Spray ignition experiments for alkylbenzenes and alkylbenzene/n-alkane blends

•The spray ignition behavior of alkylbenzene/n-alkane blends was investigated.•A blending model is proposed based on an overall reaction order for each component.•The nonlinearity of DCN against molar composition is well described by the model.•Synergism between aromatic ring and alkyl group is seen to enhance reactivity.

Spray ignition experiments were carried out in a heated constant volume vessel for pure n-octylbenzene and n-decylbenzene and blends of smaller alkylbenzenes (toluene, 1,3,5-trimethylbenzene, n-propylbenzene, and n-butylbenzene) with n-heptane and n-decane. The experiments provide determinations of the derived cetane number (DCN) and the temperature dependence of the spray ignition delay time in air for initial ambient conditions of 650-820 K and 2.14 MPa. The alkylbenzene/n-alkane blends were found to exhibit nonlinear blending for DCN that is well explained using a proposed DCN blending model that accounts for an apparent reaction order of the blend components. Comparisons between n-octylbenzene and n-decylbenzene with blends of smaller n-alkylbenzenes (toluene or n-propylbenzene) and n-alkanes that seek to match functional group distributions, illustrate a synergistic reactivity promotion that occurs for n-alkylbenzenes with long chain alkyl side chain substitutions. This synergism is thought to be result of the weaker benzylic bond strengths within n-alkylbenzenes, providing increased rates of alkyl radical formation and subsequently enhanced low-temperature oxidation. Hence, this finding shows that mixtures of n-alkanes and n-alkylbenzenes with short side chains (e.g., toluene or n-propylbenzene) are not suitable surrogates to emulate low-temperature reactivity of n-alkylbenzenes with long side chains.