Investigations on Combustion and Heat Transfer in a Large Gaseous Fuelled Engine

The 3D CFD method has become an essential and reliable tool for the development of modern large gaseous-fuelled engines. This holds especially true for the optimization of mixture formation and charge motion in prechamber engines to ensure suitable conditions near the spark plug at ignition time. In order to initialize a quick combustion process, an ignitable mixture with high turbulence but moderate velocity must prevail round the spark plug. However, suitable models for combustion and heat transfer are inevitable for a realistic simulation of the whole engine cycle. Within 3D CFD codes the combustion process is usually calculated using the PDF (probability density function) – model; heat transfer is modeled based on the logarithmic wall function. Experimental investigations were carried out on a single cylinder research engine in order to validate the combustion model used and different heat transfer models. Time and spatially resolved heat fluxes were measured applying the surface temperature method. Optical measurements, including the determination of local OH concentrations, were carried out to obtain more information on flame propagation. Local rates of heat release were determined and compared to the measured traces of OH concentration. The paper shows the results of these investigations for two different combustion concepts (prechamber and direct ignition) under different operating conditions. In general, the combustion process predictions are in good agreement with the experimental data.