Technical review of opportunities to reduce the warm-up time of lubricant oil in a light-duty diesel engine

Cold-phase related emissions from internal combustion engines have a significant impact in most daily driving cycles. In particular, when the engine is started from a cold state, lubricant oil viscosity is very high and this affects the friction performance of the mechanical components of the engine. When the engine is warmed up, then, the viscosity of the oil can be up to 15 times lower than the cold phase and even more in very cold climates, producing significant reduction in specific fuel consumption and, so, carbon dioxide emissions. In this work, the Authors demonstrate the effectiveness of some technical opportunities to reduce the warm up time of the oil, with particular reference to a 3.0 L turbocharged diesel engine during a light duty homologation driving cycle. Experimental assessments have been done on different oil circuit layouts and proposing prototyped technologies. Oil sump modification, coolant-to-oil heat exchanger bypass, external heater, heat recovery option, and thermal storage have been tested and compared with each other. Among them, exhaust heat recovered to accelerate the warming up of lubricant oil seems to be the most promising one and it could be easily integrated with a thermal storage section. It is the opinion of the Authors that these technical options could be easily implemented on a vehicle and they can represent a significant step forward to a more efficient thermal management and friction reduction in internal combustion engines.