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Research ArticleTwo-Stroke Thermodynamic Cycle Optimization of aSingle-Cylinder Free-Piston Engine Generator

Houliang Yu Zhaoping Xu Qinglin Zhang Liang Liu and Ru Hua

School of Mechanical Engineering Nanjing University of Science and Technology Nanjing 210094 China

Correspondence should be addressed to Zhaoping Xu xuzhaopingnjusteducn

Received 4 March 2019 Accepted 7 April 2019 Published 2 May 2019

Academic Editor Fuat Kara

Copyright copy 2019 Houliang Yu et al -is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

A free-piston engine generator (FPEG) is a new type of energy converter which eliminates the crankshaft and connecting rodmechanism In order to achieve efficient energy conversion the two-stroke thermodynamic performance optimization of a single-cylinder free-piston engine generator is investigated in this paper Firstly the components four-stroke thermodynamic cycle two-stroke thermodynamic cycle and prototype system of the FPEG are presented in detail -e one-dimensional flow simulationmodel of the FPEG is created based on the gas dynamics equation Weber combustion function and heat transfer function andthen the model is validated by the data tested from the prototype system According to the four-stroke experimental results of theFPEG an effective power of 475 kW and a peak pressure of 2102 bar have been obtained -en the two-stroke thermodynamiccycle is simulated and compared under the different control parameters of intake air pressure injection timing ignition timingand valve timing through the simulation model -e optimized results show that an indicated thermal efficiency of 276 anindicated power of 67 kW and a maximal working frequency of 25Hz can be achieved by the prototype system when the two-stroke thermodynamic cycle is used

1 Introduction

Concerns about energy saving and emissions reduction haveresulted in modifications in the structure of an internalcombustion engine (ICE) one method to address this issueis via the free-piston engine [1ndash3] A free-piston enginegenerator (FPEG) is a new type of power plant which hasattracted the research interests of worldwide scholars be-cause of its particular advantages in terms of high efficiencyand low emission

Compared with a conventional generator system thisnew energy conversion device shows the superiority such asstructural simplicities low manufacturing cost and highpower -e biggest difference in structure is the eliminationof the crankshaft and flywheel of engine and the piston andthe mover of the linear generator are directly connected-us the free-piston can oscillate between its two endpointsand be influenced by all forces acting on it Without thelimitation of the connection rod mechanism pistonmovement friction dropped significantly and the FPEG

structure was more compact [4 5] -e free-piston enginegenerator has the ability to accommodate multifuel by easilycontrolling the compression ratio and the indicated powerand system efficiency could be improved by optimizing thethermodynamic cycle

Studies showed that most of the two-stroke free-pistonengines have similar working principle Based on the the-oretical analysis the two-stroke engine has achieved highpower density and thermal efficiency In the past decadesClark and other researchers from West Virginia Universityhad done much research work on the free-piston enginegenerator -ey developed the first prototype system of afree-piston engine generator in 1998 which is a spark-ignitedual-piston structure with a cylinder bore of 365mm and amaximum piston stroke of 50mm [6 7] As reported that theprototype was working at the frequency of 231Hz themaximum output electric power is 316W and the energyconversion efficiency is 11 However the output powerand energy conversion efficiency are significantly lower thanthe simulated results of 50

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 9783246 11 pageshttpsdoiorg10115520199783246

Suat Sarıdemir and Fuat Kara at Duzce University de-veloped an articial neural network (ANN) model in orderto predict the torque and power of a beta-type Stirlingengine After comparing the predicted valves of the modelwith the experimental results the validity of the establishedANN model is veried ey also used a multiple regressionmethod to evaluate the prediction capability of the modeland the results showed that the ANN is a dependable modelto predict the torque and power of the beta-type Stirlingengine [8 9]

Researchers at Toyota Central RampD Labs Inc also de-veloped a single-piston free-piston engine linear generator(FPEG) which consisted of an integrated combustionchamber a gas spring chamber and a linear generator FPEGadopted the two-stroke working mode and it could operatecontinuously for many hours After conducting a powergeneration experiment on FPEG prototype system the resultsdemonstrated that it can realize reliable and stable operationsin all the modes of start-up motoring and ring [10]

In [11 12] Xu et al at Nanjing University of Science andTechnology developed a novel single-cylinder four-strokeFPEG prototype in 2010 As an internal combustion lineargenerator the prototype system achieved continuous andstable operation of the four-stroke working cycle It isequipped with electromagnetic valve train to complete thescavenging process Moreover the 58Nm peak torque withthe maximum output power of 10 kW has been obtained Onthis basis Xu proposed an improved method which opti-mized the two-stroke thermodynamic cycle of FPEG toachieve the thermodynamic performance of high eciencyand energy saving

In this paper in order to achieve the characteristic ofhigher power and optimize the two-stroke thermodynamicperformance an experiment system of the FPEG is estab-lished and made appropriate modications In the followingsections the components and working principle of middlespring-rebounded FPEG are introduced In Section 3 theone-dimensional ow simulationmodel of the FPEG is builtwhich is validated by means of a four-stroke experimenten the two-stroke thermodynamic cycle of FPEG issimulated under diiexclerent inuential factors and the sim-ulation results are compared and analyzed in detail eoptimized results will help us to understand how the two-stroke thermodynamic cycle of FPEG aiexclects the indicatedpower and system eciency

