Determination of Optimal Piston Trajectories for High Efficiency 4-Stroke Cycles by Using Predictive Combustion Modeling

The potential regarding the indicated efficiency of an alternative piston trajectory for a spark ignited methane combustion engine has been investigated in this study. A physics-based cylinder model including a predictive combustion model was used to account for the interaction of the thermodynamics with altered kinematics. Using a genetic optimization algorithm on an adjustable spline, piston trajectories for different piston acceleration limits have been found for both full and part load operating points. All optimization processes led to increased indicated efficiencies up to a maximum of 52%. The increase in efficiency of the optimized piston trajectory is analyzed based on the results of the numeric simulation and can be explained by the following effects: deeper expansion of the working gas, reduced pumping losses, reduced wall heat losses, shorter heat release, and increased trapped air mass.