Numerical study of combustion initiation in a supersonic flow of H₂–air mixture by resonance laser radiation

Abstract

A comparative analysis of the efficiency of approaches based on the exposure of reacting gas to resonance laser radiation to enhance combustion in a supersonic flow of H2–air mixture is conducted. The kinetic processes responsible for the intensification of chain reactions in premixed and non-premixed H2–air flows upon photodissociation of O2 molecules by 193.3 nm laser radiation, excitation of these molecules to the singlet sigma state by laser photons with 762.346 nm wavelength and heating the mixture by laser radiation are analysed in a detailed manner. It is shown that both photochemical methods, photodissociation and excitation of O2 molecules, are much more effective in shortening the ignition delay length than merely heating the mixture. For the premixed flow, the photodissociation of O2 molecules ensures a slightly higher reduction in the ignition delay than the laser-induced excitation of molecular oxygen to the singlet sigma state. However, in the non-premixed flow the situation is inverted. The analysis shows that both photochemical methods make it possible to raise the efficiency of conversion of reactant chemical energy to thermal energy released during combustion compared with the method of heating the mixtures.

Numerical study of the enhancement of combustion performance in a scramjet combustor due to injection of electric-discharge-activated oxygen molecules

“…The application of RANS makes it possible to reproduce with high accuracy the pressure profiles measured along the wall of the scramjet combustor [33,34]. As was demonstrated earlier in [23], even a simpler approach based on the PNS equations with a detailed reaction mechanism makes it possible to describe accurately the experimental data [35] on the evolution of the concentrations of the main species H 2 , O 2 , N 2 and H 2 O in the mixing layer of hydrogen and air supersonic flows. The main advantage of the application of the simplified PNS version of RANS for modelling the combustion characteristics is that this approach allows one to use a detailed reaction mechanism involving the processes with excited O 2 (a 1 g ), O 2 (b 1 + g ) and ozone molecules and to utilize the accurate computational grid.…”

“…To describe turbulent mixing of air flow with oxygen and hydrogen jets, the one-parameter turbulent model developed especially for compressible flows [29] was used. So, as in our earlier studies [6,23], we supposed that turbulent diffusion coefficients were the same for all mixture components, and the Lewis numbers were equal to unity for all species. The system of PNS equations can be written in the form…”

“…This makes it possible to use the marching (in the longitudinal direction) method that is based on the stationary analogy of the Godunov scheme for supersonic flow [32]. Details of the methodology of numerical simulation were reported earlier [6,23]. It is worth noting that the use of 'corrected' boundary conditions does not allow proper reproduction of the flow structure in the near-wall region and details of the shock-boundary layer interaction.…”

“…For the analysis of the influence of the injection of oxygen stream, activated in an electric discharge and comprising singlet oxygen molecules O 2 (a 1 g ) and O 2 (b 1 + g ), atomic oxygen and ozone molecules, the reaction mechanism reported recently in [23] was used as the basic one. It should be emphasized that the basic reaction mechanism comprised both the reaction channel for the interaction of atomic hydrogen with singlet delta oxygen…”

“…As was demonstrated in [6], a very promising concept to facilitate the ignition of hydrogen-air mixtures in such a combustor is the injection of a thin stream of oxygen molecules activated in a specially arranged electric discharge. Our earlier studies [8,12,[22][23][24] demonstrated that the generation of both excited O 2 (a 1 g ) and O 2 (b 1 + g ) molecules and atomic oxygen can enhance the ignition of H 2 -O 2 (air) and CH 4 -O 2 (air) mixtures in a supersonic flow. The advantages of one method against another were revealed to be dependent on the mixture composition and parameters of the flow.…”