagar - Head of Laboratory for Polymer Chemistry and

Technology, National Institute of Chemistry)

• Swisserland (Dr. Nabil Ouerhani, Institut des Systèmes Interactifs et

Communicants-ISIC-Arc, Neuchatel)

• Hungary (Dr. Brigitta Bodzay - Budapest University of Technology and

Economics)

• Estonia (assoc. prof. Hans Orru - University of Tartu)

• Russia (prof.dr. Vladimir Vilorievich An, prof.dr. Yuri Borisov, prof.dr. Valery

Perminov – Tomsk Polytechnic University)

• Serbia (prof.dr. Lazar Savin – University of Novi-Sad)


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• Poland (dr. Anna Kowalska – Wroclaw Institute of Technology)

, and at national level:

• National Institute for Research and Development and Environmental

Protection (INCDPM) - Bucharest

• Ceprocim SA - Bucharest

• Research Institute Ceprocim SA - B Bucharest

• Agricultural Science University of Banat - Timisoara,

• University of Oradea.

The collaboration with above presented colleagues was under form of participation in

joint research teams for ERA NET, CNCSIS and SEE calls proposals and co-authors of

scientific articles (in progress).

Considering that professional training is required to be performed continuously for up to

date with the latest news and findings in research activity, the candidate participated at

national and international scientific conferences and symposiums, as well as, followed

postgraduate training courses:

• To use modern equipment for IC engines testing procedures (AVL -

2010/2011)

• To use and apply of modern means and techniques in education

(DIDATEC - 2010/2013)

• To use modern methods in management (Southern Connecticut State

University (USA) and Leader XXI Foundation - 2004/2005)

• Certificated as Project Manager for projects financed with European

funds (CNFPA - 2010).

The results of research carried out on possibilities to increase the use of biofuels, were

awarded by:

• Award for research activity UEFISCDI - PN-II-RU-2382 PRECISI- 2013-

7-2382 program (Romanian Executive Unit for Financing of High

Education, Research, Development and Innovation).

• Diploma of Excellence and the Gold Medal at the International


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Exhibition of Research "ProInvent 2014" Cluj-Napoca, Gold Medal at

the International Exhibition "Inventica 2014" Iasi and Silver Medal at

International Exhibition "Inventika" Bucharest 2014, for patent

application RO 127 032-A2, "Cold start device of internal combustion

engines fueled with biodiesel", authors: Mariasiu F., Burnete N., Varga

B.

• Award of Excellence at the International Exhibition of Research

"ProInvent 2012" Cluj-Napoca for patent application RO 128 768-A2,

"Device to reduce lubricating oil viscosity for internal combustion

engines start at low ambient temperatures ", authors: Mariasiu F., Varga

B., Deac T.

The candidate activate as editor inside editorial group for Central European Journal of

Engineering (Energy & Fuels domain), and as reviewer for several mainstream scientific

journals: Energy Conversion and Management, Tribology Transactions, Transport, Annals of

Operational Research, Central European Journal of Engineering, African Journal of

Agriculture Research, International Journal of Energy Technology and Policy.

As can be see, both research and educational activity of candidate demonstrate the

competences, abilities and skills necessary to confirm the habilitation process (obtaining the

habilitation title), process can be considered further to be a stimulant for continues the

academic activity on higher standards.


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4. CONTEXT OF RESEARCH WORK

4.1. NECCESITY AND CONTEMPORARY CONTEXT OF RESEARCH ACTIVITIES

Contemporary society is fully characterized by the concept of 'mobility'. Mobility of

ideas, people and goods requires a high dynamic of vehicle use in everyday life by

human society. Unfortunately with the use of motor vehicles (as means of transport)

there are immediate problems related to environmental pollution, caused by pollutant

emissions from the combustion of fuels.

Transportation sector is currently responsible for over 20% of the emission of

greenhouse pollutants, emission that directly affect climatic conditions of the planet.

Increased emissions in conjunction with achieving maximum degree of natural

regeneration of the environment, leading to serious problems related to pollution.

Naturally, the European Union (mainly) occurred policies and actions to reduce

emissions from activities associated with human society.

As an immediate energetic solution to reducing atmospheric pollution caused by

compression–ignition (CI) engines, biofuels offer (with some limitation) a viable

alternative to fossil fuels due to their renewable characteristics. Also, the use of biofuels

is considered to be the short-term solution, until new proposed technologies (e.g. electric

vehicles) will be mature. Starting from this premise, the European Union establish

mandatory regulations that stipulate the use of min. 10% of biofuels in blends with fossil

fuels (dead line for members to implement the EU Directive 2009/28/EC is 2020 year -

[17]).


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Figure 2. The renewable character of biofuels

In addition to the advantage afforded by closing the natural CO2 life cycle (Figure 2),

utilization of biofuels for powering internal combustion engines is immediately possible

without major structural changes to the engines and fuel distribution network. In

transportation domain, standards and regulations related to exhaust emissions, are

becoming increasingly stringent, relative to the maximum quantity of exhaust gases,

which is accept to be emitted into the atmosphere, from the operation of an internal

combustion engine. The adoption of constructive solutions to achieve this goal it is

absolutely necessary but not sufficient (due to economic efficiency).

Therefor, due to the complex characteristics and particularities of a internal

combustion engine functioning, it is necessary to conduct complementary studies and

researches related to the occurring processes in internal combustion engines and their

optimization (by increasing energy efficiency) for lowering emissions level, in case of

biofuels use.

The issues related to the specific conditions of internal combustion engines

processes (and their subsequent effects) is require today an immediate, novelty and

original approach, but using good scientific arguments, modern and efficient methods

and approaches (but also unconventional) in research activity. Based on these premises,

were crystallized, developed and maintained the scientific activity of the candidate, with


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the major purpose of investigating any possible improvement in operation of internal

combustion engines fuelled with biofuels. The detailed directions of candidate researches

and results will be presented in following chapters, based on the articles published by

candidate in ISI Thompson indexed journals and on patent applications.

4.2. POSSIBILITIES TO INCRESE BIOFUEL’S POTENTIAL USED IN INTERNAL COMBUSTION ENGINES FUELLING

The researches of candidate related to identify direct actions to improve energetic

efficiency of compression ignition (CI) engines and also to reduce pollutant emissions, were

done trough complex analysis of factors of influence (both, qualitative and quantitative) by

biofuels use in CI engines fuelling. The studies and researches were conducted at:

A) Microscopic level (effect of biofuel characteristics on nozzle injector

cavitation process)- modern approaches trough CFD simulation techniques.

B) Macroscopic level (effect of applied ultrasonic external energy on biofuels

physico-chemical characteristics and reduction of engine friction losses) –

unconventional approaches trough ultrasounds use.

4.2.1. Effects of biofuel characteristics on injection process1

It is widely know that, biofuels can be used both in the form of methyl esters (and/or

mixed with diesel fuel) and as pure vegetable oil (PVO) to fuelling a compression ignition

engine (diesel engine). However, there are problems with cold engine starts (caused by their

lower energy content, higher viscosity, and cloud point value) and their high emissions of

NOx compared to fossil fuels. The NOx emissions are high due to both the existence of

oxygen in the molecular composition of biofuels as well as the particular issues created by

the characteristics of the fuel injection process of compression ignition.

The density of high viscosity of biofuels result in a poorer quality fuel spray in terms of

jet breakup, penetration, and atomization, with direct effects on functional performance and

engine emissions (compared to petro diesel [39]). In particular, fuel atomization !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"!#$%&!'()$*!+,-!.(/0()012!34!567"89!:1;$/0<(=!>,?$)&0@(&0+,!AB!#C$!DBB$<&)!AB!E0+B1$=!FC(/(<&$/0)&0<)!A,!#C$!>,G$<&+/!:+HH=$!D/+)0+,!I/+<$))J2!#/0'+=+@K!#/(,)(<&0+,)!LM569-!"M"N"MO4!

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characteristics depend on both the injection processes (pressure, timing, rate [58]) and the

geometric characteristics of the injector nozzle (orifice discharge coefficient, inclination angle

of the nozzle hole, radius of the inlet of the nozzle orifice, diameter of the nozzle exit [83],

[85]). Experiments conducted by Gavaises and Andriotis [20], He and Ruiz [26], Nurick [50],

and Tamaki et al. [71] showed that nozzle orifice erosion due to cavitation can lead to

negative changes in fuel jet temporal development and directly influence the performance of

the engine’s injection process.

Many scientific papers have studied the cavitation phenomena, in terms of

mathematical model development (to accurately describe the many processes and factors

that influence the particularities of cavitation flow), computer simulation, or physical models.

From the point of view of theoretical considerations, according to the assumption of

Giannadakis [22] and Giannadakis et al. [23], cavitation phenomena are attributed to the

dynamics of small bubble nuclei, which are nucleated in the liquid after certain criteria are

met. Further, the cavitation bubbles, influenced by direct interaction with the liquid flow, break

up and coalescence, especially in the case of a nozzle injector (characterized by very high-

pressure injection, short injection rate, and small orifice discharge coefficient).

From the early experiments of Badock, et al. [3] it was found that the cavitation number

(CN) is independent of the Reynolds number and can be calculated using Eq. (1):

!" ! !!"#!!!"#!!"#!!!"#

(1)

, where pinj is the pressure at the inlet of the nozzle, pout is the pressure at the outlet of the

nozzle, and pvap represents the vapor pressure. Research in the cavitation domain has

shown that calculation of the cavitation number is not sufficient to characterize the fluid flow

[45], [46]; flow scale effects (associated with the imperfect micro- and macro-geometry of the

flow [59]) and liquid quality (in particular the viscous nature of the flow [81]) affect the quality

prediction of cavitation characteristics of fluid flow.

