Studies of the combustion of branched-chain hydrocarbons

Abstract

The cool-flame oxidation of both 3-ethylpentane and 3-methylpentane has been studied in the temperature range 250°–410°C. The results show that, with these two branched-chain hydrocarbons, the principal chain-propagating cycle involves alkylperoxy radical isomerization, followed by decomposition of the resulting hydroperoxyalkyl radicals; evidence is presented for the first time that ethyl group shifts can occur during the breakdown of the latter radicals. The “alkene-hydroperoxy radical addition” route appears to play only a minor role, even at 403°C. It is also shown that the higher the octane number of a hydrocarbon fuel the more likely it is to lead to β -scission products. Since many of these products are lower molecular weight alkenes, this result is very relevant to the problem of pollution from vehicle exhausts, since alkenes may react photochemically to form smog.