Impact of Fuel Injection on Dilution of Engine Crankcase Oil for Turbocharged Gasoline Direct-Injection Engines

Turbocharged gasoline direct injection (TGDI) engines often have a flat torque curve with the maximum torque covering a wide range of engine speeds. Increasing the high-speed-end torque for a TGDI engine provides better acceleration performance to the vehicle powered by the engine. However, it also requires more fuel deliveries and thus longer injection durations at high engine speeds, for which the multiple fuel injections per cycle may not be possible. In this study, results are reported of an experimental investigation of impact of fuel injection on dilution of the crankcase oil for a highly-boosted TGDI engine. It was found in the tests that the high-speed-end torque for the TGDI engine had a significant influence on fuel dilution: longer injection durations resulted in impingement of large liquid fuel drops on the piston top, leading to a considerable level of fuel dilution. Test results indicated that the higher the torque at the rated-power, the greater the level of fuel dilution. In a cyclic-load engine test simulating the customer drives of a target vehicle powered by the engine, the maximum level for fuel dilution was found to be up to 9%, causing significant drop in the oil viscosity. The causes for fuel dilution and impacts of it on the oil consumption and formation of carbon deports on the piston ring area, and methods for mitigating impacts of fuel dilution are discussed in the paper.