Roosen et al. [59] and Winklhofer et al. [81] showed that the cavitation of fluids is

characterized by the same strain rates but different viscosities and reported that they found

differences between calculated (predicted) and experimental results. Furthermore, they

showed that the shear stress mechanism of cavitation is consistent with the measurements

of cavitation flows in liquids with different viscosities. As Qu et al. [56] showed, the modern


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and advanced heavy-duty diesel fuel injection system will be required to operate at higher

pressure and temperatures and with fuels that have poorer lubricity (the ability to reduce

friction between moving parts in a machine or mechanism). These characteristics indicate a

greater probability for cavitation phenomena with a direct influence on fluid flow

characteristics [37], [80].

Therefore, this work presents the results of computational fluid dynamics (CFD)

simulation concerned with the erosion phenomena in the injector nozzle for different types of

biofuels, considering that are important differences between the viscosities of petro diesel

fuels and biodiesels [39], [40].

Starting to the computational model considerations, the CFD cavitation model

implemented in the FIRE software package (AVL Advance Simulation Technologies [1]) is

based on a Eulerian-Eulerian approach and is suitable for the presented injector orifice type

and the considered conditions of functionality. Multiphase flow can be simulated in this way

because each individual fluid is considered as a continuous phase, and conservation laws

are applied for each fluid. The Eulerian-Eulerian approach is capable of handling an arbitrary

number of phases and allows the use of the following complementary models [1]:

• Homogenous (equilibrium) model—a volume fraction equation is calculated

for each phase but only a single momentum r equation is calculated because

the phases are assumed to be in momentum equilibrium.

• Multi-fluid model—the complete set of the conservation equations for each

phase is considered for calculation. These equations are coupled through the

interfacial interactions derived through an averaging process.

• Volume-of-fluid (VOF) free-surface model—based on solving the VOF

equation using a higher order discretization scheme and used for capturing

sharp interfaces of immiscible fluids.

The multi-fluid model was adopted to simulate multiphase flow, because offer the

possibilities to calculate a complete set of conservation equations (momentum and energy),

for all phases by coupling through the interfacial interaction derived through the averaging

process. For brevity, further details of the physical model and governing equations can be

found in AVL Advance Simulation Technologies documentation [1].

Using the above considerations, the FIRE software package was applied to simulate

the flow of fuel in injection nozzles in IC engines. In addition, the Eulerian approach can be

adopted for application where the bubble collapse process induces erosion damage through

a moment method by solving the bubble number density (average number of bubbles per


!

!

unit volume) equation and the interfacial area density equation [6], [18].

The erosion process model implemented in the FIRE software package is based on

the work of Berchiche et al. [6] and Franc and Riondet [18]. The erosion estimation rate is

given by:

!"#$ ! !! ! !! ! !! ! !! ! !! ! ! !!!!

!! ! ! (2)

where Ni, Si, and L are the impacts per unit area (1.9-1011), the size of the impact loads

(1-10.9), and the maximum thickness of the hardened layer (2-10.3 m), respectively. The

theta factor (+ = 3) is considered the shape factor and )* and )U are the surface strain and the

ultimate strain rate related to the corresponding stress , by Eq. (3):

! ! !! ! !!!!! (3)

In Eq. (3) ,' is the yield stress for the injector material (4-108 Pa), K is the K-factor, and

nss = 0.5 is the stress–strain relation exponential. The K-factor depends on the injector nozzle

material dependent (K = 8.64-108 [1]).

The surface strain rate )* can be obtained by considering the energy law of

conservation and considering the thickness of the hardened layer (l = 2-10.4 m):

( )( )!"#

$%

&

++++

+''=

(()

(

*)) +

nnKSlW

n

111)(

(4)

After the incubation period, at steady state (the number of bubbles follows a linear

growth law and the erosion rate has a constant value—the material removal rate reaches

steady state, represented by Mean Depth of Penetration Rate [MDPR]), the system energy is

considered to be:

( ) ( ) ( )Ul WWW !!! +=' (5)


!

!

where )l is computed with the strain rate stress estimated by Eq. (6):

!"

#$%

&'(

)*+

,= max,min -.-dt

drsC bubblelpl

(6)

! The coefficient Cp = 1 is the proportionality constant (related to surface roughness), s is

the speed of sound in fluid (Table 1), and ,max = 8.64-108 Pa is the maximum stress

allowed for injector material.

Using as a mean indicator, the MDPR, it is possible to indicate how the cavitation

process influences the material erosion. Considering the incubation time of the cavitation-

type flow, the MDPR (as a function of the impact rate, impact size, and material properties)

take into consideration geometrical changes as a result of material erosion due to cavitation

and, hence, their effect on the fuel spray behavior in the combustion chamber [9], [61].

In order to investigate the effect of fuel characteristics on nozzle erosion phenomena,

three different fuels were considered: diesel fuel, rapeseed methyl ester (RME), and

rapeseed pure vegetable oil (R-PVO). The characteristics of the fuels used and the main

boundary conditions of the computational simulation to determine the erosion process are

presented in Table 1.

The boundary conditions specify the physical properties of the faces on the volume

mesh. The boundaries of the volume mesh include the inlet, outlet, and wall boundary.

Considering the particularities of the cavitation process, boundary conditions will require

specification for two phases (liquid and gas). For both phases, the inlet boundary conditions

turbulent kinetic energy and turbulent length scale were adopted as 0.1 m and 0.001 m2/s2,

respectively.

For the outlet boundary condition the fixed volume fraction was adopted for the liquid

phase (0.999) and the gas phase (10.6). To define the wall boundary condition the velocity

components were all set to zero and the temperature was considered to be 293.15 K.

The model was discretized using least square fit method to calculate the derivatives

and considering both phases, the following under relaxation factors were adopted:

momentum = 0.3, pressure = 0.1, turbulent kinetic energy = 0.15, turbulent dissipation rate =

0.15, energy = 0.8, and mass source = 1.


!

!

Table 1. Simulation conditions for fuels

Parameter Diesel fuel

(Diesel)

Rapeseed methyl ester

(RME)

Rapeseed pure vegetable oil

(R-PVO)

Density

[kg/m3] 830 a 880 a 890 a

Dynamic viscosity

[x10-3Ns/m2] 2.14a 4.61a 6.31a

Saturation vapor

pressure

[kPa]

892b 0.923c 0.996c

Sound speed

[m/s] 1370a 1415a 1502a

Fuel temperature

[K] 293.15 293.15 293.15

Bubble number density

(x1011) 1.9 1.9 1.9

Critical distance of

bubble collapse

[x 10-6m]

5 5 5

a-[40]; b-measured; c-calculated from Eq.7-8.

Pressure boundary conditions were considered for the inlet and outlet of the injector

nozzle. The pressure at the inlet of the nozzle was set to 500 MPa (at injected fuel

temperature of 293.15 K), and the outlet pressure was set to 5 MPa. The vapor pressures for

the cavitation mass exchange for the considered fuels are presented in Table 1. Because the


!

!

RME and R-PVO are a mixture of many fatty acid methyl esters (FAMEs), the total vapor

pressure of the mixtures could be calculated using Raoult’s law, defined as Eq. (7):

! "=i

iivapmixvap xpp __ (7)

where pvap_i and pvap_mix are the vapor pressure of the ith pure FAME and the mixture,

respectively, as research methodology presented and used by Yuan et al. (25).

For each FAME component, the vapor pressure was calculated based on the work and

results of Mariasiu et al. [40], Yuan et al. [84], and Goodrum [25], using the Antoine equation

as defined in Eq. (8):

CTBApvap +

!=)log(

(8)

, were A, B, and C are constants depending on the material and T is temperature.

For numerical investigation of cavitation and erosion processes in a nozzle injector, a

VCO-type multihole injector was considered. The geometrical model and characteristics were

built into the computational model, presented in Figure 3. Because the injector holes were in

a symmetric distribution along the axis of the injector and because they were also in a

circumferential distribution, for the computational simulation a 30o segment model was

adopted. The moving grid was built to achieve a mesh of about 180,500 cells. The hole was

meshed with 116,448 cells (with an average size of 3 µm). The body and the rest of the sac

were meshed with 74,564 cells. The domain of the constant-volume vessel was built from

approximate 400,000 cells, characterized by a constant mesh size of 0.30 mm.

The sector angle of the nozzle flow simulation was considered to be at 180o, and the

angle between the axis of the cylindrical nozzle and the injector cone was 75o. The length

and exit diameter of the nozzle were 1.05 and 0.22 mm, respectively. The injector model was

based on a joined moving mesh type considering the movement of the injector needle in the

injection process, according to observations made by Ngondi et al. [49], to improve the

quality of the results (Figure 4).


!

!

Figure 3. Computational segment model.

Figure 4. Injector needle movement law


!

!

Table 2. Spatial coordinates of injector nozzle computational model

Parameters Coordinates [m]

x y z

Nozzle direction 0 1 0

Hole center -5.1·10-5 -1.09·10-4 0

Hole direction (spray axis) 1.65·10-4 -4.4·10-5 0

To improve the input data from the simulation model, the movement of the injector

needle law was correspondent to the experimental data achieved from the engine test bed;

the values were averaged from 100 sets of data.

