Experimental Investigation of Diesel and Surrogate Fuels: Spray and Ignition Behavior 2011-01-1921
In this work, surrogate fuels composed of n-decane and alpha-methylnaphthalene (AMNL) with different compositions according to the reference cetane numbers 53, 45, 38, and 23 are investigated. In addition to the two-component mixtures, we examine a three-component mixture composed of n-decane, AMNL, and di-n-butyl ether (DNBE) corresponding to a reference cetane number of 53. Spray characteristics of liquid and fuel vapor phase and the relationship between ignition quality and lift-off length are investigated. The experimental results show, first of all, that for these mixtures, the cetane number is a good indicator for the ignition delay. Diesel and surrogate fuels have different liquid penetration lengths, which depend on the evaporation rate, and hence vapor pressure and boiling point of the fuels. Spray tip penetration of all investigated fuels except diesel are similar for the vapor-phase, because the differences in fuel properties are too small to considerably affect the momentum flux. Furthermore, we discuss the overlap number (OL) of the fuels to estimate the soot formation tendency under compression ignition (CI) engine like conditions. It is found out that the OL generally increases with decreasing cetane number, although there are substantial variations for the studied fuels with the same cetane number. Most interestingly, the low cetane number fuel, which has a substantially higher content of a two-ring aromatic, is shown to have diminished soot formation, which is consistent with its higher OL number.