Experimental study of role of instabilities in turbulent premixed combustion

Laminar and turbulent burning velocities were measured for H2 - CO mixtures. It has been shown that the unsteady flame development is an important factor for comparing the burning rates obtained in different experiments. For the atmospheric pressure flames, the mixtures with faster laminar flame velocities burnt faster in turbulent flow despite the fact that the lean flames exhibit cellular structures. However, even a modest increase of the initial pressure promotes cellularity and causes a significant acceleration of a lean laminar flame. The same lean flame burns faster in turbulent flow as well and this increase in the rate of combustion is greater than one that can be deduced from variation of the molecular heat diffusivity and laminar flame speed, thus indicating the enhancement of the turbulent burning rate by a laminar flame instability.