The simulation time for the cases considered was set to 2.5 ms with a maximum

injector needle lift of 0.5 mm. Spatial coordinates that define the nozzle position are

presented in Table 2 and Figure 3.

For the simulation process, the convergence criteria considered a maximum of 500

iterations and a minimum of 5 iterations. Normalized residuals were 0.001 for pressure and

momentum and 0.005 for turbulent kinetic energy.

Considering the results and observations of Som et al. [67], two models were adopted

for the injection spray development in a combustion chamber. To predict the spray evolution,

the Kelvin-Helmholtz-aerodynamic cavitation turbulence model (KH) for primary liquid

breakup and the Kelvin-Helmholtz-Rayleigh-Taylor model (KH-RT) for secondary droplet

breakup were used [1].

For model validation, the simulation results were compared with the experimental data,

considering two important characteristics of jet fuel (penetration length and cone angle).

Experimental data were obtained from experiments performed on an engine test stand

developed by AVL GmbH (Graz, Austria). The experimental stand consists of an AVL 5402

optical diesel engine, single cylinder, direct injection with common rail injection (1,800 bar

maximum injection pressure (AVL List GmbH, Graz, Austria)), Bosch CR1 injector, bore 85

mm, stroke 90 mm, con rod 138 mm, 17.5 compression ratio, and ETAS ETK 7.1 ECU

engine management system.


!

!

An AVL Visioscope system was used for video acquisition of fuel spray development

inside the combustion chamber and an AVL rapid prototype electronic management system

was used to record the movement of the injector needle law.

Table 3. Average values of considered erosion and cavitation indicators

Parameter average

value

Fuel density [kg/m3]

830 880 890

MDPR

[x 10-12m/s] 6.65 6.31 5.88

Turbulence kinetic energy

[m2/s2]

16436.01 16179.81 16127.17

Velocity at nozzle exit

[m/s]

876.63 699.36 657.25

The results from the computational simulation were focused on the erosion processes

developed in the volume of a nozzle injector, which are graphically presented only for three

positions of moving injector needle, corresponding to 0.0055, 0.0083, and 0.011 s from the

start of the injection process (Figure 5). Validation of the model was performed by

comparisons with experimental results considering the spray length penetration and cone

angle.

Erosion process that characterized the flow regimes was evaluated in terms of the

MDPR factor, turbulence kinetic energy, and nozzle exit velocity. The turbulent kinetic energy

was higher for petro diesel fuel, and all simulated fuels presented peak values (17,663 m2/s2

for diesel, 17,474 m2/s2 for RME, and 17,377 m2/s2 for R-PVO) at 1.67 msec from the start of

the injection process (Figure 5).

The effects of the fuel characteristics on the magnitude and spatial development of the

cavitation process are presented in Figures 6 and 7.


!

!

The values of the MDPR factor increased gradually to maximum values of 1.30-10.11,

1.20-10.11, and 1.10-10.11 m/s for the simulations using diesel fuel, RME, and R-PVO,

respectively. It can be seen (Figure 7) that the erosion process developed up and down the

volume of the injector nozzle entrance (considering the axial axis of the nozzle injector) with

a maximum area (and magnitude) of development with regard to the petro diesel fuel.

The differences in magnitude of MDPR between the simulated fuels were smaller at the

start of the injection process (.3.76% for RME and .13.69% for R-PVO compared to diesel

fuel) than at the end of the injection process (.7.69% for RME and .15.38% for R-PVO

compared to diesel fuel). The same tendency was observed for the fuel velocity at the nozzle

exit (Figure 8). At the end of the injection process, the differences between the values

(664.06 m/s for diesel, 353.92 m/s for RME, and 263.04 m/s for R-PVO) were much higher

than those determined at the start of the injection process (1,089.8 m/s for diesel, 1,056.7

m/s for RME, and 1,050.1 m/s for R-PVO).

The average values of the parameters investigated using CFD simulation for the

whole injection process are presented in Table 3; these values highlight the differences

between the fuels. The variations in the considered indicators (erosion, turbulent kinetic

energy, and velocity at nozzle exit) are presented for all injection periods in Figures 9–11.

The magnitude of the injector nozzle cavitation erosion process was greater for diesel fuel

compared to RME biodiesel and R-PVO (+5.11% and +11.57%, respectively). The

turbulence kinetic average values were not very different depending on the fuel considered.

Variations in turbulence kinetics for RME and R-PVO cases were .1.56 and .1.88%

lower than for diesel fuel, respectively. A .20.22% difference between biodiesel (RME) and

diesel fuel and a .25.02% difference between R-PVO and diesel fuel was recorded from the

velocity magnitude at the nozzle exit. Considering the above-presented results, the effects of

cavitation strongly influenced the magnitude of nozzle exit velocity for RME and R-PVO

(compared to diesel fuel).

The field of speed uniformity at the exit of the injector nozzle using RME and R-PVO

(compared to diesel fuel) explained the differences between the spray structures, differences

already presented in previously published experimental research [15, 44, 60, 65].


!

!

Figure 5. Turbulent kinetic energy along the nozzle axial direction.


!

!

Figure 6. Variation in MDPR parameter (top view).


!

!

Figure 7. Variation in MDPR parameter (bottom view).


!

!

Considering the results presented in Figures 9–11, the following observations can be

made: The fuel injection velocity at the nozzle orifice exit is an important parameter with

further influence on spray development in the combustion chamber being directly influenced

by cavitation process. The differences in injection velocity patterns (Figure 11) also influence

the fuel mass rate flow rate at the orifice exit. For the same injection period (compared to

diesel fuel), a lower quantity of biodiesel (RME and R-PVO) is injected in combustion

chamber. This can explain the lower engine effective power when biodiesel is used.

Figure 8. Velocity pattern at the injector nozzle exit.


!

!

Figure 9. Erosion estimation rate variation vs. fuel density.

Figure 10. Turbulence kinetic energy variation vs. fuel density.

From the point of view of turbulence kinetic energy at the nozzle exit, the average

values were also lower for biodiesel (compared to diesel fuel) as a direct influence of lower

Reynolds number (due to higher viscosity). The differences in turbulent kinetic energy values

and patterns have direct implications for spray development and characteristics. The

turbulent kinetic energy pattern at the orifice exit influences the primary breakup and the

spray penetration length. The biodiesel spray has more homogeneous structure and drop

size. Thus, the biodiesel droplets agglomerate quickly, leading to greater penetration of the

jet inside the combustion chamber.


!

!

Figure 11. Magnitude of fuel velocity at the nozzle exit vs. density.

Figure 12. Comparison between simulation and experiment for RME spray development.

Figure 12 presents the spray penetration (development) in the combustion chamber for

RME fuel, in a comparative presentation of experimental and computational results (as an


!

!

example to validate the computational model). The computer simulation of a spray jet

showed the tendency of RMS fuel drops to agglomerate as a direct effect of exit nozzle

velocity pattern and values.

The spray penetration length predicted from simulation considering (not considering)

the influence of cavitation was 0.74% (.1.48%) for diesel fuel and 1.8% (.2.45%) for RME

compared to the experimental results (Figure 13). The differences for the cone angle

between predicted and experimental results considering (not considering) the influence of

cavitation were 2.27% (.3.64%) for diesel fuel and .1.02% (4.06%) for RME (Figure 14).

The results obtained from computer simulation were consistent with the experimental

results that showed that the penetration length was higher for RME (R-PVO) fuel corroborate

with a smaller spray cone angle than diesel fuel (and confirmed the results of other

researchers, including Som et al. [67] and Wang et al. [78, 79]), leading to the conclusion

that in the future simulations the effects of cavitation on spray behaviour must be taken into

consideration.

Figure 13. Measured and simulated fuel spray liquid length penetration.

!


!

!

Figure 14. Measured and simulated fuel spray cone angles.

As a major conclusion, the results obtained by CFD simulation confirmed the direct

effects of fuels’ physical properties on the phenomenon of injector nozzle cavitation and

erosion, with immediate influence on the quality of jet fuel, emissions, and operational

performance of CI engines.

The effects were highlighted by the differences in MDPR, turbulence, and nozzle exit

velocity for the cases studied.

The lower magnitude of the cavitation process and turbulence intensity for RME and

R-PVO fuels (compared to diesel fuel) was the direct effect of lower vapor pressure and

greater viscosity, respectively, of biodiesel fuels. The immediate effects at the nozzle exit

were highlighted by the higher spray penetration, poor primary breakup process, and smaller

cone angle with biodiesel use.

It can be said that the cavitation process and related turbulence generated inside the

injector nozzle (using different types of fuels) influence the spray jet. The influences are

present in the atomization process, initial velocity, primary breakup process, and spray

penetration. All of these influences of the biodiesel injection process require changes, new

visions, and new solutions for designing on piston bowl, injection strategy, and initial bowl

swirl ratio to optimize the efficiency of the biodiesel combustion process.


!

!

4.2.2. Effects of external energy (ultrasonic) application on biofuel use performances2

It is widely accepted that biodiesel is one of the current solutions in an attempt to limit

the effect of IC engines greenhouse emissions. Effectuate researches until present [31, 32],

confirms that increasing the percentage of methyl ester in diesel-biodiesel blends lead to a

greater reduction of CO2 emissions (comparative with diesel fuel), but biodiesel and biodiesel

blends have been shown to have higher NOx pollutant emissions than petroleum diesel (with

direct and immediate influence on human health).

