research article influence of exhaust gas recirculation

Research ArticleInfluence of Exhaust Gas Recirculation, and Injection Timingon the Combustion, Performance and Emission Characteristicsof a Cylinder Head Porous Medium Engine

Chidambaram Kannan and Thulasi Vijayakumar

School of Mechanical and Building Sciences, VIT University, Vellore, Tamil Nadu 632 014, India

Correspondence should be addressed to Chidambaram Kannan; [email protected]

Received 25 July 2015; Revised 22 September 2015; Accepted 27 September 2015

Academic Editor: Philip De Goey

Copyright © 2015 C. Kannan and T. Vijayakumar. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

Homogeneous combustion has the potential of achieving both near-zero emissions and low specific fuel consumption. However,the accomplishment of homogeneous combustion depends on the air flow structure inside the combustion chamber, fuel injectionconditions, and turbulence as well as ignition conditions. Various methods and procedures are being adopted to establish thehomogeneous combustion inside the engine cylinder. In this research work, a highly porous ceramic structure was introducedinto the combustion chamber (underside of the cylinder head). The influence of operating parameters such as exhaust gasrecirculation (EGR) and injection timing on the combustion, performance, and emission characteristics of such developed enginewas investigated in this research work.

1. Introduction

Reduction in diesel engine emissions, in particular nitrogenoxide and particulate emission, is becoming serious problemto be tackled, as emission norms are getting more and morestringent nowadays. Numerous research works have beenperformed on the influence of in-cylinder mixture formationand combustion process on the outcome of exhaust emissionsfrom an internal combustion engine [1–3]. It is well proventhat homogeneous mixture results in lower particulateemission from diesel engines [4–6]. Researchers are tryingvarious technologies to accomplish homogeneous mixtureformation, combustion, and subsequently lower particulateemission. One such technique to realize lower particulateemission from diesel engines is porous medium combustion[4, 5]. Lownitrogen oxide emissionwill be the supplementarybenefit of porous medium combustion technique [7, 8].

The most critical process in this technique is the fuelvapourization. Imperfections within this process directly influ-ence the quality of the combustible fuel-air mixture, result-ing in higher exhaust gas emissions of carbon monoxide,

nitrogen oxide, and unburned hydrocarbons [9]. Withenhanced evaporation of liquid fuels by the presence ofporous medium and in the presence of oxygen, rapid andcomplete combustion can always be achievable, which leadsto much lower emissions from the porous medium (PM)engine.

2. Literature Review

Shahangian et al. [10] investigated the role of porous mediumin the homogenization of high pressure diesel fuel spray in aconstant volume chamber. In this work, the author exploredthe influence of porous medium on the air-fuel mixtureformation through image processing techniques and heatrelease and heat transfer models. The system pressure andtemperature on themixture formation were also investigated.

Shahangian and Ghojel [11] performed an investigationabout the interaction between diesel sprays and porousmedium in a constant volume chamber. The author foundthat increasing the injection pressure increased the numberof secondary sprays emerging fromporousmedium and their

Hindawi Publishing CorporationJournal of ermodynamicsVolume 2015, Article ID 927896, 10 pageshttp://dx.doi.org/10.1155/2015/927896

2 Journal of Thermodynamics

penetration. It was also concluded that the fuel distributioninside the chamber volume was strongly affected by thecharacteristics of porous medium.

Weclas et al. [12] simulated the thermodynamic condi-tions of the heat release process of a diesel engine in a specialcombustion chamber. The analysis was further extended to afree volume combustion chamber with no porousmedium. Acommon rail diesel injection system was used for simulationof fuel injection process andmixture formation conditions assuch in a real engine.The results showed that thermodynamiccondition of heat release process depends on porous mediumheat capacity, pore density, specific surface area, and porestructure.

Weclas et al. [12] investigated low and high temperatureoxidation processes including thermal autoignition underdiesel engine-like conditions (nonpremixedmixtures). A spe-cial combustion chamber, characterized by constant volumeand adiabatic conditions, was used as an engine simulator. Inthis study, five characteristic regions of the processes wereconsidered: region 1 corresponds to processes occurring atlow initial pressure over a wide range of initial temperatures;region 2 corresponds to low initial temperatures over a widevariation of initial pressure; region 3 corresponds to middlepressure and higher temperatures; region 4 corresponds tomiddle temperatures and higher pressure; and region 5 cor-responds to high initial pressure and high temperatures. Thisresearch work ended with a conclusion note that the ignitiondelay reduces with increasing chamber temperature andpressure.

