The effect of NO 2 group on the ignition delay times of straight and cyclic hydrocarbons

Abstract

Ignition delay times of cyclopropane and of three hydrocarbons containing one NO 2 group—nitromethane, nitroethane and nitrocyclopropane—were measured over a wide temperature range and were compared with ignition delays of the same hydrocarbons without the nitro group. These experiments were performed in order to examine the effect of the NO 2 group on the oxidation rate of cyclic and straight hydrocarbons. The experimental results reveal three significant features. 1. The nitro-aliphatic compounds are much more reactive than the corresponding hydrocarbons, judging from the duration of the ignition delay at a given temperature. 2. Contrary to aliphatic hydrocarbons, the increase in the nitroaliphatic concentration causes a decrease in the ignition delay time. 3. The spread of the log τ vs. 1/T curves among the −NO 2 containing substances is considerably smaller than that corresponding to the ignition of the simple hydrocarbons. There is a good correlation between the initiation rates and the ignition delays of the six fuels in question. It is suggested that the opening of a new avenue for initiation, namely rupture of the weak C−NO 2 bond, increases the oxidation rate.