Optimization Of The Charge Process In Modern Motor Vehicle Spark Ignition Engines

The torque of an engine is principally determined by the efficiency of the combustion process and of the charging and emptying process of the individual cylinders. The precondition for high torque at full load is maximum and uniform filling of the cylinders. A high degree of efficiency of the combustion process in other operating ranges of the engine however is generally achieved by higher compression. At full load maximum filling and too-high compression are causes of an uncontrolled combustion process having a low degree of efficiency (knocking). The desired torque can however also be achieved with higher compression and a lower degree of filling. To achieve the desired torque curve in the engine an optimum charge process matched to compression is necessary, permitting favourable, knock-free combustion. Optimisation of the charge process is effected with the geometric parameters of intake pipe and inlet port geometry, exhaust pipe and exhaust port geometry and valve timing. The paper deals with the theoretical influences and their experimental analysis. The effect of filling/compression/charge movement on fuel consumption and the effective efficiency of the engine is examined. In conclusion, guidelines for optimum design of the charge process components are given, together with guidelines for the optimisation process and examples of optimally-designed engines.