2 Structure andWorking Principle of the FPEG

21 Basic Structure of the FPEG e elementary structure ofthe free-piston engine generator is shown in Figure 1 emain parts of the FPEG are a gasoline engine back springand linear electric generator e system has only onecombustion chamber a rebounding device and a re-ciprocating moving componente combustion chamber isa single-cylinder free-piston engine which is equipped withelectromagnetic valves injector and spark plug A backspring is assembled between the combustion chamber andlinear electric generator e single piston and the movingcoil of the linear generator are connected into one compact

component as a whole mover of FPEG e free-piston willmove freely between the top dead center (TDC) and thebottom dead center (BDC) and its reciprocating motion isdetermined by the imbalance of all forces acting on themover [11 13]

e free-piston engine will operate with trapped fuelmixture and spark plug ignition Because the generatingeciency of a linear electrical generator reduced signi-cantly at low-speed conditions the back spring pushes thepiston upward to achieve continuous operation A super-capacitor is used to incorporate the electricity output by thegenerator e power converter is used for matching thelinear generator and storing the electric energy [14 15] eelectronic controller unit (ECU) could control the system toadjust engine performance after acquiring the signals ofcylinder pressure piston displacement armature currentand others Besides scavenging is implemented by theelectromagnetic valves which are xed on the cylinder headIn a complete working cycle the linear generator works inthe motoring mode only in the intake stroke while otherstrokes work in the generating mode

In the FPEG system there is a great deal of freedom indening the piston motion e FPEG working cycle can beswitched by changing the movement law of the piston usthe four-stroke thermodynamic cycle and two-stroke ther-modynamic cycle can be used for diiexclerent working cycles ofthe FPEG

22 ermodynamic Cycle of the FPEG Four-stroke free-piston engines have relatively more energy saving and highereciency than two-stroke free-piston engines but two-stroke has the advantages of power density At the sameworking frequency the two-stroke working cycle number istwice that of the four-stroke and the time of gas exchange isshorter than the four-stroke [16] e four-stroke and two-stroke thermodynamic cycles of FPEG are presented tooptimize the thermodynamic performance

As can be seen from Figure 2 the remarkable charac-teristics of the four-stroke thermodynamic cycle are the

x

i

ECU

Free-piston engine

Linear generator

Back spring

Super capacitor

Power converter

Engine controller

p

Figure 1 Basic congurations of FPEG

2 Advances in Materials Science and Engineering

short intake and compression stroke which are supple-mented by pressurized the intake air [17] During the intakestroke the linear generator works as an electric machine todrive the piston assembly move downward from point x0 topoint x1 to absorb the fuel mixture It can adjust the intakepressure or air temperature to increase the mixture ow andimprove the combustion process When the piston moves toTDC and approaches the point x2 the fuel mixture iscompressed in the compression stroke During the expan-sion stroke the ignition of the spark plug is the start point forthe combustion process and it will end at point x3 Afterthat the piston moves from bottom to top and reaches thepoint x4 to expel the burned gas us the expansion andexhaust strokes are longer than intake and compressionstrokes and it can achieve the full combustion to increasethe power density

As shown in Figure 3 the two-stroke thermodynamiccycle is characterized by short compression and expansionstroke which is supplemented by adjusting the spark ad-vance angle to realize more full combustione longer valveoverlap can increase the valve opening duration of the intakeand exhaust strokes Before the piston reaches the point x0the spark plug ignites the fuel mixture and the piston movesupward to accomplish the compression stroke During theexhaust stroke the piston moves from point x1 to point x3en the piston moves from point x2 to point x4 in theintake stroke When the piston moves from point x2 to pointx3 the valve overlap realizes the intake and exhaust valvesopen simultaneously to absorb the fuel mixture and expel theresidual gas It can increase the volumetric eciency andimprove the process of gas exchange Besides the advanceignition can achieve the sucient combustion to releasemore energy

23 Prototype and Experiment System e prototypestructure of FPEG is described in Figure 4e prototype is asingle-piston four-stroke gasoline engine which is equip-ped with four electromagnetic valves It employs the water-cooled cooling method closed-loop control of intake portfuel injection and electronically controlled spark-ignition

system Compared with the design requirements of theFPEG the prototype performances are very consistent andfacilitate to ret Table 1 lists the main structure parametersof prototype

e overall structure of the electromagnetic valve isshown in Figure 4e tubular structure consists of iron corecoil skeleton coil permanent magnet layer and outer wall ofactuator In the electromagnetic valve system the coil andvalve are connected rigidly and the back spring is assembledbetween the coil skeleton and the cylinder head e elec-tromagnetic valve is used for providing the scavenging air andrealizing eiexclective control of the gas exchange process Underthe control of electronic controller unit (ECU) it can changevalve lift valve opening time and valve opening duration so itcan achieve exible control of the valve mechanism

Figure 5 shows the 3-D structures of a tubular movingcoil linear generator (MCLG) e MCLG is a single-phasemoving-coil permanent magnet generator also called thevoice coil motor (VCM) e linear generator consists of apermanent magnet (PM) core moving coil and end coverAn air-gap reserved between outer core and inner core Inorder to acquire high air-gap ux density the PM adoptsradial magnetization and the magnetization direction ofPM-A and PM-B is opposite e nonmagnetic coil skeletonis wound two coils which is the whole mover of MCLGFurthermore the coil current is not commutated current

Exhaust

ExpansionCompression

Intake

Pres

sure

Piston displacement

x2

x4

x1

x3

x0

x3 expansionx2 ~x4 exhaustx3 ~x2 compressionx1 ~

x1 intake x0 ~

Figure 2 e four-stroke thermodynamic cycle of FPEG

Pres

sure

Piston displacement

Expansion

Compression

x0 compressionx4 ~x4 intakex2 ~

x3 exhaustx1 ~x1 expansionx0 ~

x0x1

x4

x2

x3

Figure 3 e two-stroke thermodynamic cycle of FPEG

ValveSkeleton

Cylinder head

Intake port

Exhaust port

Electromagneticvalve

End cover

Figure 4 e prototype structure of FPEG

Advances in Materials Science and Engineering 3

that can increase the eciency of MCLG system estructure has the advantages of less moving mass fast re-sponse and low coil inductance [18 19]

Based on the components of the prototype electromag-netic valve moving coil linear generator and sensors theexperiment system of FPEG has been built As shown inFigure 6 the experiment system is used to test and validate thethermodynamic performance of the FPEG e system alsoincludes an engine controller and power converter which isequipped with the cylinder pressure sensor displacementsensor and current sensor e sensors can collect the in-formation of the system at working state and transfer theinformation to the controller which calculates the test results

