Background
The purpose of this project was to examine the effect of engine lubricant oil on particle emissions from a modern gasoline direct injection (GDI) light-duty vehicle. In recent years, GDI engines have been widely adopted by manufacturers in the light-duty market to meet stringent fuel economy and emissions regulations. Despite improved fuel economy and lower carbon dioxide emissions, these engines emit higher particulate matter (PM) emissions compared to other engine technologies such as port fuel injected (PFI) engines and diesel engines equipped with diesel particulate filters (DPF). PM emissions from GDI engines are typically composed of soot particles (or black carbon) with a small fraction (15 to 20 percent) of semi-volatile hydrocarbons generated from unburned/partially burned fuel and lubricating engine oil. Between 2017 and 2025, PM emissions are expected to become progressively more stringent going down from the current level of 6 mg/mile to 1 mg/mile in 2025. As PM emissions (especially soot) are reduced, lubricant oil derived semi-volatile PM will become a bigger fraction of total PM emissions. The preliminary objective of this research was to study the effect of lubricating engine oil on physical and chemical characteristics of PM emitted from a modern light-duty vehicle equipped with a GDI engine that had a PM emission level well below the current standard of 6 mg/mile, which was closer to 1 mg/mile.
Approach
Two lubricating engine oils with widely differing physical and chemical properties — one with low volatility and low ash content (Oil A), and another with high volatility and high ash content (Oil B) were tested. Testing included three repeats of cold-start FTP-75 followed by hot-start US06 for each engine oil. SwRI’s Direct Electronic Vehicle Control (DEVCon™) driving method was utilized to ensure high levels of repeatability between tests, instead of using a human driver. Gaseous and PM mass emissions along with real-time solid and total (solid plus volatile species) particle number (PN), solid and total particle size distribution, ash number emissions, and soot mass emissions were examined.
Accomplishments
Results from this program showed that particle emissions could be influenced by lubricating engine oil properties. PM mass, solid PN, total PN and ash number emissions showed an increase with the oil having higher volatility and ash content (Oil B). For composite FTP-75, Oil B showed approximately 17 percent more PM mass and total PN emissions compared to Oil A. Another significant observation showed that Oil B led to higher PN emissions in the sub 23 nm particle size range. While this range is currently below the size threshold required to be measured by the European Union PN regulation, it could be included in future PN regulations because this size range is of critical health concern.
This work sheds light on the potential impact of lubricating engine oil on particle emissions. Such information could be beneficial during lubricating engine oil development and formulation in light of more stringent future PM and PN regulations.
Detailed information about this program can be found in SAE Technical Paper 2018-01-1708.