Measurement of Temperature and Velocity Vectors in a Combusting Environment Using Low-Cost Probes

Abstract

Radial traverses were made to measure temperature distributions and velocity vectors in an atmospheric pressure test combustor burning gaseous fuels with heating values in the low-medium range. Temperature was measured using an aspirated pyrometer probe. Velocity vectors were determined from measurements of a five-hole probe (a two-hole probe was used prior to the five-hole probe to determine whether the flow was directed upstream or downstream). The measuring traverse was carried out across the entire diameter at ten sections along the combustor (which was specially designed to allow in insertion of probes at the ten axial sections, through three holes at 120 deg from each other around the circumference). These measurements were repeated for ten runs that incorporated a variety of operating conditions of the combustor. Temperature measurements were validated by application of the first law of thermodynamics. Velocities were validated using the principles of conservation of mass and angular momentum. The analysis showed that temperatures can be measured to within 10°C in a combusting environment of gaseous fuels for which the temperature is in the vicinity of 1500 K, by an aspirated pyrometer. The axial velocity component can be measured to an average accuracy of 7.6 percent using five-hole probes. The radial component of velocity can be obtained within ± 5 percent in most of the combustion space. The accuracy of measuring the circumferential velocity component could not be validated, partly because it was extremely small. Also, in order to validate it, some independent means of establishing its origin is needed. In this case, due to the lack of precision in fabricating the combustor and the holes for air admission, as well as due to the extremely small value of this component in the present study, it was not possible to establish the reliability of the measured values. The study recommends the use of aspirated pyrometers and five-hole probes in a combusting environment, provided that the yaw angle does not exceed 60 deg and the three components of velocity have comparable magnitudes. The probes should be made as small as possible and frequent purging should be practiced in their operation to avoid errors due to blockage of probes’ passages by water or dust particles. These probes were chosen for this application because of the ease with which they can be used, as well as for cost considerations.