Experimental and analytical investigation of the heat transfer and thermal stresses in a cylinder head of a diesel engine

An experimental and theoretical study has been carried out to investigate the mechanism of crack development in cylinder heads of two-stroke diesel engines. The cracks initiate in the valve bridge region, between a pair of exhaust valves, where high temperatures exist during operation of the engine. The experiments included steady state and transient modes (cold start, loading and shut off), and temperature distributions were measured in the metal and the cooling water. The hot surface temperature as well as the maximum stresses are estimated using an analytical model. It is concluded that the dominant process of cracking is low cycle thermal fatigue and residual tensile stresses which appear after engine shut off.