P. K. Tretyakov

Combustion initiation by an optical discharge in a supersonic methane-air jet

The first experimental studies of the effect of the laser plasma generated by focused pulsed-periodic radiation of a CO2 laser on the formation and evolution of combustion in a supersonic flow of homogeneous methane-air mixtures are performed. Results of multispectral investigations testify to a principal possibility of combustion initiation by an optical discharge. Conditions necessary for combustion stabilization are formulated.

Investigation of the Structure of a Diffusion Hydrogen Plume in a Supersonic High-Enthalpy Air Jet

The results of investigation of the plume structure in the case of diffusion combustion of hydrogen in a cocurrent supersonic high-enthalpy off-design air jet are presented. Based on the registration of radiation within the wavelength range of 260–350 nm across and along the flame, a three-dimensional tomographic reconstruction of the plume was obtained, which confirmed the interrelation between the gas-dynamic structure and combustion intensity. A possibility of existence of combustion regimes with periodically repeated cycles of complete extinction and subsequent ignition of hydrogen in accordance with the barrel-shaped structure of the off-design jet is established experimentally. The existence of local peripheral regions of combustion is noted, which can indicate the presence of vortex structures. In the three-dimensional representation (obtained under the assumption of axial symmetry of radiation), these vortex structures have the form of annular zones. In a real flow, helical structures are possibly formed at the plume periphery.

Initiation of homogeneous combustion in a high-velocity jet of a fuel–air mixture by an optical discharge

The effect of a focused pulsed-periodic beam of a CO2 laser on initiation and evolution of combustion in subsonic and supersonic flows of homogeneous fuel–air mixtures (H2 + air and CH4 + air) is experimentally studied. The beam generated by the CO2 laser propagates across the flow and is focused by a lens at the jet axis. The flow structure is determined by a schlieren system with a slot and a plane knife aligned in the streamwise direction. The image is recorded by a high-speed camera with an exposure time of 1.5 μs and a frame frequency of 1000 s−1. The structure of the combustion region is studied by an example of inherent luminescence of the flame at the wavelengths of OH and CH radicals. The distribution of the emission intensity of the mixture components in the optical discharge region is investigated in the present experiments by methods of emission spectroscopy.

Organization of a pulsed mode of combustion in scramjets

A new method is proposed to organize the working process in the combustion chamber of a scramjet. The flow velocity in the combustor is maintained close to the velocity of sound. In a constant-area channel, this situation is achieved by organizing combustion in a pulsed wave structure of the pseudo-shock type whose position is determined by parameters of the external thermal-gas-dynamic pulsed-periodic action on the flow. In the channel part with a variable cross section, the mean Mach number close to unity is maintained by choosing an appropriate degree of combustor expansion and appropriate places of fuel injection. The pulsed mode assists in improvement of fuel-air mixing and in reduction of the combustion zone length. The main advantage of this method is the high efficiency of the process determined by the minimum loss of the total pressure and the maximum increase in temperature. Experimental results are given to confirm the possibility of realization of the pulsed combustion mode.

Stabilization of a lifted diffusion hydrocarbon flame by an external periodic electric field

Results of studying the influence of periodic application of a weak electric field on diffusion combustion of gaseous hydrocarbons are presented. The main attention is paid to investigating the effect of the electric field parameters on flame stabilization. Two types of electric fields are considered: (1) with a pulsed-periodic variation of the field strength in time and a constant configuration of force lines (pulsed-periodic electric field); (2) with a change in the field configuration in time and a constant field strength (electric field with a time-varying configuration). Direct photo and video recording was used, as well as spectrozonal registration of the natural luminescence of the flame (at wavelengths of emission of excited radicals OH* and CH*). It is shown that the region of flame stabilization (ignition point) tends to the place with the maximum strength of the electric field. The effect of the electric field with a time-varying configuration on combustion is the flame stabilization in the plane of electrodes and local intensification of combustion.

Diffusion flame in an electric field with a variable spatial configuration

The influence of an electric field whose intensity vector rotates around the flame axis on the shape of the diffusion flame of propane is experimentally studied. Application of spectrozonal registration makes it possible to obtain information about the radiation intensity distribution at wavelengths of intermediate reaction products (OH, CH, and C2). Different positions of the peak intensity of the own radiation of the flame at different wavelengths testify to the influence of such an electric field on the mixing processes, namely, mixing is more intense than that in the regime without application of the electric field. This feature may turn out to be useful for increasing the efficiency of combustion of gaseous hydrocarbon fuels.

Laminar propane-air flame in a weak electric field

Three mechanisms of the electric field influence on combustion of gases are considered: ohmic heating, effect of chemical reactions on the kinetics, and ionic wind, which is the most important factor. Experimental data presented in the paper testify to a local action of the electric field directly on the zone of chemical reactions, which leads to deformation of the flame front.

Vortex Structures in Combustion of Hydrogen in a Supersonic Cocurrent Air Stream

The existence of vortex zones at the outer boundary of the hydrogen plume in a cocurrent air flow is confirmed. An analysis of experimental results and a comparison with available calculations show that the formation of such zones can be associated with the wave structure arising in the case of nonisobaric outflow of the air stream. The size of vortex zones of combustion increases along the plume, and these zones can improve mixing of the fuel and air jets.

Specific features of the diffusion flame in the transition from the laminar to turbulent regime of combustion

In studying lifted diffusion flames in the transitional regime from laminar to turbulent combustion, structures with a reduced intensity of own luminescence and a clearly expressed contour are observed in the combustion front. The emergence of such structures in the flame has a spontaneous character and may occur at significant distances from the ignition points (region of lifted flame stabilization).

The effect of heat and mass addition on the base pressure of bodies of revolution at supersonic speeds

The results of an experimental investigation of the influence of mass addition and afterburning of combustion products of pyrotechnic mixtures in the base region of axisymmetric bodies in supersonic air flow at Mach numbers of 1.2–3.0 are reported. It is shown that the base-pressure increment increases monotonically to a maximum value with an optimum injected-mass flow rate. The value of this increment reduces as the Mach number decreases. A dependence generalizing the experimental data is presented.