Visualization of Dome Region Mixing in a Quartz Combustor

Abstract

To improve the performance of gas turbine combustors (i.e. stability and emissions), the process of fuel-air mixing, within the dome region, must be better understood and enhanced. This paper takes a preliminary step by evaluating the influences of nozzle air/fuel ratio, swirl angle, and dome geometry on fuel-air mixing. A model combustor, fabricated from quartz and designed to utilize flow visualization as the primary diagnostic, was operated at atmospheric pressure with JP-4 injected through a twin-fluid (air-assist) atomizer. Photographs of the dome region were acquired for a variation in (1) nozzle air/fuel mass flow ratio from 2.0 to 4.0, (2) swirl angle from 45° to 60°, and (3) the shape of the dome from a dump to a 45° conical expansion configuration. The results show trends of improved mixing for higher nozzle air/fuel ratios as manifested by the improved homogeneity and reduced intermittency of the reaction structure. The effects of dome geometry and swirl strength also affect mixing, with the degree and direction of effect depending on the atomizer operating conditions.

Mixing in the dome region of a staged gas turbine combustor

“…Ineffective mixing in the dome will lead to increased residence times of stoichiometric and near-stoichiometric packets of fuel and air Presented as Paper 92-3089 at the AIAA 28th Joint Propulsion Conference, Nashville, TN, July [6][7][8]1992; received July 28, 1992; revision received April 12, 1993; accepted for publication April 17, 1993 which can promote the formation of NO^. 10 Nonuniform gas temperatures and gas species profiles can also degrade the performance of the air addition stage.…”

“…8 After a decade of relative inactivity, studies have recently been initiated to identify effective mixing approaches in both the fuel-rich and air addition stages of these combustors. 7 ' 9 This research is especially important given the trend to produce more efficient and lighter gas turbine engines by increasing the operating temperatures and pressures in the combustors.…”