Simulation On Performance Of Variable Stroke Engines

Variable stroke engines combine two-stroke and four-stroke together. To improveengine load, it can switch between the two modes timely according to engine operatingcondition, which provides a new method for engine miniaturization and lightweight design.As an important technical parameter, valve timing directly affects the volumetricefficiency of the engine. Reasonable organization with the valve timing will ensure the gasexchange thoroughly and reduce the exchange losses. Because two-stroke cam of thevariable stroke engine needs to be redesigned, research on valve timing has an importantsignificance for variable stroke engine.To provide technical support for establishing of the switch strategy, this topic,sub-project of reseach on variable stroke engine, focuses on valve timing optimization andperformance simulation under different modes. BOOST is used to establish the four-strokesimulation model of Honda CB125 engine and accuracy of the simulation model is provedthrough the bench test. To improve engine performance under four-stroke, the valvetiming optimization method using Campbell diagram is proposed through analysing theexisting optimization methods and it works as expected.With analysis requirements of this paper, compound evaluation coefficient isinnovatively raised to evaluate engines’ comprehensive performance.Its physical meaningand dimensionless method is elaborated at the same time. To test the availability ofcompound evaluation coefficient, analytic hierarchy process and fuzzy matter-elementmethod are respectively used to analyse the height of rectangular exhaust port. Bothanalysis results are consistent with the results of compound evaluation coefficient. UsingCampbell diagram, combined with the maximum principle of compound evaluationcoefficient, defines the exhaust port’s cross-sectional shape, position, parameters and thebest valve timing under the "top-inlet and side-exhaust" mode of two-stroke.