Investigation of the combustion of neat cottonseed oil or its neat bio-diesel in a HSDI diesel engine by experimental heat release and statistical analyses

An experimental study is conducted to evaluate the effects of using neat cottonseed oil or its neat ME (methyl ester) bio-diesel, on the combustion behavior of a standard, high speed, direct injection (HSDI), ‘Hydra’ diesel engine located at the authors’ laboratory. Combustion chamber and fuel injection pressure diagrams are obtained at medium and high load using a developed, high-speed, data acquisition and processing system. A heat release analysis of the experimentally obtained cylinder pressure diagrams is developed and used. Plots of histories in the combustion chamber of the heat release rate and other related parameters reveal some interesting features, which shed light into the combustion mechanism when using these bio-fuels. These results, combined with the differing physical and chemical properties of the bio-fuels between themselves and against those for the diesel fuel, which constitutes the baseline fuel, aid the correct interpretation of the observed engine behavior performance- and emissions-wise. Moreover, the possible existence of cyclic (combustion) variability is examined as reflected in the pressure indicator diagrams, by analyzing for the maximum pressure and its rate, and the dynamic injection timing and ignition delay, by using statistical analysis for averages, standard deviations and probability density functions. The key results are that with the use of these bio-fuels against the neat diesel fuel case, the ignition delay is hardly affected, the fuel injection pressure diagrams are very slightly advanced accompanied with higher injection pressures, maximum cylinder pressures remain the same with the vegetable oil and slightly increased with the bio-diesel, maximum cylinder pressure rates are increased with the bio-diesel and decreased with the vegetable oil, while the cyclic irregularity is not affected with these bio-fuels remaining at the acceptable neat diesel fuel case levels.     

Investigation of the performance and emissions of bus engine operating on butanol/diesel fuel blends

An experimental investigation is conducted to evaluate the effects of using blends of n-butanol (normal butanol) with conventional diesel fuel, with 8% and 16% (by vol.) n-butanol, on the performance and exhaust emissions of a fully instrumented, six-cylinder, water-cooled, turbocharged and after-cooled, heavy duty, direct injection (DI), Mercedes-Benz engine, installed at the authors’ laboratory, which is used to power the mini-bus diesel engines of the Athens Urban Transport Organization sub-fleet. The tests are conducted using each of the above fuel blends, with the engine working at two speeds and three loads. Fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides, carbon monoxide and total unburned hydrocarbons are measured. The differences in the measured performance and exhaust emissions of the two butanol/diesel fuel blends from the baseline operation of the engine, i.e. when working with neat diesel fuel, are determined and compared. It is revealed that this fuel, which can be produced from biomass (bio-butanol), is a very promising bio-fuel for diesel engines. The differing physical and chemical properties of n-butanol against those for the diesel fuel, aided by sample cylinder pressure and heat release rate diagrams, are used to interpret the observed engine behavior.     

The influence of n-butanol/diesel fuel blends utilization on a small diesel engine performance and emissions

Nitrogen oxides and smoke emissions are the most significant emissions for the diesel engines. Especially, fuels containing high-level oxygen content can have potential to reduce smoke emissions significantly. The aim of the present study is to evaluate the influence of n-butanol/diesel fuel blends (as an oxygenation additive for the diesel fuel) on engine performance and exhaust emissions in a small diesel engine. For this aim five-test fuels, B5 (contains 5% n-butanol and 95% diesel fuel in volume basis), B10, B15, B20 and neat diesel fuel, were prepared to test in a diesel engine. Tests were performed in a single cylinder, four stroke, unmodified, and naturally aspirated DI high speed diesel engine at constant engine speed (2600 rpm) and four different engine loads by using five-test fuels. The experimental test results showed that smoke opacity, nitrogen oxides, and carbon monoxide emissions reduced while hydrocarbon emissions increased with the increasing n-butanol content in the fuel blends. In addition, there is an increase in the brake specific fuel consumption and in the brake thermal efficiency with increasing n-butanol content in fuel blends. Also, exhaust gas temperature decreased with increasing n-butanol content in the fuel blends.     

