Concept for Modeling and Optimization of the Mixture Formation Using Gasoline Direct Injection in Compact High Speed Engines

The paper presents a concept for modeling and optimization of the mixture formation process during gasoline direct injection, using a high-pressure single fluid injection system which allows the modulation of the injection rate independently on the engine speed. Going from this favorable premise for the adaptation of the mixture formation to various load and speed conditions, the aim of modeling is to find the optimum combination between the adaptable elements as follows: form of the fuel pressure wave, injection timing, spray form, injector location, form of the combustion chamber. Moreover, the interaction between fuel and air flow within the cylinder during the mixture formation is considered as a determining factor for the combustion process, and forms thereby an important part of the modeling. Considering the most advanced GDI strategy, which consists in two stage control of mixture formation - at high load, respectively at low load - the paper is focused on the mixture stratification process at low load as extremely sensible problem. The model was generated using the commercial code FLUENT. Different combinations of injected fuel quantity, injection start, engine speed as well as the interaction between fuel and air flow will be presented as time and space related sequences of fuel distribution and velocity within the combustion chamber. The program validation by spray visualization for distinct cases gives the possibility to calibrate the model, for the reliable simulation of a great number of parameter combinations, the extreme configurations being tested on the bench.