An Investigation Into Effects Of Pressure Wave In CR On Diesel Engine Combustion And Emissions

With continuous requirement for reducing CO2 emissions and increasingly enhanced regulations to vehicle emissions,study into flows and combustion processes in diesel engines is very important for optimizing the engine energy efficiency and reducing pollutant emissions.In diesel engines,fuel injection plays a very critical role to influence the air-fuel mixing and combustion performances.All parameters of fuel injection system must be designed and calibrated with adequate attention.With the multi-injection strategy’s implementation,it has been noticed pressure wave in common-rail system can result in significant influence on actual injection pressure and rate of following injection pulses.Consequently in-cylinder mixing and combustion process would be affected.Therefore,it is essential to investigate the pressure wave in common-rail system and its effect on diesel engine working processes.In this research,experimental works on an established common rail fuel injection test rig was at first carried out for examining pressure wave inside the common-rail and injector under conditions of single injection and double injection pulses.Then based on KIVA-3V code developed by American Los Alamos National Laboratory,a numerical model of a diesel engine in-cylinder combustion was built and validated.Simulations were conducted for exploring effects of pressure wave in common-rail system on air-fuel mixing,combustion and emissions.The research has achieved the following outcomes:1.Fuel injection experiment for observing pressure wave in common rail system was completed on established common rail fuel injection experiment rig.Characteristics of pressure wave was monitored and recorded under conditions of single and double injection pulse.2.A diesel engine in-cylinder flow and combustion CFD model was built based on Ford 2.2 L diesel engine.With necessary validation to the model,effects of pressure wave on air-fuel mixing,combustion process and emissions were studied using KIVA-3V CFD program.Curves of pressure and temperature under different operating conditions and results about temperature and emissions were produced.3.Initial simulation was conducted by considering the influence of injection interval on characteristics of pressure wave.An injection strategy including a pilot and two main injection pulses was implemented.Results show obvious variations of in-cylinder distributions of air-fuel ratio,pressure,temperature,NO_x,CO,HC and soot emissions.4.In main simulation,effects of induced injection pressure variation by pressure wave for the following injection pulses were investigated.The influence of induced injection pressure variation on in-cylinder distributions of air-fuel ratio,pressure,temperature,NO_x,CO,HC and soot emissions was output.5.The final simulation mainly studied the influence of induced variation of injection rate profiles on in-cylinder distributions of air-fuel ratio,pressure,temperature,NO_x,HC,CO,soot emissions.