Effect of pressure oscillations on in-cylinder heat transfer – through large eddy simulation

As fuel consumption is a key issue for next-generation internal combustion engines, the heat release rate is increased and the duration shortened towards partially premixed combustion and in extreme cases towards homogeneous charge compression ignition to increase thermal efficiency. However, a steep rise in the heat release rate may trigger pressure oscillations in the combustion chamber, which have shown to increase the heat transfer, lowering efficiency and increasing fuel consumption. The aim of this research is to find the physical mechanisms that cause the increased in-cylinder heat transfer in the presence of pressure oscillations. According to the author’s knowledge, the physical mechanisms responsible for the increased heat transfer have yet not been well understood for this application. Several of the hypotheses for this work are therefore based on the research performed for pulsating turbulent pipe flow. A numerical study has been performed using the large eddy simulation approach, where the pressure oscillations in the combustion chamber have been triggered by an artificially imposed heat source. The results show an increase in heat transfer in relation to pressure amplitude, in accordance with previous experimental studies. The mechanism found is a rapid transport of high-temperature fluid from the heat source towards the wall due to large-scale velocity fluctuations emerged from the pressure oscillations resulting in increased heat transfer.