An experimental and kinetic modeling study on the autoignition characteristics of indene

Indene is an important intermediate in the ring growth process of polycyclic aromatic hydrocarbons (PAHs) which are soot precursors in the fuel combustion. Ignition delay times of indene/3.3% O2/Ar and indene/air mixtures were measured behind reflected shock waves over temperatures of 1098–1618 K, pressures of 2.5–10.0 atm, and equivalence ratios of 0.5, 1.0 and 2.0. An Arrhenius-type formula can describe all the measured indene/3.3% O2/Ar ignition delay data. But three Arrhenius-type formulas were used to describe the measured indene/air ignition delay data for three pressures because the activation energy varies with different ignition pressures. Indene ignition characteristics in different dilution conditions were compared and discussed. Current results show that the indene ignition delay follows τ ∝ Φ+n diluted in Ar with fuel-lean mixture igniting the fastest and τ ∝ Φ−n at real fuel-air condition with fuel-rich mixture igniting the fastest. For indene/air, when the pressure increases, the effect of equivalence ratio on ignition becomes stronger and the sensitivity of ignition to the variation of temperature becomes weaker. Furthermore, an indene combustion mechanism was developed. The predictions of the developed mechanism are in good agreement with the measured data. Reaction pathway and sensitivity analyses were carried out to determine reaction pathways during the ignition process and dominate reactions which affect ignition delay times. Current experimental results are useful for understanding the ignition properties of indene and studying the formations of larger PAHs and soot. To our knowledge, experimental ignition delay times and a detailed combustion mechanism for indene are firstly reported in this work.