Increasing energy demand and environment concerns have prompted an evolution of alternative fuel sources. As an alternative fuel source, biodiesel is attractive because it reduces engine emissions. However, biodiesel produces higher NOx emissions compared to ordinary diesel fuel. Previous researches have established many factors that cause biodiesel to produce elevated NOx emissions. This study reviews the impacts of biodiesel combustion on NOx emissions and their reduction approaches in diesel engines. The first part of this study recaps the NOx formation mechanisms for understanding the kinetics behind the NOx forming reactions. The second part describes the factors affecting on NOx emissions. This paper established that higher NOx emissions are produced for biodiesel combustion which influenced by several factors such as physicochemical properties and molecular structure of biodiesel, adiabatic flame temperature, ignition delay time, injection timing and engine load conditions etc. The final section discusses on the reduction of NOx emissions from biodiesel fuelled engines for both pre and post combustion techniques. The results of reduction approaches of the NOx emissions implies, exhaust gas recirculation (EGR) and retarded injection timing are effective as well as low cost techniques than others. Between these two techniques, EGR reduces the NOx emissions at 5–25% EGR rate adequately in biofuelled engine by controlling oxygen content and combustion peak temperature with slightly decreasing HC and CO emissions. However this technique shows few penalties on smoke and PM emissions as well as brake specific fuel consumption if not perfectly optimized.

Impacts of biodiesel combustion on NOx emissions and their reduction approaches

Emission reduction in a Di diesel engine using exhaust gas recirculation (Egr) of palm biodiesel blended with TiO2 nano additives

Impacts of additives on performance and emission characteristics of diesel engines during steady state operation

Biodiesels are gaining more importance as a promising alternative energy resource. Engine performance and emission characteristics of unmodified biodiesel fueled diesel engines are highly influenced by its ignition and combustion behavior. This review article presents the literature review on ignition delay (ID), combustion and emission characteristics of biodiesel fueled diesel engine. More than hundred articles report which have been published mostly in the last decade are reviewed in this paper. The investigation results report that the combustion characteristics of bio fueled engine is slightly different from the engine running with petroleum diesel. Most of the investigation results have reported that as compared to diesel, biodiesel has early start of combustion (SOC) and shorter ID of between 1–5° and 0.25–1.0°, respectively. Higher cetane number (CN), lower compressibility and fatty acid composition of biodiesel have been identified as the main elements for early SOC and shorter ID. In addition, it is also found that, the heat release rate (HRR) of biodiesel is slightly lower than diesel owing to the lower calorific value, lower volatility, shorter ID and higher viscosity.

Ignition delay, combustion and emission characteristics of diesel engine fueled with biodiesel

Due to the shortage of the conventional fossil fuels and air pollution from combustion, new, sustainable and cleaner fuel resources are urgently required. Biodiesel has been introduced as a potential and alternative fuel for years. Biodiesel can be produced from different sources such as vegetable oils, animal fat, waste oil, etc. All of them are renewable and do not affect the food security. When biodiesel is used as a fuel resource for diesel engines, the performance and emission characteristics such as brake thermal efficiency (BTE), brake specific fuel consumption (BSFC) and brake power are almost maintained while hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM) is decreased significantly. However, higher NOx concentration is observed. This disadvantage of using biodiesel or biofuels in general is improved in recent years. The purpose of this work is to do a comprehensive investigation of different approaches applying to biodiesel fueled engine like biodiesel additives, exhaust gas recirculation (EGR), water injection (WI), emulsion technology (ET), injection strategy modification, simultaneous technologies (ST), combustion chamber geometry modification and low temperature combustion (LTC) mode. By the way, the impacts of these technologies on engine performance and emission characteristics are summarized. Upon the comparison, using LTC mode is more efficient and feasible than the others. It can reduce both NOx and PM emissions simultaneously by up to 95% and 98%, respectively, while engine performance is slightly reduced. Looking inside the LTC mode, the most efficient model is the reactivity controlled compression ignition (RCCI) combustion system. Applying RCCI combustion model might lead to the increase of CO and HC emissions, but this issue can be easily solved by using some available technologies.

Effect of different technologies on combustion and emissions of the diesel engine fueled with biodiesel: A review

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

Experimental study of inlet manifold water injection on combustion and emissions of an automotive direct injection Diesel engine

NOx and PM emissions reduction on an automotive HSDI Diesel engine with water-in-diesel emulsion and EGR: An experimental study

Influence of EGR unequal distribution from cylinder to cylinder on NOx–PM trade-off of a HSDI automotive Diesel engine

Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in-cylinder NOx 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 NOx 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 NOx 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 NOx emissions and a decrease in PM emissions. The result of NOx–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 NOx 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.

Alain Maiboom

Papers

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

Experimental study of inlet manifold water injection on combustion and emissions of an automotive direct injection Diesel engine

NOx and PM emissions reduction on an automotive HSDI Diesel engine with water-in-diesel emulsion and EGR: An experimental study

Influence of EGR unequal distribution from cylinder to cylinder on NOx–PM trade-off of a HSDI automotive Diesel engine

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