Multidimensional simulation of combustion and knock onset in gas engines

Natural gas fuelled internal combustion engines enable efficient energy conversion with relatively low environmental impact. Depending on the specific application, the available fuel quality, and the emission regulations to be fulfilled, different types of gas-engine combustion systems are in use. The major performance and hence efficiency limiting factors in gas fuelled engines are related to the lower ignitability of natural gas at part load and the appearance of abnormal combustion (knock) at high load conditions. This article provides an overview of the multidimensional CFD simulation workflow for the investigation and assessment of flame propagation and knock onset characteristics in different types of natural gas fuelled internal combustion engines. The most common approaches for simulating flame propagation/combustion under engine conditions are presented together with selected models for describing the pre-flame reactions finally leading to knock onset in the unburned in-cylinder charge ahead of the flame. Based on selected application examples, the models’ performance and capabilities with respect to reflecting the essential characteristics of flame propagation and knock onset are presented.