The pollution caused by nitric oxides emissions is capable to forming a variety of

cytotoxic species, which contribute to lung pathology and disease, with implication in

pathogenesis of acute respiratory distress syndrome [77].

Nabi and Hustad [48] and Zhu et al. [86] shown that in case of biodiesel use for

fuelling diesel engine, emissions of NOx increase by 2 - 4% (for B20 blend) as much 12-20%

(for B100). The biodiesel NOx specific increase effect is related to the differences in physico-

chemically characteristics (viscosity, density, bulk modulus of compressibility, bond structure,

and cetane number), fuel injection timing and spray characteristics, and engine operation

condition, with major influences on the combustion process [30,47].

The differences between the physical properties of methyl ester based biodiesel and

diesels are major [33] and some are presented in Table 4. These differences lead to

difficulties in using biodiesel in high blends (> 30%) with diesel fuel in existing compression

ignition engines [29, 52, 54].

One way to improve the physical parameters of biodiesel (to reduce the pollutant

emissions) is to use external energy transfer irradiation with different sources (ultrasound,

microwaves, infrared waves, ultraviolet, etc.). Some of these energy sources are able to

modify at the micro molecular level the chemical structure of the biodiesel, with immediate

influence on its physical properties [16, 34, 68]. Ultrasonic irradiation is able to make these

changes due to the phenomenon of cavitation, which takes place through the interaction of

ultrasound waves with the molecular structure of the biodiesel [27, 68, 82].

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!6!#$%&! '()$*! +,-! .(/0()012! 34! 567"P9! Q&&$;R&)! &+! /$*1<$! '0+*0$)$=! '=$,*)! :AS! R+==1&(,&! $;0))0+,)! 'K! 1=&/()+,0<! <+,*0&0+,0,@2!#/(,)R+/&!6T5"9-!P8NPT4!


!

!

Table 4. Comparative physical properties of some methyl esters with diesel fuel [40]

Fuel Density at 15° C [kg/m3]

Kinematic

viscosity at

40°C [mm/s2]

Cetane number

Cloud point

[o C]

Flash point

[o C]

Diesel fuel 841 2.7 54.1 –14 64

Rapeseed oil methyl ester

882 4.60 52.7 1 181

Soybean oil methyl ester

865 4.08 46.4 –1 168

Sunflower oil methyl ester

883 4.16 49.2 2 178

Olive oil methyl ester

881 4.18 59.8 –2 182

The models proposed by Kang et al. [27] and Mason and Lorimer [42, 43], explain the

kinetics of chemical transformations whereby the action of external energy influences the

cavitation process at the molecular level. The models describe how through the process of

ultrasonic irradiation conditioning and characteristics such as high local pressure and

temperature, substances undergo chemical reactions in two main directions:

• Pyrolysis-type chemical reactions – the transformation mechanism is

decisive in the development of a chemical high-intensity thermal effect

(local temperature can reach 5000 K) at the molecular level;

• A multiphase chemical reaction in the formation of radicals.

Availability (affinity) of hydroxyl compounds formed in the process of irradiation and

combined (being in excess in the mechanism of chemical reactions) leads to the formation of

peroxides. Peroxide formations of these groups increases the efficiency of fuel combustion

process, with beneficial influences on the further development of thermal processes in the


!

!

functional cycle of an internal combustion engine, as well as providing changes in the

biodiesel’s physical properties.

The amount of peroxide formed depends directly on the intensity and duration of the

ultrasonic irradiation process [34, 40].

The aim of the research was to provide a primary image of the processes taking

place during the ultrasonic irradiation of biodiesel. Was used experimental methods and

methodologies employed (and validated) by other researchers. For the sound of speed

measurement we used the proposed methodology of Dziza and Prusakiewicz [16], and for

determining the intensity of the ultrasonic waves we took into account the experiments

carried out by Wu et al. [82] and Gogate and Kabadi [24]. Also taken into account were the

related observations made by other researchers [51, 52, 54, 72].

The biodiesel chosen for experimentation was rapeseed methyl ester (RME), mainly

used in Europe. The samples of vegetable oil-based biofuels blended with diesel fuel used

as the subject for the experiments had the following composition:

• Fuel sample control – Diesel (diesel fuel);

• Fuel 1 – B25 (75% diesel fuel + 25% rapeseed oil methyl ester);

• Fuel 2 – B50 (50%diesel fuel + 50% rapeseed oil methyl ester);

• Fuel 3 – B75 (25% diesel fuel + 75% rapeseed oil methyl ester);

• Fuel 4 – B100 (100% rapeseed oil methyl ester).

The BXXUs_irr abbreviation was used for the ultrasonic irradiated biodiesel blends

(where XX represents the volumetric percentage of methyl ester in the blends with the diesel

fuel). The initial properties of the biodiesel were determined in laboratory conditions and are

presented in Table 5.

The variations of the physical parameters on which the experiments were focused,

were the density (determined by Anton Paar 5000 apparatus), the speed of sound passing

through the medium (Optel measuring device) and the viscosity (Haake viscometer). The

isentropic bulk modulus of the biofuels conditioned by irradiation with ultrasound was

determined by using the Newton-Laplace formula [16, 73]:


!

!

!! ! ! ! !! (9)

, where !’ is the isentropic bulk modulus (in Pa), u is the speed of sound (in m/s) and ! is

density of the sample (in kg/m3). Determination of the isentropic bulk modulus value is

significant in measuring the effect of ultrasonic irradiation on the process of ignition and

combustion of conditioned biofuels. This is because the isentropic bulk modulus value

influences the injection time. Furthermore, Tat and Van Gerpen [72], Szybist et al. [69, 70]

and Bakeas et al. [4] noted that a higher value of isentropic bulk modulus corresponded to

higher NOx values. The experiments conducted by Boehman et al. [10], Torres-Jimenez et

al. [74] confirm totally or partially this hypothesis.

Ultrasound propagation in vegetable oil and also in biofuel causes cavitation (under

specific conditions). Because of the expansion and contraction of the transfer media are

conditions to generate locally bubbles of very high temperature and of pressure (cavitation

process). As an immediate result, the physical and chemical properties of the transfer media

are modified [68].

Gogate and Kabadi [24] show that the effectiveness (efficiency) of the ultrasonic horn

in creating a cavitation effect depends on the magnitude of energy and operating frequency

supplied by the equipment. It was observed that the cavitation intensity decreases

exponentially at a specific distance from ultrasonic horn until it vanishes completely. To

create the cavitation phenomenon in the ultrasonic irradiation of biofuels for the present

experiment, we used a small volume of biofuel for conditioning (VBD=300 ml) and an

ultrasonic horn that produces 35 W/L, PZT type, at 35 kHz frequency emission, which was

applied continuously.

Measurements of physical properties considered in the experiments were carried out

after a duration of ultrasonic irradiation of 0, 100, 200, 300, 400, 500 and 600 seconds and

were compared with the values of the same physical properties of diesel fuel that was not

irradiated (sample control). The energy density transferred to the biofuel volume was

analyzed by the method proposed and used by Ramirez del Solar et al. [57] and Lee et al.

[34].

The ultrasonic power (Pus) was calculated from:

!!" ! !!"! (10)


!

!

Table 5. Physico-chemical characteristics of tested fuels

Property Diesel fuel Rapeseed methyl ester

(RME)

Chemical formula C14H30 C16-C18

Molecular weight

[g/mol] 198.4 209.6

Density

at 20oC [kg/m3] 831 879

Kinematic viscosity

at 40oC [mm2/s] 2.7 4.9

Boiling point [oC] 278 322

Higher heating value

[MJ/kg] 46.94 37.5

Carbon content

(%) 87 78.7

Sulphur content

(ppm) 233 0.036

Water content

[mg/kg] 64 86

Cetane number 54.1 52.7


!

!

, where ultrasonic energy is Eus and t is time in seconds. The Pus is constant (from the

installation construction) and therefore the energy density can be calculated using [34]:

!!" ! !!" ! !!!"

(11)

, where VBD (in ml) is the volume of irradiated biofuel (biodiesel).

For the experimental conditions described above, the values of the transferred

ultrasonic energy density in biodiesel blends are presented in Table 6. Moreover, the

ultrasonic conditioning process gives rise to conditions where peroxide compounds might

form (as oxidation mechanism of fatty acid methyl ester - FAME), resulting in a beneficial

influence on fuel combustion, but this may also have negative influence on the storage

properties of the biodiesel (especially in the long term).

To determine the influence of the instantaneous ultrasonic irradiation process on

biodiesel with regard to NOx emission, were used an experimental test bed equipped,

developed and adjusted in accordance with the methodology of the research in the field [29,

70].

The experiments were carried out to determine the differences between the emission

of NOx, for irradiated and non-irradiated biodiesel (compared with the same values for diesel

fuel) using an engine experimental test bed, presented in Figure15.

The constructive details of vessel use to ultrasonic conditioning the biodiesel blends

(patent pending) are presented in Figure 16. The engine was run at constant speed of 2400

min-1, and a Weinlich M 8000 dynamometer was also use to load the engine. The loads at

25, 50, 75 and 100% correspond to 0.10, 0.20, 0.31 respectively 0.41 MPa of BMEP.

The structural parameters and functional characteristics of the Yanmar diesel engine

L 100 AE used in the experiments are presented in Table 7.

