About possibility of using the method of diesel cranking with external power source to evaluate the friction of piston rings

This study investigates the applicability of diesel cranking with an external power source for evaluating piston ring friction. Experiments were conducted on an air-cooled 2Ch10.5/12 diesel engine with a nominal power of 22 kW. The temperatures of the motor oil in the crankcase and of the ambient air were maintained constant at 85 ± 1 °C and 30 ± 1 °C, respectively. Mechanical losses were evaluated by two methods: 1) diesel cranking with an external power source and 2) comparison of indicated and effective powers at 30 % of nominal engine load. Mineral oils I-20A, MS-20, as well as their mixtures, were used as motor oils during testing. Mechanical losses determined by diesel cranking with an electric motor were approximately 16 % lower than those determined by comparison of indicated and effective powers. Assuming that the major fraction of the reduction in mechanical losses is caused by a lower force pressing the piston rings against the cylinder wall, the friction coefficients of the piston rings were calculated. The obtained friction coefficient values exceeded those reported in scientific literature by more than five times. This indicates that the change in piston ring friction is not the main cause of the reduction in mechanical losses during the transition from motor operation to diesel cranking. Therefore, piston ring friction cannot be determined by comparing mechanical losses obtained in cranking and motor regimes. An analysis of the causes of the reduction in mechanical losses during the transition from motor operation to diesel cranking was carried out.