Investigation of the effects of hydrogen on cylinder pressure in a split-injection diesel engine at heavy EGR

The distinctive properties of hydrogen have initiated considerable applied research related to the internal combustion engine. Recently, it has been reported that NO_x emissions were reduced by using hydrogen in a diesel engine at low temperature and heavy EGR conditions. As the continuing study, cylinder pressure was also investigated to determine the combustion characteristics and their relationship to NO_x emissions. The test engine was operated at constant speed and fixed diesel fuel injection rate (1500 rpm, 2.5 kg/h). Diesel fuel was injected in a split pattern into a 2-L diesel engine. The cylinder pressure was measured for different hydrogen flow rates and EGR ratios. The intake manifold temperature was controlled to be the same to avoid the gas intake temperature variations under the widely differing levels (2%-31%) of EGR. The measured cylinder pressure was analyzed for characteristic combustion values, such as mass burn fraction and combustion duration.The rising crank angle of the heat release rate was unaffected by the presence of hydrogen. However, supplying hydrogen extended the main combustion duration. This longer main combustion duration was particularly noticeable at the heavy EGR condition. It correlated well with the reduced NO_x emissions.     

Experimental study of the performances of a modified diesel engine operating in homogeneous charge compression ignition (HCCI) combustion mode versus the original diesel combustion mode

Homogeneous charge compression ignition (HCCI) combustion mode provides very low NO_x and soot emissions; however, it has some challenges associated with hydrocarbon (HC) emissions, fuel consumption, difficult control of start of ignition and bad behaviour to high loads. Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production in diesel and HCCI combustion mode. However EGR has different effects on combustion and emissions, which are difficult to distinguish. This work is intended to characterize an engine that has been modified from the base diesel engine (FL1 906 DEUTZ-DITER) to work in HCCI combustion mode. It shows the experimental results for the modified diesel engine in HCCI combustion mode fueled with commercial diesel fuel compared to the diesel engine mode. An experimental installation, in conjunction with systematic tests to determine the optimum crank angle of fuel injection, has been used to measure the evolution of the cylinder pressure and to get an estimate of the heat release rate from a single-zone numerical model. From these the angle of start of combustion has been obtained. The performances and emissions of HC, CO and the huge reduction of NO_x and smoke emissions of the engine are presented. These results have allowed a deeper analysis of the effects of external EGR on the HCCI operation mode, on some engine design parameters and also on NO_x emission reduction.     

Analysis of reformed EGR on the performance of a diesel particulate filter

The use of a diesel particulate filter (DPF) in combination with an upstream diesel oxidation catalyst (DOC) has been successfully implemented and shown to reduce carbon monoxide (CO), hydrocarbon (HC) and Particulate Matter (PM) diesel exhaust gas emissions. However issues including cost, size and uncontrolled active regeneration under a low temperature window still require attention. This study therefore primarily focuses on the potential benefits of using a single catalytic coated DPF (cDPF) and a combined DOC-cDPF instead of the DOC-DPF aftertreatment system utilising a passive, low temperature regeneration method. Comparisons were made through monitoring exhaust gas compositions from an experimental single cylinder diesel engine as well as measuring the pressure drop across the filters to analyse the accumulation of soot particles. The influence of reformed EGR (REGR), enriched simulated hydrogen (H₂) and CO, on DPF and cDPF soot loading was of interest as H₂ promotes the NO to NO₂ oxidation. Similarly the addition of simulated reformate (added either directly into the engine intake or exhaust manifold) for optimal performance of the aftertreatment systems was examined.The effects of adding REGR resulted in a significant decrease in total engine-out NO_x emissions, as well as an increase in both NO₂ concentration and NO₂/NO_x ratio. This resulted in improved filter efficiency and overall loading, especially under a DOC-cDPF aftertreatment configuration system. As a whole, a simultaneous NO_x and PM reduction was achieved.     

