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 performanceimprovements in spark ignition engines. Gasoline directinjection (GDI) offers the possibility of multi-modeoperation, homogeneous and stratified charge, with benefitsrespect to conventional SI engines as higher compressionratio, zero pumping losses, control of the ignition process atvery lean air-fuel mixture and good cold starting.The impingement of liquid fuel on the combustion chamberwall is generally one of the major drawbacks of GDI enginesbecause its increasing of HC emissions and effects on thecombustion process; in the wall guided engines an increasingattention is focusing on the fuel film deposits evolution andtheir role in the soot formation. Hence, the necessity of adetailed understanding of the spray-wall impingementprocess and its effects on the fuel distribution. Theexperimental results provide a fundamental data base forCFD predictions.In this paper investigations have been performed using a 7-hole injector, 0.179 mm in hole diameter, spraying in aconstant volume vessel with optical accesses. To examine theeffects of various factors on development of the sprayimpinging on the wall, experiments have been conducted atdifferent injection pressures, diverse wall inclination anglesand at atmospheric pressure. The acquired images have beenprocessed for extracting the characteristic parameters of theimpinging fuel at the different operative conditions.The multi-hole spray has been simulated by Star-CD codetaking into account the commercial gasoline properties andthe real mass flow rate derived from experimentalmeasurements. In order to correctly reproduce sprayimpingement and fuel film evolution, a numericalmethodology has been defined. Lagrangian sub-models andnumerical parameters have been validated againstexperimental results.