In-Cylinder Particulate Matter and Spray Imaging of Ethanol/Gasoline Blends in a Direct Injection Spark Ignition Engine

A single cylinder Direct Injection Spark Ignition (DISI) engine with optical access was used to investigate the effects of ethanol/gasoline blends on in-cylinder formation of particulate matter (PM) and fuel spray characteristics. Indolene was used as a baseline fuel and two blends of 50% and 85% ethanol (by volume, balance indolene) were investigated. Time resolved thermal radiation (incandescence/natural luminosity) of soot particles and fuel spray characteristics were recorded using a high speed camera. The images were analyzed to quantify soot formation in units of relative image intensity as a function of important engine operating conditions, including ethanol concentration in the fuel, fuel injection timing (250, 300 and 320 degrees bTDC), and coolant temperature (25 degrees C and 90 degrees C). Spatially-integrated incandescence was used as a metric to quantify the level of in-cylinder PM formed at the different operating conditions. The experiments were conducted at stoichiometric conditions, fixed engine speed of 1500 RPM, a load condition of approximately 5.5 bar IMEPn, with a fixed intake manifold absolute pressure of 76 kPa. Significant reduction in in-cylinder soot formation was observed with the higher ethanol content in the fuel, regardless of fuel injection timing. Fuel impingement was documented in the spray imaging, and fuel impingement was a large factor affecting the level of PM emissions. Retarded fuel injection timing reduced the PM formed in-cylinder for the two fuel blends and the baseline gasoline. Higher coolant temperatures reduced liquid fuel on piston and cylinder wall surfaces, and therefore also reduced in-cylinder PM formation. The in-cylinder crank-angle-resolved data presented in this study are the first of their kind to document in-cylinder PM formation of ethanol fuel blends. The results provide insight on how ethanol fuel blends can be used to reduce DISI PM formation at varying levels of ethanol concentration in the fuel.