A new burner for studying auto-ignition in turbulent dilute sprays

This paper paper introduces a new burner to study the auto-ignition characteristics of dilute turbulent spray flames. The spray is formed upstream of the exit plane and carried with air or nitrogen into a hot co-flowing stream of vitiated combustion products. The fluid dynamics is kept intentionally simple and the boundary conditions are well-defined such that the burner lends itself easily to computations. The stability characteristics are presented here for a range of liquid fuels as a function of the controlling parameters. For each fuel, three types of flames are identified based on their visual appearance. These flames are all lifted but differ in the shape of the leading edge and heat release zones. These characteristics are similar for all fuels and three flames, one from each type, are selected for further study. Measurements of mean temperature, velocity and droplet fields as well as high-speed LIF images of OH, Mie scattering from droplets and chemiluminescence of CH* are made in the selected flames of ethanol. It is found that the leading edge of the flame, which is a hardly visible light-blue zone close to the jet exit plane, is marked by the presence of OH (but not CH*), and slight increases in peak temperature above the levels of the co-flow. Further downstream, there exists an intense blue region that is characterized by higher OH levels, significant emission of CH*, and temperatures that are much higher than those of the co-flow. This is the region where the bulk of the heat release is taking place. Pockets of CH* are seen to appear in this region and grow as they are advected further downstream. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.