2013-01-2887

AbstractBiodiesel is a non-toxic, biodegradable and renewablealternative fuel that can be used as a replacement for diesel indiesel engine. Liquefied Petroleum Gas (LPG) is consideredto be one of the most promising alternative fuels. LPG canreplace petrol and also it reduces NOx, soot and particulatematter. Therefore, it is more inexpensive and of ecologicaladvantage to use gaseous fuel in diesel engines approved forthe dual fuel concept. The fuel injection pressure is one of theimportant operating parameters which affect atomization offuel and mixture formation and hence it determines theperformance and emissions of a diesel engine. There will be adecrease in the particle diameter due to increase in the fuelinjection pressure and it leads the diesel fuel spray tovaporize quickly. However, with decreasing fuel particlestheir inertia will also decrease and for this reason fuel can notpenetrate deeply into the combustion chamber. The objectiveof this study was to use palm oil methyl ester (POME) aspilot fuel in dual fuel engine so as to find out the effects ofinjection pressure on emissions and engine performance in adiesel engine. Injection pressure was changed from 190 bar to230 bar in experiment. A single cylinder diesel engine wastailored to operate in dual fuel mode. In dual fuel mode, LPGwas used as primary fuel and (POME) was used as pilot fuel.Experiments are conducted by fuelling the diesel engine withPOME and its LPG blends for an injection pressure of190bar, 210bar and 230bar. The performance of the diesel isstudied on the dual fuel engine using LPG fuel along withPOME. The highest brake thermal efficiency of diesel with2LPM LPG blend is obtained for an injection pressure of210bar and that for Palm oil Methyl ester blend with LPG at2LPM, highest brake thermal efficiency is obtained for230bar. Low emissions and high brake thermal efficiency ofdiesel engine with LPG blend for pure diesel are obtained at

an injection pressure of 210bar and that for bio-diesel withLPG blends at an injection pressure of 230bar.

IntroductionInternal combustion engines operating on gaseous fuels are inpractice since long time. Many large stationary engines haveused two types of fuels, one is gaseous and other one is aliquid fuel. The two fuels could be taken in a widely varyingproportion to run an engine; such an engine is called a Dualfuel engine. A Dual fuel engine can be considered as aconventional diesel engine. Some supplemental devices arearranged for this engine so that it can also use natural gas asanother fuel. This engine is a true diesel engine and requiressome amount of diesel for operation, for ignition of gaseousfuel. Dual fuel engine has been available to the industry since1930s. The dual fuel engine has various qualitycharacteristics. A primary advantage is the fuel flexibility,operating with natural gas which is cheaper, when availableand on diesel alone when required.

The first dual fuel engine was patented by Dr. Diesel. Theengine runs on gaseous fuel ignited by oil injection in thecombustion chamber. The shortage of liquid fuels andavailability of the gaseous fuels have led to increasedattention on dual fuel engine. Gaseous fuels require highcompression ratio to burn efficiently because they have highself ignition temperature. For this reason, mainly dieselengines have been used as dual fuel engines. Moreover, adiesel engine has ability to run over a wide range of fuelsranging from light weight fuels like JP-4 and kerosene toheavier fuels and crude oils. The conversion of diesel engineto duel fuel functioning is somewhat easy. The engine can beswitched from dual fuel operation to diesel operation almostinstantaneously in case of emergency. When higher speedsare essential, a few dual fuel engines are controlled by

Effect of Injection Pressure on Performance ofDual Fuel Diesel Engine

2013-01-2887Published

11/27/2013

Hariprasad TSree Vidyanikethan Engineering College

Copyright © 2013 SAE International

doi:10.4271/2013-01-2887

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utilizing a fumigation system that supplements natural gas tothe engine. Based on the load and performance necessities, tomake certain regarding the supply of optimal ratio of naturalgas and diesel fuel to the engine, computer controlled duelfuel systems are utilized. The performance of the system andalso the emissions contrast based on the operating conditionsand the complexity of the control system even though theycan attain very lower emissions, especially of NOx andparticulate matter.

