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Analysis of Thermo-acoustic Vibration Generated by Combustion Equipment
Thermo-acoustic vibrations often occur in combustion devices and combustion gas exhaust systems, causing noise and reducing the life of the combustion devices. This is caused by acoustic pressure fluctuations coupled with heat generation fluctuations in combustion and exhaust systems. With this study, we analyze this physical process and investigate the suppression technology.
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.
Osamu Fujita Professor -
Elucidation of Combustion Phenomena Using Microgravity Fields
Combustion phenomena are accompanied by a local temperature rise, which always results in natural convection in the surrounding air . This complicates the phenomenon and makes it difficult to fundamentally understand it. In this study, we will try to understand the combustion phenomena from a fundamental standpoint by utilizing the microgravity environment to remove the natural convection.
Research
Combustion phenomena are accompanied by a local temperature rise, which always results in natural convection in the surrounding air . This complicates the phenomena and makes it difficult to understand the fundamentals. In this study, we will utilize the microgravity environment to remove the natural convection and understand the fundamental processes (diffusion, heat conduction, soot formation, ignition, flame propagation, etc.) of combustion phenomena, which will be useful for numerical prediction and modeling of combustion devices. Hokkaido University has an approximately 40-meter drop tower that can be used at any time, making it easy to conduct microgravity experiments, and is also involved in international joint research to conduct microgravity experiments using aircraft and the International Space Station. Thus, we are in a favorable environment to conduct combustion research using the microgravity environment.
Osamu Fujita Professor -
Fire-safety Improvement Technology for Lithium-ion Batteries
The use of lithium-ion batteries has been expanding rapidly due to their high energy density. On the other hand, since organic solvents are used in lithium-ion batteries, it is important to ensure their fire safety. With this study, we focus on the combustion phenomenon of organic solvents and study combustion inhibition technology.
Research
The use of lithium-ion batteries has been expanding rapidly due to their high energy density. On the other hand, since organic solvents are used in the battery electrolyte, it is important to ensure their fire safety. With this study, we intend to develop a method to quantify the effect of adding a combustion inhibitor to suppress the combustion of organic solvents, search for additives that are effective in suppressing combustion, and study the effect of the lithium salt contained in the electrolyte itself on the flammability of organic solvents. We also conduct modeling and numerical analysis of fire phenomena taking the elementary reaction kinetics of combustion in an electrolyte into consideration.
Osamu Fujita Professor -
Time-resolved Two-dimensional Surface Acoustic Wave Imaging
Excitation and detection of arbitrary frequency response by optical pulse train with fixed period
This technique visualizes the propagation of surface acoustic waves up to the GHz frequency range as a time-resolved two-dimensional image. Conventional methods involve the problem of low frequency resolution, but this method can excite and detect acoustic waves of any frequency.
Research
Visualization of acoustic wave propagation is extremely useful in the evaluation of physical properties and the design, fabrication and evaluation of functional devices using acoustic waves. For this purpose, we excite surface acoustic waves by irradiating the sample with an ultrashort optical pulse of subpicosecond duration (pump light), and observe their propagation with delayed optical pulse (probe light). Time-resolved two-dimensional images of the acoustic waves are obtained by scanning the delay time and the irradiation position of the probe light. The time resolution is in picoseconds, the spatial resolution is 1μm, and the frequency range is in GHz. Since this method uses a periodic optical pulse train, it was previously only possible to excite and detect acoustic waves at integer multiples of the repetition rate. However, with the newly developed technique, we have realized the excitation and detection of acoustic waves of any frequency. By developing this technique, we have also achieved image vibrations that are completely asynchronous to the repetition frequency of the optical pulse, thereby expanding the range of applications.
Osamu Matsuda Professor
