Combine Effect of Exhaust Gas Recirculation (EGR) and Varying Inlet Air Pressure on Performance and Emission of Diesel Engine

Abstract

To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post treatment techniques have been employed in modern engines. Also concern of environmental pollution and energy crisis all over the world have caused the research attention on reduction of diesel engine exhaust emissions and saving of energy simultaneously. This investigation mainly focuses on reducing exhaust emission and energy saving by investigating diesel combustion with neat diesel fuel and a new attachment of pressurized inlet air with Exhaust Gas Recirculation (EGR) system. Experiment was conducted in a four stroke direct injection water cooled constant speed diesel engine with pressurize inlet air attachment and EGR system, which is typically used in agricultural farm machinery. EGR was applied to the experimental engine separately and also with varying pressure of inlet air. In this study, compressor was used to pressurize the inlet air. The experiments were carried out to experimentally evaluate the performance and emissions for combine effect different EGR rates and varying inlet air pressure of the engine. Emissions of hydrocarbon (HC), NOx, carbon monoxide (CO), carbon dioxide (CO2) and temperature of the exhaust gas were measured. Performance parameters such as Brake thermal efficiency, brake specific fuel consumption (BSFC) were calculated. It was found that combined effect of pressurize inlet air attachment and EGR system provided better result on engine performance than individual EGR effect. Reductions in NOx and exhaust gas temperature were observed but emissions of HC, CO and CO2 were found to have increased with combine usage of EGR and inlet air pressure. Thus the modified engine provides more NOx reduction and better fuel economy without reducing useful characteristics (brake power, brake thermal efficiency etc) of the engine. Keyword: Diesel engine, Emission, Exhaust gas recirculation, Inlet air pressure, NOx. I. Introduction Better fuel economy and higher power with lower maintenance cost has increased the popularity of diesel engine vehicles. Diesel engines have inherently high thermal efficiencies, resulting from their high compression ratio and fuel lean operation. The high compression ratio produces the high temperatures required to achieve auto-ignition, and the resulting high expansion ratio makes the engine discharge less thermal energy in the exhaust. The extra oxygen in the cylinders is necessary to facilitate complete combustion and to compensate for non-homogeneity in the fuel distribution. However, high flame temperatures predominate because locally stoichiometric air-fuel ratios prevail in such heterogeneous combustion processes (11). Consequently, Diesel engine combustion generates large amounts of NOx because of the high flame temperature in the presence of abundant oxygen and nitrogen (6, 7). NOx comprise of nitric oxide (NO) and nitrogen dioxide (NO2) and both are considered to be deleterious to humans as well as environmental health. NO2 is considered to be more toxic than NO. It affects human health directly and is precursor to ozone formation, which is mainly responsible for smog formation. The ratio of NO2 and NO in diesel engine exhaust is quite small, but NO gets quickly oxidized in the environment, forming NO2. Since diesel engine mainly emits NO hence attention has been given to reduce the NO formation (3). Diesel engines are used for bulk movement of goods, powering stationary/mobile equipment, and to generate electricity more economically than any other device in this size range. In most of the global car markets, record diesel car sales have been observed in recent years (1). The exhorting anticipation of additional improvements in diesel fuel and diesel vehicle sales in future have forced diesel engine manufacturers to upgrade the technology in terms of power, fuel economy and emissions. Diesel emissions are categorized as carcinogenic (2). Also the stringent emission legislations are compelling engine manufacturers to develop technologies to combat exhaust emissions. To meet these emission regulations with competitive fuel economy, exhaust gas after-treatment and optimized combustion are necessary. In fact, partial recirculation of exhaust gas, which is not a new technique and also well-established technology for NOx reduciton, has recently become essential, in combination with other techniques, for attaining lower emission levels (18).