Optimization of All SI Engine Combustion Control and Related Events for Efficiency

There are two parts to achieving the optimization reported here. The development of an engine simulation model and an optimization algorithm. The engine performance is evaluated using a quasi-dimensional engine combustion model with sub models to incorporate friction, heat losses and abnormal combustion, that is knocking. After extensive search and development a new Particle Swarm Optimizer (PSO), has been developed. Optimization includes, for the first time, the search of discontinuous design variables. The input variables considered for this investigation are manifold air pressure, air-fuel ratio, spark timing, compression ratio, valve timing events including valve open duration, maximum valve lift and engine speed. This enables the identification of the maximum thermal efficiency at a given power output at any engine operating speed. A focus of this paper was to establish if the team's ultra lean burn HAJI (hydrogen assisted jet ignition) system offered any further benefit over a fully optimised engine with conventional ignition within the limitations of the simulation. Results show that there is the potential for the SI engine to achieve diesel like thermal efficiencies, most likely at reduced cost.