Influence of in-cylinder airflow on fuel vaporization and mixture uniformity in compression ignition engines

This study investigates the influence of in-cylinder airflow patterns and fuel-injection conditions on the performance of compression ignition engines through a cold simulation of diesel injection. A coupled simulation of the fuel system flow and spray formation was employed to analyze spray characteristics under various conditions. Initially, a zero-dimensional model was used to simulate the fuel system, followed by a three-dimensional analysis of fuel injection into the cylinder under different injection pressures and airflow patterns. Three types of in-cylinder airflows—swirl, tumble, and nonrotational— were considered to assess fuel distribution within the cylinder chamber. In addition, the effects of injection pressure on cylinder conditions and fuel vapor penetration were evaluated. The results indicate that increasing the injection pressure from 400 to 1600 bar enhances fuel vaporization, improving the vapor phase by approximately 0.4 g at the cycle end, indicating a more efficient mixing process. Furthermore, swirl flow promotes better air-fuel mixture uniformity compared to tumble and nonrotational flows, providing a higher volume fraction of fuel throughout the cylinder. Therefore, controlled increases in the injection pressure and the use of swirl flow improve engine efficiency.