Experimental analysis of the influence of coolant and oil temperature on combustion and emissions in an automotive diesel engine

Since many trips are of short duration and include a cold start, automotive engines run quite often without having reached their nominal temperature. This is known to have some major drawbacks, such as increased fuel consumption and higher emissions due to lower efficiency of after-treatment devices, but detailed description of these various effects is seldom presented in the literature. In this article, experiments were conducted on an automotive diesel engine by varying independently the coolant and oil temperatures between 30？°C and 90？°C. Three different operating conditions (low, mid and full load) were studied. The experimental set-up is briefly described as well as the uncertainty of the associated measurements and the development of analytic tools. Then, the evolution of volumetric efficiency, energy share, combustion heat release and exhaust emissions (NOx, particulate matter, CO, unburned hydrocarbons) are described in detail and analysed. Several strategies were considered, including some corrections used in the standard engine control unit to compensate for the low coolant temperature. Some effects of the coolant and oil temperature reduction were clear: increase in friction losses, volumetric efficiency and ignition delay and decrease in NOx emissions. On the contrary, the evolution of brake thermal efficiency, particulate matter, CO and unburned hydrocarbon emission depended on the operating point