Search Results

A study was undertaken to establish what happens to engine emissions, and to turbocharger and injection pressure requirements, as the specific output is raised. For any given engine package, increasing specific output increases injection pressures while reducing air/fuel ratios. Thus, if the highly rated engine must satisfy the same design constraints, then raising the engine operating torque by only 10% resulted in more than 30% increase in total particulates! However, the same emission levels may be maintained if increases in specific output are accompanied by changes to engine design so as to maintain the air-fuel mixing parameters, specifically air/fuel ratio and injection pressures, throughout the entire engine operating conditions.

Some results of a systematic numerical study of the effects of injection characteristics on the transient evaporating spray mixing process in a diesel like environment are presented. The study uses an existing two-dimensional stochastic thick spray model. It was found that, for a fixed injection quantity, changes in the nozzle hole number, nozzle hole size, and injection duration changed significantly the evaporation and mixing processes of a transient evaporating spray. In particular, It is found that, for a fixed nozzle geometry, reduced injection duration is most effective in increasing the mixing rate. The results also show that the injection rate shape greatly influences the mixing process of a transient spray, especially during the injection period. After the end of injection, the global effect of injection rate shape can be characterized by the mass averaged injection pressure alone. The higher the mass averaged injection pressure, the faster the mixing rate.

Some results of a systematic study of the effects of fuel and chamber gas properties on the transient evaporating spray mixing process are presented. The study uses an existing two-dimensional stochastic thick spray model. The results show that the combustion process in typical heavy duty, quiescent, DI diesel engines can be mixing limited rather than vaporization limited. In addition, the results show that the mixing process of a transient evaporating spray is characterized by the combined effects of fuel evaporation and its turbulent mixing with the surrounding air. In general, increasing the evaporation rate alone does not necessarily increase the fuel-air mixing rate. Furthermore, two dimensionless parameters have been used to quantify the relative effects of fuel and chamber gas properties on the transient spray evaporation process. Finally, through detailed comparisons between spray and gas jet results, the transient evaporating spray mixing process is better understood.