At part load conditions, effective utilization of fuel is critical for drivability of an IC engine driven automobile, with minimum emissions and fuel consumption. It becomes cardinal to study the mixture preparation in engines to understand the injection strategy that helps in achieving the prime objectives of lower emission and reliable operation. To add to the complexity of the problem being studied, the injection phenomenon is rapid, turbulent, multi-phase, two-way coupled (where the continuous phase affects the droplets and vice versa) and involves turbulence length scales and time scales, few orders of magnitude lower compared to the characteristic length in the turbulence integral scale. A methodology is developed in Star-CD and ES-ICE to simulate the mixture preparation in Port Fuel Injection (PFI) engines.
High quality mixture preparation which is essential for combustion stability and lower emissions is aimed at part load conditions which constitute the majority of driving cycle. This methodology is helpful to understand and solve the injection timing development issues and in improving the combustion stability and lowering the emissions. The fuel injection parameters have been studied in detail both experimentally and numerically in a specialized spray chamber. The fuel injection parameters are correlated to the source of injection to obtain similar fit of droplet distribution profile obtained experimentally. The parameters like - injection timing, injection location and injection pressure can be efficiently optimized through this methodology for efficient mixture formation. Extensive studies have been done on different injection timing in order to reduce the wall film thickness and fuel short circuit losses and to increase the overall evaporation rate of fuel droplets by increasing the residence time. Two injection timing strategies namely - open valve injection and closed valve injection have been analyzed to understand the effect of fuel short circuit losses and its impact on HC (hydro-carbon) emissions. It is observed that, open valve injection has lower short circuit losses compared to closed valve injection, which is experimentally verified and thus has a great significance in reducing the HC emissions. However, open valve injection comparatively affects the in-cylinder charge homogeneity and standard deviation of equivalence ratio. This paper also discusses on the strategies that have been undertaken to achieve best-in-cylinder homogeneity with an adverse effect on increased fuel film thickness on the port walls. Efforts are made to optimize the injection timing and location for best mixture formation in production automotive vehicles and in extending the methodology for the corresponding emission prediction.
Being a computationally intensive problem with an additional complexity of moving mesh, opens an opportunity for parallel performance study. Parallel performance study shows that the methodology proposed above uses a Message Passing Interface (MPI) and shows a good scale up for 2-16 cores, above which it saturates. Multi-cycle analysis is carried out to understand the variation in Air-Fuel ratio homogeneity and Coefficient of variation of Indicated Mean Effective Pressure (IMEP) which provides a fundamental vista on the transient behavior of the spray dynamics.