Experimental-stochastic investigation of the combustion cyclic variability in HSDI diesel engine using ethanol–diesel fuel blends

An experimental investigation is conducted to evaluate the combustion characteristics of a fully instrumented, high-speed, direct injection (HSDI), standard ‘Hydra’ diesel engine, at various loads when using ethanol–diesel fuel blends up to 15% by vol. ethanol. In each test, combustion chamber and fuel injection pressure diagrams of many consecutive cycles were obtained using a specially developed, high-speed, data acquisition and processing system. Following a performance and exhaust emissions investigation and a heat release analysis of the measured cylinder pressure diagrams reported by the authors, the present work focuses on the cycle-by-cycle combustion variation (cyclic variability) as reflected in the pressure indicator diagrams, by analyzing for the maximum pressure, maximum pressure rate, (gross) indicated mean effective pressure, and dynamic injection timing and ignition delay. These parameters were analyzed using stochastic analysis techniques for averages, standard deviations, coefficients of variation, probability density functions, auto-correlations, power spectra and cross-correlation coefficients. Thus, any cause and effect relationship between cyclic pressure variations and the injection system or the kind of fuel used can be revealed, given the concern for the low cetane number of ethanol blends promoting cyclic variability that can lead to degraded performance and emissions characteristics.     

Combustion, performance and emission characteristics of a DI diesel engine fueled with ethanol-biodiesel blends

In this study, Euro V diesel fuel, biodiesel, and ethanol-biodiesel blends (BE) were tested in a 4-cylinder direct-injection diesel engine to investigate the combustion, performance and emission characteristics of the engine under five engine loads at the maximum torque engine speed of 1800 rpm. The results indicate that when compared with biodiesel, the combustion characteristics of ethanol-biodiesel blends changed; the engine performance has improved slightly with 5% ethanol in biodiesel (BE5). In comparison with Euro V diesel fuel, the biodiesel and BE blends have higher brake thermal efficiency. On the whole, compared with Euro V diesel fuel, the BE blends could lead to reduction of both NO_x and particulate emissions of the diesel engine. The effectiveness of NO_x and particulate reductions increases with increasing ethanol in the blends. With high percentage of ethanol in the BE blends, the HC, CO emissions could increase. But the use of BE5 could reduce the HC and CO emissions as well.     

Experimental study on performance and emissions of a high speed diesel engine fuelled with n-butanol diesel blends under premixed low temperature combustion

In the present paper, results of an experimental investigation carried out in a modern diesel engine running at different operative conditions and fuelled with blends of diesel and n-butanol, are reported. The exploration strategy was focused on the management of the timing and injection pressure to achieve a condition in which the whole amount of fuel was delivered before ignition. The aim of the paper was to evaluate the potential to employ fuel blends having low cetane number and high resistance to auto-ignition to reduce engine out emissions of NOx and smoke without significant penalty on engine performance. Fuel blends were mixed by the baseline diesel (BU00) with 20% and 40% of n-butanol by volume. The n-butanol was taken by commercial production that is largely produced through petrochemical pathways although the molecule is substantially unchanged for butanol produced through biological mechanisms.The experimental activity was performed on a turbocharged, water cooled, DI diesel engine, equipped with a common rail injection system. The engine equipment includes an exhaust gas recirculation system controlled by an external driver, a piezo-quartz pressure transducer to detect the in-cylinder pressure signal and a current probe to acquire the energizing current to the injectors. Engine tests were carried out at 2500 rpm and 0.8 MPa of BMEP exploring the effect of start of injection, O₂ concentration at intake and injection pressure on combustion behavior and engine out emissions. The in-cylinder pressure and rate of heat release were investigated for the neat diesel and the two blends to evaluate engine performance and exhaust emissions both for the conventional diesel and the advanced premixed combustion processes.The management of injection pressure, O₂ concentration at intake and injection timing allowed to realize a partial premixed combustion by extending the ignition delay, particularly for blends. The main results of the investigation made reach smoke and NOx emissions due to the longer ignition delay and a better mixing control before combustion. The joint effect of higher resistance to auto ignition and higher volatility of n-butanol blends improved emissions compared to the neat diesel fuel with a low penalty on fuel consumption.     

