Assessing the Impact of Lubricant and Fuel Composition on LSPI and Emissions in a Turbocharged Gasoline Direct Injection Engine 2020-01-0610

Downsized turbocharged gasoline direct injection (TGDI) engines with high specific power and torque can enable reduced fuel consumption in passenger vehicles while maintaining or even improving on the performance of larger naturally aspirated engines. However, high specific torque levels, especially at low speeds, can lead to abnormal combustion phenomena such as knock or Low-Speed Pre-Ignition (LSPI). LSPI, in particular, can limit further downsizing due to resulting and potentially damaging mega-knock events. Herein, we characterize the impacts of lubricant and fuel composition on LSPI frequency in a TGDI engine while specifically exploring the correlation between fuel composition, particulate emissions, and LSPI events. Our research shows that: (1) oil composition has a strong impact on LSPI frequency and that LSPI frequency can be reduced through a carefully focused approach to lubricant formulation. In addition, (2) we observed significant improvement potential in Brake Mean Effective Pressure (BMEP) achievable with zero LSPI events using both experimental and market-representative lubricant formulations. Finally, (3) fuels blended with high polyaromatic content were shown to increase LSPI frequency significantly; these fuels also caused a significant increase in particulate mass (PM) and particulate number (PN) emissions. In this paper, we discuss the above results along with the development and use of a high-fidelity test method to measure LSPI under steady-state test conditions.