Combustion of Simulated Biogas in a Dual-Fuel Diesel Engine, Energy Conversion and Management

COMBUSTION OF SIMULATED BIOGAS IN A DUAL-FUEL

DIESEL ENGINE

A. HENHAM* and M. K. MAKKAR$

School of Mechanical and Materials Engineering, University of Surrey, Guildford, GU2 5XH, U.K.

AbstractTechnology related to biogas has been steadily developed over the last 50 years from smallindividually designed units to larger production plants. The development, however, has largely takenplace on the side of biogas production and anaerobic waste treatment. Utilization of the gas producedby these methods has only recently been the subject of more scientific evaluation. The transformationof energy through biogas into the thermodynamically higher valued mechanical energy successfully andeconomically is now the most important research area in this field.Of the engine work already published, most concerns spark-ignited engines. The authors research

work concerns the use of biogas in dual-fuel diesel engines. It examines engine performance using simu-lated biogas of varying quality representing the range of methane:carbon dioxide composition whichmay be encountered in gas from dierent sources. The total programme includes the eects of biogasquality and of the proportion of energy from pilot fuel injection over a range of speeds and loads, in-vestigations into the performance parameters over a range of compositions of gaseous mixture. A two-cylinder, indirect-injection diesel engine of stationary type is being used as the first experimental testbed in this work and the variation of quality is provided by mixing natural gas and carbon dioxide. Adata acquisition system for in-cylinder pressure and crank angle is being used successfully and someemissions measurements are also available, particularly for CO and O2.One of the authors is from India where there is thought to be considerable potential for exploiting

the gaseous products from resources such as biogas, landfill and sewage gas through small stationarydual-fuel engines for irrigation and CHP applications. The nature of combustion process in the dual-fuel engine is examined by the authors through pressure-crank angle data and studies of characteristicsaecting engine eciency. # 1998 Elsevier Science Ltd. All rights reserved

Biogas Dual-fuel engine Alternative fuels

INTRODUCTION

The gaseous fuels are getting more positive response from researchers and end-users comparedwith the past because of current unfolding developments. The first development of importance iscertainly the issue of the 1990 sthe environment. Gas is clearly the fossil fuel of least environ-mental impact. When burnt, it produces virtually no SOx and relatively little NOx, the mainconstituents of acid rain, and substantially less CO2, a key culprit in the greenhouse debate,than most oil products and coal. The second unfolding development is driven by technology.There has been a steady increase in the use of alternative transportation fuels. Our main empha-sis is on the gaseous fuels. Use of natural gas for power generation in combined cycle plant hasled thermal eciency to 52% while it is only 40% from state-of-the-art coal or oil fired powerplants which also require desulphurization. Other gases like biogas, landfill gas and sewage gashave also attracted the researchers worldwide to realise and tap their energy potential to the op-timum use.

The analysis of the various gaseous fuels from the various sources like natural gas, biogas,landfill and sewage gas reveals that the main constituent contributing to the heating value of thefuel is methane. Thus methane number can be used to classify the various gaseous fuels in simi-lar ways to octane number and cetane number being used for petrol and diesel respectively.

The focus of the present research is not only the use of biogas in internal combustion enginesalready explored very well by so many researchers [3, 4, 610] but to explore the eects of vary-ing the quality of gaseous fuel in terms of the methane number of the fuel by mixing naturalgas and carbon dioxide in dierent proportions while using gasoil as pilot fuel. It will be very

Energy Convers. Mgmt Vol. 39, No. 1618, pp. 20012009, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0196-8904/98 $19.00+0.00

PII: S0196-8904(98)00071-5

*To whom all correspondence should be addressed.$Currently at Thapar Corporate R&D Centre, India.

2001

significant to obtain the relationship of methane number versus eciency of dual fuel engineand to compare the same with the diesel engine eciency.