3 Modeling of the FPEG

e thermodynamic cycle of FPEG is aiexclected by variousfactors such as gas dynamic heat release process and heattransfer loss In this section the simulation model of theFPEG is established based on an one-dimensional gas dy-namics equation Weber combustion function and heattransfer function

31One-DimensionalGasDynamics In order to describe theone-dimensional gas dynamics in the pipe of free-pistonengine the following points are assumed (1) the state ofthe working medium in the combustion chamber is idealhomogeneous gas (2) e temperature pressure and volume

are in accordance with the ideal gas state equation (3) emass of the gas in the cylinder is constant and the ow leakagein the gas exchange process is ignored So the one-dimensionaldynamics model in a pipe is described by three equations

e energy equationzE

ztminusz[u middot (P + E)]

zxminus u middot (P + E)

middot1AmiddotzA

zx+qwV

V A middot dx

E ρ middot Cv middot T +12middot ρ middot u2

(1)

e equation for the conservation of momentumz(ρ middot u)

ztminusz ρ middot u2 + P( )

zxminus ρ middot u2 middot

1AmiddotzA

zxmiddotFRV (2)

e continuity equation of the working mediumzρztminusz(ρ middot u)

zxminus ρ middot u middot

1AmiddotdA

dx (3)

where E represents the energy content of the ideal gas urepresents the ow velocityP represents the static pressureArepresents the cross-sectional area of the pipe qw representsthe heat ow of the wall V represents the unit volume ρrepresents the density of the working medium Cv representsthe specic heat in a content volume and FR represents thefriction force between the uid and the pipe wall

32 Gas Pressure in the Cylinder According to the as-sumptions above we also assumed that the in-cylinder gaspressure is equal to intake pressure PC0 and so is the exhauststrokeWhen the volume of the combustion chamber is zero

Moving coil

Inner core

PM-B

PM-A

End cover

Outer core

Coil skeleton

Figure 5 ree-dimensional structure of MCLG

Free-pisionengine

Spring

Lineargenerateor

Engine controller

Powerconverter

Figure 6 Experiment system of FEPG

Table 1 Specication of prototype

Parameters Unit ValueBore mm 102Stroke mm 126Volume cm3 695Valve seat diameter mm 36Minimal top dead center mm 18Maximal bottom dead center mm 120Motor maximal displacement ccr 182Compression ratio mdash 93Generation eciency of MCLG 952Maximum thrust force of generator N 3200


the piston position is set as the origin of displacement Usingthe first law of thermodynamics and the ideal gas-stateequation the in-cylinder gas pressure can be written asthe following equation

zP

zt1V

(cminus 1) middotdQ

dtminus c middot p middot

dV

dt1113890 1113891 (4)

whereP represents the in-cylinder gas pressureV representsthe volume of cylinder c represents the specific heat ratio ofthe working medium and Q represents the heat release rateof fuel

33 Combustion in the Cylinder -e exothermic character-istic of free-piston engine is determined by the flame prop-agation velocity and the shape of the combustion chamber Inthis paper the simulation model adopts a zero-dimensionalsingle-zone combustion model which defined the wholecombustion chamber as a closed space and ignored the flowleakage AWeber function can be used to represent the actualcombustion process and express the heat release -e heatreleased by the combustion process is as follows

dQ

dt 6908 middot Hu middot Gu middot η middot

n + 1T

middottminus tc

T1113874 1113875

n

middot eminus6908 tminustc( )T( )[ ]

n+1

(5)

where Q represents the heat release rate of the fuel Hurepresents the lower calorific value of the fuel Gu representsthe injected fuel mass per cycle η represents the combustionefficiency n represents the combustion quality index T

represents the combustion duration and t represents thetime variable tc represents the start time of combustion

34 Heat Transfer from the Cylinder During calculating theheat transfer loss the heat transfer irreversibility of re-ciprocating heat cycle is nonnegligible It is assumed that thelosses happened only in the combustion and expansionstrokes and the heat transfer from the combustion chamberto outside is negligible From the in-cylinder gases to cyl-inder walls the calculation equation of the heat transfer is

dQ

dt αw middot π middot D middot (05D + x) middot Tw minusT( 1113857 (6)

where Q represents the heat release rate of the fuel αwrepresents the heat transfer coefficient D represents cylinderdiameter x represents the piston position Tw represents thetemperature of the cylinder walls and T represents the in-cylinder gas temperature

Hereinto the calculation equation adopts the heat transferfunction of Woschni 1978 -e function is suitable for thehigh-pressure cycle and the heat transfer coefficient is

αw 820Dminus02

P08c Tminus053c times C1Cm( 1113857

08

C1 228 + 0308 timesCu

Cm

(7)

where D represents the cylinder diameter Pc represents thein-cylinder gas pressure Tc represents the in-cylinder gastemperature Cu represents the circular speed and Cmrepresents the mean velocity of piston

35 Simulation Model During the process of establishingthe FPEG model the one-dimensional simulation model ismainly divided into two parts -e first part included thedimensional parameters of the engine such as cylinderdiameter the length of intake pipe and exhaust pipe -eother part contained the thermodynamic model combus-tion model and the heat transfer model

FPEGmodeling steps areas follows [20] (1) study themainmeasurement parameters of the engine and collect the dataand information of the structure (2) Divide the actual free-piston engine into several easy-to-operate subsystems and useof AVL BOOST submodules to establish the correspondingphysical submodels (3) According to the theoreticallyknowledge of dynamics heat transfer thermodynamicscombustion a simple physical model has been built whichcontains the collected data and the input information for theengine submodule (4) Use the established model to accom-plish the elementary simulation and find the physical pa-rameters of simulation model in order to modify the error

