Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.
Hydrogen-fuelled internal combustion engines are a possible solution to make transportation more ecological. A thermodynamic model of the engine cycle enables a cheap and fast optimization of engine settings. NO, emission occurs at high loads and is a constraint for power and efficiency optimization. The thermodynamic model has to predict accurately the heat transfer in the engine because the NOx emission is influenced by the maximum gas temperature. The existing engine heat transfer models in the literature are developed for fossil fuels and they have been cited to be inaccurate for hydrogen. We have measured the heat transfer inside a spark ignited engine with a thermopile to investigate the heat transfer process of hydrogen and to find the differences with fossil fuels. This paper describes the effects of the compression ratio, ignition timing and mixture richness on the heat transfer process. A convection coefficient is introduced to separate the effect of the temperature difference between the gas and the wall from the influence of the gas movement and the combustion process. The paper shows that the convection coefficient gives more insight in the heat transfer process in a combustion engine
despite its doubtful definition. The maximum in the heat flux corresponds with the maximum of the temperature difference between the gas and the wall. The initial increase in the heat flux is caused by the combustion flame passage. The maximum of the convection coefficient occurs at the moment that the initial rising slope in the heat flux ends.