A combined Combustion-Conjugate heat transfer analysis for Design of partially insulated pistons

Abstract

Insulating engine combustion chamber surfaces with thermal barrier coatings (TBCs) provides engine thermal efficiency improvement by reducing the heat transfer to the coolant when done appropriately. However, reducing heat losses using traditional ceramic insulation increases combustion chamber wall temperatures during the whole engine cycle, including intake stroke resulting in a decreased engine volumetric efficiency due to excessive intake air heating. This paper presents the concept of partial insulation coverage on a selective area of combustion chamber wall by simulations to improve the engine's thermal efficiency. A combined combustion–conjugate heat transfer analysis methodology was developed to determine the partial-coverage insulation area by analyzing the heat flux and surface temperature distribution across the combustion chamber wall. Engine cycle simulations were run to compare the engine performance with various partial insulation designs, and an optimal insulation area was proposed. To validate the simulation results, the full-coverage coated piston technology with 0.5 mm thick Yttria Stabilized Zrconia (YSZ) coating has been experimentally evaluated on a prototype engine and compared to the non-insulated baseline aluminum piston. It was found that the partial coverage insulation showed a thermal efficiency improvement of 1.98% relative to a full-coverage insulated piston efficiency of 2.06%.