Effect of Lubricant Oil on Particle Emissions from a Gasoline Direct Injection Light-Duty Vehicle

Gasoline direction injection (GDI) engines have been widely used by light-duty vehicle manufacturers in recent years to meet stringent fuel economy and emissions standards. Particulate Matter (PM) mass emissions from current GDI engines are primarily composed of soot particles or black carbon with a small fraction (15% to 20%) of semi-volatile hydrocarbons generated from unburned/partially burned fuel and lubricating oil. Between 2017 and 2025, PM mass emissions regulations in the USA are expected to become progressively more stringent going down from current level of 6 mg/mile to 1 mg/mile in 2025. As PM emissions are reduced through soot reduction, lubricating oil derived semi-volatile PM is expected to become a bigger fraction of total PM mass emissions. The primary objective of this research was to study the effect of lubricating oil on PM emissions from a modern light-duty vehicle equipped with a GDI engine without a GPF with a PM emission level near 1 mg/mile which is well below the current standard. Testing included two lubricating engine oils with 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). A 2013 US model year Mercedes-Benz GLK 350 was used as the test vehicle for the program. SwRI’s Direct Electronic Vehicle Control (DEVCon) driving method was utilized to ensure high levels of repeatability between tests. Three repeats of cold-start FTP-75 followed by hot-start US06 for each engine oil were conducted. Criteria gaseous and PM mass emissions along with 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. Results indicate that total PM mass, solid PN, total PN and ash number emissions increase with the oil having higher volatility and ash content (Oil B). This work also shows that lubricating oil can have an influence on solid particle number in the sub-23 nm size range, which is a size range below the current European Union (EU) PN regulatory limit but under consideration to be included in the near future. Results from this program reaffirm that PM emissions could be influenced by lubricating engine oil properties and formulation.