CFD based optimization of the mixture formation in spark ignition direct injection CNG engine

This paper describes optimization of the combustion chamber geometry and injection timing of a new generation of EF7 engine, where CNG is directly injected to the combustion chamber, with the aim of providing the best mixture at low and high speeds. The Multi-Objective Genetic Algorithm (MOGA) is coupled with the KIVA Computational Fluid Dynamics (CFD) code, with grid generation, in order to maximize the ammable mass of the mixture. This would result in better combustion and improved fuel economy. The optimization variables related to the combustion chamber are seven geometry variables and injection timing. Through the present optimization, a great improvement in mixture distribution is achieved. The optimization results show that early injection with a shallow bowl shape can be advantageous at high speeds, while late injection would result in better results at low speeds