CFD Analysis of Injection Timing and Injector Geometry Influences on Mixture Preparation at Idle in a PFI Motorcycle Engine

The optimization of the air-fuel mixture formation plays a very important role in order to reduce the total amount of emissions from an SI engine. To comply with the EURO5 emission restrictions is necessary to understand the influence of injection timing (with respect to engine load) and injector geometry on the air-fuel dynamic interaction. The aim of this paper is to define a CFD methodology for the simulation of a PFI engine. The goals of this analysis are the evaluation of the injector geometry and injection timing influences on the air-fuel mixture preparation and so on the equivalence ratio distribution inside the combustion chamber. Preliminary assessments of the wall-film and droplet-wall interaction sub models have been carried out in order to validate the methodology [1]. In particular a three-step work procedure has been adopted; the first two steps are necessary to properly initialize the secondary breakup model while the third step regards the CFD RANS simulation of the PFI engine considered for this analysis. In particular, a motor-scooter SI engine at a low load operating condition has been considered in the present work. This operating condition has been chosen because of the urban stop-and-go use of a motor-scooter implies that frequently the engine is running at a low load operating condition.