The structure of triple flames stabilized on slot burner

Abstract

A triple flame is a partially premixed flame that contains two premixed reaction zones (one fuel-lean and the other rich) that form exterior wings and a nonpremixed reaction zone that is established in between these wings. The three reaction zones merge at a "triple point." Triple flames may play an important role in the stabilization and liftoff of laminar nonpremixed flames. They are also of fundamental importance in the reignition of turbulent mixtures. Despite their importance, many aspects of triple flames have not been adequately investigated and are, consequently, not clearly understood. Herein, laminar triple flames stabilized on a Wolfhard-Parker slot burner are investigated. The flow consists of a rich mixture of methane and air emerging from the inner slot and a lean mixture from two symmetric outer slots. In this configuration the three reaction zones that characterize a triple flame can be clearly distinguished. The loci of the "triple points" form a "triple line" in this planar configuration. The velocity field is characterized using laser Doppler velocimetry, and the temperature distribution using laser interferometric holography. In addition, C* 2 -chemiluminescence images of the three reaction zones are obtained. A detailed numerical model is employed to completely characterize the flame. It is based on a 24-species and 81-reaction mechanism. The numerical results are validated through comparisons with the experimental measurements. Our results focus on the detailed structure, the interaction between the three reaction zones, the dependence of the flame structure on the initial velocities and mixture equivalence ratios, and the dominant chemical pathways. The lean premixed reaction zone (external wing) exhibits different features from the rich premixed reaction zone. In particular, it is characterized by strong HO 2 formation and consumption reactions, and by relatively weak methane consumption reactions. Radical activity is higher in the nonpremixed reaction zone than in the other reaction zones. Overall, radicals from the nonpremixed reaction zone are transported to both the rich and lean premixed reaction zones where they attack the reactants. Simplifying the chemical mechanism by removing the C 2 -containing species produces significant differences in the predicted results only for the inner rich premixed reaction zone.

Novel Combustion Concepts for Sustainable Energy Development

“…However, the methane mass profile for the 90 % case seems to indicate the extinction of the lean premixed flame due to ultra lean conditions at low load. This is consistent with previous studies (Azzoni et al 1999;Aggarwal 2009) dealing with PPFs, indicating that the most of CO is produced in the rich premixed zone, while the most of CO 2 is produced in the diffusion combustion zone, where the temperature is highest. Figure 13 presents the CO, CO 2 , and HO 2 mass fraction contours at different crank angles for the single-fuel case.…”

Using Petroleum and Biomass-Derived Fuels in Duel-fuel Diesel Engines

“…For instance, the high CO region locates the rich premixed zone with ϕ between 2.0 and 3.0, while the high CO 2 region corresponds to diffusion combustion zone with ϕ near 1. This is consistent with previous studies (Azzoni et al 1999;Aggarwal 2009) dealing with PPFs, indicating that the most of CO is produced in the rich premixed zone, while the most of CO 2 is produced in the diffusion combustion zone, where the temperature is highest. Thus, the rich premixed zone is characterized by n-heptane decomposition and partial oxidation, producing CO, H 2 , and intermediate hydrocarbon species.…”

Structure of Unsteady Partially Premixed Flames and the Existence of State Relationships

“…The first is to examine the effects of coflow on the structure and stability of normal-and zero-gravity partially premixed flames established on a Wolfhard-Parker slot burner, which is a geometry that we have used extensively to characterize PPFs [7,[17][18]. Here the flame response to inherent and forced perturbations and the associated flame-vortex interactions are also investigated.…”

“…Since partially premixed flames contain regions of both premixed and nonpremixed combustion, a modified mixture fraction has been employed to examine the flamelet model for partially premixed turbulent combustion [34,35]. We have employed the conserved scalar approach based on a modified mixture fraction in characterizing state relationships for steady partially premixed flames [17] and for examining the similitude between partially premixed flames in different configurations [4]. Here we employ a similar approach to examine the existence of state relationships for unsteady partially premixed flames.…”