Content of research

Thermo-acoustic vibrations are often generated in combustion equipment and combustion gas exhaust systems, leading to noise generation and reduction of the life of combustion equipment. This is caused by acoustic pressure fluctuations linked to heat generation fluctuations in the combustion and exhaust systems, and we are analyzing the physical processes that cause these fluctuations and investigating techniques to suppress them. With this study, a single circular tube is filled with a combustible premixed gas that is ignited at one end, and a thermo-acoustic vibration phenomenon that occurs during flame propagation in the tube is used. Various boundary conditions (open end condition, direction of propagation, composition of the gas mixture, diameter and length of the propagating tube, structure of the flame surface, etc.) are applied to this propagation phenomenon to induce the thermo-acoustic vibration phenomenon, and the factors behind it can then be understood using the combustion instability analysis method. The vibration phenomena reproduced here are observed in a simplified system, but they are general phenomena and lead directly to the understanding of thermo-acoustic vibration phenomena that occur in actual combustion equipment and exhaust systems.

Potential for social implementation

• Although the combustion-induced vibration phenomena handled in this study are observed in a simplified system, they can be correlated with the thermo-acoustic vibration phenomena that occur in actual combustion equipment and exhaust systems, which leads directly to an understanding of the thermo-acoustic vibration phenomena in actual equipment and measures to suppress them.

Appealing points to industry and local governments

Unstable vibration caused by combustion often occurs in gas turbines, boilers, incinerators, and in ducts that discharge combustion gases, and it is not easy to suppress such vibration technically. This is due to the fact that it is not easy to physically understand the causes of the vibration. With this study, we attempted to understand the physical processes and find a method to suppress the phenomena by reproducing them in a simple system.