The experimental test was performed examining the full range of engine load. The

NOx emissions were measured with a Testo 330 XL exhaust gas analyzer (with NOx

measurement cell). The calibration procedure for the gas analyzer was done before each test

(in accordance with the manufacturer’s recommendations in order to achieve measurements

errors of less than 2%). The experimental tests were performed 10 times, and the results of

those repetitions were averaged to reduce the level of uncertainty.


!

!

As research results, the biodiesel parameters considered for determining the

influence of the ultrasonic irradiation process were: speed of sound through the medium,

density, isentropic bulk modulus and kinematic viscosity. The results obtained from the

experiments are presented in Figures 17-20 (laboratory tests) and Figures 21-24 (engine test

bed experiments).

Table 6. Biodiesel blends’ physical characteristics after 600 seconds of irradiation process

Blend Density

(g/cm3)

Mean heat

capacity

(J/gK)

Ultrasonic

energy density

(kJ/L)

B25 0.836 1.958 3519.3

B50 0.853 1.978 3931.3

B75 0.862 1.981 4166.6

B100 0.876 1.993 4521.8

Figure 15. Experimental test bed structure (1 –fuel tank, 2 –pollutant emissions analyzer, 3 –injector, 4

–exhaust pipe, 5 –data acquisition system, 6 – engine speed sensor, 7 –single cylinder engine, 8 – air

intake pipe, 9 – injection pump, 10 – ultrasonic irradiation device, 11– fuel filter)


!

!

Figure 16. Constructive details of conditioning device (1-fuel-out pipe, 2-vessel,

3-cap, 4-fuel-in pipe, 5 - ultrasonic emitter)

!Table 7. Technical characteristics of test engine

Parameter Value

Type 4-stroke, air cooled,

vertical single cylinder

Bore x Stroke 86x70 mm

Displacement 406 cm3

Combustion type direct injection

Continuous rating

output

6.6 kW at 3600 min-1

Fuel injection pressure 19.6 MPa

Fuel injection timing 17±0.5o BTDC


!

!

!

Figure 17. The influence of the ultrasonic irradiation process on the speed of sound

through the medium

!

Figure 18. The influence of the ultrasonic irradiation process on the density

through the medium


!

!

Figure 19. The influence of the ultrasonic irradiation process on the

isentropic bulk modulus

!

Figure 20. The influence of the ultrasonic irradiation process on the

kinematic viscosity


!

!

As the duration of treatment increased, the overall trend for the speed of sound

variation among the ultrasonic irradiated blends was downward (Figure 17). After 600

seconds of irradiation, all values (except for B100Us_irr) were equal or smaller than the

value for the diesel fuel speed of sound.

The induced thermal effect caused by the ultrasounds interaction with the conditioned

volume of blends was measured, to determine the magnitude of the induced temperature on

biodiesel blends physical parameters characteristics. The variation is linear with the time; a

slope of 2.15oC/min, 2.21oC/min, 2.36oC/min, and 2.44oC/min was measured for the B25,

B50, B75 and respectively for B100 blend. The maximum temperature was achieve for B100

blend (42.4oC after 600 seconds of ultrasonic conditioning; initial biodiesel blends

temperature was 18oC), but according to the experiments effectuated by Bari et al. [5], a

temperature of the fuel less than 60oC, did not have a significant effect on the fuel

consumption and effective power.

For a period of approximately 420 seconds of ultrasonic irradiation conditioning, the

density of biodiesel B25Us_irr density fell below that of the diesel fuel (Figure 18). For the

other blends (B50, B75 and B100) the density decreased by an average value of –2.49 %,

but the final values were higher than those of the diesel fuel. The effect of density decreasing

is beneficial regarding the fuel injection process, with immediate consequences for the

pollutant emission levels [52].

In general, the trend of the isentropic bulk modulus variation was decreasing, with a

minimum value of –4.71 % (B100Us_irr) and a maximum of –9.68 % (B25Us_irr) (Figure 19).

Isentropic bulk modulus values dropped below those of the diesel fuel mixture for B25Us_irr

(after 100 seconds) and B50Us_irr (after 350 seconds) blends. Szybist et al. [69, 70] and

Bakeas et al. [4] show that higher bulk modulus causes advanced injection timing, one of the

reasons for increased NOx pollutant emissions.

From the point of view of the presented experiments, the decreasing tendency of the

isentropic bulk modulus for all the blends shows possibilities for reduced NOx emissions from

biodiesel-fuelled engines. The variation of isentropic bulk modulus has direct effect on

biodiesel’s ignition timing (that are more appropriate in conditions of ultrasonic irradiation to

diesel fuel one). Further, from this reason, the peak combustion temperature in the NOx

formation interval is decrease, because the premixed combustion intensity is reduced [78].


!

!

Figure 21. NOx emissions for the B25 blend (ultrasonic irradiated

and basic biodiesel)



!


!

!

!






!

!

Only B25Us_irr blend’s kinematic viscosity shows lower values than those of diesel

fuel in the process of ultrasonic irradiation (after 350 seconds). The difference between the

kinematic viscosity of the B25Us_irr blend subjected to the full irradiation time of 600

seconds and that of the diesel fuel after 600 seconds was –28.25 % (Figure 20). Ultrasonic

irradiation was also beneficial for the other considered blends (B50, B75 and B100):

kinematic viscosity was reduced by an average of –19.74 %. Viscosity is considered a more

important biodiesel parameter that density, owing to its direct influence on the operation of

fuel injection engines’ equipment [40]. Szybist et al. [69] highlight the beneficial effect of a

fuel with lower viscosity on injection process parameters. Furthermore, the effect is related to

reduced NOx emissions.

The results obtained in experiments to test the fuelling of a DI diesel engine with

ultrasonically irradiated biodiesel confirm the interpretation of previous assumptions about

biodiesels’ physical parameter changes under the effects of ultrasonic irradiation. The

generally decreasing tendency of the treated biodiesels’ density, viscosity and isentropic bulk

modulus brings beneficial effects to the injection and combustion processes, with a direct

influence on NOx pollutant emissions formation.

According to the results presented in Figures 21-24, there are reductions in NOx

pollutant emissions for all regimes of the engine. The maximum value obtained is –18.2%

(for B25Us_irr, no engine load case) and the minimum is –1.4% (for B100Us_irr, 100%

engine load case), compared with emissions from untreated basic biodiesel. Using the

ultrasonically irradiated biodiesel, reductions in NOx emissions of greater than 10% were

obtained for low and medium load engine regimes. For B25Us_irr these load regimes are 0%

and 75% (–18.2% and –11.9%); for B50Us_irr they are between 0% and 50% (–14.3% and –

11.1%); and for B75Us_irr, they are for 0% engine load regime only, (–10.7%).

To can judge about the real effect of ultrasonic biodiesel blends treatment on NOx

pollutant emission, were analysed also the engine’s specific fuel consumption (BSFC) and

the brake power variations. The results are presented in Figures 25 and 26, considering the

relative variation of measurements before and after ultrasonic conditioning of biodiesel

blends.


!

!

Figure 25. Differences in BSFC for non-irradiated and irradiated biodiesel blends

Figure 26. Differences of engine’s brake power for non-irradiated and irradiated biodiesel blends


!

!

From above presented results it can said that the effect of ultrasonic irradiation

conduct to a generally (but smaller as values) decreasing tendency of BSFC. The major

reduction in BSFC was achieve for the B100Us_irr blend equal to -2.95% (at 0% engine

load). In the case of effective brake power a increasing tendency was measured with major

influence on B75Us_irr and B100Us_irr blends (+4.28% at 0% engine load, respectively

+4.43% at 75% engine load).

Based on the presented results, it can say that the reduction of NOx pollutant

emission is major caused by the effect of ultrasonic biodiesel blends conditioning on the

isentropic bulk modulus parameters change. The decreasing in BSFC correlated with a small

increasing of engine’s effective power, are the immediate effect of a more appropriate

ignition timing (that are influenced by the value of isentropic bulk modulus) of ultrasonic

biodiesel conditioned, to that of diesel fuel.

However, the NOx pollutant emission values, using the ultrasonic irradiated biodiesel

to fuel a DI diesel engine, remain higher than that using diesel fuel.

As a major conclusion, the ultrasonic irradiation process leads to important variations

in the physical parameters of biodiesels. In terms of density and viscosity (important

parameters for the injection process) the obtained results show equal values for the B25

blend and diesel fuel for an ultrasonic irradiation period of 420 seconds and 350 seconds

respectively. The variations of ultrasonically irradiated biodiesel physical characteristics show

potential in NOx pollutant emission reduction: potential confirmed through experimental

bench research on the performance of a direct injection diesel engine.

The major reduction in NOx pollutant emissions was observed for the B25Us_irr

blend conditioned by ultrasonic irradiation (–18.2% for no engine load to –8% for 100%

engine load) when compared to basic untreated biodiesel. However, there were still NOx

emissions values greater than those measured from the diesel fuel and the biodiesel’s

conditioning process by ultrasonic irradiation worse storage properties for long periods (by

increasing oxidative products in blends).

Through the ultrasonic irradiation process it is feasible to incorporate biodiesel fuels

into blends (with diesel fuel) for use in compression ignition engines without having to make

major or important changes and adjustments to the fuel injection systems of these engines.


!

!

