Optimization of spark timing and air-fuel ratio of an SI engine with variable valve timing using genetic algorithm and steepest descend method

In this study, optimization of inlet and exhaust valve timing as well as spark timing and air-fuel ratio in XU7/L3 engine has been conducted in order to reduce fuel consumption and increase engine torque. At first, engine model in GT-POWER software is produced, and then it is optimized using sensitivity analysis. Unknown input data are arranged based on their sensitivity and the most effective of them is selected and optimized. Heat transfer coefficient of the cylinder, temperature and friction coefficient of the inlet port are the most important unknown parameters which affect the model, and optimization of them reduce errors of the model with the experimental results. Since determining the optimal operation points of the engine is not possible just with GT-Power software, it is coupled with MATLAB. The results are in full load case and shows 5% and 5.1% reduction in the fuel consumption as well as enhancement of 5.65% and 6% in torque by using genetic algorithm and steepest descend, respectively.