Spray characterization and reactivity study for low temperature combustion engine

Abstract

Compression ignition engines have high thermal e ciency but su er from harmful oxides of nitrogen and soot emissions. The near zero engine emissions can be obtained by using the knowledge of fuel spray formation, reactivity strati cation and chemical kinetics of combustion. For conducting the macroscopic spray characterization experiments of various biodiesels a constant volume spray chamber and fuel injection test rig is developed while spray images are captured by high-speed shadowgraphy technique. Diesel and neem biodiesel, macroscopic spray characteristics under single and split injection are studied. Flash boiling spray characteristics of diesel, neem biodiesel and biodieselethanol blend (BDE50) are studied for improving the fuel dispersion. A light duty water cooled single cylinder compression ignition engine operating on steady-state (at 1.71 kW and 1500 RPM) is used for understanding the e ect of single and split fuel injection on engine combustion, performance and emissions. A novel strategy is presented for obtaining the low temperature combustion and reactivity charge compression ignition mode, with hot charge dilution and without modifying the engine combustion geometry for high compression ratio operation. Spray characteristics show poor spray atomization characteristics and inferior fuel-air mixing with unsaturated biodiesels while saturated biodiesels show spray characteristics similar to diesel. For various biodiesels a modi ed Roisman correlation for far- eld spray tip penetration prediction validates well. With considering the macroscopic spray characteristics the implementation of saturated biodiesels in compression ignition engine requires no modi cations. The blends of neem biodiesel with ethanol/gasoline shows spray characteristics similar to diesel (and provides small reactivity strati cation due to dual fuel reactivity). The high vapor pressure and rapid depressurization of ethanol in ambient gas density results in cavitation induced ashing which improves the spray atomization characteristics of neem biodiesel-ethanol blend. The increase in jet momentum and instability on spray jet periphery with the split injection of fuel improves the spray atomization of neem biodiesel. The biodiesel and its blends for charge dilution shows near zero nitrogen oxide and reduced soot emissions. Split injection of fuel in compression ignition engine, improves the fuel-air mixing, lowers the combustion temperatures and increases the soot emissions. The diesel-gasoline blend under low temperature combustion mode shows high thermal e ciency and near zero nitrogen oxide-soot emissions. The diesel+gasoline and diesel+methanol blend under reactivity controlled compression ignition mode shows decreased fuel consumption and near zero nitrogen oxide-soot emissions. The low reactivity of methanol/gasoline and charge dilution provides more time for fuelair mixing, improves the premixed combustion and o ers more exibility for controlling the engine operation even at high compression ratio.