4.2.3. Possibilities to improve cold-start process of engines fuelled with biofuels3

It is well known and establishes that diesel engines’ easy start depends directly on fuel

self-ignition quality and indirectly on fuel’s cetane index, viscosity, fuel freezing point and

cloud point temperature [7, 40]. In terms of behavior at low temperatures due to high

amounts of vegetable oils cloud point temperature is from +12°C to +30°C, compared to

diesel (-22°C to + 0°C); some problems will appear related to flow through the injection pump

(loss of engine power), clogging filters and supply lines [13]. Based on these considerations

we can say that physical and chemical properties of biodiesels have an important role on

technical considerations related to their use in compression ignition engines [40, 41].

Given that currently there is mainly machinery and vehicles that are equipped with

engines built with older technology than that used in 2000, in order to increase reliability as

well as fuel engines to use vegetable oil (pure or mixed form) technical changes must [13,

14]: ensure the possibility of using alternative fuels in compression ignition engines in any

season calendar and the superior performance in terms of lower pollution than petroleum

based fuels; not involve important changes in engine design (overall piston chamber,

cylinder, cylinder head etc.), in order not to increase significantly the cost price; not affect the

strength and thermal characteristics of engine mechanism parts; increase the reliability of

compression ignition engines that work with such fuels.

On the basis of previously presented, it is considered that the minimum necessary

technical changes to be made on components and/or installation of the engine especially

when used as biodiesel or pure vegetable oil based on the percentage of biodiesel from

vegetable oil mixture biodiesel (diesel + vegetable oil) are more than 70%, to facilitate their

use in low ambient temperature conditions [75]. Currently, the following technical changes

are recommended:

• Heating the biodiesel inside the tank (with heat exchanger Figure 27 or

electrical resistance Figure 28) [13];

• Biodiesel heating with heat exchanger mounted on the supply route (after the

tank), constructive solutions are proposed as those presented in Figure 29

[13, 14].

• Mixed supply systems, starting systems that allows diesel fuel initial start,

operating with biodiesel and again using diesel fuel to stop [13]. The fuels

switch used to equip such a mixed power system is shown in Figure 30.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!8!#$%&! '()$*! +,-! .(/0()012! 342! U(/@(2! E4! 567"79! I+))0'0=0&0$)! &+! 0;R/+?$! &C$! <+=*! )&(/&! R/+<$))! +B! &/(<&+/)! $,@0,$)! B1$==$*! V0&C!'0+*0$)$=2!W+1/,(=!+B!3++*2!Q@/0<1=&1/$!(,*!D,?0/+,;$,&!O58XP9-!""67N""662!67"74!!


!

!

The proposed method use to improving the cold start process of biofuel use for IC

(diesel) engines fueling and is based on an ultrasound system (Figure 31) that consists of a

PZT ultrasound emitter (35W), an electronic system that generates the ultrasounds and a

fuel filter (Mopar type 7-41354). Achieving thermal effect induced in biodiesel is possible due

to the interaction of ultrasound with its molecular structure. With this the biodiesel energy

levels increase and so does the activation degree of molecules, which increases the intensity

of clashes between them. The result of these clashes is the energy dissipation as friction

process result (in the process of collision) as the heat in the volume of biodiesel.

Energy consumed for the biodiesel heat through ultrasound is 3-5 times smaller than

existing solutions in the cases presented above. Also, the decoupling of device is automatic

when reaching the desired temperature by using a thermal sensor (Figure 31). The ultrasonic

emitter device is positioned in the manner most advantageous to the bottom battery fuel

filter.

The measuring devices consist of an IR Testo 850 thermometer and an IR thermal

camera Wuhan Guide IR type, and were used to achieve the necessary data about the

ultrasounds thermal transfer process on biodiesel. The biodiesel was rapeseed pure

vegetable oil and the experiments start at -15°C (alleged as base temperature for

experiment).

Figure 27. The biodiesel heating process with heat exchanger

mounted inside of fuel tank (1-fuel tank; 2-biodiesel; 3- heat

exchanger; 4-from cooling circuit; 5-to cooling circuit).


!

!

Figure 28. The biodiesel heating process with electric resistor device

mounted inside of fuel tank (1-fuel tank; 2-biodiesel; 3-electric

resistor).

!

Figure 29. The biodiesel heating process with heat exchanger mounted on fuels supply circuit

(1-power supply connecting wires; 2- biodiesel in; 3- biodiesel out; 4-electrical heater).

Figure 30. Fuel switcher [13](1-biodiesel in; 2- to injection pump; 3-diesel fuel in; 4-diesel fuel

out; 5-injection pump retour; 6-electromagnetic command system; 7- power supply connecting

wires).


!

!

Figure 31. The cold start ultrasound system (1-biofuel out; 2-filter element; 3-filter case; 4-PZT

ultrasounds emitter; 5-thermal sensor; 6- biofuel in; 7-ultrasounds; 8- ultrasounds generator; 9-

electronic control unit; 10-12Vcc power supply system)

The experiments carried out by ultrasonic conditioning of biodiesel are seen as a

thermal effect occurs due to increased fuel and energy potential of increasing frequency of

collision with friction between fuel molecules. The results of experiment (the fuel filter thermal

finger-print and the temperature distribution along the filter case height) are presented in

Figures 32 to 34.

Figure 32. The temperature distribution on fuel filter longitudinal plane (10 s).


!

!




!

!

After 10 s of biodiesel ultrasonic conditioning the thermal heating process increases the

temperature from -15 to -9°C but the heating is limited only to the base of fuel filter. After 20 s

of biodiesel ultrasonic conditioning the heating effect is present in almost half of the fuel filter

volume, the maximum temperature of biodiesel increase is -2.5°C from initial value of -15°C.

After 30 s of biodiesel ultrasonic conditioning the heated volume grows at the filter base

is to obtain a positive temperature of +5.5°C and also is obtained a higher average

temperature of biodiesel volume content in the filter (which leads to improve the engine cold

start process).

Considering the physical properties of biodiesel we can say that at least 20 s is

necessary for biodiesel ultrasonic conditioning to realize the necessary conditions for a

proper cold start process of a compression ignition engine fuelled with biodiesel [14, 75].

As a major conclusion, the cold start process of internal combustion engines fuelled

with biodiesel eliminates the presented disadvantages (of other systems) by being fitted with

an ultrasound-producing system, having reduced weight and being easy to assemble all

forms of fuel filter battery construction that are currently existing in the construction of internal

combustion engines fuel supply systems.

By applying the cold start system into the construction of a diesel engines fueling

system obtains the following advantages: simple and reliable construction due to lack of

moving mechanical elements; effect of heat transfer instantly to biodiesel; automating of

diesel engines cold start process; weight and reduced dimensions; ease of installation and

operation. Energy consumed for the actual heat through ultrasound is 3-5 times smaller than

existing solutions in the cases presented. Also, the decoupling device is automatic when

reaching the desired temperature. Another important advantage is the increasing of the

engine’s battery life with direct impact on environment protection and economical profit from

engine exploitation.

The device is positioned in the manner most advantageous to the bottom ultrasonic

emitter battery fuel filter. Location at the fuel filter bottom offers the innovative advantages:

quick release hole in the filter output of biodiesel by engine; already heated biodiesel will

further upward movement leading to the thermal effect of ultrasound near the amount of fuel

and contribute to melting paraffin deposits and agglomerations of the filter elements.


!

!

4.2.4. Possibilities to reduce engine’s friction losses at cold-start4

An original direction of research was the study of possibilities for reducing engine

friction losses at cold start using an ultrasonic irradiation technique. This unconventional

approach use an ultrasound emitter device (that manages minimum energy consumption

from engine’s battery) in order to modify the rheological properties of engine oil lubrication

and reduce friction losses. The results of laboratory experiments were processed in a

computer simulation of the diesel engine tractor cold start process. Losses due to internal

friction among engine components were comparatively analysed, and a lower percentage of

friction loss was obtained through ultrasonic conditioning of lubricating oil. The proposed

method offers benefits in terms of rational use and can prolong engine life with positive

effects on the economic efficiency of agricultural processes.

Desantes et al. [15] explained that the diesel engines offer advantages including ease

of operation, simple construction and reduced costs, relatively high thermal efficiency, and

good operational performance [i.e. power, torque, and brake specific fuel consumption

(BSFC)]. However, one of the great disadvantages of the diesel engine is that it can be

difficult to start at low ambient temperatures [12, 38]. The difficulty of cold start is due to the

mass of the cylinder block. In addition, the cylinder head absorbs the heat generated by the

compression stroke, which prevents the self-ignition of the fuel mixture (due to the higher

surface-to-volume ratio). This disadvantage is corrected by: using a glow plug to generate

heat inside the combustion chamber, having a higher compression ratio (19:1 to 23:1), or

modifying the fuel injection pattern [38].

A low temperature environment also affects the diesel engine lubrication processes.

Because the temperature directly affects lube oil viscosity, diesel engine start-up lubrication

is one of the most critical moments for lubrication. When lube oil has too high a viscosity at

cold start there is a risk of damage to the diesel engine including broken piston rings,

plugged filters, and oil pump failure. This is because, at engine start, all of the oil is in the

sump and the oil pressure is zero. The pump cannot begin to deliver the requested quantity

of oil until it sucks cold oil through the filter and delivers it to the engine lubrication system.

As the oil circulates and warms up (through contact with hot engine parts), the flow

increases, and the oil pressure drops to a stable level.

