Velocity and scalar characteristics of the isothermal and combusting flows in a combustor sector rig

Abstract

Measurements have been carried out with isothermal and combusting flow to determine the flow characteristics of a sector of an annular combustion chamber which included two fuel holes. The three components of mean velocity were measured in isothermal flow with a direction sensitive pitot probe and confirmed with laser-Doppler anemometry. The distributions of a passive scalar (helium) injected into the fuel holes were also determined in isothermal flow. In combustion flow, with natural gas as fuel, two components of mean velocity were measured with laser-Doppler anemometry, mean temperature measurements with fine wire thermocouples, and concentrations of unburned hydrocarbon, carbon monoxide, carbon dioxide, and oxygen sampled through a water-cooled probe, with flame ionization detector, infrared and paramagnetic analyzers. The uncertainties associated with the use of mean equivalence ratio and the assumption of equilibrium to obtain temperature and species concentrations are considered by comparison with the measured quantities. Equilibrium assumptions are shown to yield concentrations and temperatures which are at variance with the measured values and by a considerable amount in fuel rich regions. The reasons for the discrepancies are associated with the large fluctuations of the mixture fraction (neglected in the present calculations) and inequilibrium of reaction products. Temperatures calculated from an enthalpy balance based on the local measured species composition also exhibit important differences from the measured temperatures, again due to the omission of the concentration and temperature fluctuation covariance in the Favre averaged enthalpy balance and the closer proximity of the measured temperatures to unweighted mean values.