Abstract
The search for alternative fuels has led to the use of gas fuelled engines. Liquefied petroleum gas and especially natural gas are already widespread because they increase the energy security, have a higher knocking resistance and give lower CO2 and noxious emissions. They are still fossil fuels so sustainable alternatives like hydrogen are also investigated. A thermodynamic model of the engine cycle enables a cheap and fast optimization of engine settings. Modelling the heat transfer from the burning gases to the cylinder walls in a sub model is an indispensable keystone. Existing heat transfer models from Annand and Woschni were developed for diesel and gasoline and need to be validated for gaseous fuels. We have measured the heat flux and the wall temperature in an engine that can run on methane and hydrogen. This paper describes an evaluation of the models of Annand and Woschni with those heat flux measurements. Both models can be calibrated to account for the influence of the specific engine geometry on the heat transfer. But if they are calibrated for methane, they fail to calculate the heat transfer for hydrogen combustion. This demonstrates the models lack some gas or combustion properties which influence the heat transfer process in the case of hydrogen combustion.
Keywords: hydrogen, methane, engine, heat transfer, thermodynamic model