Flame Propagation and Blowout in Hydrocarbon Jets: Experiments to Understand the Stability and Structure

Abstract

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. This research supported by the U.S. Army Research Office examines a myriad of facets of lifted hydrocarbon jet flames in the presence of air co-flow. At a certain jet exit velocity, a flame will lift from the fuel nozzle and stabilize at some downstream position. The partially-premixed flame front of the lifted flame oscillates, with the oscillations becoming greater in flames stabilized further downstream. These Inventions (DD882) Scientific ProgressThe main advances in jet flame flow interaction in oblique jet/air flows, as well as flame blowout, are detailed in the attachment. blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction.Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed.For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types. IntroductionA multitude of studies have been performed on lifted jet flames and their behavior in various air flow configurations. In such partially-premixed flames, the characteristics of the surrounding air flow (velocity, temperature) can strongly impact the overall combustion process and the stability parameters. As fuel flows from a nozzle and mixes with the air, the fuel and oxidizer concentrations vary throughout space and time. The extent of mixing due to turbulence also changes depending on the surrounding flow. The perpetually varying concentrations help to determine the overall behavior of a flame: its shape, velocity, size, color, temperature, and composition. In parallel, the heat release serves to laminarize regions, and serves to limit reducing mixing.In particular, two important behavioral parameters are liftoff and blowout velocity.Initially, a jet flame will remain attached to the nozzle at low fuel velocities. However, at a critical jet velocity, the flame will lift off from the nozzle and stabilize at a position While jet behavior in coflow has been extensively studied, less attention has been devoted to jets in crossflow. In a review, Bandaru and Turns included a comprehensive list of all major crossflow research to date [9]. Many of the works relevant to this study were observation-based experiments performed by Kalghatgi, whosecrossflow flame experiments were conducted in a wind tunnel and involved propane, ...