Generating efficiency and NOx emissions of a gas engine generator fueled with a biogas–hydrogen blend and using an exhaust gas recirculation system

This paper investigates the generating efficiency and NO_x emissions of a gas engine generator with a low-pressure loop exhaust gas recirculation system, fueled by a model biogas. Experiments for improving the generating efficiency and reducing NO_x emissions were conducted, utilizing optimum spark timings based on the maximum generating efficiencies with varying exhaust gas recirculation (EGR) rates. The test results show that both the NO_x emissions and the generating efficiency generally decrease when the EGR rate is increased. Also, by utilizing optimum spark timings with varying EGR rates, the addition of hydrogen to the biogas increases the generating efficiency of the engine. In particular, the generating efficiency of the biogas–hydrogen test increased by about 1.5% in comparison with the model biogas test for the optimum spark timing at 15% EGR. Accordingly, comprehensive techniques, such as the use of a biogas–hydrogen fuel mixture and optimum spark timings with respect to EGR rates, should be employed to efficiently generate electricity with a biogas engine.     

H2 effects on diesel combustion and emissions with an LPL-EGR system

In this study, we examined H₂ effects on the combustion and emissions of a diesel engine with low-pressure loop (LPL) exhaust gas recirculation (EGR). We converted a 2.2-L four-cylinder direct-injection diesel engine satisfying Euro5 for H₂ supply. An LPL-EGR system replaced the high-pressure loop (HPL) EGR system. For all tests, the brake mean effective pressure (BMEP) was kept at 4 bar and the EGR ratio was varied from 9 to 42%. The H₂ energy percentage was varied from 0 to 7.4% independently to evaluate the H₂ effects and EGR effects separately. The heat release rate was calculated from the measured cylinder pressure. We found that substitution of H₂ for diesel fuel made the premixed burn fraction larger, and reduced the nitrous oxide (NOx) and particulate matter (PM) emissions simultaneously. For example, the NOx emissions were reduced by 36% for an EGR of 42% and an H₂ percentage of 7.4%. PM emissions were reduced by 18% for an EGR of 35% and an H₂ percentage of 7.4% compared with diesel fuel only cases.     

Numerical study of effects of reformed exhaust gas recirculation (REGR) on dimethyl ether HCCI combustion

The effects of reformed exhaust gas recirculation (REGR) on combustion and emissions of dimethyl ether (DME) homogeneous charge compression ignition (HCCI) engines are studied by multi-dimensional CFD coupled with chemical kinetic model. The results show that REGR combing EGR and DME reformed gases (DRG) improves combustion and emissions. REGR can delay ignition time by both EGR and DRG, and makes main combustion closer to top dead center (TDC), which is beneficial to reducing compression negative work and broadening load range of HCCI engines. The interaction of DRG and EGR helps avoid too high pressure rise rate or low power performance when being applied independent of each other. HC, CO and NO_x emissions can be controlled simultaneously by REGR. Both advantages of DRG and EGR are used to decrease the emissions of HCCI engines by REGR, while the disadvantages of high emissions are alleviated when one of them is applied.     

An experimental investigation on engine performance and emissions of a single cylinder diesel engine using hydrogen as inducted fuel and diesel as injected fuel with exhaust gas recirculation

Fast depletion of fossil fuels is demanding an urgent need to carry out research work to find out the viable alternative fuels for meeting sustainable energy demand with minimum environmental impact. In the future, our energy systems will need to be renewable and sustainable, efficient and cost-effective, convenient and safe. The technology for producing hydrogen from a variety of resources, including renewable, is evolving and that will make hydrogen energy system as cost-effective. Hydrogen safety concerns are not the cause for fear but they simply are different than those we are accustomed to with gasoline, diesel and other fossil fuels. For the time being full substitution of diesel with hydrogen is not convenient but use of hydrogen in a diesel engine in dual fuel mode is possible. So Hydrogen has been proposed as the perfect fuel for this future energy system. The experiment is conducted using diesel–hydrogen blend. A timed manifold induction system which is electronically controlled has been developed to deliver hydrogen on to the intake manifold. The solenoid valve is activated by the new technique of taking signal from the rocker arm of the engine instead of cam actuation mechanism. In the present investigation hydrogen-enriched air has been used in a diesel engine with hydrogen flow rate at 0.15 kg/h. As diesel is substituted and hydrogen is inducted, the NO_x emission is increased. In order to reduce NO_x emission an EGR system has been developed. In the EGR system a lightweight EGR cooler has been used instead of bulky heat exchanger. In this experiment performance parameters such as brake thermal efficiency, volumetric efficiency, BSEC are determined and emissions such as oxides of nitrogen, carbon dioxide, carbon monoxide, hydrocarbon, smoke and exhaust gas temperature are measured. Dual fuel operation with hydrogen induction coupled with exhaust gas recirculation results in lowered emission level and improved performance level compared to the case of neat diesel operation.     

