Impact of hydrogen generated by splitting water with nano-silicon and nano-aluminum on diesel engine performance

Efficient utilization of hydrogen generated during the reactions of nano-silicon/water and nano-aluminum/water in internal combustion engine has been investigated in the current work. Engine performance and emission studies of formulated and stabilized nanoemulsion fuels (water in diesel W/D), nano-aluminum in water/diesel (W/DA) and water in nano-silicon/diesel (W/DS) have been compared with those of diesel. Experimental investigations showed reduction in brake specific fuel consumption (BSFC) by 21% and 37%; rise in brake thermal efficiency (BTE) by 16% and 14% when engine was fueled with W/DA and W/DS respectively. For nanoemulsion fuels an increase in induced power was also recorded. Brake mean effective pressure, BTE and NOx emission dropped for W/D due to reduced exhaust gas temperatures. Nevertheless due to elevated peak cylinder pressures and exhaust gas temperatures a marginal rise in NOx, CO, HC and radiative heat emissions was observed with W/DA and W/DS.     

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.     

Physico-chemical properties of ethanol–diesel blend fuel and its effect on performance and emissions of diesel engines

The effects of different ethanol–diesel blended fuels on the performance and emissions of diesel engines have been evaluated experimentally and compared in this paper. The purpose of this project is to find the optimum percentage of ethanol that gives simultaneously better performance and lower emissions. The experiments were conducted on a water-cooled single-cylinder Direct Injection (DI) diesel engine using 0% (neat diesel fuel), 5% (E5–D), 10% (E10–D), 15% (E15–D), and 20% (E20–D) ethanol–diesel blended fuels. With the same rated power for different blended fuels and pure diesel fuel, the engine performance parameters (including power, torque, fuel consumption, and exhaust temperature) and exhaust emissions [Bosch smoke number, CO, NO_x, total hydrocarbon (THC)] were measured. The results indicate that: the brake specific fuel consumption and brake thermal efficiency increased with an increase of ethanol contents in the blended fuel at overall operating conditions; smoke emissions decreased with ethanol–diesel blended fuel, especially with E10–D and E15–D. CO and NO_x emissions reduced for ethanol–diesel blends, but THC increased significantly when compared to neat diesel fuel.     

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.     

Effect of ethanol blending with biodiesel on engine performance and exhaust emissions in a CI engine

The use of biodiesel as an alternative diesel engine fuel is increasing rapidly. However, due to technical deficiencies, they are rarely used purely or with high percentages in unmodified diesel engines. Therefore, in this study, we used ethanol as an additive to research the possible use of higher percentages of biodiesel in an unmodified diesel engine. Commercial diesel fuel, 20% biodiesel and 80% diesel fuel, called here as B20, and 80% biodiesel and 20% ethanol, called here as BE20, were used in a single cylinder, four strokes direct injection diesel engine. The effect of test fuels on engine torque, power, brake specific fuel consumption, brake thermal efficiency, exhaust gas temperature, and CO, CO₂, NO_x and SO₂ emissions was investigated. The experimental results showed that the performance of CI engine was improved with the use of the BE20 especially in comparison to B20. Besides, the exhaust emissions for BE20 were fairly reduced.     

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.     

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.     

Preparation,characterization, engine combustion and emission characteristics of rapeseed oil based hybrid fuels

In this study, hybrid fuels consisting of rapeseed oil/diesel blend, 1% aqueous ethanol and a surfactant (oleic acid/1-butanol mixture) were prepared and tested as a fuel in a direct injection (DI) diesel engine. The main fuel properties such as the density, viscosity and lower heating value (LHV) of these fuels were measured, and the engine performance, combustion and exhaust emissions were investigated and compared with that of diesel fuel. The experimental results showed that the viscosity and density of the hybrid fuels were decreased and close to that of diesel fuel with the increase of ethanol volume fraction up to 30%. The start of combustion was later than that of diesel fuel and the peak cylinder pressure, peak pressure rise rate and peak heat release rate were higher than those of diesel fuel. The brake specific fuel consumption (BSFC) of hybrid fuels was increased with the volume fraction of ethanol and higher than that of diesel. The brake specific energy consumption (BSEC) was almost identical for all test fuels. The smoke emissions were lower than those for diesel fuel at high engine loads, the NO_x emissions were almost similar to those of diesel fuel, but CO and HC emissions were higher, especially at low engine loads.     

