A Novel Cooling Strategy for a Diesel Engine to Improve Engine Power Efficiency and Emissions

Stringent regulations on CO₂ emission causing greenhouse effect have drawn attention of automotive manufacturers to the diesel engine. The trend is to increase the engine power per liter, and research are being carried out to satisfy the regulation. In this paper, a new cooling strategy was proposed to control coolant more efficiently. Before carrying out a new cooling strategy, preliminary tests on the cooling components were performed. Measurement of metal temperature of the engine indicates that the conventional cooling system was designed inappropriately large to endure at high load conditions. Therefore several strategies were adapted to optimize the size of the conventional cooling system using an Electric Water Pump (EWP), Electric Valve (EV) and low temperature EGR cooler. A cooling system in a 2.7 liter Direct Injection Diesel Engine was modified for the purpose of this study, and the strategies were tested in a stationary test bench. As a result, emission and fuel consumption decreased in high coolant temperature and low coolant flow. Warm-up period in which THC and CO emissions were significant was shortened by controlling the coolant flow paths using EVs. An essential component in a diesel engine is an Exhaust gas recirculation (EGR) system that decreases combustion temperature and oxygen concentration resulting in a substantial reduction of NOx emission. The coolant circulates through the EGR cooler so that the EGR gas temperature could be dropped down, resulting in more efficient combustion. New cooling strategies were found to improve emissions and fuel economy of engines.