A numerical study on the combustion and heat transfer characteristics of a spark ignited engine applying heat insulation coatings to the combustion chamber wall surface

The objective of the present study is to develop a numerical simulation model of spark ignited (SI) engine combustion and then to investigate the possibility of reducing heat losses and improving thermal efficiency by applying a low thermal conductivity and specific heat material, heat insulation coating, to the combustion chamber wall surface. A reduction in heat loss is important for improving SI engine thermal efficiency. However, reducing heat losses tends to increase combustion chamber wall temperatures, resulting in the onset of knock in SI engines. Thus, the numerical model made it possible to investigate the interaction of the heat losses and knock occurrence and to optimize spark ignition timing to achieve higher efficiency. The numerical model is developed by utilizing GT-POWER combined with three sub-models; a non-dimensional two-zone combustion model, an autoignition model in the unburned gas and an instantaneous heat transfer model in the combustion chamber wall. To reduce engine heat losses and improve the thermal efficiency, the heat insulation coating was applied to the combustion chamber wall surfaces. Specifically, combustion characteristics corresponding to the thickness of the material were investigated by using the numerical model. In case of the combustion chamber wall surface entirely coated with the material at low load, applying the heat insulation material can make the MBT earlier, resulting in highly increased thermal efficiency. The results imply that heat insulation materials should be coated at proper locations with an optimized thickness to improve overall thermal efficiency.