Modeling the Effects of Intake Flow Structures on Fuel/Air Mixing in a Direct-injected Spark-Ignition Engine

Multidimensional computations were carried out to simulate the in-cylinder fuel/air mixing process of a direct-injection spark-ignition engine using a modified version of the KIVA-3 code. A hollow cone spray was modeled using a Lagrangian stochastic approach with an empirical initial atomization treatment which is based on experimental data. Improved Spalding-type evaporation and drag models were used to calculate drop vaporization and drop dynamic drag. Spray/wall impingement hydrodynamics was accounted for by using a phenomenological model. Intake flows were computed using a simple approach in which a prescribed velocity profile is specified at the two intake valve openings. This allowed three intake flow patterns, namely, swirl, tumble and non-tumble, to be considered. It was shown that fuel vaporization was completed at the end of compression stroke with early injection timing under the chosen engine operating conditions. The mixing process and the in-cylinder fuel distribution were found to be significantly affected by the flow structures which are dominated by the intake flow details. More uniform distributions of air-fuel ratio and mixture temperature in the combustion chamber were obtained at the end of compression in the cases using tumble and swirl flow patterns.