Based on the theoretical analysis and mathematic modelabove the one-dimensional simulationmodel of the FPEG isestablished in AVL BOOST software to simulate the four-stroke thermodynamic cycle and two-stroke thermody-namic cycle As we all know a complete simulation model ofthe FPEG system should include intake system combustionsystem and exhaust system According to the structureparameters above and experiment system in the previoussection the one-dimensional flow simulation model isestablished as shown in Figure 7

36 Simulation Parameters Before running the simulationmodel the key step is to select the control parameters -einitial value of boundary conditions includes pressuretemperature and air-fuel ratio -ereinto the cylinder pa-rameters contains bore stroke connecting rod length andcompression ratio -e control parameters of heat transferand valve specification also need to be determined Table 2lists the specific parameters of each component

4 Model Validation

-e free-piston trajectory of the FPEG during a four-strokeworking cycle is simulated As shown in Figure 8 theworking period of the four-stroke free-piston engine is about100ms It is clear that the piston displacement is asym-metric the intake and compression strokes are shorter thanexpansion and exhaust strokes -e expansion ratio isgreater than the compression ratio and the longer expansionand exhaust are beneficial to achieve full expansion andreduce residual gas -erefore the characteristics of theFPEG are different from the conventional engine and it has


the great benet in terms of fuel eciency and emissionsformation

A four-stroke experiment is completed on the FPEGsystem to validate the simulation model As seen from Fig-ure 9 it compares the in-cylinder pressure of test data withsimulation results during a four-stroke working cycle whichis obtained by an in-cylinder pressure sensor Compared withthe experimental results the in-cylinder pressure curves of thetest and simulation are coincident the maximum deviation ofin-cylinder pressure variation is 52 and the average de-viation is 15 Table 3 lists the comparison results of FPEG

performance us the simulated results meet the re-quirements of the accuracy and we believe that the simulationmodel is an accurate model of the FPEG Moreover in theFPEG system the start time of the combustion is minus31ms andthe combustion duration is 64ms which are determined bythe four-stroke experimental results

5 Two-Stroke ThermodynamicCycle Optimization

e simulated motion curve of free-piston during a two-stroke working cycle is shown in Figure 10 As can be seen

Intake system

System boundary 1

Test point 1

Air cleaner

Pipe corner 1

Throttle

Pipe corner 2

Cylinder Pipe corner 3

Exhaust system

Catalyst

Container 1

Container 2

Container 3

System boundary 2

Combustion system

Test point 2

Test point 3

Test point 4

Test point 5

Test point 6

Test point 7

Test point 8

Test point 9

Weber combustion function

Heat transfer function

Figure 7 e one-dimensional simulation model of the FPEG system

Table 2 e specic parameters of the simulation model

Components Parameters ValueAir cleaner Total volume 31 Lrottle rottle angle 185deg

Cylinder

Bore 102mmStroke 126mm

Connecting rod length 150mmCompression ratio 93

Intake valve Valve opening 485msValve closing 502ms

Exhaust valve Valve opening 191msValve closed 234ms

Catalyst Monolith volume 03 L

System boundary 1 Pressure 11 barGas temperature 2485degC


BDC1

TDC1

BDC2In

take

Exhaust

Expa

nsio

n

Compression

TDC20

102030405060708090

100110

Disp

lace

men

t (m

m)

2010 30 40 50 60 70 80 90 1000Time (ms)

Figure 8 e four-stroke motion trajectory of FPEG


the working period of the two-stroke free-piston engine isabout 43ms Based on the valve overlap and advanced ignitiona long intake and exhaust stroke while a short compression andexpansion stroke are obtained is characteristic shows thatthe two-stroke thermodynamic cycle of FPEG can be optimizedby changing the control parameters of gas exchange andcombustion

In this section the validated mode is used to simulate thetwo-stroke thermodynamic cycle of FPEG With othercontrol parameters unchanged the model is simulatedunder diiexclerent intake air pressure injection timing ignition

timing intake valve timing and exhaust valve timing enthe inuence of thermodynamic cycle is analyzed and thethermodynamic performance of FPEG is optimized

51 Inuence of Intake Pressurization Research shows thatthe improvement of intake air pressure can ensure a goodcombustion state e FPEG model is simulated underdiiexclerent intake air pressure and the changing curves are asfollows Indicated power residual gas coecient indicatedspecic fuel consumption (ISFC) and intake ow are themain evaluation indexes and they can be found in simu-lation results According to the pressurize range of an actualturbocharger the range of the intake pressurization is10 barsim14 bar

Figure 11 depicts the indicated power and intake owgradually increased the residual gas coecient graduallydecreased in the range of intake pressurization and the fourevaluation indexes change more obviously in the range of10 barsim11 bar e results show that two-stroke free-pistonengine cannot obtain enough intake air ow to complete thework cycle in a normal intake air pressure is is becausemore fuel mixture can be absorbed to the cylinder as higherintake air pressure is provided Furthermore the higherintake air pressure provided a large compression pressureerefore the increasing of intake air pressure results inimproving the indicated power and fuel economy

52 Inuence of Injection Timing In the combustion systemof the one-dimensional simulation model the parameters ofinjection timing can be changed to simulate its eiexclect onFPEG performance As can be seen Figure 12 depicts theinuence of diiexclerent injection time e mean eiexclectivepressure (MEP) is the eiexclective power generated by theworking volume per unit cylinder and it is an importantindex for evaluating the power performance

e range of injection time is divided into three parts0mssim72ms 72mssim144ms and 144mssim216ms Firstlythe indicated power and MEP are maintained at a low-levelof uctuation and the residual gas coecient remainsunchanged at a higher-level Because the process of fuelinjection has completed before the intake valve openingmost of the fuel mixture failed to enter the combustionchamber Secondly the injection time and intake process areconsistent and the thermodynamic performance of FPEGhas enhanced signicantly to improve indicated power andventilation eciency Finally compared with the rst partall the performance values are similar in the range of 144msto 216ms is is because the injection time leaves behindintake process and part of the fuel mixture cannot be used inthe combustion process As can be seen the engine per-formance achieved optimal results at the moment of 144ms

