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Modelling of the Over-Expanded Cycle Combustion Engine

Abstract The study concerns numerical tests of an internal combustion engine operating according to the over-expanded cycle carried out in the AVL Fire software. The research covered the modelling of a full working cycle of a conventional engine operating in accordance with the classic Otto cycle and an engine operating on the basis of an over-expanded cycle – the Atkinson cycle. As part of the work, three cases of Atkinson’s cycle were analysed, by closing the inlet valve before BDC (21º before BDC) and closing the valve after BDC (41º and 75º after BDC). As a result of modelling, space-time distributions of velocity, pressure and temperature in the cylinder of the modelled engine were obtained. Optimizations of the analysed cycles were carried out, finding the best ignition timing, at which it is possible to obtain the highest efficiency and the highest indicated mean effective pressure. The calculations showed that the engine operating according to the over-expanded cycle in order to obtain the best operating parameters requires earlier ignition timing compared to the conventional engine. In addition, in the engine operating according to the Atkinson cycle, there is a drop in the indicated mean effective pressure and an increase in the indicated thermal efficiency compared to the engine operating by the classical cycle.