Abstract
Keywords:
Temperature, Heat rejection, Fuel economy, Performance, Coolant, Exhaust
Abstract
At high engine speed and high load conditions, closed loop feedback control of fueling is dominated by exhaust gas temperature. The objective of this study is to obtain better fuel economy and high engine performance by decreasing exhaust gas temperature. Three different factors such as combustion efficiency, heat rejection to exhaust and coolant were investigated respectively. Combustion chamber was optimized in order to increase combustion efficiency, which caused fast burning speed and improved thermal conversion efficiency of fuel. In case of heat rejection to exhaust, surface area for the heat transfer between exhaust gas and coolant was increased at the exhaust port, which converted parts of heat rejection to exhaust into heat rejection to coolant. Modification of coolant flow pattern also increased heat rejection to coolant due to the enhanced flow throughout the cylinder head and block. From this study, temperature decrease by 40℃ was obtained at the operating condition of 3000rpm and BMEP 6.0bar, which expanded the region of closed loop fueling possible by 1.2bar in BMEP, and enables to run with a stoichiometric fueling control up to vehicle speed of 160km/h. Additional power increase was also obtained at rated rpm.