The effect of ethanol blended diesel fuels on brake specific fuel consumption (BSFC), brake specific energy consumption (BSEC), smoke and NOx emissions has been investigated in a direct-injection diesel engine. Unregulated emissions including formaldehyde, acetaldehyde and unburned ethanol emissions are also analyzed. The results indicate that with the increase of ethanol in the blends, smoke reduces significantly, BSEC improves slightly and combustion duration decreases. However, the rate of heat release increases. Ignition delays. BSFC, NOx, acetaldehyde and unburned ethanol emissions increase. The maximum acetaldehyde emissions reached up to 100 ppm at low load.
Compared to a gasoline engine using ethanol blended gasoline fuels, unburned ethanol emissions of the diesel engine are higher than those of the gasoline engine at the same ethanol concentrations and similar loads. Although engine-out acetaldehyde emissions from the gasoline engine are higher than those from the diesel engine under some operating conditions, acetaldehyde emissions after a Pt/Rh based three-way catalytic converter are lower than those of the diesel engine.
To investigate the effect of ethanol blended diesel fuels on combustion processes and soot formation, the images of combustion processes were recorded using a high-speed CCD camera. The results reveal that the addition of ethanol to diesel fuels decreases combustion duration, flame luminosity and the regions of high flame luminosity, which indicates that soot formation in fuel-rich regions is suppressed by ethanol.