Ignition of isomers of pentane: An experimental and kinetic modeling study

Experiments in a rapid compression machine were used to examine the influences of variations in fuel molecular structure on the autoignition of isomers of pentane. Autoignition of stoichiometric mixtures of the three isomers of pentane were studied at compressed gas initial temperatures between 640 K and 900 K and at precompression pressures of 300 and 400 torr. Numerical simulations of the same experiments were carried out using a detailed chemical kinetic reaction mechanism. The results are interpreted in terms of a low-temperature oxidation mechanism involving addition of molecular oxygen to alkyl and hydroperoxyalkyl radicals. Results indicate that in most cases, the reactive gases experience a two-stage autoignition. The first stage follows a low-temperature alkylperoxy radical isomerization pathway that is effectively quenched when the temperature reaches a level where dissociation reactions of alkylperoxy and hydroperoxyalkylperoxy radicals are more rapid than the reverse addition steps. The second stage is controlled by the onset of dissociation of hydrogen peroxide. At the highest compression temperatures achieved, little or no first-stage ignition is observed. Particular attention is given to the influence of heat transfer and the importance of regions of variable temperature within the compressed gas volume. Implications of this work on practical ignition problems are discussed.