Spray Phenomena of Surrogate Fuels and Oxygenated Blends in a High Pressure Chamber

摘要

In this study, we investigate oxygenated blends and Diesel surrogate fuels under engine-like conditions in a high-pressure chamber. The investigated surrogate fuels are composed of n-decane and alpha-methylnaphthalene with different compositions according to the reference cetane numbers (CN) 53, 45, 38 and 23. In addition to the two-component surrogate fuel mixtures, we examine a three-component mixtures composed of n-decane, alpha-methylnaphthalene, and di-n-butyl ether with a reference cetane number of 53 to highlight the influence of adding di-n-butyl ether to the surrogate fuel at constant cetane number. Further, four blends with DNBE contents of 0, 10, 20 and 100 % in EN590 Diesel and corresponding cetane numbers of 53, 57.7, 62.4, and 100 were studied. We examine fuel spray characteristics in the liquid and vapor phases and the relationship between ignition quality and lift-off length. Vapor pressure is observed to significantly affect spray characteristics in the liquid phase. Vapor penetration lengths of the different fuels with the same injection pressure are found to be similar, because the differences of fuel density and viscosity in the vapor phase are too small to considerably affect the momentum flux. However, changing the injection pressures affects the vapor penetration lengths. Results show that CN is a good indicator for ignition delay. Furthermore, we discuss the fuel overlap number (OL) to indicate the separation between the liquid spray core and the reaction zone in engine-like conditions. It is found for the surrogate mixtures that OL generally increases with decreasing CN, while for the DNBE/Diesel mixtures, the opposite trend is observed. The OL number is found to be caused by a combination of cetane number and vapor pressure effects, where CN has the stronger effect for the surrogate mixtures, while the vapor pressure effect is dominant for the DNBE/Diesel blends. In the latter case, the high vapor pressure leads to short liquid penetration length and thereby larger OL number.