Experimental observations of complex flame propagations initiated at different locations of an impingement configuration

The effect of ignition location on the propagation of premixed and diffusion flames of hydrogen and mixtures of hydrogen and carbon dioxide towards and away from an impingement plate was studied using distance-time relations and velocity–time curves for the edge of the flame boundary at the centre line. It is shown that ignition location, fuel composition and jet velocity have large effects on the flame propagation speed, and non-linear acceleration was observed for flames ignited at the plate. The effect of the angle of mixing of the unburned fuel with the surrounding air was found to have an effect on the downwards propagation, and also, delay of downwards propagation after ignition was observed for some cases. It was found that air/fuel premixing hinders the initial downwards propagation of the flame when ignited at the plate. Propagation velocities of up to 25 m s−1 were observed when the flame was ignited at the nozzle, aided by the velocity of the fuel jet. However, accelerations much higher than the gravitational acceleration were observed, indicating that buoyancy may not be a significant factor in the high velocities of the flames. It was also found that jet velocity had a higher effect on the propagation velocity for the premixed and H2/CO2 flames than the diffusion flames.