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, Rλ, as a common parameter to compare the pressure and temperature effects. It was confirmed that Rλ 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. ST/SL was also found to be greatly affected by pressure for preheated mixtures at 573 K. The bending tendency of the ST/SL curves with u′/SL was seen regardless of pressure and mixture temperature and the Rλ 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 ST/SL with (P/P0)(u′/SL) was clearly seen when ST 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.