燃烧H2 / CH4燃料的Burke-Schumann火焰中OH PLIF 激光诱导荧光检测方案(气体流量计)

     The exact mechanism of combustion instability has not yet been elucidated, but it isknown that the occurrence of the combustion instability depends on the interaction of theflow perturbation of the reactants, the perturbation of heat release, and the perturbationdue to the acoustic boundary of the combustion chamber. If the above three perturbationsform a positive feedback loop, the probability of combustion instability increases. Conversely, if a negative feedback loop is formed, the probability of combustion instability is lowered. In order to lower the risk of combustion instability, it is necessary to understand the combustion instability conditions as mentioned above. The basis for understanding the conditions which combustion instability occurs is to study the dynamic characteristics of the flame.       In this study, the dynamic characteristics of Burke-Schumann flame, which is a specialcase of non-premixed jet flame, composed of a mixture of methane and hydrogen, wasstudied. The dynamic characteristics of the flame were represented by the perturbation ofheat release and flame shape when disturbance was generated from outside. When the flamewas at the open boundary, the heat release and the shape of the flame were measured toshow the response characteristics of the flame to the external disturbance. When the flamewas at the closed boundary, the resonance frequency of the experimental apparatus wasobtained and the effect on the resonance frequency was investigated and the cause of theself-excited pressure oscillations was analyzed.       The shape of the flame of the open boundary was three kinds. In the low frequencyregion, the flame shape was attached to the nozzle in one periodic wave form, and the flamewas broken in the above region. In the region near 250 Hz, the flame was hardly shaken.The flame composed of several waves appeared in the remaining region. The flame transferfunction also showed a very low value at the point where the flame did not shake and wasmaintained at a constant value above a certain frequency. The gain of the flame transferfunction and the fluctuation of the flame area showed a similar change tendency except forthe region where the flame was broken. The flame of the open boundary showed a linearrelationship in which the heat release perturbation was approximately proportional to the velocity perturbation magnitude, but the influence on the 2nd harmonic frequency of theexcitation frequency occurred to a large extent. Especially, the ratio of the 2nd harmonicfrequency of heat release increased sharply at the excitation frequency or fuel composition,which shows the low gain of the flame transfer function.At the closed boundary, the influence of the resonance frequency was analyzed.Although the closed boundary was formed by the movable nozzle, since the exhaust ductcontinued to exist in the longitudinal direction of the combustor, it affected the resonancephenomenon. Therefore, the orifice was installed to minimize the influence of the exhaustduct in the longitudinal direction of the combustor. Two resonant frequencies that can affectthe combustion chamber were obtained. The points where these frequencies coincided wereidentified and the conditions under which the effect of the resonant frequency was likely tobe strong were identified. In this case, the point where the effect of the resonance frequencywas largest was analyzed by measuring the magnitude of the velocity perturbation. Theconditions which the pressure fluctuation occurred in the combustion chamber when therewas no external disturbance were identified. The cause of this pressure fluctuation underthis condition was analyzed. The conditions of the pressure perturbation coincided with theoverlapping conditions between the resonance frequency of the air supply part, theintersection of the resonant frequencies affecting the combustor chamber and the flametransfer function at the open boundary.It is expected that this study can be used as a preliminary research data for studyingthe dynamic characteristics of Burke-Schumann flame as well as the mechanism ofcombustion instability of diffusion flame.