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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.

The initiation mechanism and its reduction method for combustion driven oscillation of industrial boilers with a center firing gas burner have been investigated experimentally and numerically. Eight fuel injection nozzles are arranged radially at the burner. The burner with two different diameter nozzles, main nozzle and sub nozzle, arranged alternately is proposed. When the burner proposed is set in the burner, the flame base becomes much stable compared with the standard burner in which the diameter of all fuel injection nozzles is the same because the small flame of sub nozzles is formed around the flame base of large flame of main nozzles. The ratio of diameters of main nozzle and sub nozzle and the angles of main nozzle and sub nozzle are important parameters on flame base structure. Numerical simulation confirms the stability mechanism experimentally observed.

Flame height variations of a laminar stagnating premixed flame with gas component transition between fuel mixture A (methane:92%, ethane:6.7%, propane:1.3%) and B(methane:84%, ethane:13.3%, propane:2.7%), and between A and C (methane:76%, ethane:20.0%, propane:4.0%) are discussed. The estimation of the flame speed and the flame temperature of fuel mixtures A, B and C by the Chemkin-Pro show almost the same values for all fuel mixtures. In experiments, the transition between A and B and between A and C were performed. The transition time changes from 1 s to 10 s, keeping flow velocity and equivalence ratio constant at 0.8 m/s and 0.7 respectively. The flame position was measured by using images taken by a high speed camera with 125 fps. Two transition patterns are examined, keeping the total flow rate of premixed mixture constant. One is the constant flow rate transition, which changes the gas component, keeping the fuel mixture flow rate constant. The other is the constant equivalence ratio transition, keeping the equivalence ratio constant. In the case of the constant flow rate transition, the equivalence ratio changes which results in the variation in the flame speed, the flame temperature and the flame height. It means that the combustion state changes with the transition. On the other hand, in the case of the constant equivalence ratio transition, the flame speed, the flame temperature and the flame height keep almost the same state, which means that the gas component can be changed, keeping the combustion state the same.