53 Inuence of Ignition Timing e eiexclect of advancedignition is to start burning ahead before the piston moves toTDC When the piston moves to TDC and enters the ex-pansion stroke the mixture-working medium completelyburned and released more energy erefore the range of

0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated

100 200 300 4000 600 700500 800Cylinder volume (cm3)

Figure 9 Tested and simulated FPEG in-cylinder pressure

Table 3 Comparison of test and simulation results

Name Unit Test SimulationEiexclective power kW 475 482Peak pressure bar 2102 2140Residual gas content mdash 00809 00769Start of combustion ms minus31 minus31Combustion duration ms 64 64

Intake valve opensBottom dead center

Exhaust valve closes

Exhaust valve opens

Top dead centerIntake valve closes

5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)

Figure 10 e two-stroke motion trajectory of FPEG


ignition time is -54ms to 0ms and the simulation resultsare shown in Figure 13

In the range of minus3ms to minus54ms the indicated power andMEP gradually decreased and the ISCF gradually increasedis is because the mixture ignited prematurely and theburning gas expanded Part of energy prevents the pistonfrom moving upward to TDCen the indicated power andMEP gradually decreased with diiexclerent ignition time and theISFC gradually increased in the range of minus3ms to 0ms Due tothe delay of ignition time the piston moves downward before

the mixture starts to burn It leads to a larger cylinder volumeand the decreasing combustion pressure and the thermo-dynamic performance of FPEG is in the state of high fuelconsumption and low output power Besides the engineperformance achieved optimal results at minus3ms

54 Inuence of IntakeValveTiming Under the condition ofkeeping valve lift and valve opening duration unchanged theFPEG model is simulated under diiexclerent intake opening

0

2

4

6

8

Indi

cate

d po

wer

(kW

)

11 12 13 14 1510Intake air pressure (bar)

(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)

Figure 11 e inuence of intake pressurization

58

60

62

64

Indi

cate

d po

wer

(kW

)

0 8 16 204 12Injection time (ms)

(a)

84 12 16 200Injection time (ms)

0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)

Figure 12 e inuence of injection timing


time As shown in Figure 14 with the intake opening timefrom 48ms to 168ms the indicated power and intake owshow an overall trend of rising rst then falling and get themaximum value at 108ms Meanwhile the characteristics ofthe residual gas coecient and ISFC are contrary to thechange law of intake ow

When the intake opening time is in the range of 48ms to108ms the intake and exhaust valves open simultaneously

It creates a scavenging ow in the cylinder which makes theprocess of gas exchange more complete and reduces theresidual gas After that the time of intake valve opening islate and part of the fuel mixture failed to enter the cylinderthus the combustion process is insucient and the ther-modynamic performance decreased signicantly Due to thexed time of valve duration the optimal period of intakevalve opening is from 108ms to 245ms

3

4

5

6

7

Indi

cate

d po

wer

(kW

)

ndash4 ndash3 ndash2 ndash1 0ndash5Ignition time (ms)

(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient

0ndash5 ndash2 ndash1ndash4 ndash3Ignition time (ms)

(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)

Figure 13 e inuence of ignition timing

2

4

6

8

Indi

cate

d Po

wer

(kW

)

108 12 161464Intake opening time (ms)

(a)

Resid

ual g

as co

effic

ient

025

035

045

055

4 8 10 12 14 166Intake opening time (ms)

(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)

Figure 14 e inuence of intake opening timing


55 Inuence of Exhaust Valve Timing As described inFigure 15 with the change of exhaust opening time from12ms to 108ms the indicated power and exhaust owshow an overall trend of rising rst then falling e exhaustow increased in the range of 12ms to 36ms and thengradually decreased and it gets the maximum value at36ms e indicated power residual gas coecient andISCF improved with the increase of exhaust ow

e results show that the premature opening of exhaustvalve leads to an insucient combustion process and thepower performance and fuel economy of FPEG will be re-duced With the delay of exhaust valve opening the residualgas in the cylinder cannot be expelled completely and it willaiexclect the next cycle of combustion erefore the properopening time of the exhaust valve has great improvement onthe FPEG performance and the optimal period of the exhaustvalve opening is from 36ms to 231ms

56 Optimized Performance of the FPEG According to theabove simulation results we have made adjustments for thecontrol parameters of the FPEG model e adjusted pa-rameters include ignition time injection time and valveopening time e adjusted model has been simulated at theworking frequency of 25Hz namely 25 reciprocating cyclesper second e optimized results show that the indicatedthermal eciency is about 276 the indicated power is67 kW and the ISFC is 4816 gkWh e specic results ofthe FPEG thermodynamic performance for two-strokethermodynamic cycle are shown in Table 4

6 Conclusions

e work presented the two-stroke thermodynamic per-formance optimization of a single-cylinder FPEG e

comprehensive one-dimensional ow simulation model ofthe FPEG is established and the accuracy of the model isvalidated by the experimental results tested from the FPEGprototype e four-stroke experimental results manifestedthe eiexclective power of 475 kW and the peak pressure of2102 bar has been obtained On this basis the two-strokethermodynamic cycle has been simulated and optimizede simulation results show that the indicated thermal ef-ciency of FPEG is about 276 and the indicated power of67 kW can be achieved at the working frequency of 25HzFrom these results we conclude that the thermodynamicperformance of high eciency and energy saving for theFPEG system can be signicantly promoted by optimizingthe two-stroke thermodynamic cycle

In the future an experimental test will be implementedto validate the simulation results of two-stroke thermody-namic cycle optimization in this paper Furthermore thetwo-stroke free-piston engine generator will be investigatedby the multiobjective intelligent optimization to obtainhigher output power and eiexclective eciency

Data Availability

e data used to support the ndings of this study areavailable from the corresponding author upon request

2 4 6 8 10 120Exhaust opening time (ms)

0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)

