Self-Ignition and Combustion of Gas Mixtures in a Medium with Vortex Flow
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Experiments carried out in a rapid-injection setup with tangential introduction of the mixture into the reactor show that the mixtures self-ignite at temperatures substantially lower than the values reported in the literature. The measured ignition delay times do not exceed 0.1–0.2 s, although thermal conditions in the reactor allow the mixture to ignite with delays of more than 10 s. Videorecording shows that the mixture spontaneously ignites in a small volume at the center of the reactor; i.e., tangential mixture injection produces a vortex with a hotspot having a temperature at its center by more than 200 K higher than that of the reactor walls. An obstacle destroying the vortex eliminates the anomalous behavior of the self-ignition process. Temperatures measured at the center of the reactor with a thermocouple confirm the formation of a hotspot. The flame initiated by the ignition at a hotspot propagates through the mixture at a velocity several times higher than the laminar flame speed characteristic of the mixture. The mechanism of the formation of hotspots in unsteady vortex flows and their possible effect on explosion risk assessment in some practical situations are discussed.
Keywordsself-ignition combustible mixtures vortex flow laminar flame speed
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