Blowout Limits of Flames in High-Speed Airflows: Critical Damkohler Number

Abstract

This work extends some previous research that was reported by the authors [1-4] in that empirical correlation curves are presented that summarize the lean blowout limits of cavitystabilized flames that are adjacent to supersonic, heated air flows. The correlations were obtained for two geometries: fuel injected into the cavity through the cavity aft wall and fuel injected through the cavity floor. It is found that the best correlation of the data is achieved by using the following simple representation of the Damkohler number: /

Review of cavity-stabilized combustion for scramjet applications

“…Rasmussen et al [34][35][36] investigated the flame characteristics with direct cavity fuel injection. Location of the flame was shown to vary as the mass flowrate of fuel and the location of the fuel injectors were varied.…”

“…Rasmussen et al 35,40 performed experimental studies of the stability of hydrocarbon-fueled flames in cavity flameholders with direct cavity fuel injection. Lean blowout limits showed dependence on the air mass flowrates, cavity geometry, fuel injection scheme, Mach number, and fuel type.…”

“…As large gradients in local gas composition and temperature exist in the recirculation region, stability parameter correlations developed for premixed flames can hardly be used to determine the blowout stability limits for nonpremixed flames. Based on the experimental observations, [34][35][36]40 Driscoll and Rasmussen 54 developed a correlation of blowout limits of cavity-stabilized flames in high-speed airflows from a non-premixed point of view, avoiding the 'perfectly-stirred' reactor assumption. A modified Damkohler number similar to that of Ozawa 51 was deduced to correlate the flame blowout limits measured for non-premixed flames…”

Pulsed Combustion of Hydrocarbon Fuels in a Supersonic Model Combustor

“…2 Professor, National Key Laboratory of High Temperature Gas Dynamics, xfan@imech.ac.cn, 15 Beisihuanxi Road, Beijing, China, Member AIAA. 3 Assistant Professor, National Key Laboratory of High Temperature Gas Dynamics. 4 Professor, National Key Laboratory of High Temperature Gas Dynamics.…”

“…Self-ignition and stable combustion can only occur when the flow and fuel conditions are within the limits of flame stabilization in the combustor. [1][2][3] The region for stable combustion of hydrocarbon fuels is limited by relatively long ignition delay time compared to the resident time. The stability limits could be extended by reducing the reaction time through the use of continuous heat addition such as fuels partially cracking, 4, 5 pilot hydrogen, 6,7 or plasma jet 8 This work has two main objectives: 1) to examine the possibilities of hydrocarbon fuels combustion using pulsed ignition sources with flow or fuel conditions beyond the limits of stable combustion; 2) to explore the potential combustion modes of hydrocarbon fuels.…”