Experimental investigation of the combustion characteristics,emissions and performance of hydrogen port fuel injection in a diesel engine

Diesel engines are indispensable in daily life. However, the limited supply of petroleum fuels and the stringent regulations on such fuels are forcing researchers to study the use of hydrogen as a fuel. In this study, a diesel engine is operated using hydrogen–diesel dual fuel, where hydrogen is introduced into the intake manifold using an LPG-CNG injector and pilot diesel is injected using diesel injectors. The energy contents of the total fuel, 0%, 16%, 36% and 46% hydrogen (the 0% hydrogen energy fraction represents neat diesel fuel), were tested at 1300 rpm of constant engine speed and 5.1 kW of constant indicated power. According to test results, the indicated thermal efficiency of the engine decreases and the isfc increases with an increasing hydrogen energy fraction. Additionally, indicated specific CO, CO₂ and smoke emissions decrease with an increasing percentage of hydrogen fuel. However, indicated specific NO_x emissions do not change at the 16% hydrogen energy fraction, in other words, with an increase in the hydrogen amount (36% and 46% hydrogen energy fraction of total fuel), a dramatic increase (58.8% and 159.7%, respectively) is observed. Additionally, the peak in-cylinder pressure and the peak heat release rate values increase with the increasing hydrogen rate.     

Emission characteristics of a turbocharged diesel engine fueled with gas-to-liquids

Emission characteristics of a turbocharged, intercooled, heavy-duty diesel engine operating on neat gas-to-liquids (GTL) and blends of GTL with conventional diesel were investigated and a comparison was made with those of diesel fuel. The results show that nitrogen oxides (NO _x ), smoke, and particulate matter (PM) emissions can be decreased when operating on GTL and diesel-GTL blends. Engine emissions decrease with an increase of GTL fraction in the blends. Compared with diesel fuel, an engine operating on GTL can reduce NO _x , PM, carbon monoxide (CO), and hydrocarbon (HC) by 23.7%, 27.6%, 16.6% and 12.9% in ECE R49 13-mode procedure, respectively. Engine speed and load have great influences on emissions when operating on diesel-GTL blends and diesel fuel in the turbocharged diesel engine. The study indicates that GTL is a promising alternative fuel for diesel engines to reduce emissions. Translated from Transactions of CSICE, 2006, 24(6): 489–493 [译自: 内燃机学报]     

An experimental investigation of NO2 emission characteristics of a heavy-duty H2-diesel dual fuel engine

This paper investigated the nitrogen dioxide (NO₂) emissions of a heavy-duty diesel engine operated in hydrogen (H₂)-diesel dual fuel combustion mode with H₂ supplemented into the intake air. Preliminary measurements using the 13-mode European Stationary Cycle (ESC) demonstrated the significant effect of H₂ addition on the emissions of NO₂. The detailed effects of H₂ addition and engine load on NO₂ emissions were examined at 1200 RPM. The addition of a small amount of H₂ increased substantially the emissions of NO₂ and the NO₂/NO_x ratio, especially at low load. Increasing the engine load was found to inhibit the enhancing effect of H₂ on the conversion of NO to NO₂ with the maximum NO₂/NO_x ratio observed at lower H₂ concentration. The maximum NO₂ emissions of the H₂-diesel dual fuel operation were three (at 70% load) to five (at 10% load) times that of diesel operation. Further increasing the addition of H₂ beyond the point with maximum NO₂ emissions still produced more NO₂ than for diesel-only operation. Based on the experimental data obtained, the engine load and maximum averaged bulk mixture temperature were not the main factors dominating the formation of NO₂ in the H₂-diesel dual fuel engine. A preliminary analysis demonstrated the significant effect of the unburned H₂ on NO₂ emissions. When mixed with the hot combustion product, the unburned H₂ that survived the main combustion process might further oxidize to raise the HO₂ levels and enhance the conversion of NO to NO₂. In comparison, the changes in the combustion process including the start of combustion, combustion duration and maximum heat release rate may not contribute substantially to the increased NO₂ emissions observed.     

