A novel approach to control the combustion processes by laser-induced excitation of vibrational or electronic states of target molecules is investigated. Target molecules are supposed to use to enhance the chain reactions in the gaseous combustible mixtures. The computations based on the extended physical-chemical model involving chemical processes with vibrationally and electronically excited molecules show that laser-induced excitation of O2 molecules to the a1Δg and b1Σg+ electronic states makes it possible to reduce considerably the ignition threshold in CH4(H2)/O2 (air) mixtures and to intensify the conversion of CH4 to H2 during oxidation of hel-rich CH4/air mixtures. A simultaneous excitation of O2 molecules to the electronic and vibration states enhances these processes additionally.
The theoretical and computational studies based on the novel physical and mathematical model of nonequilibrium chemical processes involving vibrationally and electronically exited molecules have shown that selective excitation of reacting species by laser radiation results in a considerable reduction of self-ignition temperature, decrease of induction and combustion times, and initiates detonation in supersonic flow at relatively low radiation energy inputted into the mixture. These effects are due to production of the novel channels of high reactive radicals formation and enhancement of chain mechanism of combustion and are not associated with the thermal action of absorbed radiation.
KEYWORDS: Molecules, Absorption, Gas lasers, Molecular lasers, Carbon monoxide, Data modeling, Infrared radiation, Temperature metrology, Solids, Far infrared
Theoretical and experimental analysis of a possibility of creation of high-energy gasdynamic laser generating infrared radiation with wavelength (lambda) equals27.971 micrometers on the vibration-rotation transition 001(633) --> 020(550) of H2O molecule is presented. It was shown that at expansion of preheated water vapour in a wedge-shaped supersonic nozzle with 30 degree(s) opening angle and critical section height h* less than or equal to mm the nonequilibrium population of vibrational levels 001 and 020 of H2O molecules is realised for the pressures P0equals0.2-0.5 MPa and the temperatures T0equals1930-2580 K at the nozzle inlet. The numerical analysis has demonstrated that for a plate profiled nozzle whose supersonic section is designed to provide uninterrupted flow at initial parameters T0equals2500 K, P0equals0.3 MPa, h*equals0.1 mm and nozzle expansion ratio (epsilon) equals20 the amplification coefficient behind the nozzle may achieve 1 m-1. In this case the specific radiation energy may be of about 20 J/g. The principal feature of H2O-gasdynamic laser is necessity to use the nozzle with rapid expansion and small values of parameter P0h*. The latter should be considerably less (in a factor of 50-100) than for traditional CO2-gasdynamic lasers.
On the basis of developed physical and mathematical model for thermal nonequilibrium chemical processes involving electronically excited molecules the analysis of the mechanisms resulting in initiation of combustion in closed reactor and detonation in supersonic flow behind inclined shock wave in H2+O2(air) mixtures at excitation of the (see paper for formula) states of oxygen molecules by resonant laser radiation with wavelengths (lambda) equals1.268 micrometers and 762 nm has been carried out. The numerical analysis has shown that induced by laser radiation excitation of O2 molecules leads to significant decrease of the autoignition temperature and allows to initiate detonation at very low temperature (~500 K) behind shock wave at relatively small values of laser radiation intensity. Excitation of (see paper for formula) state by laser radiation is more effective to influence on combustion kinetics and initiation of detonation in supersonic flow.
Theoretical and numerical analysis of energetic characteristics of gasdynamic lasers on active media containing diatomic metastable molecules H2, D2, N2 and halogen molecules was carried out. It was estimated that the most promising from the point of view of receiving the highest specific radiation energy and conversion efficiency of vibrational energy are mixtures D2-DCl, D2-HBr, N2-DCl, N2-DJ, N2-DBr, D2-HJ and H2-HCl. At thermal excitation they allow to achieve efficiency from 1% to 4% and at electrodischarge excitation from 10% to 25%, the specific radiation energy reaching 60 - 300 Joule/g.
On the basis of developed physical and mathematical model the mechanisms and tendencies of nonstationary focusing lens formation in the beam channel under propagating of a pulse laser radiation in resonance absorbing gaseous medium and in the atmosphere were studied. The dynamics of self- interactions and change in refractive index under propagating of CO2-, HF-laser radiation under resonance absorption by H2O molecules in moist atmosphere were considered. The new characteristics of change in refractive index of molecular gas due to excitation of rotation degree of freedom when spectral lines of absorbing transitions were overlapped (low troposphere) have been estimated.
An analysis is made of the influence of changes in the density and polarizability of molecules on changes in the refractive index and tendencies of propagating of pulse laser radiation when the molecules in gas absorb or amplify resonant radiation. It has been shown that under absorbing or amplifying radiation in vibrational rotational transitions in the beam channel there may be formed a nonstationary focusing lens.
The possibility of generation of coherent radiation with (lambda) equals 5 - 7 micrometer and 2.5 - 2.8 micrometer in vibrational-rotational transitions of DCl molecules under expansion of N2-DCl mixture in supersonic nozzles is analyzed. On the basis of numerical modeling energetic and spectral characteristics of gasdynamics and electro-discharge flow lasers are considered.
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