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 CO$_2$ laser on initiation and evolution of combustion in subsonic and supersonic flows of homogeneous fuel–air mixtures (H$_2$ + air and CH$_4$+ air) is experimentally studied. The beam generated by the CO$_2$ laser propagates across the flow and is focused by a lens at the jet axis. The flow structure is determined by a schlieren device with a slot and a plane sheet aligned in the streamwise direction. The image is recorded by a high-speed camera with an exposure time of 1.5 $\mu$s 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.