Shear Layer Mixing for Low Emission Gas Turbine Primary Zones

Abstract

Shear layer turbulent fuel and air mixing has been utilised in a simulated gas turbine primary zone combustor. Two methods of fuel injection and two values of the number of air injection holes have been investigated at a constant pressure loss of 4% at a reference Mach number of 0.047. The method of fuel injection and the number of air injection holes was found to influence the flame stability and NOx emissions. A large number of holes produced much higher NOx emissions which was not compensated for by the ability to operate at weaker equivalence ratios due to the greater flame stability. An optimum primary zone operating condition, for very low NOx and high combustion efficiencies involving a flame temperature of approximately 1600K was identified and there was a wide flame stability margin on this condition.

Gas and Liquid Fuel Injection Into an Enclosed Swirling Flow

“…2. The temperature profile is similar to that for direct grid plate shear layer fuel injection for the GM1B stabiliser (13,14). The lower wall temperatures for central propane injection in the swirler are caused by a slower axial development of the radial spread of the flame.…”

“…This shows that improvements in combustion efficiency and reductions in NO emissions are not incompatible, as has been stated by many workers in this area. This situation has also been found for the Grid Mix system (13,14). Emission measurements for enclosed swirling flames at gas turbine operating conditions are rare, particularly for liquid fuels.…”

“…1, results in a major extention of the flame stability limits compared with the premixed situation. However, this extension of the stability limits is no better than can be achieved using shear layer fuel injection techniques (13,14) as shown by the comparison with the GM1B weak extinction results in Table 3. The extension of the stability limits with direct fuel injection is due to the creation of locally rich zones in the flame stabilising shear layers.…”

“…An alternative low emissions technique for stabilising flames with direct fuel injection is that of fuel injection into jet shear layers (13,14,17). The results from the Grid Mix lB design (13,14) which has a similar pressure loss (4.8%) to that of the SW3 swirler, have been included in the present work for comparison with the equivalent direct propane injection swirl stabilised flames. The Grid Mix lB design consists of a simple four hole grid plate with fuel injected as eight radial jets internally within the grid plates into each air jet.…”

“…Many recent experimental combustor designs for low emissions and future fuels have advocated the use of swirl flame stabilisation with the majority of the combustor air flow passing through the swirler (8)(9)(10)(11)(12). The present work attempts to assess whether these swirl dominated systems have definite advantages over the aerodynamically simpler grid plate stabilised systems which have been investigated by one of the authors (13,14).…”