Lean Low NOx Primary Zones Using Radial Swirlers

Abstract

Swirling flow primary zones with between 30% and 60% simulated primary zone air flow were investigated using curved blade radial swirlers. Two radial swirlers were compared with the same open area but different outlet diameters, d, giving different expansion ratios, D/d, from the swirler to the combustor diameter, D. Two combustors were used, 76 mm and 140 mm diameter, the larger one corresponding to the size of several gas turbine can combustors. There was no influence of D/d on the weak extinction. It was demonstrated that an adequate efficiency was not achieved in the weak region until there was a significant outer expansion and associated recirculation zone. It was shown that these systems with central gaseous fuel injection had good flame stability with very low NOx emissions. Propane and natural gas were compared and the NOx emissions were 50% lower with natural gas. The optimum NOx emissions, compatible with a high combustion efficiency, were close to 10 ppm NOx emissions corrected to 15% oxygen.

A Liquid Fueled, Lean Burn, Gas Turbine Combustor Injector

“…A number of radial injected, lean bum combustors have been designed and demonstrated using gaseous fuels (Alkabie and Andrews, 1990;Alkabie, Andrews and Ahmad, 1988;Matsuzaki et al, 1992;Smith, 1992). It is important to note, however, that the design developed in this work utilizes liquid, aviation gas turbine fuel (Jet A).…”

Ultra Low NOx Emissions for Gas and Liquid Fuels Using Radial Swirlers

“…Nejad et al (1988) also determined the large axial velocity gradients and high turbulence intensities in the jet boundary shear layer, equivalent to that in Fig.2. Alkabie et al (1988) previously investigated this radial swirler with the central fuel injector shown in Fig.1. This had eight radial fuel injection holes and these injected fuel into the base of the swirling jet shear layer.…”

“…However, the NOx emissions for propane were nearly twice that for natural gas and were only just inside the EPA limits scaled to the one atmosphere operating pressure. Alkabie et al (1988) also investigated a smaller outlet diameter (40mm) radial swirler with the same swirler flow area as the 76mm swirler. The much larger vane passage depth of 30mm gave some premixing of the fuel and air inside the swirler and very low NOx emissions were achieved but with a flame stability little better than a fully premixed system.…”

“…Andrews et al (1988) have developed a range of techniques for low NOx gas turbine primary zones with good flame stability, all of which use fuel injection into the base of jet shear layers. Low NOx emissions have been demonstrated for non-swirling jet shear layer systems for both gas and liquid fuels Abdul Aziz et al, 1987) and for swirl stabilised systems (Alkabie et al, 1988). The present work investigates techniques to produce further reductions in NOx emissions for radial swirlers, using the radial swirler passage as a partial fuel and air premixing zone.…”

“…Ahmad et al (1986) found problems in the achievement of an adequate combustion efficiency and stability with lean primary zones using large air flow axial swirlers with central fuel injection. Alkabie et al (1988) showed that these problems could be overcome by the use of radial swirlers, with their quite different near swirler aerodynamics. Ahmad and Andrews (1984) and Andrews and Kowkabi (1987) showed that for a fixed axial swirler the position and direction of fuel injection had a major influence on the flame development and NOx emissions.…”