Effect of Thin-Film Coating on Wear in EGR-Contaminated Oil

Increased use of higher-efficiency compression ignition direct injection (CIDI) diesel fueled engines instead of today's gasoline engines will result in reduced fuel consumption and greenhouse gases emissions. However, nitrogen oxides (NO_x) and particulate exhaust emissions from diesel engines must be significantly reduced due to their possible adverse health effects. Exhaust gas recirculation (EGR) is an effective way to reduce NO_x emissions from diesel engines, but the particulates and acidic exhaust products in the recirculated gas will contaminate engine lubricant oil by increasing the soot content and total acid number (TAN). These factors will increase the wear rate in many critical engine components and seriously compromise engine durability. We have investigated the use of commercially available thin and hard coatings (TiN, TiCN, TiAlN, and CrN) to mitigate the negative effects of EGR on wear. In friction and wear tests with the four-ball machine, we found that all the four coatings deposited on M-50 steel significantly reduced wear in EGR-contaminated oils when compared with uncoated M50 steel balls.