The dual fuel engine working principle is similar to theprinciple of diesel cycle. The gaseous fuel is supplied to theair inducted by the engine or supplied by the supercharger ata pressure to some extent above the atmospheric pressure. Asair is compressed in the standard diesel engine operation, themixture of air and gaseous fuel is compressed in the cylinder.In the compression stroke, near the top dead centre, a smallcharge of liquid fuel is induced through a conventional dieselfuel system. This injection is considered as a source forignition. In the vicinity of the injected spray, the mixture ofair and gaseous fuel ignites at a number of places establishinga number of flame fronts and thereby combustion startssmoothly and quickly. It can be noted that event though thecombustion in a dual fuel engine is similar to a diesel engine,the propagation is through the flame fronts, i.e., in a similarmanner to the S.I engine. The power output of the engine iscontrolled by varying the gaseous fuel added to the inletmanifold. The fuel quantity is eventually kept constant for aspecified engine. The ability of the dual fuel engine is to runeither on gas or diesel oil or a combination of these two overwide range of mixtures.

LITERATUREFor development of both present and future high performanceengines with a reasonable fuel economy and with lowemission levels, engine design need to consider variousfactors. A few of them may be the shape of the combustionchamber, inlet port, injection rate, nozzle geometry, spraypattern, injection timing and pressure. The quality ofatomization in diesel engines is majorly affected by thecharacteristics of emission and combustion. The considerableoperating parameter is the fuel injection pressure which mayimpinge on atomization of fuel and mixture formation; andhence it may determine the performance and emissions of adiesel engine. There will be a decrease in the particlediameter due to increase in the fuel injection pressure and itleads the diesel fuel spray to vaporize quickly. Nevertheless,with decreasing fuel particles their inertia will also decreaseand for this reason fuel can not penetrate deeply into thecombustion chamber. Primarily, the higher injectionpressures produce more rapid combustion rates, resulting inhigher cylinder gas temperatures. Though the combustion atthe start with the spray was confined to a small region nearthe injector, the flame spreads around the chamber by slowpropagation. Since the air near the cylinder surfaces are notutilized effectively, the combustion may deteriorate leadingto inefficient process of converting heat to work. Hence, therewill be more reduction in torque and power. Due to the

decrease in fuel injection pressure, the particle diameterincreases and needs more time for the diesel fuel spray tovaporize. Due to the longer delay in ignition, the process ofconverting heat to work will become unproductive, therebyincreasing the smoke formation as there is no time tocomplete combustion of carbon particles [1, 2, 3, 4, 5, 6, 7].

In the recent years, a lot number of developments are noticedin the field of Alternative fuels as the supply of petroleumfuels is strongly dependent on a small number of oilexporting countries. The demand for diesel and gasoline isincreased drastically. It has been estimated that the demandfor diesel will be 66.90 Mt for the year 2011-2012. In theyear 2004 - 2005, India imported 75 % of crude oil fromother countries to overcome the energy necessities. Thegovernment of India has taken essential measures to meetfuture diesel and gasoline demand and also in confining to theemission norms. India is considering alcohol and biodiesel asthe additional fuels to the petroleum products. The biofuelsbeing considered will provide a lot of employmentopportunities to the people of rural areas through plantationof vegetable oils and can be beneficial to sugarcane farmersthrough the ethanol program (Subramanian et al., 2005).When liquefied petroleum gas was used as fuel in dieselengine, it results in poor performance and higher CO andUBHC emissions in comparison with those measured indiesel engines at part loads. But the efficiency improved andsurpassed that of diesel fuel at full load (Karim, 1980). Fromthe experimental results it was observed that the palm oilcould be easily substituted up to 20% in diesel engine,without any significant difference in power output, brakespecific fuel consumption and brake thermal efficiency (Bhattet al., 2004). When methyl ester of palm oil was used as fuelin diesel engine, it results in performance comparable todiesel operation but increases fuel consumption due to itslower calorific value. Methyl ester of palm oil results inlower UBHC, CO emissions and smoke at optimum operatingconditions (Sankaranarayanan et al. 2006). The performanceand emission of LPG - Diesel dual fuel engine is comparablewith diesel operation at higher load (Sethi et al. 2004). Fromthe experimental investigations, it was observed that the lowefficiency and poor emissions at light loads of dual fuelengine can be improved significantly by advancing theinjection timing of the pilot fuel (Abd Alla, 2002). “Gaseousfuels” play a vital role among the low emission fuels. Biogas,producer gas, hydrogen, LPG (Liquefied Petroleum Gas) andCNG (Compressed Natural Gas) are some of the gaseousfuels that are suitable for Internal Combustion Engines. LPGand CNG are the better alternatives because of their simplerstructure with low carbon content, resulting in reduction ofexhaust emissions significantly. In India, LPG is easilyavailable compared to CNG. Hence, for the present workLPG was taken as gaseous fuel. Palm name for a medium tolarger tree, Madhuca longifolia of family Sapotaceae withwider and round canopy. The drying and decortification yield70% kernel on the weight of the palm seed. The kernel ofseed contains about 50 % oil. The oil yield in an expeller isnearly 34 % - 37%. The fresh oil from properly stored seed is