Hydrogen assisted diesel combustion

Hydrogen assisted diesel combustion was investigated on a DDC/VM Motori 2.5L, 4-cylinder, turbocharged, common rail, direct injection light-duty diesel engine, with a focus on exhaust emissions. Hydrogen was substituted for diesel fuel on an energy basis of 0%, 2.5%, 5%, 7.5%, 10% and 15% by aspiration of hydrogen into the engine's intake air. Four speed and load conditions were investigated (1800 rpm at 25% and 75% of maximum output and 3600 rpm at 25% and 75% of maximum output). A significant retarding of injection timing by the engine's electronic control unit (ECU) was observed during the increased aspiration of hydrogen. The retarding of injection timing resulted in significant NO_X emission reductions, however, the same emission reductions were achieved without aspirated hydrogen by manually retarding the injection timing. Subsequently, hydrogen assisted diesel combustion was examined, with the pilot and main injection timings locked, to study the effects caused directly by hydrogen addition. Hydrogen assisted diesel combustion resulted in a modest increase of NO_X emissions and a shift in NO/NO₂ ratio in which NO emissions decreased and NO₂ emissions increased, with NO₂ becoming the dominant NO_X component in some combustion modes. Computational fluid dynamics analysis (CFD) of the hydrogen assisted diesel combustion process captured this trend and reproduced the experimentally observed trends of hydrogen's effect on the composition of NO_X for some operating conditions. A model that explicitly accounts for turbulence–chemistry interactions using a transported probability density function (PDF) method was better able to reproduce the experimental trends, compared to a model that ignores the influence of turbulent fluctuations on mean chemical production rates, although the importance of the fluctuations is not as strong as has been reported in some other recent modeling studies. The CFD results confirm that temperature changes alone are not sufficient to explain the observed reduction in NO and increase in NO₂ with increasing H₂. The CFD results are consistent with the hypothesis that in-cylinder HO₂ levels increase with increasing hydrogen, and that the increase in HO₂ enhances the conversion of NO to NO₂. Increased aspiration of hydrogen resulted in PM, and HC emissions which were combustion mode dependent. Predominantly, CO and CO₂ decreased with the increase of hydrogen. The aspiration of hydrogen into the engine modestly decreased fuel economy due to reduced volumetric efficiency from the displacement of air in the cylinder by hydrogen.     

Remarkable improvement of NOx–PM trade-off in a diesel engine by means of bioethanol and EGR

In order to realize a premixed compression ignition (PCI) engine, the effects of bioethanol–gas oil blends and exhaust gas recirculation (EGR) on PM–NO_x trade-off have been investigated focusing on ignition delay, premixed combustion, diffusion combustion, smoke, NO_x and thermal efficiency. The present experiment was done by increasing the ethanol blend ratio and ethanol and by increasing the EGR ratio in a single cylinder direct injection diesel engine. It is found that a remarkable improvement in PM–NO_x trade-off can be achieved by promoting the premixing based on the ethanol blend fuel having low evaporation temperature, large latent heat and low cetane number as well, in addition, based on a marked elongation of ignition delay due to the low cetane number fuel and the low oxygen intake charge. As a result, very low levels of NO_x and PM, which satisfies the 2009 emission standards imposed on heavy duty diesel engines in Japan, were achieved without deterioration of brake thermal efficiency in the PCI engine fuelled with the 50% ethanol blend diesel fuel and the high EGR ratio. It is noticed that smoke can be reduced even by increasing the EGR ratio under the highly premixed condition.     

The influence of hydrogen-enriched gas on the performance of lean NOx trap catalyst for a light-duty diesel engine

Modern diesel engines have improved engine fuel economy and significantly reduced nitrogen oxides (NO_x) and particulate matter (PM) emissions achieved by advances in both combustion and exhaust aftertreatment technologies. Recently, it has been shown that the vehicle emissions can be further improved by several catalytic systems including fuel reformers and aftertreatment systems, such as the Lean NO_x Trap (LNT). This NO_x removal system, called LNT, absorbs NO_x under lean exhaust gas conditions and releases NO_x under rich conditions. This technology can provide high NO_x conversion efficiency, but the right amount of reducing agent should be supplied into the catalytic converter under appropriate conditions.     