Figure 15 e inuence of exhaust opening timing

Table 4 Optimized thermodynamic performance of FPEG

Items Unit ValueIndicated power kW 67Indicated thermal eciency 276Indicated specic fuel consumption (ISCF) gkWh 4816Residual gas content mdash 0285Mean eiexclective pressure bar 26Cycle intake mass g 0671


Conflicts of Interest

-e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

-e authors would like to appreciate the National NaturalScience Foundation of China (Grant no 51875290)

References

[1] F Kara and B Ozturk ldquoComparison and optimization ofPVD and CVD method on surface roughness and flank wearin hard-machining of DIN 12738 mold steelrdquo Sensor Reviewvol 39 no 1 pp 24ndash33 2019

[2] B Ozturk L Ugur and A Yildiz ldquoInvestigation of effect onenergy consumption of surface roughness in X-axis andspindle servo motors in slot milling operationrdquoMeasurementvol 139 pp 92ndash102 2019

[3] N B Hung and O Lim ldquoA review of free-piston linear en-ginesrdquo Applied Energy vol 178 pp 78ndash97 2016

[4] E Nas and B Ozturk ldquoOptimization of surface roughness viathe Taguchi method and investigation of energy consumptionwhen milling spheroidal graphite cast iron materialsrdquo Ma-terials Testing vol 60 no 5 pp 1136ndash1143 2009

[5] P Sun C Zhang J Chen et al ldquoDecoupling design andverification of a free-piston linear generatorrdquo Energies vol 9no 12 p 1067 2016

[6] N N Clark T L McDaniel and R J Atkinson ldquoModelingand development of a linear enginerdquo in Proceedings of theASME Spring Conference Internal Combustion Engine Di-vision pp 49ndash57 Clymer NY USA December 1998

[7] P Famouri W R Cawthorne N Clark S Nandkumar andC Atkinson ldquoDesign and testing of a novel linear alternatorand engine system for remote electrical power generationrdquo inProceedings of the IEEE Power Engineering Society WinterMeeting pp 108ndash112 New York City NY USA January 1999

[8] Y O Ozgoren S Ccediletinkaya S Sarıdemir A Ccediliccedilek andF Kara ldquoArtificial neural network based modelling of per-formance of a beta-type stirling enginerdquo Proceedings of theInstitution of Mechanical Engineers Part E Journal of ProcessMechanical Engineering vol 227 no 3 pp 166ndash177 2016

[9] Y O Ozgoren S Ccediletinkaya S Sarıdemir A Ccediliccedilek andF Kara ldquoPredictive modeling of performance of a heliumcharged stirling engine using an artificial neural networkrdquoEnergy Conversion and Management vol 67 pp 357ndash3682013

[10] K Moriya S Goto T Akita H Kosaka Y Hotta andK Nakakita ldquoDevelopment of free piston engine lineargenerator system Part 3-novel control method of lineargenerator for to improve efficiency and stabilityrdquo in Pro-ceedings of the SAE Technical Paper pp 1ndash685 Detroit MIUSA April 2016

[11] Z Xu and S Chang ldquoPrototype testing and analysis of a novelinternal combustion linear generator integrated power sys-temrdquo Applied Energy vol 87 no 4 pp 1342ndash1348 2010

[12] Z Xu and S Chang ldquoHierarchical hybrid control of a four-stroke free-piston engine for electrical power generationrdquo inProceedings of the International Conference on Mechatronicsand Automation pp 4045ndash4049 Changchun China August2009

[13] S Goto K Moriya and H Kosaka ldquoDevelopment of freepiston engine linear generator systemrdquo in Proceedings of the

SAE Technical Paper vol 1 p 1193 Detroit MI USA April2014

[14] Z Zhang X Chen and Z Xu ldquoA control strategy of free-piston linear generator for reducing the fuel consumption perunit powerrdquo Energies vol 11 no 1 p 135 2018

[15] Z Xu and S Chang ldquoImproved moving coil electric machinefor internal combustion linear generatorrdquo IEEE Transactionson Energy Conversion vol 25 no 2 pp 281ndash286 2010

[16] Z Zhao and D Wu ldquoExperimental investigation of the cycle-to-cycle variations in combustion process of a hydraulic free-piston enginerdquo Energy vol 78 pp 257ndash265 2014

[17] J Lin Z Xu S Chang and N Yin ldquo-ermodynamic sim-ulation and prototype testing of a four-stroke free-pistonenginerdquo Engineering for Gas Turbines and Power vol 136no 5 article 051505 2014

[18] X Pei A Smith D Shuttle worth and M Barnes ldquoHybridsystem modeling and full cycle operation analysis of a two-stroke free-piston linear generatorrdquo Energies vol 10 no 2p 213 2017

[19] H Feng Y Guo Y Song C Guo and Z Zuo ldquoStudy of theinjection control strategies of a compression ignition freepiston engine linear generator in a one-stroke starting pro-cessrdquo Energies vol 9 no 6 p 453 2016

[20] B Qin ldquoSimulation analysis of piston engine based onBOOSTrdquo in Proceedings of International Conference on Me-chanical and Electrical Technology Singapore July 2010


CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018


Journal of

Chemistry

Analytical ChemistryInternational Journal of


ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of



Advances in Condensed Matter Physics


International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of


High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in



ChemistryAdvances in


Advances inPhysical Chemistry


BioMed Research InternationalMaterials

Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

Suat Sarıdemir and Fuat Kara at Duzce University de-veloped an articial neural network (ANN) model in orderto predict the torque and power of a beta-type Stirlingengine After comparing the predicted valves of the modelwith the experimental results the validity of the establishedANN model is veried ey also used a multiple regressionmethod to evaluate the prediction capability of the modeland the results showed that the ANN is a dependable modelto predict the torque and power of the beta-type Stirlingengine [8 9]

