Turbulent premixed flame characteristics of a CO/H2/O2 mixture highly diluted with CO2 in a high-pressure environment

Abstract

Characteristics of turbulent premixed flames of a CO/H2/O2 mixture highly diluted with CO2 (CO/H2/CO2/O2 flame) at high pressures up to 1.0MPa were experimentally investigated. The CO/H2 ratio, equivalence ratio and CO2 mole fraction were determined considering the typical composition of coal gasification syngas, laminar burning velocity, adiabatic flame temperature and stoichiometry for IGCC gas-turbine combustors connected to CCS systems. OH–PLIF and flame radiation measurement were performed for Bunsen-type flames stabilized in a high-pressure chamber. Using OH–PLIF images, flame surface density, mean volume of turbulent flame regions and turbulent burning velocity were calculated and compared with those for CH4/air flames and model coal gasification syngas flames burnt with air (CO/H2/CO2/air flame). The flame surface density for the CO/H2/CO2/O2 flames was much greater than that for the CH4/air flames, even greater than that of the CO/H2/CO2/air flames, presumably due to less flame passivity against turbulent vortex motion caused by smaller Markstein length and smaller scales of flame wrinkles at high pressure. The mean volume of the turbulent flame region for the CO/H2/CO2/O2 flames was close to that of CO/H2/CO2/air flames, while much smaller than that of the CH4/air flames, which was also explicable based on the Markstein length effects on turbulent flames at high pressure. ST/SL of the model syngas flames was larger than that of the CH4/air flames and it was noted that the difference in turbulence Reynolds number caused by smaller kinematic viscosity of the CO/H2/CO2/O2 mixture should be considered to understand the ST/SL characteristics. Total radiation intensity of the CO/H2/CO2/O2 flame was about 1.6 times stronger than that of CH4/air flames due to the very high CO2 concentration, CO2 being a highly radiative species, indicating very high heat-load for gas-turbine combustors that should be considered for combustor design.