Unsteady Flames in Gaseous and Spray Turbulent Combustion
Yale School of Engineering & Applied Science
Department of Mechanical Engineering
and Materials Science
Unsteady Flames in
Gaseous and Spray Turbulent Combustion
Yuval Dagan
Department of Aerospace Engineering
Technion, Israel Institute of Technology, Haifa, Israel
Abstract
Flame instabilities play an important role in combustion. Unsteady flame characteristics in turbulent gaseous and liquid fuel combustion were studied using Large Eddy Simulation (LES). The study focused on the phenomenon of intermittent flame lift-off which was observed both experimentally and computationally.
In the first stage, gaseous fuel combustion was investigated. The mean statistics of the computed flow field were found to be in very good agreement with experimental data. Detailed time-dependent, long duration flame propagation and three-dimensional flame structures were analyzed, utilizing quantification of flame inhomogeneity and dynamics. Two new criteria for the characterization of flame structure were developed in the current study, allowing for the quantification of the overall spatial inhomogeneity in the combustor. Using these criteria, it was possible to characterize the influence of swirl on flame propagation for each swirling case. A significant correlation was found between dominant circumferential and radial fluctuations of the flame.
The research was then extended by introducing a liquid fuel spray into the computation, using a stochastic spray modeling approach. Unsteady turbulent spray-flame propagation was computationally investigated in the current study. Spray-flame propagation was characterized by two repetitive developmental stages, in which the jet spray is either radially diverted or blocked by the recirculation zone. Local statistics of fuel droplet dispersion were investigated by a new approach, revealing low frequencies of the repetitive flame stages, while retaining the turbulent characteristics.