Improvement on ignition and lean blowout performances of a piloted lean-burn combustor

Abstract

This work focuses on optimizing the flame stability by matching the primary spray with swirling air streams in swirl cup which is used as pilot stage of a lean-burn fuel injector. Two configures of pressure-swirl atomizer for pilot spray have been investigated for their ignition and lean blowout (LBO) performances, the new designed pilot atomizer decrease fuel–air ratio ( f/ a) of the ignition limit by about 35%, and capability of LBO is greatly improved with decreasing fuel–air ratio from 0.015 to 0.005. Furthermore, in order to relate the pilot spray characteristics with the combustion performances, the performances of pilot pressure-swirl atomizer working both single and together with swirlers are carried out by optical spray diagnostics in a quiescent open air environment. Fuel planar laser induced fluorescence method for fuel distribution, particle image velocimetry method for velocity of droplets, and Fraunhofer diffraction technique for line-of-sight measurement of D32 are used to visualize the spray. The interactions between pilot spray and pilot, main swirling air streams are analyzed. The relative pressure loss of swirling air streams larger than 3% is recommended for this type of spray facility to make sure high quality of atomization at ignition and near LBO conditions. Improvements of ignition and LBO performances by optimizing the pilot spray illustrate that matching pilot spray with swirling air streams is an effective method to improve capability of stable combustion in fuel-staged multi-injection combustors.