High-speed Schlieren imaging and post-processing for investigation of flame propagation within droplet-vapour-air fuel mixtures

Studies in practical spray combustion systems are complex due to the presence of various dependent parameters such as turbulence and inhomogeneity of physical properties of the reactants. Therefore, fundamental aerosol combustion studies are required so that practical combustion of aerosols and sprays can be understood. To another extent, data on laminar burning velocities, which is well known to play an important role in turbulent combustion, is still very scarce particularly for droplet-vapour-air mixtures. Previous researches demonstrated that the presence of liquid droplets in the combustion of aerosol mixtures could influence flame instabilities. These instabilities, which are characterized by cellular and wrinkling flame structures, promote a faster burning rate. Nevertheless, due to the technique and condition of the imaging system available in the past, the critical properties related to flame instabilities, for instance the point of the onset of cellularity, were unclear. In this paper, applications of high-speed schlieren imaging and a digital image processing techniques are presented and discussed. It is shown that the use of a digital camera coupled with an accurate synchronisation system produces better image quality of the flames as compared to the previous techniques. The improved image processing technique is shown to be potential in reducing the processing time and errors