Researchers at Toyota Central RampD Labs Inc also de-veloped a single-piston free-piston engine linear generator(FPEG) which consisted of an integrated combustionchamber a gas spring chamber and a linear generator FPEGadopted the two-stroke working mode and it could operatecontinuously for many hours After conducting a powergeneration experiment on FPEG prototype system the resultsdemonstrated that it can realize reliable and stable operationsin all the modes of start-up motoring and ring [10]

In [11 12] Xu et al at Nanjing University of Science andTechnology developed a novel single-cylinder four-strokeFPEG prototype in 2010 As an internal combustion lineargenerator the prototype system achieved continuous andstable operation of the four-stroke working cycle It isequipped with electromagnetic valve train to complete thescavenging process Moreover the 58Nm peak torque withthe maximum output power of 10 kW has been obtained Onthis basis Xu proposed an improved method which opti-mized the two-stroke thermodynamic cycle of FPEG toachieve the thermodynamic performance of high eciencyand energy saving

In this paper in order to achieve the characteristic ofhigher power and optimize the two-stroke thermodynamicperformance an experiment system of the FPEG is estab-lished and made appropriate modications In the followingsections the components and working principle of middlespring-rebounded FPEG are introduced In Section 3 theone-dimensional ow simulationmodel of the FPEG is builtwhich is validated by means of a four-stroke experimenten the two-stroke thermodynamic cycle of FPEG issimulated under diiexclerent inuential factors and the sim-ulation results are compared and analyzed in detail eoptimized results will help us to understand how the two-stroke thermodynamic cycle of FPEG aiexclects the indicatedpower and system eciency

2 Structure andWorking Principle of the FPEG

21 Basic Structure of the FPEG e elementary structure ofthe free-piston engine generator is shown in Figure 1 emain parts of the FPEG are a gasoline engine back springand linear electric generator e system has only onecombustion chamber a rebounding device and a re-ciprocating moving componente combustion chamber isa single-cylinder free-piston engine which is equipped withelectromagnetic valves injector and spark plug A backspring is assembled between the combustion chamber andlinear electric generator e single piston and the movingcoil of the linear generator are connected into one compact

component as a whole mover of FPEG e free-piston willmove freely between the top dead center (TDC) and thebottom dead center (BDC) and its reciprocating motion isdetermined by the imbalance of all forces acting on themover [11 13]

e free-piston engine will operate with trapped fuelmixture and spark plug ignition Because the generatingeciency of a linear electrical generator reduced signi-cantly at low-speed conditions the back spring pushes thepiston upward to achieve continuous operation A super-capacitor is used to incorporate the electricity output by thegenerator e power converter is used for matching thelinear generator and storing the electric energy [14 15] eelectronic controller unit (ECU) could control the system toadjust engine performance after acquiring the signals ofcylinder pressure piston displacement armature currentand others Besides scavenging is implemented by theelectromagnetic valves which are xed on the cylinder headIn a complete working cycle the linear generator works inthe motoring mode only in the intake stroke while otherstrokes work in the generating mode

In the FPEG system there is a great deal of freedom indening the piston motion e FPEG working cycle can beswitched by changing the movement law of the piston usthe four-stroke thermodynamic cycle and two-stroke ther-modynamic cycle can be used for diiexclerent working cycles ofthe FPEG

22 ermodynamic Cycle of the FPEG Four-stroke free-piston engines have relatively more energy saving and highereciency than two-stroke free-piston engines but two-stroke has the advantages of power density At the sameworking frequency the two-stroke working cycle number istwice that of the four-stroke and the time of gas exchange isshorter than the four-stroke [16] e four-stroke and two-stroke thermodynamic cycles of FPEG are presented tooptimize the thermodynamic performance

As can be seen from Figure 2 the remarkable charac-teristics of the four-stroke thermodynamic cycle are the

x

i

ECU

Free-piston engine

Linear generator

Back spring

Super capacitor

Power converter

Engine controller

p

Figure 1 Basic congurations of FPEG








Exhaust


Intake

Pres

sure

Piston displacement

x2

x4

x1

x3

x0


x1 intake x0 ~


Pres

sure

Piston displacement

Expansion

Compression



x0x1

x4

x2

x3


ValveSkeleton

Cylinder head

Intake port

Exhaust port


End cover









e energy equationzE



middot1AmiddotzA

zx+qwV

V A middot dx


(1)




1AmiddotzA

zxmiddotFRV (2)



1AmiddotdA

dx (3)



Moving coil

Inner core

PM-B

PM-A

End cover

Outer core

Coil skeleton


Free-pisionengine

Spring

Lineargenerateor

Engine controller

Powerconverter






zP

zt1V

(cminus 1) middotdQ


dV

dt1113890 1113891 (4)



dQ


n + 1T

middottminus tc

T1113874 1113875

n


n+1

(5)




dQ




αw 820Dminus02


08

C1 228 + 0308 timesCu

Cm

(7)






4 Model Validation








Intake system

System boundary 1

Test point 1

Air cleaner

Pipe corner 1

Throttle

Pipe corner 2


Exhaust system

Catalyst

Container 1

Container 2

Container 3

System boundary 2

Combustion system

Test point 2

Test point 3

Test point 4

Test point 5

Test point 6

Test point 7

Test point 8

Test point 9






Cylinder








BDC1

TDC1

BDC2In

take

Exhaust

Expa

nsio

n

Compression

TDC20

102030405060708090

100110

Disp

lace

men

t (m

m)

2010 30 40 50 60 70 80 90 1000Time (ms)











0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated







Exhaust valve opens


5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)







0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls










Exhaust


Intake

Pres

sure

Piston displacement

x2

x4

x1

x3

x0


x1 intake x0 ~


Pres

sure

Piston displacement

Expansion

Compression



x0x1

x4

x2

x3


ValveSkeleton

Cylinder head

Intake port

Exhaust port


End cover









e energy equationzE



middot1AmiddotzA

zx+qwV

V A middot dx


(1)




1AmiddotzA

zxmiddotFRV (2)



1AmiddotdA

dx (3)



