Quantitative Determination of Methane, Ethene, Ethyne, and Benzene From Within the Sector of a Gas Turbine Combustor

Abstract

This paper describes experimental work undertaken in the quantitative measurement of specific hydrocarbons found at different axial locations within a gas turbine combustor. The motivation for this work was to gain a greater understanding of the combustion process and obtain data which could be used to provide validation for computational fluid dynamic and chemical kinetic models. Chemical species routinely measured using the QinetiQ internal traversing facility are: H2, O2, NO, NO2, THC, CO2, CO and smoke. For this work, a Fourier Transform Infrared spectrometer (FTIR) was added to the suite of gas analysers to measure the concentration of individual hydrocarbons in real time. Gaseous samples were also acquired in pressurised stainless steel cylinders and analysed for individual hydrocarbons using Gas Chromatography Mass Spectrometry (GCMS), thus providing validation for the FTIR methodology. A “water cooled” gas-sampling probe was utilised to perform the measurements at realistic operating conditions within a generic gas turbine combustor sector. Heated sample lines were used to convey the sample from the probe to a heated, variable-pathlength sample cell incorporated into the optical path of the FTIR analyser. FTIR spectra were acquired in the mid-infrared region between 400 to 4000 cm−1. H2O and CO2 have absorption bands that overlap with some of the hydrocarbons of interest in this spectral region: it was therefore necessary for spectral subtraction to be undertaken. The predominant hydrocarbons found at all axial locations within the combustor were CH4, C2H2, and C2H4. Benzene was found in the primary zone but not at other axial locations. Simultaneous measurements made using a total hydrocarbon analyser compared favourably with total hydrocarbon values obtained using GCMS and FTIR. This suggests that the majority of the unburned hydrocarbons were accounted for.