Mohammadi et al. [13] performed the simulation of inter-nal combustion engine equipped with a chemically inertporous medium to homogenize and stabilize the combustionof engine. A three-dimensional numerical model for porousmedium engine was developed based on a modified versionof the KIVA-3V code. In this simulated study, methane gasinjected directly inside the hot porous medium (mounted oncylinder head) was considered as fuel.Mixture formation andpressure and temperature distribution in porousmedium andin-cylinder fluidwith the production of pollutants such asCOand NO were also studied. The numerical results of porousmedium enginewere validatedwith experimental data of leanmethane-air mixture under filtration in packed bed.

Zhou et al. [14] developed an axisymmetric model withdetailed chemistry and two-temperature treatment into avariant of KIVA-3V code to simulate the working process of aporousmedium engine.The comparisonsweremadewith thesame engine without porous medium implementation. Thekey factors affecting heat transfer, combustion and emissionsof the porous medium engine such as porosity, the initialtemperature of porous medium, and equivalence ratio wereanalyzed. The results showed that the characteristics of heattransfer, emissions, and combustion of the porous mediumengine are superior to the engine without porous medium.Moreover it was found that porous medium engine is able tosustain ultra lean combustion.

At the end of literature review, it is evident that prop-erly implemented porous medium will produce positiveinfluence on emissions and performance characteristics of

Figure 1: Photographic view of cylinder head with ceramic coatedwire mesh PM implementation.

an internal combustion engine. Majority of previous worksthat reported on porous medium are confined to eithernumerical simulation or experimentation in a constant vol-ume chamber. Limited research works have reported on thepractical implementation of porous medium in an enginewhose operation is limited to lean mixture strength. In thisresearch work, an attempt was made to achieve the porousmedium combustion in direct injection (DI) diesel enginewith the inclusion of highly porous ceramic material intothe space of combustion chamber (underside of the cylinderhead). In addition, the porous medium engine was beingoperated from no load to peak load conditions; that is, theengine operation was not limited to lean mixture strength.The influence of operating parameters such as EGR andinjection timing on the combustion, performance, and emis-sion characteristics of such developed porous mediumengine was analyzed and compared with the conventionalengine.

3. Development of Cylinder Head PorousMedium Engine

After detailed literature survey, a suitable porous mediumwith high porosity was selected for developing a porousmediumengine.High porositymade themedium transparentfor gas flow, spray, and flame. In a porousmedium engine, theporous medium can be placed in one of the following loca-tions: cylinder, cylinder head, or piston. In this investigation,porous medium was placed on the underside of the cylinderhead. In order to accommodate the porous medium on thislocation, a certain volume of material was removed from theunderside of cylinder head and porous medium was placedin that recess and detained in its position by an appropriatelocking mechanism. Due to the removal of material fromthe underside of cylinder head, the compression ratio ofporous medium engine reduced to 16 : 1 as against 17.5 : 1in the conventional engine. The photographic view of suchcylinder head with porousmedium implementation is shownin Figure 1. The dimensions and important properties ofporous ceramic medium used in this experiment are givenin Table 1.

Journal of Thermodynamics 3

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(1) Engine (2) Dynamometer (3) Dynamometer controls(4) Air box (5) U tube manometer (6) Fuel tank(7) Fuel measurement (8) Pressure transducer (9) TDC position sensor(10) Charge amplifier (11) TDC amplifier circuit (12) Analog to digital card(13) Computer (14) Exhaust gas analyzer (15) AVL smoke meter(16) EGR control valve (17) Electrical heater

Figure 2: Experimental setup.

Table 1: Dimensions and properties of porous ceramic medium.

Diameter of porous medium 30mmHeight of porous medium 20mmPorosity 75%Melting point 2700∘CDensity 5.89 g/cm3

Thermal heat conductivity 2W/mKSpecific heat capacity 400 J/kgKThermal expansion coefficient 11 × 10−6/∘C

4. Experimental Setup and Testing Procedure

The engine setup used for the experimental investigation isshown in Figure 2.The tests were conducted on a single cylin-der four-stroke, naturally aspirated, air cooled direct injectiondiesel engine which was operated from no load to peakload through an eddy current dynamometer coupled to thatengine.Themain specifications of the test engine are given inTable 2.

