Performance and emission characteristics of an automotive diesel engine using biodiesel fuel with the influence of air intake variables

摘要

The air induction system plays a major role by providing necessary air charge for combustion to take place in an engine cylinder. The pressure drop across the air intake manifold is known to have a significant effect on the indicated power of the internal combustion engine. Most car manufacturers locate the air grill at the front of a vehicle to enhance the volumetric efficiency. However due to wading performance, for a sport utility vehicle like a Land Rover Freelander the air grill is located at the side of the front tyre. The air speed at the grill side is high and creates negative pressure, thus reducing the volumetric efficiency. Therefore, a thorough study of the design of the air induction system (AIS) with negative pressure at the air grill is vital, in order to fully understand the flow behavior in this AIS. Moreover, when the engine is equipped with turbocharger, the performance of the air intake system is also affected by the exhaust parameter which depends on the combustions of fuel in the engine cylinder. The properties of biodiesel are slightly different in density, viscosity and cetane number. These parameters are potentially affecting the combustion in engine cylinder. Thus, the investigation of the effect of fuel on the air intake system is vital for the study of the diesel engine operating with biodiesel. The analysis of the combustion of biodiesel in a V6 diesel engine includes the ignition delay, rate of heat release, in-cylinder peak pressure as well as the exhaust emissions. The study consists of 3 parts; (1) three-dimensional CFD analysis on the performance of the Land Rover Freelander AIS, (2) one-dimensional analysis of a V6 diesel engine with the effect of the AIS, (3) experimental study of a V6 diesel engine operating with RME and ULSD; The three-dimensional analyses on the performance 2 of a Freelander AIS have been conducted to study the effect of negative pressure on pressure-drop in the intake manifold. The results show that the magnitude of negative pressure gives significant effect not just to pressure drop but also to the flow behavior in the intake manifold. The steady flow tests on the actual intake manifold of a Freelander model have been conducted to validate the simulation outcome. The results show good agreement between experiment and simulation. In order to improve understanding on the flow wave action on the intake manifold of a V6 diesel engine, one-dimensional engine simulations have been conducted using commercial Ricardo WAVE v7.2 software. The result shows good agreement between simulation and experiment. The simulation result shows a significant affect on the wave action as pressure drop increases from zero to 20% in the intake manifold. The research continued further to investigate the effect of air induction parameters in the V6 diesel engine such as pressure drop and flow temperature on the performance and emissions of the engine. The effect of intake flow parameter to the engine when operated with RME has been studied and the comparisons have been made when ULSD is used as base fuel. The experimental results show that in general, the engine operating with RME produces lower power and higher bsfc due to low energy content of RME as compared to ULSD. The emissions of NOx are slightly higher, but lower CO and HC are produced. The pressure drop along the AIS has significantly affected the performance as well as emissions of the engine. The performance of the diesel engine drops significantly as the pressure drop increases and exhaust emissions increase considerably.