Ignition probability of a partially premixed burner using LES

To comply with stringent pollutant emission regulation, low-emission aeronautical gas turbines rely on lean premixed combustion. Such technology raises the issue of ensuring a reliable ignition since the combustor operates closer to blow-off. Ignition is however known as a stochastic phenomenon, associated to various sources of system variability. These variabilities and their impact on the success or failure of ignition are still not fully understood. In this paper, Large Eddy Simulation (LES) of laser ignition sequences in an academic swirled turbulent partially premixed burner are performed to obtain statistical information at three selected ignition locations representative of the various ignition scenarios observed. The velocity and mixing fields are first validated against measurements to eliminate uncertainty associated with the non-reacting flow. LES is then shown to recover the ignition statistical behavior and probability for the selected ignition locations. Moreover, LES analysis allows to identify the various mechanisms that drive ignition failure or success. Statistics of flame displacement speed are used to demonstrate the effect of curvature and stretch in regions of intense turbulence and the impact of partial premixing on the ignition process.