Wall impingement process of a multi-hole GDI spray: experimental and numerical investigation

The Direct Injection (DI) of gasoline in Spark Ignition (SI) engines is very attractive for fuel economy and performance improvements in spark ignition engines. Gasoline direct injection (GDI) offers the possibility of multi-mode operation, homogeneous and stratified charge, with benefits respect to conventional SI engines as higher compression ratio, zero pumping losses, control of the ignition process at very lean air-fuel mixture and good cold starting. The impingement of liquid fuel on the combustion chamber wall is generally one of the major drawbacks of GDI engines because its increasing of HC emissions and effects on the combustion process; in the wall guided engines an increasing attention is focusing on the fuel film deposits evolution and their role in the soot formation. Hence, the necessity of a detailed understanding of the spray-wall impingement process and its effects on the fuel distribution. The experimental results provide a fundamental data base for CFD predictions. In this paper investigations have been performed using a 7- hole injector, 0.179 mm in hole diameter, spraying in a constant volume vessel with optical accesses. To examine the effects of various factors on development of the spray impinging on the wall, experiments have been conducted at different injection pressures, diverse wall inclination angles and at atmospheric pressure. The acquired images have been processed for extracting the characteristic parameters of the impinging fuel at the different operative conditions. The multi-hole spray has been simulated by Star-CD code taking into account the commercial gasoline properties and the real mass flow rate derived from experimental measurements. In order to correctly reproduce spray impingement and fuel film evolution, a numerical methodology has been defined. Lagrangian sub-models and numerical parameters have been validated against experimental results.