Solubility of a diesel–biodiesel–ethanol blend,its fuel properties,and its emission characteristics from diesel engine

In this work, we studied the phase diagram of diesel–biodiesel–ethanol blends at different purities of ethanol and different temperatures. Fuel properties (such as density, heat of combustion, cetane number, flash point and pour point) of the selected blends and their emissions performance in a diesel engine were examined and compared to those of base diesel. It was found that the fuel properties were close to the standard limit for diesel fuel; however, the flash point of blends containing ethanol was quite different from that of conventional diesel. The high cetane value of biodiesel could compensate for the decrease of the cetane number of the blends caused by the presence of ethanol. The heating value of the blends containing lower than 10% ethanol was not significantly different from that of diesel. As for the emissions of the blends, it was found that CO and HC reduced significantly at high engine load, whereas NO_x increased, when compared to those of diesel. Taking these facts into account, a blend of 80% diesel, 15% biodiesel and 5% ethanol was the most suitable ratio for diesohol production because of the acceptable fuel properties (except flash point) and the reduction of emissions.     

Effects of dimethyl-ether (DME) spray behavior in the cylinder on the combustion and exhaust emissions characteristics of a high speed diesel engine

The purpose of this study was to analyze the exhaust emissions of DME fuel through experimental and numerical analyses of in-cylinder spray behavior. To investigate this behavior, spray characteristics such as the spray tip penetration, spray cone angle, and spray targeting point were studied in a re-entrant cylinder shape under real combustion chamber conditions. The combustion performance and exhaust emissions of the DME-fueled diesel engine were calculated using KIVA-3V. The numerical results were validated with experimental results from a DME direct injection compression ignition engine with a single cylinder.The combustion pressure and IMEP have their peak values at an injection timing of around BTDC 30°, and the peak combustion temperature, exhaust emissions (soot, NO_x), and ISFC had a lower value. The HC and CO emissions from DME fuel showed lower values and distributions in the range from BTDC 25° to BTDC 10° at which a major part of the injected DME spray was distributed into the piston bowl area. When the injection timing advanced to before BTDC 30°, the HC and CO emissions showed a rapid increase. When the equivalence ratio increased, the combustion pressure and peak combustion temperature decreased, and the peak IMEP was retarded from BTDC 25° to BTDC 20°. In addition, NO_x emissions were largely decreased by the low combustion temperature, but the soot emissions increased slightly.     

Study of oxygenated biomass fuel blends on a diesel engine

Vegetable methyl ester was added in ethanol–diesel fuel to prevent separation of ethanol from diesel in this study. The ethanol blend proportion can be increased to 30% in volume by adding the vegetable methyl ester. Engine performance and emissions characteristics of the fuel blends were investigated on a diesel engine and compared with those of diesel fuel. Experimental results show that the torque of the engine is decreased by 6%–7% for every 10% (by volume) ethanol added to the diesel fuel without modification on the engine. Brake specific fuel consumption (BSFC) increases with the addition of oxygen from ethanol but equivalent brake specific fuel consumption (EBSFC) of oxygenated fuels is at the same level of that of diesel. Smoke and particulate matter (PM) emissions decrease significantly with the increase of oxygen content in the fuel. However, PM reduction is less significant than smoke reduction. In addition, PM components are affected by the oxygenated fuel. When blended fuels are used, nitrogen oxides (NO_x) emissions are almost the same as or slightly higher than the NO_x emissions when diesel fuel is used. Hydrocarbon (HC) is apparently decreased when the engine was fueled with ethanol–ester–diesel blends. Fuelling the engine with oxygenated diesel fuels showed increased carbon monoxide (CO) emissions at low and medium loads, but reduced CO emissions at high and full loads, when compared to pure diesel fuel.     

Effect of dimethoxy-methane and exhaust gas recirculation on combustion and emission characteristics of a direct injection diesel engine

The effect of fuel constituents and exhaust gas recirculation (EGR) on combustion characteristics, fuel efficiency and emissions of a direct injection diesel engine fueled with diesel-dimethoxymethane (DMM) blends was investigated experimentally. Three diesel-DMM blended fuels containing 20%, 30% and 50% by volume fraction of DMM, corresponding to 8.5%, 12.7% and 21.1% by mass of oxygen in the blends, were used. By the use of DMM, it is observed that CO and smoke emissions as well as the total number and mass concentration of particulate reduce significantly, while HC emissions and particulate number with lower geometric mean diameters (D_i < 0.039 μm) increase slightly. For each fuel, there is an increase of ignition delay whereas a decrease of cylinder pressure and heat release rate in the premixed combustion phase when the diesel engine was operated with EGR system. The brake thermal efficiency fluctuates at small EGR ratio, while decreases with the further increase of EGR ratio. With an increase of EGR ratio, NO_x emission is reduced at the cost of increased smoke, HC and CO emissions as well as the total number and mass of particulates for each fuel.     