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yellow in color (Bringi, 1987). For the present work, POMEwas used as pilot fuel in dual fuel engine.

Present WorkThe aim of the present work is to use POME as a substitutefor diesel in dual fuel engine. A single cylinder diesel enginetest rig was tailored to operate in dual fuel mode. In dual fuelmode, LPG was used as primary fuel and POME was used aspilot fuel. To improve the performance of the dual fuelengine, the injector opening pressure were increased. Theinjector opening pressure is 190 bar. The viscosity of thePOME is higher than diesel and hence to improve theperformance of the dual fuel engine, the injector openingpressure was increased to 210 bar and 230 bar.

Palm oilPalm oil is produced from fleshy endosperm of the oil palm.Oil palm grows in the tropical region of Asia, Africa andAmerica. A total of seven lakh hectares of land wasrecognized for oil Palm in Southern India. 10,000 hectarescurrently under oil palm, 80,000 hectares by 1997 and200,000 hectares by 2000 AD Technology for palm oilextraction vital to match with the oil palm plantationdevelopment. Therefore, palm oil with highest productionand productivity is a promising feedstock for bio-dieselproduction especially in South East Asia regions.

Palm Oil Methyl EsterPalm oil is used for Palm oil methyl ester (POME) processingin this study. POME is prepared by transesterificationreaction. In transesterification reaction, the molar ratio ofmethanol to Palm oil is 6:1 and 1% mass of KOH to Palm oilis used. At a reaction temperature 65°C, the reactions hadtaken place for two hours. At the end of the reaction, themixtures are kept at the ambient temperature 25-30°C foreight hours and then drained the settled glycerin layer.Finally, the residual methanol in methyl ester mixtures isevaporated. Then the finished product is Palm oil bio-dieselor POME. The ester Conversion rate of POME is over 95%.

Figure 1. Methyl Esters of Palm oil used

The properties of POME are expressed in Table 1.

Table 1. Properties of Diesel and POME

LPGLiterature indicates that LPG is considered to be one of themost hopeful alternative fuels which can be used as areplacement for petroleum. LPG can also be used as a meansfor reducing NOx, soot and particulate matter. Therefore, it ismore inexpensive and of ecological advantage to use gaseousfuel in diesel engines approved for the dual fuel concept.Propane and butane are the main components of LPG andlighter methane and ethane are the components of natural gas.LPG at atmospheric pressure has a higher calorific value (94MJ/m3 equivalent to 26.1kWh/m3) than natural gas(methane) (38 MJ/m3 equivalent to 10.6 kWh/m3), whichimplies that CNG is to be supplied in more quantity to get thesame effect as LPG there by the volumetric efficiency will beeffected. CNG is stored at a pressure equal 20 to 25 timesmore than that of LPG. Moreover the CNG distributionnetworks are not yet in place in many parts of India. So,investigations are carried out on LPG and diesel/bio-dieselblends. Moreover, the present experimental set up is designedfor this purpose and is not suitable for CNG testing. Theproperties of LPG fuel are as shown in Table 2

Table 2. Properties of LPG fuel (Sethi et al (2004))

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Experimental Setup and ProcedureA single cylinder, four stroke, water cooled, direct injection,computerized diesel engine test rig was tailored to operate indual fuel mode. The particulars of the engine used for presentwork is depicted in Table 3.

Table 3. Test Engine specifications

Figure 2. Test engine and measurement devices set-up.

