Development of a practical reaction model of polycyclic aromatic hydrocarbon (PAH) formation and oxidation for diesel surrogate fuel

A practical reaction model for the formation and oxidation of polycyclic aromatic hydrocarbons (PAHs) up to coronene (A(7)) was developed focusing on two diesel surrogate fuels, i.e., a single-component surrogate including n-heptane and a multi-component surrogate including iso-octane, n-decane, methylcyclohexane, and toluene, for engine simulations. The important PAH relevant reactions are identified by using the global sensitivity analysis of the up-to-date detailed mechanisms. In the reduced PAH reaction model, the up-to-date reaction channels involving PAH formation were considered, and the variations and characteristics of the formation pathways of benzene and large PAHs for large alkanes, aromatics, and cycloalkanes with the fuel molecular structure were captured with the present under wide operating conditions. By integrating the PAH reaction model with a reduced oxidation mechanism of the two diesel surrogates, the final chemical mechanism of diesel oxidation consists of 137 species and 447 reactions. The chemical mechanism was extensively validated against the fundamental experimental data including ignition delay times in shock tubes and species profiles in premixed laminar flames, diffusion flames, and jet-stirred reactors (JSR). The performance of the mechanism for the predictions of PAHs from the oxidation of individual component, their mixtures, and diesel fuel was comprehensively evaluated. The computational results indicate that the effect of fuel structure on the PAH formation is satisfactorily reproduced by the present mechanism. Based on pathway analysis in the premixed flame, the contribution of the components in the diesel surrogate for the PAH formation behavior is understood.