Environmental concerns and legislative regulations are driving aircraft combustor manufacturers to meet more stringent pollutant emission standards while improving efficiency and reliability of future aero-engine combustors. In the case of small OPR engines, lean-premixed combustion has been introduced as a promising solution to significantly reduce NOx emissions. Too sharp a reduction in the NOx emission can, unfortunately, leads to a decline of the flame stability as well as an increase of CO and HC emissions. To obtain a better comprehension of the physical processes that govern pollutant emissions, a recent educational and research industrial chair “Powering the future with Clean and Efficient Aero-engines” (PERCEVAL) has been initiated by CORIA (COmplexe de Recherche Interprofessionel en Aérothermochimie) in close cooperation with the French aeronautic motorist SAFRAN and the French National Research Agency (ANR) to assess the optimization of combustion efficiency and reduction of pollutant emission of innovative stages lean combustors.

In this context, effects of liquid kerosene evaporation and fuel/air mixing on the flame structure and the NO formation have been initially studied by performing simultaneous measurements of Planar laser-induced fluorescence applied to NO, OH and kerosene vapor at the outlet of an industrial lean-premixed injection system fueled with kerosene (Jet A1) fuel. Experiments were performed in the new HERON (High prEssuRe facility for aerO-eNgines combustion) test rig specifically designed to study innovative aeronautical injection systems under relevant conditions of pressure. Experiments were conducted in a pressure range of 0.1-2.0 MPa, with a preheated air in a temperature ranging from 300 to 900 K and a maximum air flow rate of 300 g/s. This facility was equipped with large optical accesses to perform laser-based measurements inside the combustion chamber.

The methodology adopted to perform quantitative instantaneous 2D NO concentration distributions ensuring a minimal detection of a few ppm of NO as well as minor interferences with potential presence of O~2~ is first presented. Then, results of experiments using NO-PLIF combined with OH-PLIF and kerosene-PLIF were discussed. Kerosene-PLIF imaging was specifically developed to measure the absolute kerosene concentration as well as the air-to-fuel ratio. The optimization of the excitation process and detection of kerosene fluorescence signals also enable a well-separation of kerosene vapor and NO fluorescence signals on the raw fluorescence images recorded with ICCD cameras. For the OH-PLIF diagnostic, this one was applied to obtain key data about the flame topology. Therefore, the flame front position and its thickness were determined and correlated with the zones of production of NO. To compare the NO concentration measurements recorded inside the flame, NO concentration measurements were also taken into the exhaust gases with a multi-hole sampling probe in combination with a conventional gas analysis system. Additional PIV (Particle Imaging Velocimetry) measurements were also performed to study the effect of the aerodynamic field on the NO production. Finally, the link between NO production, Fuel-air-ratio, pressure and flame topology was presented and discussed.


Experimental Investigation on NO Pollutant Formation in High-Pressure Swirl-Stabilized Kerosene/Air Flames Using NO-, OH- and Kerosene-PLIF and PIV Laser Diagnostics

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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