Measurements of ignition probability in turbulent non-premixed counterflow flames

Spark ignition of turbulent counterflow non-premixed flames has been examined in terms of the ignition probability P-ign and evolving flame structure. It was found that in the case of successful ignition, the flame spread as an edge flame with a large scatter in its radial position between individual realizations at the same time from the spark. P-ign decreased with bulk velocity, which suggests that the local strain rate can be detrimental to ignition so that, even with the strongest spark tested, ignition could not be achieved at a bulk velocity about 90% of the extinction velocity. P-ign was greater than zero even in regions well into the fuel and air streams where the mixture fraction fluctuations were virtually zero, giving zero probability of finding flammable mixture at the spark location. This observation was attributed to non-local effects, for example the convection of the spark heat to the flammable region. The data can assist the validation of advanced combustion models. (C) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.