However, after this initial period of time (50 cycles at least) — to eliminate the effects

of transitory regime [21] — the engine and the engine components begin to receive proper

lubrication. Although cold start lubricating conditions are not critical for the crankshaft

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!P!#$%&! '()$*! +;-! .(/0()012! 34! 567"89! I+))0'0=0&0$)! B+/! /$*1<0,@! &/(<&+/! $,@0,$! B/0<&0+,! =+))$)! (&! <+=*! )&(/&! 1)0,@! (,! 1=&/()+,0<!0//(*0(&0+,!&$<C,0Y1$J2!#1/Z4!W4!Q@/0<4!3+/4!8[-!M68NM8"4!


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bearings, other engine components such as the camshaft, lifters, connecting rod bearing,

piston pin, piston, piston rings, and cylinder walls are not fully lubricated in the time it takes

for the oil pump to pressurize the lubrication system and supply the necessary oil to the

engine [36]. The common solution for this problem is the use of engine lubricants with

additive technology (in combination with higher quality base stocks) that assure the

necessary oil viscosity for all temperature start conditions [8, 19, 35]. This can help to

maintain adequate engine wear protection during extended operation and under the more

severe conditions of an engine cold start-up process, as Plomer and Benda [55] and

Katafuchi and Masai [28] have shown. The disadvantages of this solution lie in the higher

costs and pollution concerns.

The present paper studies the possibility of developing electronic devices based on

ultrasonic wave emissions to decrease lubricating oil viscosity at cold start. Experimental

results were modelled through computer simulation using CRUISE software [2], which

facilitates calculation of engine friction losses at cold start-up.

The current study explored ultrasound (as external energy application) to change oil

lubrication rheological properties of the oil that lubes the engine mechanisms and

subassemblies. This work derives from experiments conducted by Mariasiu and Varga [39]

on the influence of ultrasonic processes on the physical characteristics of biodiesel blends.

The influence of ultrasound on lube oil parameters relating to internal combustion

engine lubrication (viscosity, density) was tested using an experimental device. An

ultrasound emitter of 35 Hz and 30 W (Bandelin Electronic GmbH, Berlin, Germany) was

mounted in the engine crankcase oil (Figure 35). Under initial experimental conditions the

ultrasonic energy density was 5220.7 kJ L–1. The initial temperature of the crankcase

lubricating oil was –10 °C (measured by placing crankcase and oil in a cold room with climate

control), and the ultrasonic effect on the lubricating oil was considered in effect until the oil

temperature (in the vicinity of the oil sump position) reached 10 °C.

Measurement of variation in lubricating oil viscosity (dynamic and kinematic) was

performed with the Anton Paar SVM 3000 Stabinger Viscometer (Anton Paar GmbH, Graz,

Austria). Video captures of the thermal footprint of ultrasound effects on lubricating oil were

taken by thermal-acquisition video camera (Wuhan Infrared TP8 type; Guide Infrared Co.,

Wuhan, China). The lubricating oil used in the experiment was a mineral type (20W50)

produced and sold by SC MOL SRL in Romania (Table 8).

The experiments described above were carried out in order to represent the effect of

ultrasound on the physical parameters of the lubricating oil (viscosity). Ultrasonic energy

transferred into a volume of lubricating oil causes vibration and friction between molecules in


!

!

the lubricating oil. Collisions and high-frequency repeated friction causes a heating effect that

directly influences the physical parameters of lubricating oil.

The thermal effect of ultrasound in a volume of lubricating oil (under our experimental

conditions) was highlighted by video acquisition of oil volume thermal fingerprints for different

time periods. A determination of lube oil viscosity variation and values, depending on the

effects of ultrasound, was acquired as an input parameter for the computer simulation model.

Table 8. MOL 20W50 engine oil: typical properties.

Properties Value Standards

Density at 15 °C [g cm–3] 0.891 ASTM D1250

Kinematic viscosity

at 40 °C [mm2 s–1]

161.0 ASTM D445

Kinematic viscosity

at 100 °C [mm2 s–1]

17.9 ASTM D445

Viscosity index [ - ] 120 ASTM D341

Pour point [°C] –27 ASTM D97

Flash point [°C] 240 ASTM D92

Base number BN [mg KOH g–1] 5.1 ASTM D2896

Computer simulation is one of the contemporary methods used by researchers to

solve technical problems [66]. Recently, development of mathematical models has allowed

for better correspondence between the physical models and numerical models, and this has

led to the use of computer simulation of specific processes of tractors and agricultural

machinery. In order to determine the friction losses due to engine cold start-up, we used a

simulation software package (CRUISE, AVL GmbH [2]).


!

!

Figure 35. Ultrasonic transmitter location in the oil crankcase (1 - electrical connections, 2 - ultrasonic

emitter, 3 - oil pump sump, 4 - transfer pipe, 5 - oil crankcase).

The CRUISE computer simulation package is used through an interface that allows

for total or partial construction of components, subassemblies, and assembly models that

constitute a vehicle and its operating parameters and conditions. The CRUISE friction model

had the advantage of allowing for engine design variables such bore, stroke, and number of

valves in addition to operating conditions (engine speed, load, and oil temperature).

The values of friction loss coefficients were calculated, considering relevant engine

design and operating condition variables. Using the SLM (Shayler, Leong, and Murphy)

model proposed and developed by Shayler et al. [62, 63], we calculated the effect of ambient

temperature on the functional parameters and emissions of internal combustion engines

(spark ignition or compression ignition) to determine friction losses in the motor mechanisms.

The Shayler, Leong, and Murphy [64] model fits friction teardown data from motored engine

tests on 4-cylinder diesel engines.

The original purpose of the experimental work was to examine friction losses at low

temperatures and low engine speeds in connection with studies of cold start behaviour. The

SLM model generates an estimate for friction mean effective power (FMEP), which is then

subtracted from the engine-indicated mean effective pressure (IMEP) to obtain brake mean

effective pressure (BMEP).


!

!

The magnitude of friction processes is determined empirically from engine layout and

characteristics and is a function of engine speed, oil viscosity, and ambient temperature [62,

63].

As seen in Equations (12–15), the SLM model takes into account the important

parameter of lubrication process quality (oil viscosity), a physical parameter that varies in the

case of ultrasonic conditioning.

The crankshaft friction mean effective pressure is:

!"#$!"#$%&!!"# ! !!!!!!!!!!

!!" ! !!!! ! !!! ! !! ! !!!

!!"#

!! !!" (12)

, considering the oil lubrication viscosity index n = 0.24; N – engine rotational speed [min–1]; µ

– oil dynamic viscosity [Pa s]; µref – oil dynamic viscosity at 40 °C [Pa s].

The friction mean effective pressure in the piston group is:

!"#$!"#$%& ! !!!"#

!!!" ! !

!!!!!!!!!!!!!!

! !!!!!!!

!!" ! !!" !!!

(13)

where the oil lubrication viscosity index is n = 0.4, and Vp = 15.17 m s–1 is piston average

speed.

The friction mean effective pressure in the valve train is calculated using Eq. (14):

!"#$!"#!$%&"'(

! !!!"#

!!!"

!!!! ! !!!!! ! ! ! !!

! !!!!!!!! ! !!!! ! !!!! ! ! ! !!

! !!"

! !!" ! ! !"! ! !"

!! ! !!! ! !!

!!"#$!"#

!"#$!"# ! !!" ! ! !"!!!!!

!!!!!!

(14)


!

!

, where the oil lubrication viscosity index is n = 0.7, and Lv = 0.0085 is maximum valve lift [m].

The auxiliary losses (for oil and water pump) can be calculated using Eq. (15):

!"#$!"# ! ! ! !" ! !!! !!!"#

! (15)

The values for the constants (%, &, ') and the viscosity index (n) are, respectively:

1.28 kPa, 7.9 · 10–3 kPa mm3 min, –8.4 · 10–7 kPa mm3 min2, and 0.3 for the oil pump; for the

water pump: 0.13 kPa, 2 · 10–3 kPa mm3 min, 3 · 10–7 kPa mm3 min2, and 0.7 [11].

Considering the design particularities of the engine; the experimental results of

Shayler et al. [64], and Patton et al. [53], and the theory of lubrication [76], the values and

relationships of the friction model coefficients are presented in Table 9 (N was estimated at

700 min–1). The relationships used to calculate the SLM friction model coefficients presented

in Table 9 couldn’t be used for other engine models; however, they can be used for further

research and simulations regarding the influence of different oil viscosities on friction losses

for the diesel engines considered.

The simulation model was based on the D-110 diesel engines (direct injection, 4 in-

line cylinders, water cooling system) that equip Romanian U650 agricultural 2 WD tractors.

The structure of U650 CRUISE simulation model is presented in Figure 36 and the

Simulink friction model structure in Figure 37.

The engine general technical characteristics considered as input parameters in the

computer simulation are presented in Table 10. Additional data required are lubricating oil

viscosity function of environmental temperature. The model is also used to determine

functional and dynamic tractor performance for specific agricultural work.

In terms of lubricating oil ultrasound conditioning, related experimental data obtained

from viscosity variation are shown in Figure 38. Note that baseline for kinematic viscosity

considered at –10 °C decreases by 26.1%, 44.8%, 58.4%, and 68.3% after 63.2, 125, 221.2,

and 261.1 s, of ultrasonic process, respectively. The values shown above were measured for

lubricating oil temperatures of –5 °C, 0 °C, and 5 °C; the maximum temperature (10 °C)

considered during the experiment was obtained after 261.1 s.


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!

Table 9. Calculation relationships of SLM friction model coefficients.

