High-Frequency Oscillatory Combustion in Tubular Flame Burners(Thermal Engineering)

High-frequency oscillatory combustion in tubular flame burners has been experimentally investigated using two prototype burners of 1MW and 2MW. Oscillatory combustion regions have been mapped in the plane of equivalence ratio and air flow rate, and pressures fluctuations also have been recorded. Results show that large-amplitude, high-frequency oscillatory combustion occurs for near stoichiometric mixtures and when the mean axial velocity exceeds about 5m/s. With increasing the air flow rate, the oscillatory combustion region gradually expands on both lean and rich sides. According to FFT analyses, the peak frequencies during the oscillatory combustion exceed 1000Hz. A simple analysis shows that these high frequencies cannot be explained on the basis of the Helmholtz resonator, or attributed to the axial mode of acoustic instability of the burner tube. These high frequencies can be explained on the basis of coupling of tangential and radial modes of acoustic instability of the burner tubes. Just before the onset of the intense oscillatory combustion, the fundamental tangential mode, which is of asymmetry, appears, and during the subsequent intense oscillatory combustion, higher radial modes appear coupled with the asymmetric and symmetric tangential modes. Since the first asymmetric tangential mode of acoustic instability seems to trigger the intense, high-frequency oscillatory combustion, it is suggested to design the burner as symmetric as possible, and in addition, to make the flame as round as possible

管状火炎バーナにおける高周波振動燃焼(熱工学,内燃機関,動力など)

High-frequency oscillatory combustion in tubular flame burners has been experimentally investigated using two prototype burners of 1MW and 2MW. Oscillatory combustion regions have been mapped in the plane of equivalence ratio and air flow rate, and pressures fluctuations also have been recorded. Results show that large-amplitude, high-frequency oscillatory combustion occurs for near stoichiometric mixtures and when the mean axial velocity exceeds about 5m/s. With increasing the air flow rate, the oscillatory combustion region gradually expands on both lean and rich sides. According to FFT analyses, the peak frequencies during the oscillatory combustion exceed 1000Hz. A simple analysis shows that these high frequencies cannot be explained on the basis of the Helmholtz resonator, or attributed to the axial mode of acoustic instability of the burner tube. These high frequencies can be explained on the basis of coupling of tangential and radial modes of acoustic instability of the burner tubes. Just before the onset of the intense oscillatory combustion, the fundamental tangential mode, which is of asymmetry, appears, and during the subsequent intense oscillatory combustion, higher radial modes appear coupled with the asymmetric and symmetric tangential modes. Since the first asymmetric tangential mode of acoustic instability seems to trigger the intense, high-frequency oscillatory combustion, it is suggested to design the burner as symmetric as possible, and in addition, to make the flame as round as possible

Combined Pre-Supernova Alert System with Kamland and Super-Kamiokande

International audiencePreceding a core-collapse supernova, various processes produce an increasing amount of neutrinos of all flavors characterized by mounting energies from the interior of massive stars. Among them, the electron antineutrinos are potentially detectable by terrestrial neutrino experiments such as KamLAND and Super-Kamiokande via inverse beta decay interactions. Once these pre-supernova neutrinos are observed, an early warning of the upcoming core-collapse supernova can be provided. In light of this, KamLAND and Super-Kamiokande have been monitoring pre-supernova neutrinos since 2015 and 2021, respectively. Recently, we performed a joint study between KamLAND and Super-Kamiokande on pre-supernova neutrino detection. A pre-supernova alert system combining the KamLAND detector and the Super-Kamiokande detector is developed and put into operation, which can provide a supernova alert to the astrophysics community. Fully leveraging the complementary properties of these two detectors, the combined alert is expected to resolve a pre-supernova neutrino signal from a 15 M$_{\odot}$ star within 510 pc of the Earth, at a significance level corresponding to a false alarm rate of no more than 1 per century. For a Betelgeuse-like model with optimistic parameters, it can provide early warnings up to 12 hours in advance

Combined Pre-Supernova Alert System with Kamland and Super-Kamiokande

International audiencePreceding a core-collapse supernova, various processes produce an increasing amount of neutrinos of all flavors characterized by mounting energies from the interior of massive stars. Among them, the electron antineutrinos are potentially detectable by terrestrial neutrino experiments such as KamLAND and Super-Kamiokande via inverse beta decay interactions. Once these pre-supernova neutrinos are observed, an early warning of the upcoming core-collapse supernova can be provided. In light of this, KamLAND and Super-Kamiokande have been monitoring pre-supernova neutrinos since 2015 and 2021, respectively. Recently, we performed a joint study between KamLAND and Super-Kamiokande on pre-supernova neutrino detection. A pre-supernova alert system combining the KamLAND detector and the Super-Kamiokande detector is developed and put into operation, which can provide a supernova alert to the astrophysics community. Fully leveraging the complementary properties of these two detectors, the combined alert is expected to resolve a pre-supernova neutrino signal from a 15 M$_{\odot}$ star within 510 pc of the Earth, at a significance level corresponding to a false alarm rate of no more than 1 per century. For a Betelgeuse-like model with optimistic parameters, it can provide early warnings up to 12 hours in advance