Study on the Emissions Performance of a CMC Combustor With Weakly Coupled Stratified Swirl Flames at Engine-Relevant Conditions

Experimental and theoretical studies were conducted to investigate the overall emissions of CO, NOx, and UHC in a centrally staged lean premixed prevaporized (LPP) combustor featuring weakly coupled stratified swirl flames. The combustor consisting of a ceramic matrix composites (CMC) plate was run at aero engine-relevant conditions, with inlet temperatures and pressures up to 810 K and 2.2 MPa. The combustor adopted the concept of impinging cooling thanks to the heat-resistant property of CMC. The cooling air entering from the dome subsequently participated in combustion. The design of the test matrix was based on the typical operating conditions of practical LPP combustor. Without downstream cooling holes on the liner, the injector equivalence ratio was equal to global equivalence ratio of the entire combustor. The overall emissions data including EICO, EINOx, and EIUHC were obtained using a gas analyzing system under 15 different operating conditions. With a low fuel-air ratio (FAR), EINOx reached its lowest value when the pilot-to-total fuel split ratio (SR) was close to 0.13. With the increase in FAR, the main stage and pilot stage started to collectively dominate the emissions performance, eventually making the EINOx-versus-SR curve level off at a high FAR. Since the trend of CO emissions is normally contrary to that of combustion efficiency, EICO consistently remained at a low level in this combustor under the currently investigated conditions. EIUHC varied significantly with SR, where the pilot stage contributed more to emissions at low SfR while the main stage played a more important role with the increment of SR. Moreover, a new empirical correlation for NOx emissions in LPP staged CMC combustor was proposed.