Velocity, temperature, and species characteristics of the flow in a gas-turbine combustor

Abstract

The isothermal and combusting flow characteristics of a model can-type gas-turbine combustor are reported. In isothermal flow a laser-Doppler velocimeter was used to measure the longitudinal and tangential velocity characteristics, and the mean concentration of a tracer of helium gas, injected through the fuelling device, was used to obtain the mixture fraction distribution. In combusting flow, with propane as fuel, the velocimeter measured density weighted velocity characteristics, thin digitally compensated bare-wire thermocouples measured unweighted temperature characteristics, and a sampling probe transported gas samples to various instruments which measured near density weighted concentrations of O 2, UHC, H 2, CO 2, CO, and NO x . The mean velocity results show that, relative to isothermal flow, combustion increases the strength and decreases the width of the primary vortex and, further downstream, attenuates the magnitude and strength of the swirl by the longitudinal acceleration of the flow. Turbulence measurements indicate that the production of turbulent kinetic energy in the dilution zone of the combustor is due to “conventional” mechanisms by the interaction of shear stress with shear strain. In the recirculation zone, however, gradient transport is negligible and the effect of the mean pressure gradient is likely to be important in the balance of turbulent kinetic energy. The scalar field is dominated by the primary jets. An increase of 34% in the air-fuel ratio causes a similar increase in the pattern factor at the exit plane and a 14% decrease in the combustion efficiency. The pattern factor is improved by 15% and optimal combustion efficiency is obtained by increasing the inlet air temperature by 432K. In the primary zone, combustion is controlled more by physical than chemical kinetic processes and the formation of pollutants is well described by a partial equilibrium model. Downstream of the primary holes the fuel breakdown and the CO oxidation are reaction-rate limited, and the scalar field may be described by a constrained equilibrium model.