Study on the application of DME/diesel blends in a diesel engine

In this paper fuels, based on various DME to diesel ratios are investigated. Physical and chemical properties of DME and diesel display mutual solubility at any ratio. The vapor pressure of DME/diesel blends is lower than that of pure DME at the same temperatures and it decreases with an increase of diesel mass fraction in blends, which is beneficial to the elimination of vapor lock in the fuel supply system on CI engines. Performance, emission and other features of three kinds of DME/diesel blend fuels and diesels are evaluated in a four-cylinder test engine. By taking relative advantages of DME and diesel, the DME/diesel blends could achieve satisfactory properties in lubricity and atomization, which contributed to improvements in spray and combustion characteristics. Simultaneously, smoke emission could be reduced significantly with a little penalty on CO and HC emissions for DME/diesel blended engine at high loads, in comparison to diesel engine. NO_x emissions of the engine powered by DME/diesel blends are decreased somewhat. Moreover, the power output would be improved a little and NO_x emission could be reduced further if the fuel supply advance angle is retarded appropriately.     

A comprehensive experimental investigation of combustion and heat release characteristics of a biodiesel (hazelnut kernel oil methyl ester) fueled direct injection compression ignition engine

In the present study, hazelnut (Corylus avellana L.) kernel oil was transesterified with methanol using potassium hydroxide as catalyst to obtain biodiesel and a comprehensive experimental investigation of combustion (cylinder gas pressure, rate of pressure rise, ignition delay) and heat release (rate of heat release, cumulative heat release, combustion duration and center of heat release) parameters of a direct injection compression ignition engine running with biodiesel and its blends with diesel fuel was carried out. Experiment parameters included the percentage of biodiesel in the blend, engine load, injection timing, injection pressure, and compression ratio. Results showed that hazelnut kernel oil methyl ester and its blends with diesel fuel can be used in the engine without any modification and undesirable combustion and heat release characteristics were not observed. The modifications such as increasing of injection timing, compression ratio, and injection pressure provided significant improvement in combustion and heat release characteristics.     

Performance, emission and combustion characteristics of poon oil and its diesel blends in a DI diesel engine

Experimental tests have been carried out to evaluate the performance, emission and combustion characteristics of a diesel engine using Neat poon oil and its blends of 20%, 40%, and 60%, and standard diesel fuel separately. The common problems posed when using vegetable oil in a compression ignition engine are poor atomization; carbon deposits, ring sticking, etc. This is because of the high viscosity and low volatility of vegetable oil. When blended with diesel, poon oil presented lower viscosity, improved volatility, better combustion and less carbon deposit. It was found that there was a reduction in NO_x emission for Neat poon oil and its diesel blends along with a marginal increase in HC and CO emissions. Brake thermal efficiency was slightly lower for Neat poon oil and its diesel blends. From the combustion analysis, it was found that poon oil-diesel blends performed better than Neat poon oil.     

First and second generation biodiesels spray characterization in a diesel engine

Potential improvement on exhaust emissions, biodegradability and the possibility to reduce dependence on fossil fuel resources has led to an increasing interest on the use of biofuels for transport application. In this work, the analysis of the spray behaviour of first and second generation biodiesel in a Euro 5, common rail transparent diesel engine has been performed. GTL, SME and RME fuels have been used in blends at 100% and 50% in volume; while reference fuel consisted of commercial diesel. Two engine operating conditions of the NEDC have been selected: 1500 rpm at 2 bar of brake mean effective pressure (BMEP) and 2000 rpm at 5 bar BMEP. The injection process has been accurately studied, and the influence of the combustion process on the spray behaviour has been taken into account. Typical jets parameters such as penetration and cone angles have been detected and a comparison with theoretical models of Hiroyasu and Siebers has been performed. A new correlation for the forecasting of the jet penetration has been obtained starting from Hiroyasu equations. An image-based method has been applied for the identification of the phenomena that control the spray behaviour during its evolution in the combustion chamber.First generation biodiesels, pure and blends, show longer penetration with respect to the reference fuel at both the engine speed analysed. Moreover, they penetrate for a longer time in the combustion chamber, because of the longer energizing time set, so impingement phenomena can be observed. On the other hand, the second generation biodiesels penetrate less than reference one, due to its lower density, but also because the combustion of the pilot injection causes an increase of pressure that obstructs the penetration in the combustion chamber. Finally, a good agreement between the breakup times computed by means of the Hiroyasu and Siebers correlations and the ones from the experimental data has been found.     

