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flame propagation

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Yuyan Li
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The flame propagation behavior of premixed N2O–NH3/N2O–NH3–C3H8 was experimentally investigated in elongated vented cylindrical vessels with central ignition. The effect of vessel diameter and propane concentration ([C3H8] = 1.96–7.41 wt.%) on the process of flame acceleration was studied and discussed. The results revealed that the maximum value of flame acceleration rate was found in the cylindrical vessel with an inner diameter of 7 mm, followed by 5 mm, 10 mm, and 15 mm. At a constant vessel diameter, the rate of flame acceleration was noticeably improved by adding propane ([C3H8] = 1.96–3.85 wt.%) to the premixed N2O–NH3. However, a further increase in the propane fraction up to 5.66%, caused a decline in the flame acceleration rate, probably as a consequence of a combined effect between the reduction of oxygen and greater dilution of the ammonia in the total concentration.
The ignition sensitivity and flame propagation of zirconium powder clouds are investigated with the influence of initial turbulence. The effect of initial turbulence on the zirconium powder explosion is studied by the change of ignition delay time and dispersion pressure. Hartmann apparatus and Godbert-Greenwald furnace are used to evaluate the minimum ignition energy and minimum ignition temperature, respectively. The high-speed camera is used to analyze the flame propagation behaviors of zirconium powder cloud. The experimental results show that the minimum ignition energy is between 1 mJ and 3 mJ and minimum ignition temperature is 503 K. The ignition energy reaches the minimum value of 30 mJ at the 0.7 MPa. The ignition energy with the effect of ignition delay time has revealed the similar rule. The maximum flame speed increases with the increase of dispersion pressure. Although, the instantaneous flame speed with the lowest dispersion pressure (0.4 MPa) is significantly higher than two others in the early stage of flame propagation.