Investigation by LES of a Rich burn – Quick mix – Lean burn lab-scale combustion chamber operating in high-pressure conditions

• A novel RQL lab-scale combustor operating in high-pressure conditions is designed. • LES simulations are performed at 13 bar for kerosene (vapor/liquid) / air mixtures. • Distinct RQL combustion areas and a combustion efficiency of ̴100% are obtained. • A V-shaped swirled flame with a predominant premixed combustion regime is found. • Experiments of Jet A-1 kerosene / air combustion proved LES simulations reliability. The Rich burn - Quick mix - Lean burn (RQL) concept is a staged combustion technology that guarantees flame stability at all operating conditions while significantly reducing the concentration of pollutants at the outlet of a combustion chamber. A lab-scale RQL combustion module equipped with a new-generation double-circuit fuel injection system and large optical accesses is designed to be integrated into the visualization module of a high-pressure combustion facility fed with aeronautic multi-component liquid fuels. This new optical RQL module will be devoted to perform a simultaneous study into the three RQL sections of the physico-chemical processes involved in soot production and oxidation and NOx formation under realistic high-pressure / high-temperature operating conditions encountered in helicopter combustors by means of advanced coupled laser-based diagnostics. To this end, the architecture of the RQL module has been designed to satisfy various constraints such as a reactive zone height comparable to that of a helicopter combustor sector, an overall pressure drop of ∼ 3 %, realistic fuel / air mass flowrates, an efficient heat transfer between the walls and the flame and the ability to introduce laser sheets through the RQL areas for optical measurements. The optimized geometry of the RQL module was achieved by performing iterative Large-Eddy Simulations (LES) of the reactive flowfield of a kerosene vapor / air mixture with the AVBP numerical solver at a nominal operating condition (13 bar), then by LES simulations performed with a liquid kerosene / air mixture. Numerical LES results obtained from both single-phase and two-phase reactive flows are discussed. They highlight the ability to provide distinct RQL areas, a V-shaped jet opening at the injector outlet, a swirling flame topology, a predominant premixed / partially-premixed combustion regime in the primary rich area, as well as a high combustion efficiency of ∼ 100 % at the outlet of the combustion chamber. Experimental results of kerosene / air flame emission at 8 bar and 11 bar confirmed the potential to produce well-distinct RQL combustion areas accessible with laser-based diagnostics while ensuring the combustor’s thermal resistance. Finally, the effectiveness of the iterative LES methodology adopted to design the lab-scale optical RQL combustion chamber was also highlighted.