Biodiesel production from inedible animal tallow and an experimental investigation of its use as alternative fuel in a direct injection diesel engine

In this study, a substitute fuel for diesel engines was produced from inedible animal tallow and its usability was investigated as pure biodiesel and its blends with petroleum diesel fuel in a diesel engine. Tallow methyl ester as biodiesel fuel was prepared by base-catalyzed transesterification of the fat with methanol in the presence of NaOH as catalyst. Fuel properties of methyl ester, diesel fuel and blends of them (5%, 20% and 50% by volume) were determined. Viscosity and density of fatty acid methyl ester have been found to meet ASTM D6751 and EN 14214 specifications. Viscosity and density of tallow methyl esters are found to be very close to that of diesel. The calorific value of biodiesel is found to be slightly lower than that of diesel. An experimental study was carried out in order to investigate of its usability as alternative fuel of tallow methyl ester in a direct injection diesel engine. It was observed that the addition of biodiesel to the diesel fuel decreases the effective efficiency of engine and increases the specific fuel consumption. This is due to the lower heating value of biodiesel compared to diesel fuel. However, the effective engine power was comparable by biodiesel compared with diesel fuel. Emissions of carbon monoxide (CO), oxides of nitrogen (NO_x), sulphur dioxide (SO₂) and smoke opacity were reduced around 15%, 38.5%, 72.7% and 56.8%, respectively, in case of tallow methyl esters (B100) compared to diesel fuel. Besides, the lowest CO, NO_x emissions and the highest exhaust temperature were obtained for B20 among all other fuels. The reductions in exhaust emissions made tallow methyl esters and its blends, especially B20 a suitable alternative fuel for diesel and thus could help in controlling air pollution. Based on this study, animal tallow methyl esters and its blends with petroleum diesel fuel can be used a substitute for diesel in direct injection diesel engines without any engine modification.     

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.     

Effect of Exhaust Gas Recirculation (EGR) on performance,emissions, deposits and durability of a constant speed compression ignition engine

To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post-treatment techniques have been employed in modern engines. Exhaust Gas Recirculation (EGR) is a pre-treatment technique, which is being used widely to reduce and control the oxides of nitrogen (NO_x) emission from diesel engines. EGR controls the NO_x because it lowers oxygen concentration and flame temperature of the working fluid in the combustion chamber. However, the use of EGR leads to a trade-off in terms of soot emissions. Higher soot generated by EGR leads to long-term usage problems inside the engines such as higher carbon deposits, lubricating oil degradation and enhanced engine wear. Present experimental study has been carried out to investigate the effect of EGR on soot deposits, and wear of vital engine parts, especially piston rings, apart from performance and emissions in a two cylinder, air cooled, constant speed direct injection diesel engine, which is typically used in agricultural farm machinery and decentralized captive power generation. Such engines are normally not operated with EGR. The experiments were carried out to experimentally evaluate the performance and emissions for different EGR rates of the engine. Emissions of hydrocarbons (HC), NO_x, carbon monoxide (CO), exhaust gas temperature, and smoke opacity of the exhaust gas etc. were measured. Performance parameters such as thermal efficiency, brake specific fuel consumption (BSFC) were calculated. Reduction in NO_x and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to have increased with usage of EGR. The engine was operated for 96 h in normal running conditions and the deposits on vital engine parts were assessed. The engine was again operated for 96 h with EGR and similar observations were recorded. Higher carbon deposits were observed on the engine parts operating with EGR. Higher wear of piston rings was also observed for engine operated with EGR.     

CNG-diesel engine performance and exhaust emission analysis with the aid of artificial neural network

This study investigates the use of artificial neural network (ANN) modelling to predict brake power, torque, break specific fuel consumption (BSFC), and exhaust emissions of a diesel engine modified to operate with a combination of both compressed natural gas CNG and diesel fuels. A single cylinder, four-stroke diesel engine was modified for the present work and was operated at different engine loads and speeds. The experimental results reveal that the mixtures of CNG and diesel fuel provided better engine performance and improved the emission characteristics compared with the pure diesel fuel. For the ANN modelling, the standard back-propagation algorithm was found to be the optimum choice for training the model. A multi-layer perception network was used for non-linear mapping between the input and output parameters. It was found that the ANN model is able to predict the engine performance and exhaust emissions with a correlation coefficient of 0.9884, 0.9838, 0.95707, and 0.9934 for the engine torque, BSFC, NO_x and exhaust temperature, respectively.     

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.     

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.     

Combustion performance and emission reduction characteristics of automotive DME engine system

This article is a condensed overview of a dimethyl ether (DME) fuel application for a compression ignition diesel engine. In this review article, the spray, atomization, combustion and exhaust emissions characteristics from a DME-fueled engine are described, as well as the fundamental fuel properties including the vapor pressure, kinematic viscosity, cetane number, and the bulk modulus. DME fuel exists as gas phase at atmospheric state and it must be pressurized to supply the liquid DME to fuel injection system. In addition, DME-fueled engine needs the modification of fuel supply and injection system because the low viscosity of DME caused the leakage. Different fuel properties such as low density, viscosity and higher vapor pressure compared to diesel fuel induced the shorter spray tip penetration, wider cone angle, and smaller droplet size than diesel fuel. The ignition of DME fuel in combustion chamber starts in advance compared to diesel or biodiesel fueled compression ignition engine due to higher cetane number than diesel and biodiesel fuels. In addition, DME combustion is soot-free since it has no carbon–carbon bonds, and has lower HC and CO emissions than that of diesel combustion. The NO_x emission from DME-fueled combustion can be reduced by the application of EGR (exhaust gas recirculation). This article also describes various technologies to reduce NO_x emission from DME-fueled engines, such as the multiple injection strategy and premixed combustion. Finally, the development trends of DME-fueled vehicle are described with various experimental results and discussion for fuel properties, spray atomization characteristics, combustion performance, and exhaust emissions characteristics of DME fuel.     