MODIFICATION IN INTERNAL COMBUSTION ENGINES WORKING ON GASEOUS

FUELS

The modification of a spark ignition engine is comparatively easy as the engine is designed tooperate on air/fuel mixture with spark ignition. The basic modification is the provision of agasair mixer instead of the carburettor. The engine control is performed by the variation ofmixture supply, i.e. throttle valve position as has been the case with petrol fuel. Spark ignitionengines converted to natural gas show a power decrease of 1520% attributed to a decrease involumetric eciency because of the gaseous fuel and the lower flame speed of airgas mixturecompared with airgasoline mixtures. This power loss can be decreased to some extent by utilis-ing the higher compression ratio possible with gas and advancement in spark timing. In station-ary applications this loss of power is less important as they are mainly run at full load.In dual-fuel diesel engines, the normal diesel fuel injection system still supplies a certain

amount of diesel fuel. The engine however induces and compresses a mixture of air and gaseousfuel which has been prepared in the external mixing device. The mixture is then ignited byenergy from the combustion of the diesel fuel sprayed in. The diesel fuel spray is termed as pilotfuel. The amount of diesel fuel needed for sucient ignition is between 1020% of the amountneeded for operation on diesel alone at normal working loads. It diers with the point of oper-ation and engine design parameters. Operation of the engine at partial load requires a reductionof the fuel gas supply by means of a gas control valve. A simultaneous reduction of the airsupply would, however, decrease the quantity induced hence the compression pressure and themean eective pressure. This would lead to a drop in power and eciency. With drastic re-duction the compression conditions might even become too weak to eect self-ignition. Dualfuel engines should, therefore, not be throttled/controlled on the air side.Biogas as a fuel for vehicles has been an issue since the 1950 s. While in Europe the use in

tractors seems to be the issue [1, 2] in Brazil the aim is to substitute petrol and diesel fuel in theautomotive sector using purified and compressed biogas or natural gas [11]. Biogas originatesfrom bacteria in the process of biodegradation of organic material under anaerobic conditionsand can also be produced by partial combustion of biomass in a gasifier. A typical dry-gascomposition [6] may be 1820% CO, 810% CO2, 1820% H2, 23% CH4 and a balance ofN2. The widely variable composition of the gas from the gasifier makes this fuel better suited todiesel engines operating in a dual fuel mode. Mukunda et al. [6] have discussed the completegasifier/diesel engine system in some detail. Stone et al. [8] have analysed biogas combustion(typical composition is 35% CO2 with 65% CH4) in spark-ignition engines by means of exper-imental data and a computer simulation.Ideally, there is a need for optimum variation in the liquid fuel quantity used any time in re-

lation to the gaseous fuel supply so as to provide for any specific engine the best performanceover the whole load range desired [3]. Usually, the main aim, for both emissions and economicreasons, is to minimize the use of the diesel fuel and maximize its replacement by the cheapergaseous fuel throughout the whole load range. The dual-fuel engine can operate eectively on awide range of dierent gaseous fuels while maintaining the capacity for operation as a conven-tional diesel engine. Normally, the change over from dual fuel to diesel operation and viceversa, can be made automatically even under load.

EXPERIMENTAL SET-UP

The test engine for the present research work is a two-cylinder, four-stroke, water-cooled,indirect injection Lister Petter LPWS2 diesel engine. The set-up for experimental work includinggas supply line with pressure cut-o and safety devices and other instrumentation used is shownin Fig. 1.

HENHAM and MAKKAR: COMBUSTION OF SIMULATED BIOGAS2002

Design for mixing device

The mixing device was designed according to recommendations of von Mitzla [5]. It is a T-joint with the gas pipe protruding into the device as shown in Fig. 2. The gas pipe is cut obliquewith the opening facing the engine inlet. The protruding section increases the active pressuredrop for the gas to flow into the mixing device. The pressure drop increases further withincrease in engine speed and thus sucks more gas also. The design calculations to evaluate diam-eter of the pipe for gas inlet are based on the parametersrated power, cubic capacity, ratedspeed, volumetric eciency, manifold diameter, diesel substitution, gas calorific value and vel-ocity of gas. To improve mixing further a turbulence grid shown in Fig. 3 has been introducedin the above mixing device.

