Development of a CFD Approach to Model Fuel-Air Mixing in Gasoline Direct-Injection Engines 2012-01-0146

Direct-injection represents a consolidated technology to increase performance and efficiency in spark-ignition engines. It reduces the knock tendency and makes engine downsizing possible through the use of turbocharging. Better control of CO and HC emissions at cold-start is also ensured since there is no wall-impingement in the intake port. However, to take advantages of all the theoretical benefits derived from GDI technology, detailed investigations of both fuel-air mixing and combustion processes are necessary to extend the stratified charge operations in the engine map and to reduce soot emissions, that are now severely regulated by emission standards. In this work, the authors developed a CFD methodology to investigate and optimize the fuel-air mixing process in direct-injection, spark-ignition engines. The Eulerian-Lagrangian approach is used to model the evolution of the fuel spray emerging from a multi-hole injector. To account for the effects of cavitation inside the nozzle and wall impingement under different conditions, specific sub-models were developed for fuel-injection, break-up and droplet-wall interaction and liquid film dynamics.

Simulations of gas-exchange and fuel injection were performed with two different injector configurations for different operating points, representing relevant engine speeds and loads for the tested engine. Distribution of equivalence ratio and liquid film evolution were analyzed in detail to provide suitable guidelines for soot emission reduction in direct-injection, spark-ignition engines.