Effect of flow number of pilot-stage centrifugal atomizer on idle performance of internally staged combustor

Idle performance is critical to the combustion stability of internally staged combustors. Five pilot-stage atomizers are compared in an internally staged combustor, and the effects of the flow number (FN) on the combustion characteristics and emissions are investigated under idle conditions. Experimental results show that the maximum outlet temperature is 1.02-1.04 times the average outlet temperature, and the maximum temperature is located at the dimensionless radial location of 0.66. The key influencing mechanism of the temperature distribution lies in the matching between the spray angle of the pilot-stage atomizer and the angle of the recirculation zone. When the flow number (FN) of the pilot-stage atomizers was increased from 1.6 to 10, the combustion efficiency (eta) showed a "decrease-increase-decrease" trend, whereas the emission of unburned hydrocarbon (UHC) showed a opposite trend. At the meantime, the emission of CO remained unchanged, and NOx remained at the undetectable level. In addition, the low sensitivity of pressure loss (3.3%-4%) and combustion stability (0.66%-0.85%) to idle conditions is attributed to the influence of combustion efficiency and outlet temperature. After a comprehensive evaluation, it is determined that an intermediate FN of 5.0 possesses the most balanced combustion characteristics and emissions under idle conditions in the pilot-stage atomizer.