Effects of Ethanol on In-Cylinder and Exhaust Gas Particulate Emissions of a Gasoline Direct Injection Spark Ignition Engine

The effects of ethanol on reducing the particulate emissions of a direct injection spark ignition (DISI) engine were investigated using a single-cylinder, optically accessible engine. Neat anhydrous ethanol was compared with a baseline fuel of reference grade gasoline. A high speed camera was used to record crank-angle resolved in-cylinder images of the fuel spray, combustion, and thermal radiation from the soot formed for the engine operating conditions studied. Particulate emissions in the engine exhaust gas were also measured using opacity measurements (i.e., using a smoke meter). All experiments were conducted at the same load conditions with a net indicated mean effective pressure of IMEPnet ≈ 5.5 bar and an intake manifold absolute pressure of 76 kPa. The engine speed was fixed at 1500 rpm, and the fuel injection duration was controlled to achieve stoichiometric combustion. Spark timing was adjusted to target combustion phasing (CA50) of 8° aTDC. The effects of engine coolant temperature and fuel injection timing on fuel spray characteristics and soot formation were studied for each fuel. The imaging data indicate that soot formation is a strong function of liquid fuel impingement on the piston surface, consistent with previous in-cylinder imaging studies of soot formation in DISI engines using different engine hardware and imaging orientation. A quantitative metric was applied to the imaging data of this work, and the in-cylinder soot formation based on the imaging data were in good agreement with the engine-out smoke measurements, indicating the optical imaging results are representative of engine-out particulate emissions. Higher coolant temperatures and later fuel injection timing significantly mitigated the in-cylinder soot emissions for both fuels by altering the fuel spray interactions with the piston surface and cylinder liner. As expected based on previous studies, ethanol systematically produced less soot than gasoline for each operating condition. Features of the fuel spray roll-up were identified as important indicators of pool fires on the piston surface for the earliest fuel injection timings.