Combustion of n-butanol in a spark-ignition IC engine

Alcohols, because of their potential to be produced from renewable sources and because of their high quality characteristics for spark-ignition (SI) engines, are considered quality fuels which can be blended with fossil-based gasoline for use in internal combustion engines. They enable the transformation of our energy basis in transportation to reduce dependence on fossil fuels as an energy source for vehicles. The research presented in this work is focused on applying n-butanol as a blending agent additive to gasoline to reduce the fossil part in the fuel mixture and in this way to reduce life cycle CO₂ emissions. The impact on combustion processes in a spark-ignited internal combustion engine is also detailed. Blends of n-butanol to gasoline with ratios of 0%, 20%, and 60% in addition to near n-butanol have been studied in a single cylinder cooperative fuels research engine (CFR) SI engine with variable compression ratio manufactured by Waukesha Engine Company. The engine is modified to provide air control and port fuel injection. Engine control and monitoring was performed using a target-based rapid-prototyping system with electronic sensors and actuators installed on the engine [1]. A real-time combustion analysis system was applied for data acquisition and online analysis of combustion quantities. Tests were performed under stoichiometric air-to-fuel ratios, fixed engine torque, and compression ratios of 8:1 and 10:1 with spark timing sweeps from 18° to 4° before top dead center (BTDC). On the basis of the experimental data, combustion characteristics for these fuels have been determined as follows: mass fraction burned (MFB) profile, rate of MFB, combustion duration and location of 50% MFB. Analysis of these data gives conclusions about combustion phasing for optimal spark timing for maximum break torque (MBT) and normalized rate for heat release. Additionally, susceptibility of 20% and 60% butanol-gasoline blends on combustion knock was investigated. Simultaneously, comparison between these fuels and pure gasoline in the above areas was investigated. Finally, on the basis of these conclusions, characteristic of these fuel blends as substitutes of gasoline for a series production engine were discussed.     

Experimental evaluation of DI diesel engine operating with diestrol at varying injection pressure and injection timing

The use of biodiesel as an alternative in a diesel engine for extended period causes several engine operating problems such as injector coking, piston ring sticking, unfavorable pumping and spray characteristics due to the high viscosity of biodiesel compared to conventional diesel. In this study, a blend of 30% waste cooking palm oil (WCO) methyl ester, 60% diesel and 10% ethanol was selected based on stability test conducted and named as diestrol. The effect of diestrol fuel on the performance, emission and combustion characteristics of a direct injection diesel engine at varying injection pressure and timing was studied through experimental investigation. Maximum brake thermal efficiency of 31.3% was obtained at an injection pressure of 240 bar and injection timing of 25.5° bTDC. Compared to diesel, diestrol fuel showed reduction in carbon monoxide (CO), carbon dioxide (CO₂) and smoke emission by 33%, 6.3% and 27.3% respectively. Diestrol fuel decreased nitric oxide (NO) emission by 4.3%, while slight increase in the levels of unburnt hydrocarbon (UHC) was observed. Diestrol fuel exhibited higher cylinder gas pressure and heat release rate compared to diesel. Minimum ignition delay of 12.7° CA was observed with diestrol fuel which was similar to diesel at same operating condition.     

Experimental investigation of fuel properties, engine performance, combustion and emissions of blends containing croton oil, butanol, and diesel on a CI engine

Emission problems associated with the use of fossil fuels have led to numerous research projects on the use of renewable fuels. The aim of this study is to evaluate the effects of blends containing croton mogalocarpus oil (CRO)-Butanol (BU) alcohol-diesel (D2) on engine performance, combustion, and emission characteristics. Samples investigated were 15%CRO-5%BU-80%D2, 10%CRO-10%BU-80%D2, and diesel fuel (D2) as a baseline. The density, viscosity, cetane number CN, and contents of carbon, hydrogen, and oxygen were measured according to ASTM standards. A four cylinder turbocharged direct injection (TDI) diesel engine was used for the tests. It was observed that brake specific energy consumption (BSEC) of blends was found to be high when compared with that of D2 fuel. Butanol containing blends show peak cylinder pressure and heat release rate comparable to that of D2 on higher engine loads. Carbon dioxide (CO₂) and smoke emissions of the BU blends were lower in comparison to D2 fuel.     