Effect of hydrogen addition on criteria and greenhouse gas emissions for a marine diesel engine

Hydrogen remains an attractive alternative fuel to petroleum and a number of investigators claim that adding hydrogen to the air intake manifold of a diesel engine will reduce criteria emissions and diesel fuel consumption. Such claims are appealing when trying to simultaneously reduce petroleum consumption, greenhouse gases and criteria pollutants. The goal of this research was to measure the change in criteria emissions (CO, NO_x, and PM_2.5) and greenhouse gases such as carbon dioxide (CO₂), using standard test methods for a wide range of hydrogen addition rates. A two-stroke Detroit Diesel Corporation 12V-71TI marine diesel engine was mounted on an engine dynamometer and tested at three out of the four loads specified in the ISO 8178-4 E3 emission test cycle and at idle. The engine operated on CARB ultra-low sulfur #2 diesel with hydrogen added at flow rates of 0, 22 and 220 SLPM.     

Effect of exhaust gas recirculation on diesel engine nitrogen oxide reduction operating with jojoba methyl ester

Jojoba methyl ester (JME) has been used as a renewable fuel in numerous studies evaluating its potential use in diesel engines. These studies showed that this fuel is good gas oil substitute but an increase in the nitrogenous oxides emissions was observed at all operating conditions. The aim of this study mainly was to quantify the efficiency of exhaust gas recirculation (EGR) when using JME fuel in a fully instrumented, two-cylinder, naturally aspirated, four-stroke direct injection diesel engine. The tests were carried out in three sections. Firstly, the measured performance and exhaust emissions of the diesel engine operating with diesel fuel and JME at various speeds under full load are determined and compared. Secondly, tests were performed at constant speed with two loads to investigate the EGR effect on engine performance and exhaust emissions including nitrogenous oxides (NO_x), carbon monoxide (CO), unburned hydrocarbons (HC) and exhaust gas temperatures. Thirdly, the effect of cooled EGR with high ratio at full load on engine performance and emissions was examined. The results showed that EGR is an effective technique for reducing NO_x emissions with JME fuel especially in light-duty diesel engines. With the application of the EGR method, the CO and HC concentration in the engine-out emissions increased. For all operating conditions, a better trade-off between HC, CO and NO_x emissions can be attained within a limited EGR rate of 5–15% with very little economy penalty.     

Enhancing the NO2/NOx ratio in compression ignition engines by hydrogen and reformate combustion,for improved aftertreatment performance

Enhanced NO₂ production (without raising total NOx) in a diesel engine combustion chamber can improve the performance of several catalytic aftertreatment systems. Thus this can facilitate a further reduction in key regulated emissions such as nitrogen oxides (NOx) and particulate matter (PM) emissions. The oxidation of NO to NO₂ is an important intermediate step involved in all current aftertreatment systems that are designed for NOx and PM catalytic removal. The performance of both NOx control systems and catalysed particulate filters depend highly on the NO₂ concentration. In this work we have examined the influence of using hydrogen (H₂) and simulated reformate (H₂, CO and EGR gases) as a supplement to diesel fuel on NO₂ production. In actual engine applications a reformer will be integrated within the engine EGR system. This will not only provide the engine with recirculated exhaust gas (i.e. EGR), but will enrich it with H₂ and CO.     

Experimental investigation of control of NOx emissions in biodiesel-fueled compression ignition engine

Biodiesel is an alternative fuel consisting of the alkyl esters of fatty acids from vegetable oils or animal fats. Vegetable oils are produced from numerous oil seed crops (edible and non-edible), e.g., rapeseed oil, linseed oil, rice bran oil, soybean oil, etc. Research has shown that biodiesel-fueled engines produce less carbon monoxide (CO), unburned hydrocarbon (HC), and particulate emissions compared to mineral diesel fuel but higher NO_x emissions. Exhaust gas recirculation (EGR) is effective to reduce NO_x from diesel engines because it lowers the flame temperature and the oxygen concentration in the combustion chamber. However, EGR results in higher particulate matter (PM) emissions. Thus, the drawback of higher NO_x emissions while using biodiesel may be overcome by employing EGR. The objective of current research work is to investigate the usage of biodiesel and EGR simultaneously in order to reduce the emissions of all regulated pollutants from diesel engines. A two-cylinder, air-cooled, constant speed direct injection diesel engine was used for experiments. HCs, NO_x, CO, and opacity of the exhaust gas were measured to estimate the emissions. Various engine performance parameters such as thermal efficiency, brake specific fuel consumption (BSFC), and brake specific energy consumption (BSEC), etc. were calculated from the acquired data. Application of EGR with biodiesel blends resulted in reductions in NO_x emissions without any significant penalty in PM emissions or BSEC.     

