Exploring a critical diameter for thermo-acoustic instability of downward propagating flames in tubes

Abstract Thermo-acoustic oscillations are observed when a flame ignited at open end of tube propagates towards the closed due to interaction between unsteady heat release rate fluctuations from and acoustic fluctuations. In our past work, it was found that thermo-acoustic instability increases with decreasing diameter 7.0 cm 3.0 cm. A recent study in propagation Hele–Shaw cells showed is not for plate separation less than or equal 0.4 cm. Thermoacoustic instabilities cannot be very narrow tubes excessive damping wall. This opens up possibility critical where would maximum. this work we perform experiments combustion range 0.5 cm 3 cm fixed length 70.2 cm. It parametric begins lowest laminar burning velocity around 1.0 cm. termed as diameter. Critical independent Lewis number mixtures. Existence thus proved experimentally. Growth rates primary increase show maximum decrease further But, growth secondary well pressure fluctuation amplitude decreases continuously Mechanisms responsible these observations existence clarified.