Experimental Investigation of Soot Production and Oxidation in a Lab-Scale Rich–Quench–Lean (RQL) Burner

Abstract

Swirl-stabilized, turbulent, non-premixed ethylene-air flames at atmospheric pressure with downstream radially-injected dilution air were investigated from the perspective of soot emissions. The velocity and location of the dilution air jets were systematically varied while the global equivalence ratio was kept constant at 0.3. The employed laser diagnostics included 5 kHz planar laser-induced fluorescence (PLIF) of OH, 10 Hz PAH-PLIF, and 10 Hz laser-induced incandescence (LII) imaging of soot particles. OH-PLIF images showed that the reaction zone widens with dilution, and that regions with high OH-LIF signal shift from the shear layer to the axis of the burner as dilution increases. Dilution is effective at mitigating soot formation within the central recirculation zone (CRZ), as evident by the smaller PAH-containing regions and the much weaker LII signal. Dilution is also effective at halting PAH and soot propagation downstream of the dilution air injection point. The high momentum dilution air circulates upstream to the root of the flame and reduces fuel penetration lengths, induces fast mixing, and increases velocities within the CRZ. Soot intermittency increased with high dilution velocities and dilution jet distances up to two bluff body diameters from the burner inlet, with detection probabilities of < 5% compared to 50% without dilution. These results reveal that soot formation and oxidation within the RQL are dependant on the amount and location of dilution air injected. This data can be used to validate turbulent combustion models for soot.

Soot particle size distribution measurements in a turbulent ethylene swirl flame

“…The 11 kW burner is a turbulent, bluff body, swirl stabilized non-premixed ethylene/air burner operating at atmospheric pressure and identical to the one used in [25,26]. Ethylene is axially injected along the axis through a straight tube 4 mm in diameter.…”

“…For all, the total fuel and air flow rates remain constant keeping the equivalence ratio constant at 0.3, but the air flow split between the primary annular (Up,a) and the secondary dilution jets (Ud,a), and the location of these jets (Hj), is different. These parametric variations were chosen as the work of [25,26] revealed that each change in air split, and dilution air location led to a varying degree of soot particle production both in flame and at the exhaust stimulating further investigations in this paper. The Base Case is without any dilution air.…”

“…The aim of the present work is to report PSD and fv measurements in an ethylene non-premixed swirl burner, in order to promote our understanding of the effect of secondary air injection on soot production and oxidation from RQL combustors, and to supplement previous work conducted on this burner using both probes and laser diagnostics [25,26]. Probe measurements were performed both within and at the exit of the combustor, as both the amount and location of dilution air were systematically varied, to provide information on how the PSD and fv changes with operating conditions and location in a flame configuration of practical relevance.…”

“…Probe measurements were performed both within and at the exit of the combustor, as both the amount and location of dilution air were systematically varied, to provide information on how the PSD and fv changes with operating conditions and location in a flame configuration of practical relevance. Additionally, extinction experiments were conducted within the flame to quantify LII measurements reported previously [26]. Thus, this work aims to be a link between in situ and ex situ measurements, usually conducted separately, and discuss the difficulties when comparing the two.…”

Soot Emission Simulations of a Single Sector Model Combustor Using Incompletely Stirred Reactor Network Modeling

“…However, a low number of ISRs with arbitrary spacing can still be useful as a rough estimate of soot emissions and inexpensive parametric analysis. Preliminary investigations in the ethylene Cambridge Rich-Quench-Lean (RQL) combustor [10,11,21,[45][46][47] [49], which is also a target flame of the International Sooting Flame workshop.…”