Homogeneous Charge Combustion and Emissions of Ethanol Ignited by Pilot Diesel on Diesel Engines

Abstract

Homogeneous charge combustion and emissions of ethanol ignited by pilot diesel fuel were investigated on a two-cylinder diesel engine. The results show that emissions depend on loads and ethanol volume fraction. At low loads, ethanol has little effects on smoke. With the increase of ethanol, NOx decreases, but CO emissions increase. At high loads, smoke emissions reduce greatly with increasing ethanol, but NOx and total hydrocarbon (THC) emissions increase. With the increase of ethanol, ignition delays, combustion duration shortens. The maximum rates of heat release for the fuel containing 10 vol% ethanol (E10) and 30 vol% ethanol (E30) increase. Brake specific energy consumption (BSEC) of E10 and E30 is improved slightly only at full loads. Compared to smoke emissions obtained on the same engine using ethanol blended diesel fuels, the tendency of smoke reduction is similar to that of homogeneous charge combustion of ethanol at the same operating conditions. But the former is more effective in reducing smoke emissions. When the engine operated at high constant loads, smoke significantly decreases with increasing ethanol and smokeless combustion can be achieved at certain ethanol volume fraction dependent on loads. In the meantime, THC emissions gradually increase. Ignition retards, peak pressure increases first and then decreases again. Indicated mean effective pressures are close to those of diesel (E0), even higher than the latter at some cases. NOx emissions are dependent on loads and ethanol volume fraction, and even are less than those of E0 under certain conditions. The results obtained from an optical diesel engine show that ethanol also shortens combustion duration, decreases flame temperature and KL factor, which indicates that ethanol can suppress soot formation in combustion chamber.