In order to determine the engine torque, the shaft of thetest engine was coupled to an electric dynamometer, whichwas loaded by an electric resistance. A strain load sensorwas employed to determine the load on the dynamometer.The engine speed was measured by an electromagnetic speedsensor installed on the dynamometer. The fuel consumptionrate of the engine was determined with a weighing scalehaving a sensitivity of 0.1 g and an electronic chronometerhaving a sensitivity of 0.1 s. The engine was equipped with anorificemeter connected to an inclinedmanometer tomeasuremass flow rate of the intake air. An air damping tank was usedfor damping out the pulsations produced by the engine, thusobtaining a steady air flow.

Table 2: Specifications of test engine.

Make KirloskarModel TAF 1Type Direct injection, air cooledBore × stroke 87.5mm × 110mmCompression ratio 17.5 : 1Swept volume 0.661 LRated power 4.4 kWRated speed 1500 rpmStart of injection 23.4 before TDCInjector operating pressure 200–205 bar

AVL GH12D miniature pressure transducer with AVL3066A02 piezocharge amplifier and angle encoder was usedto obtain the variation of pressure in the combustion cham-ber. The mean pressure history in the combustion chamberwas obtained by averaging 100 cycles in sequence. The AVL615 indimeter software was used to compute the heat releaserates from the measured values of pressure and crank angle(CA). An exhaust gas analyzer was used to measure carbonmonoxide (CO), unburned hydrocarbons (UBHC) by infra-red sensors, and NOx by electrochemical sensors.

Tests were first conducted with conventional engine toobtain the base data. Each test was repeated for three times.From the experimental measurements, it was found out thataround 90% of the measurements were within 2 standarddeviations from the average.Under the sameoperating condi-tions, the testing was repeated to the porous medium engine,which was under investigation. The influence of operatingparameters such as EGR and injection timing on the com-bustion, performance, and emission characteristics of porousmedium engine were carried out and compared with those ofconventional engine characteristics.


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Air temp. at inlet manifold = 303KEngine speed = 1500 rpmBrake power = 4.4kWCompression ratio = 17.5 (CE); 16 (PE)Injection timing = 23.4 deg. BTDC

Figure 3: Influence of EGRon cylinder gas pressure of cylinder headporous medium engine.

5. Error Analysis

Errors and uncertainties in the experiments can arise frominstrument selection, condition, calibration, environment,observation, reading, and test planning. Uncertainty analysisis needed to prove the accuracy of the experiments. The per-centage uncertainties of various parameters like brake powerand brake thermal efficiency were calculated using the per-centage uncertainties of corresponding measuring instru-ments. An uncertainty analysis was performed using thismethod and the total error was found to be = square root of{(uncertainty of total fuel consumption)2 + (uncertainty ofbrake power)2 + (uncertainty of brake thermal efficiency)2 +(uncertainty of CO)2 + (uncertainty of UBHC)2 + (uncer-tainty of NOx)

2 + (uncertainty of smoke number)2 + (uncer-tainty of pressure pickup)2} = square root of {(1)2 + (0.2)2 +(1)2 + (0.2)2 + (0.2)2 + (0.2)2 + (1)2 + (1)2} = 2.04%.

6. Influence of EGR and InjectionTiming on the Combustion, Performance,and Emission Characteristics of PorousMedium Engine

6.1. Combustion Characteristics

6.1.1. Cylinder Pressure. The combustion in porous mediumled to two-stage ignition reaction, which was inferred fromthe cylinder gas pressure versus crank angle diagram shownin Figure 3. The first stage was associated with low temper-ature reactions (LTR) and released relatively small amountof energy. The first stage might have happened in the porousmedium, which was placed on the underside of the cylinderhead.The second stage was associated with high temperatureoxidation reactions and released most of the energy, whichwas considered as main combustion stage (MCS).This mighthave happened in the free volume of cylinder outside theporous medium.

Conventional engine (CE)Porous medium engine (PE)PE with injection at 25.9 BTDCPE with injection at 20.9 BTDC

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Air temp. at inlet manifold = 303KEngine speed = 1500 rpmBrake power = 4.4kWCompression ratio = 17.5 (CE); 16 (PE)Exhaust gas recirculation = 0%

Figure 4: Influence of injection timing on cylinder gas pressure ofcylinder head porous medium engine.