Fig. 1. Set-up for experimental work and instrumentation.

Fig. 2. Gas mixing device.

HENHAM and MAKKAR: COMBUSTION OF SIMULATED BIOGAS 2003

Fig. 3. Turbulence grid.

Fig. 4. IDI dual-fuel eciency variation using gas mixture at 2000 rev/min and 40 Nm.

Fig. 5. IDI dual-fuel exhaust temperature variation using gas mixture at 2000 rev/min and 40 Nm.


Fig. 6. IDI dual-fuel CO variation using gas mixture at 2000 rev/min and 40 Nm.

Fig. 7. IDI dual-fuel eciency variation using gas mixture at 2800 rev/min and 40 Nm.

Fig. 8. IDI dual-fuel exhaust temperature variation using gas mixture at 2800 rev/min and 40 Nm.


Fig. 10. P-y diagram for gasoil only @ 2000 rev/min, 40 Nm.

Fig. 11. P-y diagram for gasoil and 60% NG substitution @ 2000 rev/min, 40 Nm.

Fig. 9. IDI dual-fuel CO variation using gas mixture at 2800 rev/min and 40 Nm.


Fig. 12. P-y diagram for gasoil and NG:CO2 (1:1) @ 2000 rev/min, 40 Nm.

Fig. 13. P-y diagram for gasoil only @ 2800 rev/min, 40 Nm.

Fig. 14. P-y diagram for gasoil and 60% NG substitution @ 2800 rev/min, 40 Nm.


RESULTS AND DISCUSSIONS

Tests have been conducted on the dual-fuel diesel engine at various proportions of gas mix-ture comprising of natural gas (NG) and carbon dioxide. Firstly gasoil substitution by NG fromthe British mains (94% methane, 34.8 MJ/m3) was at four constant levels of substitution 22%,37%, 45% and 58%. Then taking each constant level of NG as 100%, it has been mixed withCO2 to vary the composition of gas mixture. Each symbol represents a result at a particularproportion of energy from gaseous fuel.Test results in Fig. 46 are at engine speed 2000 rev/min and torque 40 Nm using NG:CO2

mixture for a range of 100:0 to 40:60 at four constant NG substitution levels.The overall eciency has been calculated on the basis of power obtained by the rate of energy

input from gasoil and gas mixture at various proportions. It falls with NG substitution at allconstant levels. On mixing NG with CO2 eciency is not much aected upto 37% NG substi-tution. With higher NG substitution eciency decreases with increasing CO2 in gas mixture. At58% NG substitution level, eciency decreases from 28.2% to 26.2% with increasing CO2 ingas mixture. With higher gas substitution a greater proportion of air is replaced by gas so volu-metric eciency is lowered resulting in less power.Figure 5 indicates that exhaust temperature is aected more by NG substitution up to 45%.

At 58% NG substitution, exhaust temperature increases with increasing CO2 in gas mixture,from 3828C to 4028C.Figure 6 indicates that CO is aected mainly by NG substitution and not so much by the pro-

portion of CO2 in the gas mixture. The increase in CO as compared to that with gasoil onlywhere it was only 0.04% is caused by lower eective air fuel ratio as gas mixture replaces moreair.Test results in Fig. 79 are at engine speed 2800 rev/min and torque 40 Nm using NG: CO2

mixture for a range of 100:0 to 30:70 at five constant NG substitution levels.Figure 7 indicates that, at 2800 rev/min, overall eciency decreases with increase in CO2 in

gas mixture at all substitution levels. Figures 8 and 9 indicate that exhaust temperature and COfollow the same patterns as at 2000 rev/min except at 65% NG substitution. At this conditionthe combustion is less controlled and knock was noticed during the test run.Figures 1012 show the in-cylinder pressure characteristics of the test engine at gasoil only,

