Quantitative measurement of temperature in oxygen enriched CH4/O2/N2 premixed flames using Laser Induced Thermal Grating Spectroscopy (LITGS) up to 1.0 MPa

The application of laser diagnostics to high pressure combustion phenomena is particularly challenging, especially in practical combustors such as rocket motors. In this study, temperature measurements using Laser Induced Thermal Grating Spectroscopy (LITGS) are demonstrated in oxygen enriched CH4/O-2/N-2 premixed laminar flames at pressures up to 1.0 MPa. We use a previously developed OH absorption LITGS technique to determine product gas temperatures from 0.3 to 1.0 MPa, for both high temperature oxygen-enriched and pure-oxygen flames, for measurements up to 3000 K. Further, we demonstrate how it is necessary to correct the measurements for the local absorption of laser light to obtain accurate temperatures, and offer a technique for producing the correction by using different laser energies. Once the correction is applied, we demonstrate that the measurements at 0.5 MPa are within 1.6% of the adiabatic non-strained flame temperatures, with a standard deviation of about 160 K, thus offering a competitive method for the challenging conditions at high pressures and temperatures. The values obtained at derived temperatures at 1.0 MPa were lower than the adiabatic unstrained flame temperatures, which could possibly be attributed to loss mechanisms. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.