Influence of high rates of supplemental cooled EGR on NOx and PM emissions of an automotive HSDI diesel engine using an LP EGR loop

Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in‐cylinder NO_x control method. Although an increase in EGR at constant boost pressure (substitution EGR) is accompanied with an increase in particulate matter (PM) emissions in the conventional diesel high‐temperature combustion (HTC), the recirculation of exhaust gases supplementary to air inlet gas (supplemental EGR) by increasing the boost pressure has been suggested as a way to reduce NO_x emissions while limiting the negative impact of EGR on PM emissions. In the present work, a low‐pressure (LP) EGR loop is implemented on a standard 2.0 l automotive high‐speed direct injection (HSDI) turbocharged diesel engine to study the influence of high rates of supplemental cooled EGR on NO_x and PM emissions. Contrary to initial high‐pressure (HP) EGR loop, the gas flow through the turbine is unchanged while varying the EGR rate. Thus, by closing the variable geometry turbine (VGT) vanes, higher boost pressure can be reached, allowing the use of high rates of supplemental EGR. Furthermore, recirculated exhaust gases are cooled under 50°C and water vapour is condensed and taken off from the recirculated gases. An increase in the boost pressure at a given inlet temperature and dilution ratio (DR) results in most cases an increase in NO_x emissions and a decrease in PM emissions. The result of NO_x–PM trade‐off, while varying the EGR rate at fixed inlet temperature and boost pressure depends on the operating point: it deteriorates at low load conditions, but improves at higher loads. Further improvement can be obtained by increasing the injection pressure. A decrease by approximately 50% of NO_x emissions while maintaining PM emission level, and brake specific fuel consumption can be obtained with supplemental cooled EGR owing to an LP EGR loop, compared with the initial engine configuration (HP moderately cooled EGR). Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of clove oil and diesel fuel blends on the engine performance and exhaust emissions of a compression-ignition engine

Diesel engines provide the major power source for transportation in the world and contribute to the prosperity of the worldwide economy. However, recent concerns over the environment, increasing fuel prices and the scarcity of fuel supplies have promoted considerable interest in searching for alternatives to petroleum based fuels. Based on this background, the main purpose of this investigation is to evaluate clove stem oil (CSO) as an alternative fuel for diesel engines. To this end, an experimental investigation was performed on a four-stroke, four-cylinder water-cooled direct injection diesel engine to study the performance and emissions of an engine operated using the CSO–diesel blended fuels. The effects of the CSO–diesel blended fuels on the engine brake thermal efficiency, brake specific fuel consumption (BSFC), specific energy consumption (SEC), exhaust gas temperatures and exhaust emissions were investigated. The experimental results reveal that the engine brake thermal efficiency and BSFC of the CSO–diesel blended fuels were higher than the pure diesel fuel while at the same time they exhibited a lower SEC than the latter over the entire engine load range. The variations in exhaust gas temperatures between the tested fuels were significant only at medium speed operating conditions. Furthermore, the HC emissions were lower for the CSO–diesel blended fuels than the pure diesel fuel whereas the NO_x emissions were increased remarkably when the engine was fuelled with the 50% CSO–diesel blended fuel.     

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.     

Review of NOx reduction technologies in CI engines fuelled with oxygenated biomass fuels

Oxygenated fuels like biodiesel and alcohols have the potential to provide a reliable and a cost effective alternative to India's increasing future energy demands. They have a prospective future since they are renewable and can be produced easily in India's rural areas. Due to rapid industrialization and the increased number of vehicles on the road, the energy needs of the country are increasing rapidly. Oxygenated fuels can substantially replace the large demand for diesel to generate power for the industries and to fuel diesel engines of the vehicles. In spite of the many advantages of using them, most of the researchers have reported higher NO_x emissions, which is a deterrent to the market expansion of these fuels. The present program aims to review the NO_x emissions from the CI engines fuelled with oxygenated fuels. To meet the stringent emission norms, the various NO_x reduction technologies like use of additives, retarded fuel injection timing, biodiesel emulsion with water, and exhaust gas recirculation are reviewed. The results of the most effective and low cost technique of EGR in DI diesel engine fuelled with biodiesel–diesel blends and tri-compound oxygenated diesel fuel blends (ethanol–biodiesel–diesel fuel blends and methanol–biodiesel–diesel fuel blends) are presented.     

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.