Autoignition of trans-decalin, a diesel surrogate compound: Rapid compression machine experiments and chemical kinetic modeling

Decahydronaphthalene (decalin), with both cis and trans isomers, is a bicyclic alkane that is found in aircraft fuels, diesel fuels, and alternative fuels from tar sands and oil shales. Between the two decalin isomers, trans-decalin has a lower cetane number, is energetically more stable, and has a lower boiling point. Moreover, trans-decalin has often been chosen as a surrogate component to represent two-ring naphthenes in transportation fuels. Recognizing the importance of understanding the chemical kinetics of trans-decalin in the development of surrogate models, an experimental and modeling study has been conducted. Experimentally, the autoignition characteristics of trans-decalin was investigated using a rapid compression machine (RCM) at compressed pressures of p_c=10-25 bar, low-to-intermediate compressed temperatures of φ=620-895 K, and varying equivalence ratios of φ=0.5, 1.0, and 2.0 in air. These new experimental data demonstrate the effects of pressure, temperature, and equivalence ratio on autoignition of trans-decalin. The current RCM data of trans-decalin at lower temperatures were also found to complement well with the literature shock tube data of decalin (cis+trans) at higher temperatures. Furthermore, a chemical kinetic model for the oxidation of trans-decalin has been developed with new reaction rates and pathways, including, for the first time, a fully-detailed representation of low-temperature chemical kinetics. This model shows good agreement with the overall ignition delay results of the current RCM experiments and the literature shock tube studies. Chemical kinetic analyses of the developed model were also conducted to help identify the fuel decomposition pathways and the reactions controlling the autoignition at varying conditions.