Observations on Upstream Flame Propagation in the Ignition of Hydrocarbon Jets

Abstract

A variety of investigators have attempted to characterize the mechanisms of how reaction zones stabilize, or propagate, against incoming reactants, particularly in stable lifted jet flames both laminar and turbulent. In this paper, experiments are described that investigate the characteristics of upstream flame propagation in turbulent hydrocarbon jet flames. An axisymmetric, gaseous turbulent jet mixing in air has been selectively ignited at downstream positions to assess the upstream propagation of the bulk reaction zone. The farthest axial position that permitted the reaction zone to propagate upstream after application of the ignition source, referred to as the "upper propagation limit", or UPL, is determined for a variety of jet and air co-flow parameters. There is an inverse relationship between the upper propagation limit position and the jet Reynolds number. Conversely, there is a direct relationship between the upper propagation limit and the co-flow velocity. Interpretation of the results is related to the velocity at the stoichiometric surface. Global discussion is made as to what these results imply about the stabilization and propagation of turbulent lifted jet flames.

Ignition of turbulent non-premixed flames

“…[251]), with failed events associated with high positive (downstream) velocities and successful events with lower velocities. The limiting downstream distance, beyond which upstream flame propagation in the jet does not occur, has been determined also by using a pilot flame as the ignition source [252]. These authors called this distance ''Upper Propagation Limit''.…”

Correlation of Spark Ignition with the Local Instantaneous Mixture Fraction in a Turbulent Nonpremixed Methane Jet

“…This can be attributed to nonlocal effects, such as the heat convection from the spark location to ignite a flammable mixture in a nearby location (Ahmed et al, 2007a;McCraw et al, 2007;Richardson and Mastorakos, 2007). Moreover, failed ignition can be noted within the flammable region due to various local effects, for instance a high local velocity (Ahmed and Mastorakos, 2006) or a high local strain rate (Ahmed et al, 2007a(Ahmed et al, , 2007bMcCraw et al, 2007;Richardson and Mastorakos, 2007). Although the PDF of the mixture fraction of the successful events peaks at 0.14 (within the flammability region) and that of the failed ones peaks at 0.175 (outside the flammability region), both PDFs have long tails to cover a wide range of the mixture fraction values (see Figure 4b).…”

“…Measurements of P(g) with Planar Laser-Induced Fluorescence of acetone added to the fuel have resulted in estimates of F. The data show that, in general, P ker 6 ¼ P ign and P ker 6 ¼ F. The difference between P ign and P ker can be understood by the fact that a local flame kernel needs to propagate possibly against the flow to reach regions favorable for flame stabilization in order to ignite the whole flame. In recirculation zones, the flame must reach regions close to the bluff body (Ahmed et al, 2007b), whereas for jets it must propagate against the mean flow (Ahmed and Mastorakos, 2006;McCraw et al, 2007). This becomes difficult for high velocities, and hence P ign decreases with jet velocity (Ahmed and Mastorakos, 2006).…”

Stability and Blowout Behavior of Jet Flames in Oblique Air Flows

“…This apparatus was used for previous experiments involving flame stability behavior in coflow and has been described in detail in earlier publications [14,15].…”