Experimental study of various effects of exhaust gas recirculation (EGR) on combustion and emissions of an automotive direct injection diesel engine

Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production and is used on most modern high-speed direct injection (HSDI) diesel engines. However EGR has different effects on combustion and emissions production that are difficult to distinguish (increase of intake temperature, delay of rate of heat release (ROHR), decrease of peak heat release, decrease in O₂ concentration (and thus of global air/fuel ratio (AFR)) and flame temperature, increase of lift-off length, etc.), and thus the influence of EGR on NO_x and particulate matter (PM) emissions is not perfectly understood, especially under high EGR rates. An experimental study has been conducted on a 2.0 l HSDI automotive diesel engine under low-load and part load conditions in order to distinguish and quantify some effects of EGR on combustion and NO_x/PM emissions. The increase of inlet temperature with EGR has contrary effects on combustion and emissions, thus sometimes giving opposite tendencies as traditionally observed, as, for example, the reduction of NO_x emissions with increased inlet temperature. For a purely diffusion combustion the ROHR is unchanged when the AFR is maintained when changing in-cylinder ambient gas properties (temperature or EGR rate). At low-load conditions, use of high EGR rates at constant boost pressure is a way to drastically reduce NO_x and PM emissions but with an increase of brake-specific fuel consumption (BSFC) and other emissions (CO and hydrocarbon), whereas EGR at constant AFR may drastically reduce NO_x emissions without important penalty on BSFC and soot emissions but is limited by the turbocharging system.     

Effect of induction on exhaust gas recirculation and hydrogen gas in compression ignition engine with simarouba oil in dual fuel mode

Biofuels extracted from non-edible oil is sustainable and can be used as an alternative fuel for internal combustion engines. This study presents the performance, emission and combustion characteristic analysis by using simarouba oil (obtained from Simarouba seed) as an alternative fuel along with hydrogen and exhaust gas recirculation (EGR) in a compression ignition (CI) engine operating on dual fuel mode. Simarouba biofuel blend (B20) was prepared on volumetric basis by mixing simarouba oil and diesel in the proportion of 20% and 80% (v/v), respectively. Hydrogen gas was introduced at the flow rate of 2.67 kg/min, and EGR concentration was maintained at 30% of total air introduction. Performance, combustion and emission characteristics analysis were examined with biodiesel (B20), biodiesel with hydrogen substitution and biodiesel, hydrogen with EGR and were compared with neat diesel operation. Results indicate that BTE of the engine operating with biodiesel B20 was decreased when compared to neat diesel operation. However, introducing hydrogen along with B20 blend into the combustion chamber shows a slight increase in the BTE by 1%. NO_x emission was increased to 18.13% with the introduction of hydrogen than that of base fuel (diesel) operation. With the introduction of EGR, there is a significant reduction in NO_x emission due to decrease in in-cylinder temperature by 19.07%. A significant reduction in CO, CO_2, and smoke emissions were also noted with the introduction of both hydrogen and EGR. The ignition delay and combustion duration were increased with the introduction of hydrogen, EGR with biodiesel than neat diesel operation. Hence, the proposed biodiesel B20 with H₂ and EGR combination can be applied as an alternative fuel in CI engines.     

Engine performance and emissions of a diesel engine operating on diesel-RME (rapeseed methyl ester) blends with EGR (exhaust gas recirculation)

The effects of biodiesel (rapeseed methyl ester, RME) and different diesel/RME blends on the diesel engine NO_x emissions, smoke, fuel consumption, engine efficiency, cylinder pressure and net heat release rate are analysed and presented. The combustion of RME as pure fuel or blended with diesel in an unmodified engine results in advanced combustion, reduced ignition delay and increased heat release rate in the initial uncontrolled premixed combustion phase. The increased in-cylinder pressure and temperature lead to increased NO_x emissions while the more advanced combustion assists in the reduction of smoke compared to pure diesel combustion. The lower calorific value of RME results in increased fuel consumption but the engine thermal efficiency is not affected significantly. When similar percentages (% by volume) of exhaust gas recirculation (EGR) are used in the cases of diesel and RME, NO_x emissions are reduced to similar values, but the smoke emissions are significantly lower in the case of RME. The retardation of the injection timing in the case of pure RME and 50/50 (by volume) blend with diesel results in further reduction of NO_x at a cost of small increases of smoke and fuel consumption.