Radial swirlers for low emissions gas turbine combustion

Radial swirler were investigated for gas turbine combustor applications. with low NOx emissions as the main aim of the project. The flow regime of the combustor which was imposed by the radial swirler flow was shown by flow visualisation to feature a conical shaped swirling shear layer boundary and a comer recirculation zone. The flow patterns was independent of the swirl-vane angle but was a function of the swirler passage depth. A minimum swirler expansion ratio of 1.8 was required to achieve an adequate combustion efficiency. A high efficiency was not achieved in the weak region until there was a significant outer expansion and associated recirculation zone. However, there was a little influence of the expansion ratio on the weak extinction limit. Various non-conventional fuel injection methods such as swirler vane passage. radial central and wall injection were used with gaseous propane and natural gas and liquid kerosene and gasoil. Passage injection was undertaken to exploit the twin benefits of peripheral fuel injection and partial fuel and air mixing upstream of the swirlers outlet. Generally, most of the mixing between fuel/air took place in the shear layer. However, there was a major influence of the method of fuel injection on the NOx emissions. Low NOx emissions were achieved with the radial central injection, but ultra-low NOx emissions, comparable with the premixed situation, were achieved for passage and wall injection. This was due to the dependency of the local shear layer mixing near the swirler exit on the fuel placement as shown by the radial gas analysis traverse results in the plane just downstream of the radial swirler. Staged air and fuel combustion was investigated using lean-lean combustion concept. Low NOx emissions compatible with a high combustion efficiency was demonstrated with stable switching from pilot to main stage combustion. Finally, a double radial swirler with a high air flow was investigated using co and counter swirl and demonstrated ultra low NOx with a good stability with central injection into counter rotating swirler. These systems were shown to have the potential for dry solution to the industrial gas turbine NOx emissions regulations with a very high combustion efficiency.