Parametric Study on a Gasoline Direct Injection Engine - A CFD Analysis 2017-26-0039
Gasoline direct injection (GDI) engines are now trending in automobile field because of good fuel economy and low exhaust emissions over their port fuel injection (PFI) counter parts. They operate with a lean stratified mixture in most of conditions. However, their performance is dependent on mixture stratification which in-turn depends on fuel injection pressure, timing and strategy. But, the main challenge to GDI engines is soot and particulate matter (PM) emissions. However, they can be reduced by employing multi-stage fuel injection strategy. Therefore, in the present work, an effort has been made to study the effect of fuel injection parameters on soot emissions of a GDI engine using the CFD analysis. In addition, the study is also extended to evaluate the performance, combustion and other emission characteristics of the engine. First the engine is modelled using the PRO-E software. The geometrical details of the engine are obtained from the literature. The CFD analysis is carried out using CONVERGE software. The boundary conditions required for the analysis are obtained from the available literature. In order to predict in-cylinder flows: mass, momentum and energy equations are solved by the finite volume scheme. The turbulence, combustion and fuel spray break up are analyzed by using RNG k-ɛ, SAGE detailed chemical kinetics, kh-rt model respectively. The pressure and the velocity coupling are carried out by using the PISO algorithm. The post processing has been bone by using ENSIGHT software. Here, a single-cylinder, four-valve, pentroof head engine, at an engine speed of 1000 rev/min., is considered. The analysis is done for a range of fuel injection pressures, spark timings, number of injector holes and multi-stage injection strategy.
From the results, we found that, for various fuel injection pressures, the soot emissions decrease by about 77.8 and 88.5% respectively for 150 and 200 bar fuel injection pressures, compared to that of 110 bar. When the spark timing is advanced, the soot emissions increase by about 3.3 and 4.5 times the order of magnitude respectively, at the spark timings of 15 and 20 CAD before TDC, compared to that of the 7.5 CAD before TDC. When 8 and 10 numbers of fuel injector holes are used, the soot emissions decrease by about 0.5 and 87.7% respectively, compared to that of the 6-hole injector. With two types of multi-stage fuel injection strategies considered, the soot emissions decrease by about 72.8 and 76.1% respectively, compared to that of single-stage fuel injection. Finally, we conclude that the fuel injection pressure, number of injector holes, spark timing and multi-stage fuel injection strategy play an important role in the mixture preparation and on soot emissions of a GDI engine.