Modeling the durability of diesel pistons with a crack on the edge of the combustion chamber

BACKGROUND: During periodic long-term tests of tractor diesel engines D-240T with a combustion chamber of the CNIDI after 4000 m-hour, a deterioration in the indicators of the working process was observed. After disassembling the diesels, it turned out that the reason for this is the development of cracks on the edge of the combustion chamber (CC), and the deterioration of indicators is detected when the crack has reached a critical length.

AIMS: The aim of study is concerned investigation of a methodology for predicting of a tractor diesel piston durability with the crack on the CC edge and development of a method for calculating the crack evolution to before the transition to the improper state.

METHODS: Both experimental and computational methods were used in the research. Experimental pistons was manufactured with some design changes: the radius of the edge rounding changed, which changed the thickness of the side wall of the CC.

RESULTS: Motor studies of diesel engines have shown that with a certain piston design, a crack either does not appear at all, or appears after a large number of cycles. Additional computational studies have shown that the crack development depends on the stress intensity coefficient at the crack tip. Using the data of experimental studies, a method has been developed for estimating the critical crack length in the edge of the CC, at which the intensity of stresses in the vicinity of its vertex exceeds the limits accepted for this material from which the piston is made.

CONCLUSIONS: A method for calculating the durability of the piston during the development of a crack on the edge of the combustion chamber is proposed. Verification of the calculated data obtained during the numerical implementation of the piston evaluation method using the example of the diesel piston D-240 showed that for a range of crack lengths up to 1 mm and operating time over 7000 m-hour, the calculation error com-pared to the operational test data does not exceed 11%.