Even with an increase in % EGR, a significant change inthe occurrence of first stage of combustion was not observedin the porous medium engine. The presence of hot porousceramic medium placed on the underside of cylinder headcould be the possible reason for this observation. But it wasfound that the second stage of combustion got retarded dueto the impact of inert gases present in recirculated gases onthe heat release rate, which in turn delayed the second stageof autoignition.The peak pressure was found to be occurringat crank angles of 367, 357, 359, 365, and 371 for conventional,porous medium engine with 0%, 10%, 20%, and 30% EGR.This is shown in Figure 3.

On advancing the injection, the cylinder pressure reacheda higher value as compared to retarded injection scheme.Thiswas mainly due to the fact that, on advancing the injection,larger amount of fuel was injected (injection starting earlierand stopping later). Higher pressure was also found beforetop dead centre (TDC)with advancement due to early start ofcombustion. With retarded injection timing, the occurrenceof peak pressure shifted towards TDC. Cylinder gas attaineda peak value of 67.60 bar, 69.10 bar, and 64.89 bar for porousmedium engine with standard, advanced, and retarded injec-tion timings. This is shown in Figure 4.

6.1.2. Heat Release Rate. The heat release from the porousmedium engine was showing a distinct two-stage heat releasepattern as such in homogeneous charge compression ignition(HCCI) engine [15]. Figure 5 showed the heat release patternfor a porous medium engine. In that, low temperature reac-tions (LTR) were found to be followed by high temperaturereactions (HTR). The conversion region of LTR to HTR withnegative temperature-coefficient was called NTCR. With anincrease in % EGR, NTCR was found to be increased inproportion. In addition to this, the amount of heat released inboth LTR and HTR region was getting reduced with increas-ing % EGR.


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Crank angle (deg.)Conventional engine (CE)Porous medium engine (PE)PE with 10% EGR


Figure 5: Influence of EGR on heat release rate of cylinder headporous medium engine.

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Figure 6: Influence of injection timing on heat release rate of cylin-der head porous medium engine.

More amount of heat was released well before TDC withadvanced injection timing. At rated power, the HTR regionwas found to be occurring at crank angles of 355, 353, and357 for porous medium engine with standard, advanced, andretarded injection timings. This is shown in Figure 6.

6.2. Performance Characteristics

6.2.1. Brake Specific Fuel Consumption. In porous mediumengine, the brake specific fuel consumption was found tobe increasing with an increase in % EGR like conventionaldiesel engine. The excess air declined with EGR causingthe loss in fuel economy as compared to porous mediumengine operation without EGR. It was found that excessivecharge dilution led to unstable combustion and misfiring,which in turn resulted in power loss and higher specificfuel consumption. This was the reason why porous medium

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Air temp. at inlet manifold = 303KEngine speed = 1500 rpmCompression ratio = 17.5 (CE); 16 (PE)Injection timing = 23.4 deg. BTDC

Figure 7: Influence of EGR on brake specific fuel consumption ofcylinder head porous medium engine.

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Figure 8: Influence of injection timing on brake specific fuel con-sumption of cylinder head porous medium engine.

engine was producing poor performance characteristics inexcess of 20% EGR.The brake specific fuel consumption was5%, 17%, and 34% higher for porous medium engine with10%, 20%, and 30% EGR than for that with 0% EGR whichis shown in Figure 7.

The influence of injection timing on brake specific fuelconsumption for conventional and PM engine configurationis shown in Figure 8.The brake specific fuel consumption forporous medium engine was found to be slightly higher foradvanced and retarded injection timing than with standardinjection timing. At advanced injection timing, more of thefuel was injected and injection started earlier in the cycleleading to earlier pressure rise before the piston reaches TDCposition. Greater pressure rise in the compression stroke


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Figure 9: Influence of EGR on thermal efficiency of cylinder headporous medium engine.

increased the negative work and consumed the most of theflywheel momentum. At retarded injection timing too, thebrake specific fuel consumption was higher than porousmedium engine with standard injection timing. This may bedue to the operation of porous medium engine at reducedcompression ratio. At rated power, the brake specific fuelconsumption for porous medium engine was 3.1% and 1%higherwith advanced and retarded injection timing thanwithstandard timing.

