Investigation of Fuel Effects on Dilute, Mixing-Controlled Combustion in an Optical Direct-Injection Diesel Engine

Effects of fuel type on dilute diesel combustion and emissions were investigated using an optically accessible diesel engine. A number 2 diesel fuel, a primary reference fuel blend, and a soy-derived biodiesel were evaluated at an engine speed of 1200 rpm, and for intake-oxygen mole fractions ranging from 21% down to 8%. Diagnostics included conventional heat-release analysis; the measurement of in-cylinder natural luminosity; in-cylinder imaging of the start of fuel injection; and the measurement of engine-out emissions of nitrogen oxides (NOx), smoke, HC, and CO. Data previously obtained using the fuel diethylene glycol diethyl ether are presented to provide further insight. Results reveal that reduced oxygen mole fractions produce a slower heat release and lower levels of soot formation. However, engine-out particulate matter levels are also dramatically influenced by subsequent soot oxidation, which is greatest at higher oxygen mole fractions. NOx emissions are observed to drop dramatically as oxygen ...