Autoignition of hydrogen-enriched n-butane-air mixture: A theoretical study

A fairly detailed reaction scheme for the oxidation of n-butane and hydrogen mixture has been employed to study the effect of hydrogen addition on the time delay of n-butane/air mixture. The intricate paths and mechanism by which autoignition is developed have been investigated by using the time-dependent kinetic flow charts technique. It was concluded that the autoignition process of n-butane/air as well as of n-butane/hydrogen/air mixture may be divided into three main periods. In the first (50 μs), the fuel molecule is attacked by HO₂ radicals to produce H₂O₂ molecules which, in turn, decompose into OH radicals. In the second (a few microseconds before ignition occurs), the OH radicals play the most important role in breaking down the hydrocarbon molecules. In the third, the CH₂O is converted into HCO and an avalanche of a series of exothermic reactions takes place and accelerate the whole process. It was also concluded that the hydrogen enrichment has a retarding effect on the autoignition process. This is attributed to the reduction of the OH population in the second stage due to the reaction H₂+OH→H+H₂O.