6.2.2. Brake Thermal Efficiency. The brake thermal efficiencyof porous medium engine was found to be reasonably goodup to 20% EGR. When EGR was further increased beyondthis limit, a substantial reduction in brake thermal efficiencywas observed. At rated power, a reduction of about 24%was observed with 30% EGR than porous medium engineoperation with 0% EGR, which is shown in Figure 10. Thismay be due to unstable combustion and misfiring that mighthave occurred inside the engine cylinder due to excessivecharge dilution.The brake thermal efficiency was found to belower for porousmedium engine with advanced and retardedinjection timing than that of standard injection timing. Atrated power, the brake thermal efficiency was found to be30.45%, 28.56%, 27.62%, and 28.37% for conventional, porousmedium engine with standard, advanced, and retarded injec-tion timings. This is shown in Figure 9.

6.3. Emission Characteristics

6.3.1. Unburned Hydrocarbons. In porous medium engine,HC emission was observed to be increasing with an increasein % EGR. Reduced burned gas temperatures due to strongheat absorption characteristics of porous medium and littleprobability for the later stage oxidation of unburned hydro-carbons that were formed during the initial stage combustionmight be the reasons for excessive hydrocarbons in theengine exhaust. A sharp increase in HC emissions was

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Figure 10: Influence of injection timing on thermal efficiency ofcylinder head porous medium engine.

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Figure 11: Influence of EGR on unburned hydrocarbon emissionsof cylinder head porous medium engine.

observed for excess of 20% EGR for the given configurationof porous medium engine. Above 20% EGR, partial enginemisfiring in addition to reduced postflame oxidation collec-tively contributed to higher HC emissions in the exhaust ofporous medium engine than in the conventional engine. Theunburned hydrocarbon emissions were 3%, 17%, and 40%higher for porous medium engine with 10%, 20%, and 30%EGR than with 0% EGR. This is shown in Figure 11.

From Figure 12, it was evident that advanced injectiontiming had the tendency of decreasing the hydrocarbonemissions at all loads. This may be due to availability of moretime for the injected fuel quantity to get burned completelyduring expansion stroke.The reverse trendwas observedwithretarded injection timing. However, the penalty was not toomuch since the presence of the hot porousmediumpermitted


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Figure 12: Influence of injection timing on unburned hydrocarbonemissions of cylinder head porous medium engine.

the fuel to burn at later stage in the expansion stroke. At ratedpower, the unburned hydrocarbons were found to be 9%, 6%,and 16% higher for porous medium engine with standard,advanced, and retarded injection timing than conventionalengine.

6.3.2. Carbon Monoxide. It is well proven that the carbonmonoxide is not capable of being completely converted intocarbon dioxide at lower in-cylinder temperatures. Due tothe heat absorption characteristics of porous medium thatwas placed on the underside of the cylinder head, the gastemperatures were lower in porous medium engine than inthe conventional engine. Thus, the reduced in-cylinder gastemperatures led to comparatively higher CO emissions fromthat engine. With an increase in % EGR, the in-cylinder gastemperatures were further getting reduced, which eventuallyresulted in higher CO emissions.The carbonmonoxide emis-sions were found to be 3%, 13%, and 39% higher for porousmedium engine with 10%, 20%, and 30% EGR than with 0%EGR. This is shown in Figure 13.

The carbonmonoxide emissions were found to be slightlyhigher for porousmedium enginewith standard and retardedinjection timings than for conventional engine. This maybe due to the reason that the heat absorption by porousmedium from the reaction zone reduced the in-cylindergas temperature, which further inhibited the oxidation ofCO into CO

2during the expansion stroke. The advanced

injection timing produced the higher cylinder temperatureand increased oxidation process between carbon and oxygenmolecules which eventually resulted in lower CO emissionsthan the standard and retarded injection schemes. At ratedpower, CO emission was 13.8% lesser than conventionalengine for porous medium engine with advanced injectiontiming. However, CO emissions were 3.4% and 13.8% higherthan conventional engine for porous medium engine with

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Figure 14: Influence of injection timing on carbon monoxide emis-sions of cylinder head porous medium engine.

standard and retarded injection timing. This is shown inFigure 14.

