Thermal analysis by numerical simulations of a multilayered coating applied on a heavy-duty diesel engine piston

A methodology to numerically study the impact of a thin, multi-layer coating applied on the piston crown surface of an internal combustion engine is proposed. It relies on a loose thermal coupling between 3D-RANS simulations of the combustion chamber and 3D conduction simulations of the piston. The approach allows to characterize the transient thermal behavior of the piston, which is crucial to capture the thermal swing effect of the coating, as well as its potential impact on the combustion, heat transfer and engine efficiency. This methodology is used to simulate the impact of a 200-µm, 3-layer coating, applied on the piston crown surface of a single-cylinder, heavy-duty Diesel engine, for one operating point. No gain in terms of efficiency is observed with the coated piston (the decrease in heat losses through the piston surface due to the coating is counter-balanced by an increase in heat losses through the non-coated cylinder head). However, the methodology proves capable of predicting a coherent thermal behavior of the coated piston (decrease in piston body temperature of 5 K, average bowl surface temperature swing amplitude of 60 K, <5 K temperature swing at the interface between the metallic substrate and the coating) and is able to provide insightful information regarding the impact of coating on volumetric efficiency, heat losses, combustion but also on the coating reliability itself, for a reduced computational cost compared to a fully coupled approach. It can then be employed to evaluate the effect of a coating applied not only on the piston but also on the cylinder head, which would certainly have a more significant impact on the engine efficiency.