gasoil and 58% NG substitution and gasoil and gas mixture (NG:CO2::1:1) respectively at 2000rev/min and 40 Nm. Peak pressure rises from 70 bar to 83 bar at 58% NG substitution andfalls to 77 bar for gas mixture of NG:CO2 (1:1). Sharper peaks may be observed in Figs 11 and12 compared to Fig. 10 and that is thought to be the result of more fuel being available at theinitiation of combustion.Figure 1315 show the in-cylinder pressure characteristics of the test engine at gasoil only,

gasoil and 60% NG substitution and gasoil and gas mixture (NG:CO2::1:1) respectively at 2800rev/min and 40 Nm. Peak pressure rises from 57 bar to 70 bar at 60% NG substitution andfalls to 67 bar for gas mixture of NG:CO2 (1:1). The dierences from the shapes of the diagrams

Fig. 15. P-y diagram for gasoil and NG:CO2 (1:1) @ 2800 rev/min, 40 Nm.


at 2000 rev/min derive from the injections required for the larger crank angle movement duringincreased power and speed.

CONCLUSIONS

The extensive range of tests which have been conducted in varying fuel quality in a dual-fuelIDI engine have shown the following characteristics:

. 60% gasoil substitution is possible by gas mixture without knock.

. Overall eciency falls with gas mixture substitution and adding CO2 aects this more athigher speed.

. Exhaust temperature is aected more by NG substitution than by CO2 addition except atmaximum NG substitution.

. CO is aected mainly by NG substitution and less by gas quality.

. There is a more rapid pressure rise on combustion with dual-fuel operation.

The authors are currently exploring the eect on combustion of using a direct-injection versionof the same engine.

AcknowledgementsThe authors are grateful for assistance in various ways from Lister Petter Diesels, British Gas andBOC. The British Council is supporting Mr Makkars research studies under Nehru Centenary British Fellowshipscheme.

REFERENCES

1. Buttner, S. and Mauser, K., Traktor mit Biogasantrieb-Umrustung and erste. Eiensatzerfahrungen. Landtechnik Nr.6, KTBL, Darmstadt, FRG (in German), 1982.

2. Fankhauser, J. and Moser, A., Studie uber die Eignung von Biogas als Treibsto fur Landwirtschaftstraktoren. FATpublication no. 18. Tanikon, Switzerland (in German), 1983.

3. Karim, G. A., Automotive Engine Alternatives. The Dual Fuel Engine, ed. Robert L. Evans. Plenum Press, NewYork and London.

4. Kulkarni, M. K., Kirlosker dual fuel biogas engines, Commonwealth Regional (Asia/Pacific) Rural TechnologyProgramme, Bombay, India, 1980.

5. Von Mitzla, K. Engines for biogas. A publication of Deutsches Zentrum fur Entwicklungstecknologien, GATE.6. Mukanda, H. S., Dasappa, S. and Shrinivasa, U., Open-top Wood Gasifiers, Renewable Energy, Earthscan

Publications, London, 1993.7. Sasse, L., Biogas Plants, GATE/Vieweg, Braunschweig, FRG, 1984.8. Stone, C. R., Gould, J. and Ladommatos, N., J. Inst. En., 1993, 66, 180.9. Werner, U. et al., Praktischer Leitfaden fur Biogasanlagen in der Tierproduktion. Oekotop/GATE. Eschborn, FRG

(in German), 1986.10. Zexi, C., Application of biogas on farm internal combustion engine, Provincial Agricultural Machinery Research

Institute of Sichuan, P.R. of China, 1982.11. Encontro de Biogas Automotive para Empresa Rural, 1-Londrina-PR, Embrater, Brazilia, Brazil (in Portuguese),

1983/84.


Combustion of Simulated Biogas in a Dual-Fuel Diesel Engine, Energy Conversion and Management

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