6.3.3. Oxides of Nitrogen. Burned residual gases left fromthe previous cycle or part of exhaust gas recirculated backto the engine acted as diluents, due to which the combus-tion temperatures started to decrease. The decrease will beproportional to heat capacity of the diluents. CO

2and H

2O

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higher specific heat. The additional effects of charge dilutionare reduction in oxygen concentration in the charge andslowing down the combustion rates. These will cause furtherreduction in the burned gas temperature. With the NOx


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Figure 15: Influence of EGR on nitrogen oxide emissions of cylinderhead porous medium engine.

formation being the exponential function of temperature,even a small reduction in flame temperature has a large effecton NOx kinetics. Increase in heat capacity of charge causedby EGR has generally been thought to result in reduction ofNOx emissions. Moreover, in this investigation, the porousmedium absorbed heat from the reaction zone, which insuccession reduced the in-cylinder temperature and NOxemissions. NOx emissions were found to be 27.1%, 30.1%,38.1%, and 44.9% lower for 0%, 10%, 20%, and 30%EGRoper-ation of porous medium engine than conventional engineoperation. This is shown in Figure 15.

Injection timing has a strong effect on NOx emissionsfor DI engines. Retarding the injection timing decreases thepeak cylinder pressure becausemore of fuel burns after TDC.In general, lower peak cylinder pressure results in lowerpeak temperature. As a consequence, theNOx concentrationsstart to decrease. However, with advanced injection timing,increasing NOx emissions were observed. This may be dueto compression of burning charge by the displacing piston.But, still, NOx emissions were lower in porous mediumengine than in conventional enginewith all different injectiontimings. At rated power, the NOx emissions were 27.1%,18.08%, and 38.4% lower for porous medium engine withstandard, advanced, and retarded injection timing than forconventional engine. This is shown in Figure 16.

6.3.4. Particulates. If oxygen availability increases duringcombustion, it will boost the flame temperature, whichwouldfurther help in oxidation of soot during the postflame reac-tions. It is proven that increase in%EGR reduces the availableoxygen content in the combustion chamber whichmay resultin higher particulate emissions. However, in porous mediumengine, this effect was found to be predominant, when EGRwas increased further beyond 20%. It was also observedthat particulate emissions in porous medium engine werestill lower than conventional engine by 31.9%, 23%, and17.6%, respectively, with 0%, 10%, and 20% EGR operation.

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Figure 16: Influence of injection timing on nitrogen oxide emissionsof porous medium engine.

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Figure 17: Influence of EGR on particulate emissions of cylinderhead porous medium engine.

This may be due to enhanced evaporation, thorough mixingof fuel vapour and air by the presence of porous medium inthe engine cylinder and with sufficient availability of oxygenfor combustion up to 20% of EGR.When EGR was increasedfurther than 30%, a sharp rise in particulate emissions wasobserved which may be due to either poor combustion orpartial engine misfiring or combination of two.This is shownin Figure 17.

Owing to lower temperature in the reaction zone, veryfast vapourization,more homogeneousmixture composition,and relatively long residence time in the reaction zone(porous medium volume) with a homogeneous temperaturedistribution, the particulate emissions were found to be lowerin porous medium engine than in conventional engine.



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Figure 18: Influence of injection timing on particulate emissions ofcylinder head porous medium engine.

The particulate emissions are 31.9%, 23%, and 27.5% lowerfor porous medium engine with standard, advanced, andretarded injection timing than for conventional engine. Thisis shown in Figure 18.

7. Conclusion

The influence of operating parameters such as EGR, injectiontiming on the combustion, performance, and emission char-acteristics of cylinder head porous medium engine has beenperformed and the findings are listed below:

(i) Two-stage combustion is found to be occurring inthe cylinder head porous medium engine, believingthat first stage of combustion is occurring in porousmedium under favourable ignition conditions subse-quently followed by second stage of combustion in therest of the combustion chamber.

(ii) The operating parameter EGR is having major influ-ence on the combustion, performance, and emissioncharacteristics of porous medium engine than theother operating parameter injection timing, which isconsidered in this investigation.

(iii) The porous medium engine is found to operate with-out any problems up to 20% EGR. In excess of that,too much charge dilution is found to initiate unsta-ble combustion due to partial engine misfiring andresults in considerable power loss.

(iv) Even though the injection timing is not having con-siderable influence on the characteristics of porousmedium engine, retarded injection scheme is prefer-able over the advanced injection scheme in the case ofcylinder head porous medium engine. But bothmod-ified injection timings are found to produce inferiorcharacteristics when compared to original injectiontiming. Hence, it is suggested to operate this porousmedium engine with original injection timing.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

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