The schematic of the experimental setup is shown in Fig.1.The dynamometer used for loading the engine is of eddycurrent type. The engine speed was sensed and is specified byan inductive pick up sensor in combination with a digital rpmindicator, which is a part of eddy current dynamometer. Theliquid fuel flow rate was measured on the volumetric basisusing a burette and a stopwatch. The gas flow rate wasmeasured using a rotameter with duralumin float. An AVL437C smoke meter was used to measure the smoke emissionand QRO tech co ltd make exhaust gas analyzer was used forthe measurement of emissions in exhaust gases.

The dual fuel engine was started by hand cranking withPOME oil as fuel and slowly LPG was introduced into thecylinder through the air intake manifold. At steady statecondition, significant observations such as gas flow rate, airflow rate, exhaust gas temperature, cylinder pressure andexhaust emissions were recorded. Then the load wasgradually increased up to full load.

Result and Discussion

Brake Thermal Efficiency (BTE)The variation of brake thermal efficiency with load atdifferent injector opening pressures, when bio-diesel is usedas injected fuel, is shown in Figure 3. At full load, for theinjector opening pressure of 190bar, 210 bar and 230 bar, theLPG flow rate of 2.0 LPM, resulting in higher brake thermalefficiency. Since the viscosity of the bio-diesel is high, itrequires large heat source for the combustion of fuel at lowerinjector opening pressure. But at higher injector openingpressure, atomization and penetration of injected fuel is goodand hence the injector opening pressure of 230 bar results inhigher brake thermal efficiency at the LPG flow rate of 2.0LPM. The lower temperatures will cause an increase indensity of air. With more oxygen present, blend POME andLPG can undergo a better combustion and produce higherengine efficiency. This phenomenon is attributed to thechemical properties of LPG where the higher octane value ofLPG compared to POME decreases the amount of fuelrequired for combustion to drive and support the sameamount of loading. The improvement in engine thermalefficiency is explained by the higher heating value of LPGwhich produces more heat for combustion for an equivalentmass flow rate compared to POME alone. Neglecting thesmall amount of fuel used in operation, the use of LPG as asubstitute for fuel offers a huge savings coupled withbeneficial performance characteristics such as increasedoverall torque and brake power output as well as providing anincrease in BTE

Figure 3. Brake thermal efficiency of POME with LPGblends

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HC EmissionsThe variation of unburnt HC emission with load at differentinjector opening pressures, when POME is used as injectedfuel, is shown in Figure 4. The HC emissions at 230 barinjection pressure are lower than 210bar and 190bar injectionpressure, because of improved atomization and better mixingprocess at higher injection pressures. Due to high viscosity ofPOME compared to diesel, high injection pressure is requiredfor improved atomization and better mixing process.

Figure 4. HC Emissions of POME with LPG blends

With increasing load, the amount of HC produced in theemission will decrease due to greater combustion efficiencyis achieved with increased temperature

CO EmissionsThe variation of carbon monoxide emission with load atdifferent injector opening pressure, when POME is used asinjected fuel, is shown in Figure 5. At full load, for theinjector opening pressure of palm oil methyl ester, due tohigher injection pressure, atomization and mixing process areimproved. Due to high viscosity of POME compared todiesel, high injection pressures are required for improvedatomization and better mixing process resulting in low COemissions. At full load, the lowest CO emission of POME isobtained for the blend of 2LPM of LPG at an injectionpressure of 230bar

Figure 5. CO Emissions of POME with LPG blends

For dual fuel the recorded CO emission is lower if comparedto diesel fuel operation. LPG produces a greater combustionefficiency leading to lower amounts of CO since LPG in itsgaseous state usually contain less contaminants than dieselfuel. Apart from that, turbulent mixing between LPG and airin the engine produces a higher quality mixture since both arein gaseous phase, thus producing a lower carbon monoxide.CO emission for dual-fuel operation increases slightly withincreasing engine load since the residence time of fuel in thecombustion chamber is decreased at high engine loads,causing higher CO formation. This result shows that dual-fueloperation is able to achieve a better combustion compared todiesel fuel under maximum load conditions.

