A Method for Enhancing Low-Pressure Ignition of n-Decane Based on Increasing Hydroxyl Free Radicals

Abstract

The flight envelope of aircrafts is hard to expand because the ignition of aviation fuel is unstable at low temperature or low pressure. Investigations on the low-pressure ignition phenomenon, like flame shape, soot formation and so on, have been done a lot. However how to enhance fuel ignition at low pressure is still a puzzle until now. This paper uses the fuel additive to enhance low pressure ignition of hydrocarbon fuel through generating more hydroxyl free radicals ($\dot{\hbox {O}}$H) in the fuel combustion. By means of fuel additive design, methoxydiethylborane (MDEB) is selected as a fuel additive in order to promote the low pressure ignition of n-decane. Experimental results show that with the additional 20% MDEB in n-decane, the minimum hot-surface ignition temperature at 1  bar is decreased from 863 to 393 K. The MDEB/n-decane hybrid fuel is able to be ignited at 0.65 bar when temperature is at 443 K. The experimental results are interpreted by the mechanism analysis of additive MDEB in n-decane, which indicates that the oxidization of MDEB produces methoxy free radicals (${\hbox {C}}{{\hbox {H}}_{{3}}}\dot{\hbox {O}}$) and ethoxy free radicals (${\hbox {C}_2}{\hbox {H}_5}\dot{\hbox {O}}$) to attack n-decane, finally generating more hydroxyl free radicals to enhance fuel ignition. This brand-new method based on increasing hydroxyl free radicals in fuel combustion, is meaningful and practical to enhance low-pressure ignition of hydrocarbon fuel and expand the flight envelope of aircrafts.