Measured and Estimated Combustion Efficiency in a Full-Annular Partially Premixed Pre-Vaporized Small-Scale Combustor

This work experimentally characterizes a partially premixed pre-vaporized combustor from a small-scale gas turbine engine over a range of relevant operating conditions. Two independent measurement methodologies are used to measure and estimate combustion efficiency. The first method measures exhaust gas species concentrations (i.e., unburned total hydrocarbons, CO, CO2, NOx, and O2) using a custom gas sampling emissions probe and calculates combustion efficiency by following the SAE ARP1533 procedure. The second method measures exhaust gas temperatures using a custom thermocouple probe and estimates combustion efficiency by comparing the measured temperature rise across the combustor with the ideal temperature rise calculated from chemical equilibrium. Both methods traverse the respective probe azimuthally through the full annulus of the combustor exit plane to characterize the spatial distribution of gas species and temperature. The results of these two methodologies are compared and are found to agree within 2% on average for the conditions considered in this work. Combustion efficiency values based on thermocouple measurements provide acceptable accuracy for combustion efficiencies greater than 90% while gas sampling measurements are required to achieve acceptable accuracy for combustion efficiencies less than 90%. Combustion efficiency is analyzed as a function of operating condition using the severity parameter and the combustor residence time. Including the residence time as a multiplier with the severity parameter enables the combustion completeness prior to the probe measurement location to be considered in small-scale combustors.