State-to-state vibrational kinetics of diatomic molecules in laser-induced ignition of a syngas-air mixture: Modeling study

Abstract

A thermally nonequilibrium model was created to describe the processes occurring in a syngas-air mixture when exposed to intense CO laser radiation. The model consistently describes the reactions of syngas oxidation in air and the state-to-state vibrational kinetics of CO, N2, O2, H2, and OH molecules and also takes into account the nonequilibrium vibrational excitation of polyatomic molecules in the mode approximation. Using the constructed model, the possibility of laser-induced ignition of syngas in air was analyzed. Special attention was paid to the influence of the efficiency of vibrational energy of CO molecules in overcoming the energy barriers of reactions on the simulation results. For the key reactions involving CO molecules, the values of the coefficients of vibrational energy usage were estimated employing the method of classical single-trajectory calculations. It was shown that these coefficients are the critical parameters determining the possibility of using the CO laser radiation to accelerate the ignition of syngas. In addition, we have shown that in the problem considered, because of the strong nonequilibrium excitation of CO vibrations, it is extremely important to take into account the deviation of the vibrational distribution functions of molecules from the Boltzmann one, which requires the use of a state-to-state model of vibrational nonequilibrium. The inaccuracy in calculating the laser-induced ignition time of syngas in air by means of a mode model can reach an order of magnitude.