Mastorakos, Marchione, Ahmed, Balachandran (UCL)
The problem of high-altitude relight is an important limitation on the size of a gas turbine combustor. Currently, quite old empirical correlations are being used for design and the computational models used for predictions are not validated as extensively as desired. There is hence a need for well-characterized, focused experiments on how gaseous and two-phase flames can be ignited. Knowledge of the phenomena involved can assist with the design of gas turbine combustors. This work aims to (i) understand forced ignition of liquid fuel sprays; (ii) assemble well-characterized data for model validation; (iii) assist gas turbine manufacturers with guidelines concerning relight at high-altitude conditions. A turbulent non-premixed jet flame has been studied first to explore the effect of spark parameters (energy, duration, electrode gap) and flow speed on the ignition probability. The spark location has also been studied extensively. Turbulent counterflow flames and sprays are also under investigation.
Click here to download a fast-camera movie (49MB) of an igniting jet diffusion flame. The fuel comes from the left at a velocity of 12.5 m/s and a single spark is given at the centreline at 30 jet diameters downstream. The lifted flame takes about 0.5 s to establish. Such data are available for other fuel velocities. The work is described in Combustion and Flame, vol. 146, 215-231 (2006).
Click here to download a movie (44Mb) of non-premixed counterflow flame ignition event taken at 8 kHz. This work is fully described in a paper in the 31st Symposium. The fuel comes from below, the air from the top, the spark is located at the centreline and at the stagnation plane.
Click here to see a movie (65Mb) of how a non-premixed counterflow flame failed to ignite fully, despite the successful formation of an initial kernel.