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The current work is based on the computational design optimisation for a two-stroke, uniflow scavenging free piston engine prototype for use in series hybrid vehicles to reach high efficiency levels combined with low emissions. Here the performance goals have been attempted via Homogeneous Charge Compression Ignition (HCCI) Diesel combustion with increased levels of exhaust gas recirculation (EGR) and direct injection. For optimal mixture preparation and composition, a highly tuned gas exchange system is required and also adapted injection parameters are needed to induce heat release at around top dead center (TDC). A computational methodology has been developed based on iterations between zero-, one-dimensional and simplified Computational Fluid Dynamics (CFD) simulations to define the operating conditions and overall geometrical parameters which give the best engine performance.

This paper uses CFD methodology to simulate a prototype Diesel engine operating at high peak pressures (HPP). Under these conditions the accurate estimation of the level of thermomechanical stress on metal components is crucial for the design process. CFD simulations have been performed of flow, combustion and heat transfer to provide detailed insight into the in-cylinder behaviour of the engine. Particular emphasis was put on improving wall heat transfer predictions which have been compared with detailed local time-resolved surface heat transfer measurements. It is demonstrated that heat transfer strongly depends on flame spread via flow field and spray-related processes. Hence local heat transfer measurements also provide a stringent testing ground for spray and combustion model performance. Additionally it is shown that widely-used empirical heat transfer correlations are incapable of estimating the critical level and nature of thermal loading.

The present research focuses on the understanding and improved prediction of knock at full load in a four-cylinder passenger car spark-ignition (SI) engine using computational fluid dynamics (CFD) methodology. The emphasis is on the possibility of controlling the knock limit via optimised engine cooling mechanisms. To date, CFD simulations of the combustion chamber and cooling circuit are performed separately, while chamber wall temperatures are derived from either experiments or experience. This, however, entails the risk of employing inadequate boundary and hence in-cylinder conditions for a combustion and knock simulation. CFD simulations are performed for all four combustion chambers and metal components, including the cooling circuit. Both types of simulations are thermally coupled via the conditions on the chamber walls.