An experimental and kinetic modeling study of the autoignition of syngas mixtures behind reflected shock waves

Abstract

The results of an experimental and kinetic modeling study of the ignition of \(\hbox {H}_{{2}}{-}\hbox {CO}{-}\hbox {O}_{{2}}{-}\hbox {Ar}\) mixtures behind the reflected shock wave are reported. The experiments were performed with test mixtures containing \(0.75{-}3.0{\%}\,\hbox {H}_{{2}}\), \(0{\%}{-}3.0{\%}\,\hbox {CO}\), and \(1.5{\%}\,\hbox {O}_{{2}}\) in argon at temperatures from 950 to 1650 K and a total gas concentration of \({\sim }10^{{-5}}~ \hbox {mol}/\hbox {cm}^{{3}}\). The reaction was monitored by recording the time evolution of the pressure behind the reflected shock wave, intensity of the chemiluminescence of electronically excited OH* radicals at 308.0 ± 2.0 nm, and the absorption by ground-state OH radicals at a 306.772-nm bismuth atomic line. The measured parameters were the time \(\uptau _{{1}}\) it took to reach a ground-state OH concentration of \(2.0 \times 10^{{-9}}~\hbox {mol}/\hbox {cm}^{{3}}\) and the time \(\uptau _{{2}}\) to reach the maximum OH* emission intensity. Kinetic simulations demonstrated that \(\uptau _{{1}}\) corresponds to the beginning of fuel consumption, and \(\uptau _{{2}}\) to the time for most of the fuel to be consumed. Therefore, the process of ignition was treated as consisting of two stages: the induction period \(\uptau _{{1}}\) and the burnout time \(\uptau _{{2}}-\uptau _{{1}}\). These two time intervals demonstrate different sensitivity to the elementary reactions of the kinetic mechanism. A numerical model capable of predicting the effects of the presence of hydrocarbon impurity, oxygen vibrational relaxation, and pressure rise was used to simulate the experiment. The best agreement between experimental and theoretical results is achieved when these additional factors are taken into account. In addition to the sensitivity coefficient analysis for identifying the most important reactions, a new criterion, referred to as the relative integrated production, was proposed, which compliments the sensitivity coefficient analysis through its ability to identify the most productive reactions.