Influence of the Pilot Flame on the Morphology and Exhaust Emissions of NH 3 -CH 4 -Air Swirl Flames Using a Reduced-Scale Burner at Atmospheric Pressure

This work presents an experimental study on the influence of the pilot flame characteristics on the flame morphology and exhaust emissions of a turbulent swirling flame. A reduced-scale burner, inspired by that fitted in the AE-T100 micro gas turbine, was employed as the experimental platform to evaluate methane (CH 4 ) and an ammonia-methane fuel blend with an ammonia (NH 3 ) volume fraction of 0.7. The power ratio (PR) between the pilot flame and the main flame and the fuel composition of the pilot flame was investigated. The pilot power ratio was varied from 0 to 20% for both fuel compositions tested. The NH 3 volume fraction in the pilot flame ranged from pure CH 4 to pure NH 3 through various NH 3 –CH 4 blends. Flame images and exhaust emissions, namely CO 2 , CO, NO, and N 2 O were recorded. It was found that increasing the pilot power ratio produces more stable flames and influences most of the exhaust emissions measured. The CO 2 concentration in the exhaust gases was roughly constant for CH 4 -air or NH 3 –CH 4 –air flames. In addition, a CO 2 concentration reduction of about 45% was achieved for X NH3 = 0.70 compared with pure CH 4 , while still producing stable flames as long as PR ≥ 5%. The pilot power ratio was found to have a higher relative impact on NO emissions for CH 4 than for NH 3 –CH 4 , with measured exhaust NO percentage increments of about 276% and 11%, respectively. The N 2 O concentration was constant for all pilot power ratios for CH 4 but it decreased when the pilot power ratio increased for NH 3 –CH 4 . The pilot fuel composition highly affected the NO and N 2 O emissions. Pure CH 4 pilot flames and higher power ratios produced higher NO emissions. Conversely, the NO concentration was roughly constant for pure NH 3 pilot flames, regardless of the pilot power ratio. Qualitative OH-PLIF images were recorded to further investigate these trends. Results showed that the pilot power ratio and the pilot fuel composition modified the flame morphology and the OH concentration, which both influence NO emissions.