Coefficient Value/Relation

Ccb 4.16 · 10-3

Ccs 1.22 · 105

Cpb 0.576

Cps 11.45

Cpr 1.58 · 103

Cvb 6.118

Cvf 600

Cvh 600

Cvm !"!!" ! !! ! !"" ! !

Cvs 1458

Figure 36. CRUISE simulation model structure.


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Figure 37. Simulink friction model structure.

Heat inducted in the lubricating oil volume as a direct effect of ultrasonic irradiation

processes, and measured as oil temperature, is presented in Figure 39. The measured

temperature variation in the oil volume slope is 5.33 °C min–1; it’s relative linear tendency

was also confirmed by Lee et al. [34].


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!

Table 10. Engine’s functional and constructive characteristics (model input data).

Parameter Value Parameter Value

Engine type Diesel Compression ratio 17:1

Displacement 4750 cm3

Engine nominal

temperature 80 °C

Bore 108 mm

Crankshaft main

bearing diameter 85.2 mm

Stroke 130 mm

Crankshaft main

bearing length 34.5 mm

Power

(at 1800 min–1)

47.8 kW

Big end con rod

bearing diameter 79.0 mm

Torque

(at 1250 min–1) 289 N m

Big end con rod

bearing

length

33.2 mm

Type of cam follower Flat follower

Type of valve

train OHV

Number of crankshaft main bearings 5

Number of intake valves

per cylinder 1

Number of camshaft bearings 6

Number of exhaust valves

per cylinder 1

Engine oil SAE 20W50 Maximum valve lift 8.5 mm


!

!

Figure 38. Effect of ultrasonic irradiation on lubricating oil’s viscosity and temperature.

Thermal prints provide a picture of the ultrasound thermal propagation effect in the

lubricating oil for the time considered (300 s). Lubricating oil’s temperature, as a direct effect

of ultrasound irradiation, was 12.1 °C (Figure 39).

Results obtained from the computer simulation (Figures 40 and 41) presented the

differences in friction loss among different engine mechanisms during cold start-up. Detailed

results for each engine component considered (crankshaft and main bearings, piston group,

valve train, and auxiliaries) are presented in Table 11. Among the components and engine

systems considered in the simulation (Table 11) the highest friction loss values were found in

the piston group (3.269 kW) and auxiliaries (3.172 kW). This justifies specialized design and

construction of these components in order to assure minimal effects of wear. Under cold start

conditions the valve train system supports high intensity wear, as presented above.

Variations of +1.62% in friction loss for cam and cam followers and +1.62% in mixed

oscillating valve train lubrication were obtained. These slight increases in friction loss may be

due to oil viscosity reduction. If the viscosity is reduced below the level required for

hydrodynamic support, the cam surface will contact the cam follower surface, creating

boundary contact friction. In total, a major (– 40.94%) reduction in friction loss was achieved

for the valve train system after 261 s of ultrasonic irradiation of the lubricating oil for an

engine cold start at –10 °C.


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Figure 39. Thermal prints of ultrasound effects (starting from –10 °C lubricating oil temperature).


!

!

Figure 40. Total friction losses for examined cold start conditions.

!

Figure 41. Friction loss distribution for valve train assembly.

!!!!


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Table 11. Comparative friction loss magnitude for different engine components.

Ultr

ason

ic ir

radi

atio

n be

fore

en

gine

igni

tion

(s)

Oil

tem

pera

ture

[°C

]

Friction losses [kW]

Cra

nksh

aft a

nd m

ain

bear

ing

Pis

ton

grou

p

Val

ve tr

ain

Aux

iliar

ies

Tota

l

0.00 -10 1.39 3.27 0.964 3.17 8.80

63.2 -5 1.07 2.68 0.776 2.17 6.70

125.0 0 0.85 2.25 0.670 1.57 5.35

221.2 5 0.70 1.92 0.60 1.19 4.43

261.1 10 0.58 1.67 0.57 0.95 3.77

The aim of this study was to present the possibility of reducing engine friction losses

at cold start by using an experimental device to ultrasonically irradiate lubricating oil. The

experiments determined variation in oil viscosity due to the thermal effect induced by

ultrasound. Furthermore, viscosities of lubricating oil at – 10 °C, –5 °C, 0 °C, 5 °C, and 10 °C

were set as input parameters for the D-110 engine cold start computer simulation.

Analysing the simulation data we found that engine friction losses decrease with

increasing ambient temperature, as expected. With positive lubricating oil temperatures there

is a more rapid lubrication of engine components. Assuming the maximum power tractor

engine D-110 is 47.8 kW, friction loss at cold start (–10 °C) is 18.41% of total engine power

(Figure 40).

The greatest variations in friction loss reduction through the ultrasonic effect on

lubricating oil were obtained for camshaft bearing hydrodynamics (–74.17%) and oscillating

valve train friction losses by hydrodynamic lubrication (–79.04%). In other areas of friction

loss there were no reductions achieved; however, these areas are important as a share in

the total value of engines friction losses (Figure 41).


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The immediate effect of the results presented above is a major increase in engine

component reliability, as well as growth in motor engine functional performance (power,

torque, and BSFC), with a direct influence on lowering pollutant emissions. Another important

advantage of using an ultrasonic device that can improve lubricating oil parameters is lower

energy consumption and a reduction in accumulator battery strain, when compared to an

electrical resistor oil heating system. In addition, the use of electrical resistors to heat the

lubricating oil leads to the rapid thermal degradation of the oil. This degradation produces

additional costs related to increased maintenance (i.e. default costs of purchasing new oil,

human labour costs, and replacement parts).

Reducing friction losses increases the lifespan of the engine with immediate benefits

in maintenance and operational costs: a mandatory process requirement. The practical

application of the device presented involves an economic cost of approximately /83

(hardware and human labour costs); this represents less than 0.3% of the purchase cost of a

new engine.


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5. CONCLUSIONS

The research activity of candidate was constant in idea to offer applicative solutions in

order improve internal combustion engines’ performance (to make the connection between

fundamental and applicative research). Both, conventional and unconventional methods and

approaches were used, and results of researches were disseminated at different levels using

different channels, to increase the public awareness about the contemporary problem of

environment pollution and subsequently, to improve IC engine performance.

There are also highlighted future directions of research, derived from actual work:

• Exploring the connecting possibilities of biodiesel injection process’

influences with new solutions in piston bowl designing, injection strategy,

and initial bowl swirl ratio to optimize the efficiency of the biodiesel

combustion process.

• Researches of the ultrasonic irradiation process on different types of

methyl esters (soy, palm oil, sun flower, etc.) and with different values of

transmitted ultrasonic density in fuel (taking into consideration the use of

low-power and also low-cost ultrasonic horns).

• Using different ultrasound emission frequencies should do future research.

In addition, the energy density of the ultrasound in relation to volume and

crankcase oil constructive shape and the optimal location and number of

ultrasonic emitters, depending on the construction of the lubrication

system, should be determined.

• New approaches regarding the creation and use of tertiary mixtures

(bioethanol + vegetable oil methyl ester + diesel fuel) to fuelling internal

combustion engines (compression ignition engines), by a novel and

innovative fumigation method using ultrasounds (Figure 42).


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!

• To reduce the influence and magnitude level of engine’s friction losses, as

a major impact factor on engine’s overall energetic efficiency.

Improvement of engine’s mechanisms and systems tribology lead to

increase of mechanic efficiency and consequently to less consumed fuel

and less amount of pollutant emission.

• Investigation of possibilities to use benign (environmental friendly) nano-

materials in green bio-lubricants.

Figure 42. Innovative fumigation method for fuels based on tertiary mixtures

(1-ultrasound emitter, 2-fan, 3-air stream, 4-bioethanol, 5-intake pipe,

6-intake air, 7-vaporized bioethanol, 8- injector, 9-exhaust pipe).


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6. CAREER DEVELOPMENT PLAN

The candidate’s career development plan will be sustained by continuous activity and

training (preparation) in both research and educational domains.

In actual context, at worldwide level, of necessity to improve energetic efficiency of

internal combustion engines (by direct actions and/or introducing of new technologies) there

are continue demands in development of application of new materials and technology. Based

on this issue the same original and unconventional approaches in candidate’s research

activity will be following.

The candidate’s research and educational activities will be oriented in future, in major

goal achievement of active contribution on above presented issue.

The short-term career objectives are follows:

o Obtaining the title of professor

o Publication of scientific articles (to disseminate the research results) in

important journals

o Application of blended and e-learning principles and also the use of

TIC instruments in students education

o Transfer to young researchers the accumulated know-how in project

management

o Continue developing of proposals for national and international

research calls (coordinator/member)

o Developing the international collaboration (institutional and research)

o Collaboration with industry stakeholders on both educational and

research levels.


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!

The long-term career objectives are follows:

o Enrolments (tutoring) of 1-2 PhD students per year

o Continue activity in national/international research calls participation

o Development of international contacts (institutional and research)

o Participating to international conferences to disseminate the research

results

o Increasing the national and international visibility of Automotive

Engineering and Transports Department

o Increasing the attractively of research activity for young researchers

o Continue transfer of accumulated knowledge to students and PhD

students

o Development of new line of study (bachelor and/or master) in advance

technologies for modelling and simulation in automotive engineering

o Continue dissemination of research activity (workshops, scientific

articles, textbooks) at national and international levels

o Extending the collaboration with industry stakeholders on both

educational and research levels


!

!

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