Detailed chemical kinetic reaction mechanisms for autoignition of isomers of heptane under rapid compression

Detailed chemical kinetic reaction mechanisms were developed for combustion of all nine isomers of heptane, and simulating autoignition of each isomer under rapid compression machine conditions tested these mechanisms. The reaction pathways emphasized the importance of alkylperoxy radical isomerizations and addition reactions of molecular oxygen to alkyl and hydroperoxyl radicals. A new reaction group was added to past models, in which hydroxyalkyl radicals that originated with abstraction of an H atom from a tertiary site in the parent heptane molecule are assigned new reaction sequences involving additional internal H atom abstractions not previously allowed. This process accelerated autoignition in fuels with tertiary C-H bonds in the parent fuel. The rates of hydroperoxyalkylperoxy radical isomerization reactions were all reduced to be equal to the rates of analogous alkylperoxy radical isomerizations, significantly improving agreement between computed and experimental ignition delay times in the rapid compression machine. The computed results were categorized into three groups, i.e., the most reactive isomers, including n-heptane, 2-methyl-hexane, and 3-methyl hexane; the least reactive isomers, including 2,2-dimethyl pentane, 3,3-dimethyl pentane, 2,3-dimethyl pentane, 2,4-dimethyl pentane, and 2,2,3-trimethyl butane; and the remaining isomer 3-ethyl pentane. Original is an abstract.