Investigation of the influence of engine settings on the heat flux in a hydrogen- and methane-fueled spark ignition engine

Hydrogen-fueled internal combustion engines are a possible solution to make transportation more ecological. Only emissions of oxides of nitrogen (NOx) occur at high loads, being a constraint for power and efficiency optimization. A thermodynamic model of the engine cycle enables a cheap and fast optimization of engine settings. It needs to accurately predict the heat transfer in the engine because the NOx emissions are influenced by the maximum gas temperature. However, 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 a fossil fuel. This paper describes the effects of the compression ratio, ignition timing and mixture richness on the heat transfer process, comparing hydrogen with methane. A convection coefficient is used to separate the effect of the temperature difference between the gas and the wall from the influence of the gas movement and combustion. The paper shows that the convection coefficient gives more insight in the heat transfer process in a combustion engine despite the assumptions involved in its definition. The comparison between hydrogen and methane demonstrates, in contrast to what is believed, that the heat loss of hydrogen can be lower.