Study of the Effect of Engine Speed and the Operating life on Blowby in Fueled Motoring for XU7JP/L3 Engine

Clearances between cylinder and piston, and pressure difference between top and bottom of piston causes a flow through the crevices termed blowby. This phenomenon results in cylinder pressure and temperature drops; some unburned mixture remains in the crevices leading to inconvenient usage of the mixture in firing cycle and reduction in engine performance. In the current work a thermodynamic blowby simulation code validated in motoring condition has been used to study and predict the blowby of XU7JP/L3 engine in terms of engine speed and engine working life. Some geometrical measurements of cylinder-piston-ring pack were performed in two engine operations, 70000km and 200000km, to apply the code after required corrections. The obtained results showed that the values of the blowby geometry increased with enhancement of engine life and engine temperature. Increasing engine life enhanced cylinder leakage significantly so the leaking value of 200000km reached to 4 times greater than that for new engine life. Also the mass lost through second compression ring at 70000km and 200000km working durations increased to about 7 and 15 times of that for new engine one, respectively.