Simultaneous High Speed Schlieren and Direct Imaging of Ignition Process with Digitally Enhanced Visualisation

In this paper, a combined method of schlieren and digital colour image processing is developed to study the effect of ignition location on the propagation of propane diffusion flames. The early weak blue flame is visualised through selective digital imaging enhancement techniques, which have revealed that a typical orange diffusion flame is often formed inside a blue flame pocket at the beginning of the ignition when ignited at the centreline of the fuel jet. When the ignition location towards the out edge of the fuel/air mixing boundary, the orange flame shifted and gradually broke the blue flame pocket. In the meantime, the flame was observed to propagate faster. The ratio of orange flame areas rose and the blue flame area fell accordingly.