Impact of CO₂/N₂/Ar Addition on the Internal Structure and Stability of Nonpremixed CH₄/Air Flames at Lifting

Abstract

International audienceThe authors focused on how adding CO2 to the air influences the transition from an attached flame to a lifted flame issued from a coaxial nonpremixed methane-air jet. To discriminate between effects due to a diluent (dilution, thermal, or chemical impacts), chemically and thermally inert N2 and chemically inert Ar were also investigated. Flame lifting always occurs, essentially controlled by the critical flow-rate ratio, (Qdiluent/Qair)lifting. CO2 has the strongest ability to break flame stability, followed by N2, then by Ar. A unique attachment height and OH thickness characterize lifting for all the diluents; lifting is attained once the same critical flame edge propagation speed is reached. (Qdiluent/Qair)/(Qdiluent/Qair)lifting is the affine parameter of similarity laws describing Ha and EpOH evolutions with dilution. Aerodynamics competes with dilution to impose lifting and boundary effects cannot be ignored in a fine analysis. The flame behaves differently according to whether lifting results from aerodynamics or dilution

On preheating and dilution effects in non-premixed jet flame stabilization

“…Note that the flame is not exposed to room influences due to wall confinement and that the furnace is large enough to avoid any flame-wall direct interaction. Additionally, there is no large-scale recirculation zone inside the combustion chamber, as confirmed both for laminar and turbulent cases through calculated values of the Craya-Curtet number for this configuration [24]. Optical access for flame diagnostics is implemented along the length of the combustion chamber.…”

“…As concerns soot reactivity [23], these three effects account for 45% (thermal), 35% (dilution) and 20% (chemical) in a CO 2 -diluted ethylene flame. It has been shown at room temperature [24,25] that when induced by dilution, flame lifting is controlled by the critical flow rate ratio (Q diluent /Q air ) lifting . The use of three different diluents, namely CO 2 , N 2 and Ar, allows to classify their ability to break anchored flame stability.…”

“…Even though diluted combustion systems have interested many researchers, the way the dilution effects interact with a higher initial temperature has not been thoroughly investigated, and motivates the present study. In our previous work [22,24,25], the influence of air-side dilution on flame stabilization mechanisms and on transitions leading to flame lift-off and extinction was carefully studied at room temperature. Pursuing this initial decoupled approach, results are presented here considering at first only preheating effects for five initial temperatures in addition to experiments at room temperature.…”

“…The present experiment consists of a non-premixed methane jet flame issuing into a co-flowing preheated and/or diluted air stream, as illustrated in figure 1. The whole set-up is a vertical atmospheric furnace, identical to the one used by Min et al [24]. Methane is injected through a straight tube made of refractory stainless-steel.…”

Lifting and Splitting of Nonpremixed Methane/Air Flames Due to Reactant Preheating

“…Experiments were performed on the same experimental burner utilized previously (Lamige et al, 2010(Lamige et al, , 2013(Lamige et al, , 2014Min et al, 2010). In brief, it consists of a vertical coflow atmospheric burner.…”