Numerical Optimization of a Gasoline Direct Injection Concept Adapted for High Speed Two-Stroke Engines

The future development of two-stroke engines will be conditioned by the drastic reduction of pollutant emission, especially of hydrocarbon. This goal is not achievable only by scavenging improvement, rather a new quality of mixture formation using direct injection is imposed. However, the internal mixture formation in a large range of speed and load, considering the scavenge flow particularities of two-stroke engines as well, appears as an extremely complex process. Thereby a numerical simulation is in this case very effective for the adaptation of a direct injection method at the engine. The paper presents a concept for modeling and optimization of the mixture formation process within a high-speed two-stroke engine with liquid fuel injection system. The injection system generates a pressure pulse which is not dependent on the engine speed. The paper illustrates the mixture formation process as time and space related, in base on the fuel volume distribution and mixture velocity within the combustion chamber. The numerical simulation of the mixture formation is based on the commercial code FLUENT. The time dependent simulations covered both the injection duration and the subsequent mixing process, in order to evaluate the charge motion and the distribution of the fuel mass fraction inside the cylinder before ignition. Different combinations of injected fuel quantities, injection start, engine speed as well as the interaction between fuel and air flow are presented. The results of such optimization regarding the performances of a two-stroke engine with 50 cm³ with gasoline direct injection are a convicting validation of the numerical optimization.