Burning velocity correlation of methane/air turbulent premixed flames at high pressure and high temperature

Turbulent burning velocities for methane/air mixtures at pressures ranging from atmospheric pressure up to 1.0 MPa and mixture temperatures of 300 and 573 K were measured, which covers the typical operating conditions of premixed-type gas-turbine combustors. A bunsen-type flame stabilized in a high-pressure chamber was used, and OH-PLIF visualization was performed with the pressure and mixture temperature being kept constant. In addition to a burner with an outlet diameter of 20 mm for the high-pressure experiments, a large-scale burner with an outlet diameter of 60 mm was used at atmospheric pressure to extend the turbulence Reynolds number based on the Taylor microscale, R-gimel, as a common parameter to compare the pressure and temperature effects. It was confirmed that R-gimel over 100 could be attained and that u'/SL could be extended even at atmospheric pressure. Based on the contours of the mean progress variable (c) = 0.1 determined using OH-PLIF images, turbulent burning velocity was measured. S-T/S-L was also found to be greatly affected by pressure for preheated mixtures at 573 K. The bending tendency of the S-T/S-L curves with U'/S-L was seen regardless of pressure and mixture temperature and the R-gimel region where the bending occurs corresponded well to the region where the smallest scale of flame wrinkling measured as a fractal inner-cutoff approaches the characteristic flame instability scale and becomes almost constant. A power law Of S-T/S-L with (P/P-0)(u'/S-L) was clearly seen when S-T was determined using (c) = 0.1 contours, and the exponent was close to 0.4, indicating agreement with the previous results using the mean flame cone method and the significant pressure effects on turbulent burning velocity. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.