Heat Transfer Characteristic of Thermal Barrier Coated Piston Crown for a Compressed Natural Gas Direct Injection Engine

Abstract

Compressed natural gas with direct injection (CNGDI) engine produces high temperature and pressure ultimately leading to high thermal stress. The piston crown material fails to withstand high temperature and operate ineffectively due to improper heat transfer. By insulating the surface namely; thermal barrier coating (TBC) such as ceramic based yttria partially stabilised zirconia (YPSZ), heat transfer to the piston might be reduced and lead to improvement of piston durability. Hence, in this research, YPSZ/NiCrAl coating was utilised to differentiate with the uncoated piston crowns in terms of the ability to reduce thermal stresses to the piston using finite element method and burner rig test. Several samples of AC8A aluminium alloy piston crowns were coated with bonding element of NiCrAl and ZrO2-7.5Y2O3namely the YPSZ as the top coat by using air-plasma spraying technique and were assessed by burner rig test. The results exhibited the durability of the YPSZ/NiCrAl coating could withstand the test and the heat flux for the YPSZ/NiCrAl-coated piston crown was about 98% reduction compared to the uncoated piston crown. Also, the lower the gradient value of the heat flux, the higher the heat resistance.