Moving coil

Inner core

PM-B

PM-A

End cover

Outer core

Coil skeleton


Free-pisionengine

Spring

Lineargenerateor

Engine controller

Powerconverter






zP

zt1V

(cminus 1) middotdQ


dV

dt1113890 1113891 (4)



dQ


n + 1T

middottminus tc

T1113874 1113875

n


n+1

(5)




dQ




αw 820Dminus02


08

C1 228 + 0308 timesCu

Cm

(7)






4 Model Validation








Intake system

System boundary 1

Test point 1

Air cleaner

Pipe corner 1

Throttle

Pipe corner 2


Exhaust system

Catalyst

Container 1

Container 2

Container 3

System boundary 2

Combustion system

Test point 2

Test point 3

Test point 4

Test point 5

Test point 6

Test point 7

Test point 8

Test point 9






Cylinder








BDC1

TDC1

BDC2In

take

Exhaust

Expa

nsio

n

Compression

TDC20

102030405060708090

100110

Disp

lace

men

t (m

m)

2010 30 40 50 60 70 80 90 1000Time (ms)











0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated







Exhaust valve opens


5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)







0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls










e energy equationzE



middot1AmiddotzA

zx+qwV

V A middot dx


(1)




1AmiddotzA

zxmiddotFRV (2)



1AmiddotdA

dx (3)



Moving coil

Inner core

PM-B

PM-A

End cover

Outer core

Coil skeleton


Free-pisionengine

Spring

Lineargenerateor

Engine controller

Powerconverter






zP

zt1V

(cminus 1) middotdQ


dV

dt1113890 1113891 (4)



dQ


n + 1T

middottminus tc

T1113874 1113875

n


n+1

(5)




dQ




αw 820Dminus02


08

C1 228 + 0308 timesCu

Cm

(7)






4 Model Validation








Intake system

System boundary 1

Test point 1

Air cleaner

Pipe corner 1

Throttle

Pipe corner 2


Exhaust system

Catalyst

Container 1

Container 2

Container 3

System boundary 2

Combustion system

Test point 2

Test point 3

Test point 4

Test point 5

Test point 6

Test point 7

Test point 8

Test point 9






Cylinder








BDC1

TDC1

BDC2In

take

Exhaust

Expa

nsio

n

Compression

TDC20

102030405060708090

100110

Disp

lace

men

t (m

m)

2010 30 40 50 60 70 80 90 1000Time (ms)











0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated







Exhaust valve opens


5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)







0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





zP

zt1V

(cminus 1) middotdQ


dV

dt1113890 1113891 (4)



dQ


n + 1T

middottminus tc

T1113874 1113875

n


n+1

(5)




dQ




αw 820Dminus02


08

C1 228 + 0308 timesCu

Cm

(7)






4 Model Validation








Intake system

System boundary 1

Test point 1

Air cleaner

Pipe corner 1

Throttle

Pipe corner 2


Exhaust system

Catalyst

Container 1

Container 2

Container 3

System boundary 2

Combustion system

Test point 2

Test point 3

Test point 4

Test point 5

Test point 6

Test point 7

Test point 8

Test point 9






Cylinder








BDC1

TDC1

BDC2In

take

Exhaust

Expa

nsio

n

Compression

TDC20

102030405060708090

100110

Disp

lace

men

t (m

m)

2010 30 40 50 60 70 80 90 1000Time (ms)











0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated







Exhaust valve opens


5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)







0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls









Intake system

System boundary 1

Test point 1

Air cleaner

Pipe corner 1

Throttle

Pipe corner 2


Exhaust system

Catalyst

Container 1

Container 2

Container 3

System boundary 2

Combustion system

Test point 2

Test point 3

Test point 4

Test point 5

Test point 6

Test point 7

Test point 8

Test point 9






Cylinder








BDC1

TDC1

BDC2In

take

Exhaust

Expa

nsio

n

Compression

TDC20

102030405060708090

100110

Disp

lace

men

t (m

m)

2010 30 40 50 60 70 80 90 1000Time (ms)











0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated







Exhaust valve opens


5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)







0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls












0

5

10

15

20

25

Cylin

der p

ress

ure (

bar)

TestedSimulated







Exhaust valve opens


5 10 15 20 25 30 350 504540 6055Time (ms)

0

20

40

60

80

100

120

140

Disp

lace

men

t (m

m)







0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








0

2

4

6

8

Indi

cate

d po

wer

(kW

)


(a)

02

04

06

08

Resid

ual g

as co

effic

ient


(b)

600650700750800850

ISFC

g (k

Wh)


(c)

01

03

05

07

09

Inta

ke fl

ow (g

)


(d)


58

60

62

64

Indi

cate

d po

wer

(kW

)


(a)


0275

0285

0295

0305

Resid

ual g

as co

effic

ient

(b)

464

472

480

488

ISFC

g (k

Wh)


(c)

260

270

240

250

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)






3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







3

4

5

6

7

Indi

cate

d po

wer

(kW

)


(a)

0240

0250

0260

0270

Resid

ual g

as co

effic

ient


(b)

600

800

1000

1200

1400

ISFC

g (k

Wh)


(c)

10

15

20

25

30

Mea

n ef

fect

ive p

ress

ure (

bar)


(d)


2

4

6

8

Indi

cate

d Po

wer

(kW

)


(a)

Resid

ual g

as co

effic

ient

025

035

045

055


(b)

150

300

450

600

ISFC

g (k

Wh)


(c)

03

04

05

06

07

08

Inta

ke fl

ow (g

)


(d)






6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







6 Conclusions




Data Availability



0

2

4

6

8

Indi

cate

d po

wer

(kW

)

(a)


028

032

036

040

Resid

ual g

as co

effic

ient

(b)

0

20

40

60

80

ISFC

100

g (k

Wh)


(c)

035

045

055

065

075

Exha

ust f

low

(g)


(d)







Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Acknowledgments


References

























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




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