Response in Bunsen flame with variation in a natural gas composition and control for stabilizing the flame variation

This study investigated experimentally a response of premixed Bunsen flame to transient change in a fuel composition and a method to control the variation. Fuel mixtures were composed of methane, ethane and propane. The volumetric fraction of methane was varied from 92 % to 76 % by 4 % and the ethane/propane ratio was 5. Transition time of the fuel composition was 1, 5, 10 and 20 s. Flow velocity and the equivalence ratio were 0.8 m/s and 0.85 respectively before the transition. Channel length L between the merging point of fuels and the point of air was 0, 500, 1000, 1500 mm. The motion of flame was recorded by a high-speed video camera at 60 fps. The experiment was conducted under the fuel flow rate constant and the equivalence ratio constant conditions. In the former condition, the flame height varied almost linearly not depending on the conditions. In the latter condition, variation of the steady flame height was smaller than the former condition. However, the unsteady flame height exceeded or fell below temporarily the steady flame height. This is due to the time lag between the transmission of fuel flow rate variation and fuel compositions variation. Therefore, considering this time lag, the experiment was conducted with a system which had a density meter to detect the fuel composition variation. The system controlled automatically the fuel flow rate. At long L and short transition time, there were some peaks in the flame height variation. It is considered that this is caused by the difference between the actual density and the output of the density meter due to Taylor dispersion and response time of the density meter. However, the flame height variation was smaller than the variation without control, and particularly at long transition time, the variation was suppressed sufficiently.