Contribution to carbon neutrality is one of the most important challenges for the automotive industry. Though CO2 emission has been reduced through electrification, internal combustion engines equipped in vehicles such as Hybrid Electric Vehicle (HEV) and Plug-in Hybrid Electric Vehicle (PHEV) are still necessary for the foreseeable future, and continuous efforts to improve fuel economy are demanded. To improve powertrain thermal efficiency, direct-injection turbocharged gasoline engines have been widely utilized in recent years. Super lean-burn combustion engine has been being researched as the next generation of turbocharged gasoline engines. It is known that an increase of the boost pressure causes deposit formation, which decrease the turbocharger efficiency, in the turbocharger compressor housing. To avoid the efficiency loss due to deposit, air temperature at compressor outlet has to be limited low. In this paper, the methodology was constructed to predict compressor efficiency loss, based on the mechanism of turbocharger deposit formation in gasoline engines.
Test procedure to reproduce compressor deposit in turbocharger unit test equipment was developed. The correlation between the temperature of compressor housing inner surface and the rate of compressor efficiency loss was clarified. In addition, the correlation between the location where deposit was formed and the compressor efficiency loss was also investigated. As opposed to steady-state operation such as engine dyno tests, vehicle operations in actual markets are transient, and the boost pressure of turbocharger and its outlet air temperature can vary widely. Due to the thermal capacity of compressor housing, the temperature of housing changes after the outlet air temperature changes with certain time delay. The temperature model considering this delay has been developed and enabled to estimate the deposit formation, turbocharger efficiency loss and engine performance deterioration in transient conditions.