予混合火炎による圧力変動増幅を考慮した振動燃焼の発生評価

抄録

Gas appliances require high performances such as low NO_x and low noise with high intensity combustion. While significant progress has been made in the development of low NO_x combustion by introducing lean premixed combustion techniques, these appliances are more likely to show a tendency to produce combustion oscillations than those with conventional burners. Conventionally, the suppression of combustion oscillation has been achieved through hardware design modifications. In general, it has been made in an attempt to prevent that the heat release fluctuation phase and the pressure fluctuation phase become the same. Rayleigh's criterion is a convenient diagnostic tool for evaluation of combustion oscillation. However, it may not always be applicable to practical combustion appliances having a complex structure. One reason is that it is difficult to model the heat release fluctuation which is strongly influenced by a type of flame, equivalence ratio and combustion intensity. In addition, combustion oscillation is sometimes generated even if the Rayleigh's criterion is positive. This paper represents an evaluation way of combustion oscillation in which amplification of the pressure fluctuation by premixed flames and the attenuation at burner are both focused on. Amplification of pressure fluctuation is measured by a burner system that the fuel-air mixture is forced to excite by a loud speaker. Obtained results are compared with the attenuation of pressure fluctuation at the burner. It is found that combustion oscillation is not observed when the attenuation excesses the amplification although Rayleigh's criterion shows a conditionally positive. It shows that present work would be a practical way to suppress combustion oscillations in the stage of designing gas appliances.