NOx EmissionsThe variation of NOx emission with load at different injectoropening pressure, when POME is used as injected fuel, isshown in Figure 7. At full load, for the injector openingpressure of 190bar, 210 bar and 230 bar, the LPG flow rate of2 LPM, results in slightly low NOx emission. At full load, thelowest NOx emission of POME is obtained for the blend ofLPM of LPG at an injection pressure of 230bar.

Figure 7. NOx Emissions of POME with LPG blends

Engines running with dual-fuel produce less NOx than dieselsince diesel fuel contains high volatile nitrogen compounds intheir composition which contributes to a higher level ofnitrogen concentration in the combustion chamber. Sincediesel engines operate primarily in the lean region whendiesel fuel is consumed, there is excess air and oxygen for thenitrogen compounds to form NOx when the combustiontemperature is high. The low emission of NOx for dual-fuelengines is attributed to several factors. Firstly, the premixedcombustion is less intense and produces less activationenergy for nitrogen and oxygen compounds to disintegrateand form NO. The reduced mixing of air and fuel also lowersthe oxidation rate of NO to NO2 in the chamber. Apart fromthat, the lower exhaust temperatures present in the dual-fuelsystem. Finally, the concentration of O2 is reduced in thechamber due to the presence of gaseous LPG fuel, which willdisplace an equal amount of air.

Smoke opacityThe variation of smoke opacity with load at different injectoropening pressure, when POME is used as injected fuel, is

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shown in Figure 8. At full load, for the injector openingpressure of 190 bar, 210 bar and 230 bar, the LPG flow rateof 2.0 LPM, resulted in lower smoke opacity.

Figure 8. Smoke opacity of POME with LPG blends

It is obvious that the smoke is decreased with increase ofLPG mass fraction, especially at high engine load. The reasonis that the boiling temperature of LPG is lower and easier toevaporate. Once injected as a free jet, LPG will vaporizerapidly because of the pressure reduction. This flash boilinginjection can enhance gas perturbation with fluctuationpressure in the spray field and the gas perturbation willdefinitely promote the spray process. Spray can, thus,improve, and the droplets of blended fuel become smallerthan those of Diesel. The longer hold-up time of the dropletslowers the particle pollution due to splitting fuel. Thepossibility of producing smoke is reduced due to reduction inthe possibility of oxygen absent at high temperature fordiesel. The combustion velocity increases and the burning isshortened, which helps to restrain smoke production.Therefore, the LPG-bio-diesel dual fuel engine's emission isreduced.

ConclusionsFrom the experimental results, the following conclusions aredrawn. The dual fuel engine runs smoothly with POME withthe higher injector opening pressure and advanced injectiontiming. The efficiency of the dual fuel engine is slightly lessas compared to neat diesel operation at part loads. The dualfuel engine results in lower smoke and NOx emissions ascompared to neat diesel operation. But it emits slightly higherCO and UBHC emission. It is derived based on the results ofthe experiments that the POME can be used as an alternativefor diesel in dual fuel engine with comparable performanceand lower smoke and NOx emissions. The effect of injectionpressure on performance and emissions of engine using LPGas fuel and POME as ignition source in a CI Diesel Engineare studied

Experiments using POME with LPG blends as Fuel

1. At full load, the highest brake thermal efficiency of dieselengine is obtained for the blend of 2LPM of LPG at aninjection pressure of 230bar.

2. At full load, the lowest HC emission of diesel engine isobtained for the blend of 2LPM of LPG at an injectionpressure of 230bar.

3. At full load, the lowest CO emission of diesel engine isobtained for the blend of 2LPM of LPG at an injectionpressure of 230bar.

4. At full load, the lowest NOx emissions of diesel engineare obtained for the blend of 2LPM of LPG at an injectionpressure of 230bar.

5. At full load, the lowest smoke opacity of diesel engine isobtained for the blend of 2LPM of LPG at an injectionpressure of 230bar.Finally it is concluded that for minimization of emissions andmaximization of brake thermal efficiency of diesel engine, itis advisable to run the diesel engine at an injection pressureof 210bar and that for bio-diesel with LPG blends at aninjection pressure of 230bar.

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International Journal of Oil, Gas and Coal Technology, 3(4),374-384.

AbbreviationsPOME - Palm oil methyl esterBTE - Brake thermal efficiencyLPG - Liquid petroleum gasLPM - Liter per minuteUBHC - Unburnt Hydrocarbons

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