Calculations of Diesel Pistons with a Crack on the Edge of the Combustion Chamber

Abstract

AbstractDuring periodic long-term tests of tractor diesels with a semi-separated combustion chamber (CC) the indicators of the operation process got worse over time. Cracks emerged on the edge of the combustion chamber and resulted first in worsening of economic indicators of the diesel engine, and then in its failure. It is shown that economic indicators worsen when the crack length is up to 1 mm. The crack growth depends on the design and parameters of the CC. According to the results of motor tests of experimental pistons, with a certain piston design, a crack either does not emerge at all, or emerges after a large number of cycles. It is shown that the crack growth depends on the stress intensity coefficient at the crack tip. The authors proposed the techniques of calculating this coefficient at the crack tip of the CC and the durability of a piston with a crack on the edge of the CC. It is also proposed to determine the critical crack length at the edge CC, at which the stress intensity at the crack tip exceeds the limit values accepted for the material from which the piston is made. When numerically implementing the calculation of the diesel piston 4CHN11/12.5, it is revealed that the calculation error in comparison with the operational test data does not exceed 11%.KeywordsInternal combustion engineTransientsPistonCombustion chamberTemperature gradientsThermal stressesStress crack