Experimental investigation of diesel engine performance and emission characteristics using jojoba/diesel blend and sunflower oil

Experimental study has been carried out to investigate performance parameters, emissions, cylinder pressure, exhaust gas temperature (T_exhaust) and engine wall temperatures (T_wall) for direct injection diesel engine. Tests were conducted for sunflower oil (S100) and 20% jojoba oil + 80% pure diesel fuel (B20) in comparison to pure diesel fuel with different engine speeds. S100 and B20 were selected for the study because of its being widely used in Egypt and in the world. Also, series of tests are conducted at same previous conditions with different percentage of exhaust gas recirculation (EGR) from 0% to 12% of inlet mass of air fresh charge. Results indicate that S100 or B20 gives lower brake thermal efficiency (η_B), brake power (BP), brake mean effective pressure (BMEP), and higher brake specific fuel consumption (BSFC) due to lower heating value compared to pure diesel fuel. S100 or B20 gives lower NO_X concentration due to lower gas temperature. S100 or B20 gives higher T_wall and T_exhaust due to incomplete combustion inside engine cylinder. S100 or B20 gives higher CO and CO₂ concentrations due to higher carbon/hydrogen ratio. The position of maximum pressure (P_max) change for pure diesel fuel is earlier than for S100 or B20. The results show that S100 or B20 are promising as alternative fuel for diesel engine. The utilization of vegetable oils does not require a significant modification of existing engines. This can be seen as the main advantage of vegetable oils. The main disadvantages of biodiesel fuels are high viscosity, drying with time, thickening in cold conditions, flow and atomization characteristics.     

Selection of a diesel fuel surrogate for the prediction of auto-ignition under HCCI engine conditions

Homogeneous charged compression ignition (HCCI) is a promising combustion concept able to provide very low NO_x and PM diesel engine emissions while keeping good fuel economy. Since HCCI combustion is a kinetically controlled process, the availability of a kinetic reaction mechanism to simulate the oxidation (low and high temperature regimes) of a diesel fuel is necessary for the optimisation, control and design of HCCI engines. Motivated by the lack of information regarding reliable diesel fuel ignition values under real HCCI diesel engine conditions, a diesel fuel surrogate has been proposed in this work by merging n-heptane and toluene kinetic mechanisms. The surrogate composition has been selected by comparing modelled ignition delay angles with experimental ones obtained from a single cylinder DI diesel engine tests. Modelled ignition angle results are in agreement with the experimental ones, both results following the same trends when changing the engine operating conditions (engine load and speed, start of injection and EGR rate). The effect of EGR, which is one of the most promising techniques to control HCCI combustion, depends on the engine load. High EGR rates decrease the n-heptane/toluene mixture reactivity when increasing the engine load but the opposite effect has been observed for lower EGR rates. A chemical kinetic analysis has shown that the influence of toluene on the ignition time is significant only at low initial temperature. More delayed combustion processes have been found when toluene is added, the dehydrogenation of toluene by OH (termination reaction) being the main kinetic path involved during toluene oxidation.     

Combustion analysis of Jatropha, Karanja and Polanga based biodiesel as fuel in a diesel engine

Non-edible filtered Jatropha (Jatropha curcas), Karanja (Pongamia pinnata) and Polanga (Calophyllum inophyllum) oil based mono esters (biodiesel) produced and blended with diesel were tested for their use as substitute fuels of diesel engines. The major objective of the present investigations was to experimentally access the practical applications of biodiesel in a single cylinder diesel engine used in generating sets and the agricultural applications in India. Diesel; neat biodiesel from Jatropha, Karanja and Polanga; and their blends (20 and 50 by v%) were used for conducting combustion tests at varying loads (0, 50 and 100%). The engine combustion parameters such as peak pressure, time of occurrence of peak pressure, heat release rate and ignition delay were computed. Combustion analysis revealed that neat Polanga biodiesel that results in maximum peak cylinder pressure was the optimum fuel blend as far as the peak cylinder pressure was concerned. The ignition delays were consistently shorter for neat Jatropha biodiesel, varying between 5.9^° and 4.2^° crank angles lower than diesel with the difference increasing with the load. Similarly, ignition delays were shorter for neat Karanja and Polanga biodiesel when compared with diesel.