Effects Of Oxygenated Fuels On Premixed Low Temperature Combustion In A Diesel Engine Based On Fuel Design

Biodiesel and ethanol are used in premixed low temperature combustion (LTC) mode based on the fuel design theory. The combustion and emission characteristics are investigated in this study.Fuel injection and spray are investigated on a common rail system. It is found that biodiesel and diesel have similar injection delay time and injection rate. Compared to diesel, biodiesel produces longer spray tip penetration, smaller spray cone angle and larger sauter mean diameter. Blending ethanol into biodiesel causes reduced spray tip penetration, increased spray cone angle, reduced sauter mean diameter and improved fuel atomization.Soot formation is simulated and it is found that biodiesel and ethanol can suppress soot formation and produces lower soot than diesel. In LTC, for a given equivalence ratio, biodiesel-ethanol blend produces the lowest soot, followed by biodiesel.In engine tests operated in the premixed LTC mode, compared to diesel, the smoke emission of biodiesel-ethanol blend is greatly reduced, as a combined result of better spray atomization, longer ignition delay and fuel oxygen effect on smoke formation. The smoke/NOx trade-off is defeated by biodiesel-ethanol, and low smoke, low NOx and high combustion efficiency are possible with biodiesel-ethanol. The maximum load, with smoke emissions less than0.5FSN, NOx emissions less than1g/kg-fuel and combustion efficiency more than96%, is extended to0.82MPa IMEP by using biodiesel-ethanol blend and intake boost.Experiments show that in premixed LTC, compared to diesel, biodiesel produces increased particles with diameter less than70nm and reduced particles with diameter more than70nm. Biodiesel-ethanol increases the amount of particles with diameter less than20nm and decreases the amount of particles with diameter more than20nm. The total particle number of biodiesel is about38%higher than diesel, and the total particle number is33-47lower than diesel.Effects of fuel oxygen on emissions from the premixed LTC are investigated by isolating fuel oxygen from other fuel properties. It is fouond that increased fuel oxygen can significantly reduce smoke emission, but has minor effect on CO, HC and NOx emissions. Further analysis show that intake (CO2+H2O) concentration is the main influential parameter for NOx emission, global equivalence ratio and peak bulk gas temperature are the main parameters for CO emission, and peak bulk gas temperature and ignition delay are the main factors for HC emission.