Effect of Nonequilibrium Excitation on the Ignition of Combustible Mixtures

摘要

A review of experimental and theoretical investigations of the effect of atomic particles and electronically excited O_2(a~1Δ_g) molecules on the induction delay time and on shift of the ignition temperature threshold of combustible mixtures is presented. The addition of oxygen and hydrogen atoms to combustible mixtures may cause a significant reduction of the induction time and decrease the ignition threshold. However, the latter effect is observed only in the vicinity of the ignition limit. At relatively low initial temperatures, the shift of the ignition threshold is largely associated with the heating of mixture due to recombination of atomic particles being added. In so doing, the non-equilibrium pattern of the impact is less pronounced.Molecules of singlet oxygen O_2(a~1Δ_g) may be involved in both chain initiation reactions and chain branching reactions H + O_2(a~1Δ_g) →OH + O(3P). Most of the collisions between singlet oxygen molecules and atomic hydrogen, O_2(a~1Δ_g) + H, lead to quenching of O_2(a~1Δ_g). The efficiency of this channel is more than 80% and the fraction of the reaction H + O_2(a~1Δ_g) → OH + O(~3P) is only 10 - 20%. The impact of the singlet oxygen O_2(a~1Δ_g) admixture on the ignition of combustible mixtures was investigated. The effect of singlet oxygen on the ignition delay time turns out to be relatively weak because of O_2(a~1Δ_g) deactivation by H atoms and low efficiency of SDO production in gas discharge plasmas. Oxygen atoms produced by the discharge are more efficient in the ignition of hydrogen-oxygen and hydrogen-air mixtures than O_2(a~1Δ_g) molecules. Thus, to reduce the ignition delay time and to decrease the temperature threshold of combustive mixtures, the use of gas discharge systems providing the efficient production of atomic particles is recommended.