Experimental Study of Ceramic Coated Piston Crown for Compressed Natural Gas Direct Injection Engines

The top land of a piston normally known as the piston crown is an engine part that is continuously exposed to extreme temperature and pressure during combustion. For a compression ratio level, the compressed natural gas with a direct injection system (CNGDI) typically uses a range of compression ratio between gasoline and diesel engines, producing extremely high temperature and pressure which lead to high thermal stresses. Consequently, the piston crown is exposed to direct combustion due to the vertical movement of the piston, leading to various possible damages of thermal stresses. In contrast to a petrol fuelled internal combustion engine, natural gas combustion creates a dry condition in the combustion chamber, inducing cooling difficulties in the engine. Without good heat transfer, the piston crown materials will soon fail to withstand high temperature and operate effectively. Alternatively, any sort of insulation inside the combustion chamber such as applying ceramic coatings may protect the piston crown surface and affect the overall combustion process, as well as improving the engine performance and the exhaust emissions. By reducing the heat loss of a cylinder bore, a higher thermal efficiency of an engine can also be improved by applying a surface thermal insulation, namely; thermal barrier coating (TBC). Thus, in this study, a ceramic based TBC, yttria partially stabilised zirconia (YPSZ) coating was used to compare with conventional tin coated (Na2SnO3) and uncoated piston crown in terms of heat concentration. Moreover, a set of average value of combustion temperature of a CNGDI engine was selected. Detailed analyses using a finite element analysis (FEA) technique was utilised in order to determine the location of hotspots via distribution profiles of temperature. It was noted that the maximum heat flux of the uncoated piston crown was much higher than that of tin coated and YPSZ coated piston crown. Heat flux value reached about 62% of decrement due to lower conductivity levels of piston crown.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.663.304 ◽

2014 ◽

Vol 663 ◽

pp. 304-310

Author(s):

Ahmad Jalaludin Helmisyah ◽

Shahrir Abdullah ◽

Mariyam Jameelah Ghazali

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

High Temperature ◽

Natural Gas ◽

Thermal Stresses ◽

Direct Injection ◽

Thermal Barrier ◽

Air Plasma ◽

Compressed Natural Gas ◽

Piston Crown

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.

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