Stimulation of diesel-fuel ignition by benzyl radicals

Detailed chemical kinetic models for the low-temperature combustion of hydrocarbons with application to gasoline and diesel fuel surrogates

“…The idea of a fourth channel, (iv) the formation of benzyl hydroperoxy radicals, which can isomerise and decompose to give benzaldehyde and •OH radicals, is supported by experimental results of Ellis et al [243] and theoretical calculations of Clothier et al [302]. This sequence of reactions, which was taken into account by Lindstedt and Maurice [258], was included in the model of Nancy with the rate constant for the addition to oxygen molecule proposed by Fenter et al [303] over the temperature range 298-398 K, k iv = 4.6x10 11 exp(190/T) cm 3 mol -1 s -1 .…”

Experimental study of the kinetic interactions in the low-temperature autoignition of hydrocarbon binary mixtures and a surrogate fuel

“…The reason is to be found in the multiantagonistic action of the double bond and of the alkyl chains on the overall reactivity. The double bond has a stabilizing effect on the allylic-type radicals, but a promoting effect on HO 2 radicals by reaction (11), whereas the linear alkyl chains of 1-hexene and isooctane undergo the same sequence of reactions, contributing to the generation of a common pool of small radicals. The results are the low-temperature features typical of the long-chain alkanes, i.e., two-stage ignitions with cool flames and negative temperature coefficients.…”

“…Pritchard, using theoretical arguments based on ab initio calculations, suggested that both mechanisms are active according to the temperature [11,12]. Reaction (3) should proceed through reversible addition of oxygen to the benzyl radical followed by an internal H-transfer reaction and an O-O scission:…”

“…The transition state is a strained four-center cycle [11]. The same type of strained internal H-transfer may be responsible for the formation of aldehydes by other aromatics [15].…”

Density Functional Study of the High-Temperature Oxidation of o-, m- and p-Xylyl Radicals

“…Clothier et al 6 first calculated the reaction pathway forming OH radicals and benzaldehyde by thermal decomposition of benzylperoxy radicals using ROMP2//3-21G approximation and suggested that the benzylperoxide radical can act as the effective diesel-fuel ignition improver. Later, Murakami et al 7 calculated the product branching ratios for all of the plausible reaction channels of the benzyl + O 2 reaction using the CBS-QB3 method combined with RRKM/master-equation analysis.…”