Propane flame speed

It has been shown by Palmer at the Fire Research Station (FRS) that a crucial variable governing the performance of a flame arrester is the flame speed incident on the arrester. The critical flame speed (minimum speed at which the flame can pass through the arrester) is discussed by Phillips and Pritchard (1986), drawing largely on the FRS work on propane-air mixtures at atmospheric pressure. A simple model based on heat removal from the flame yields the following relation for deflagration flame arresters ... 

The influence of hemispherical wire mesh screens (obstacles) on the behavior of hemispherical flames was studied by Dorge et al. (1976) on a laboratory scale. The dimensions of the wire mesh screens were varied. Maximum flame speeds for methane, propane, and acetylene are given in Table 4.1b. 

These experiments are described in detail in Chapter 5, and will not be described further here. The overall conclusion, from an explosion point of view, is that flame speeds are relatively low, although atmospheric conditions alone may increase flame speed somewhat. The maximum flame speed observed for LNG was 13.3 m/s (China Lake), and for propane (Maplin Sands), 28 m/s. 

The presence of horizontal or vertical obstacles (Figure 4.4) in the propane cloud hardly influenced flame propagation. On the other hand, flame propagation was influenced significantly when obstacles were covered by steel plates. Within the partially confined obstacle array, flame speeds up to 66 m/s were observed (Table 4.2) they were clearly higher than flame speeds in unconfined areas. However, at points where flames left areas of partial confinement, flame speeds dropped to their original, low, unconflned levels. 

Van Wingerden and Zeeuwen (1983) demonstrated increases in flame speeds of methane, propane, ethylene, and acetylene by deploying an array of cylindrical obstacles between two plates (Table 4.3). They showed that laminar flame speed can be used as a scaling parameter for reactivity. Van Wingerden (1984) further investigated the effect of pipe-rack obstacle arrays between two plates. Ignition of an ethylene-air mixture at one edge of the apparatus resulted in a flame speed of 420 m/s and a maximum pressure of 0.7 bar. 

Urtiew (1981) performed experiments in an open test chamber 30 cm high x 15 cm wide x 90 cm long. Obstacles of several heights were introduced into the test chamber. Possibly because there was top venting, maximum flame speeds were only on the order of 20 m/s for propane-air mixtures. 

Elsworth et al. (1983) report experiments performed in an open-topped channel 52 m long x 5 m high whose width was variable from 1 to 3 m. Experiments were performed with propane, both premixed as vapor and after a realistic spill of liquid within the channel. In some of the premixed combustion tests, baffles 1-2 m high were inserted into the bottom of the channel. Ignition of the propane-air mixtures revealed typical flame speeds of 4 m/s for the spill tests, and maximum flame speeds of 12.3 m/s in the premixed combustion tests. Pressure transducers recorded strong oscillations, but no quasi-static ovetpressure. 

Taylor (1987) reports some experiments performed in a horizontal duct (2 m long, 0.05 X 0.05 m cross section). Obstacles were placed in the channel. The top of the duct could be covered by perforated plates with a minimum of 6% open area. Terminal flame speeds of 80 m/s were reported for propane in a channel with a blockage ratio of 50% and a 12% open roof. 

Figure 4.2.13 shows the variation of the flame speed with the maximum tangential velocity obtained with vortex ring combustion in the same mixture atmosphere [29]. The cylinder diameter was 100 mm and various lean, stoichiometric, and rich methane/ air and propane/air mixtures were examined. The diameter of the propagating flame was also determined and the ratio of the flame diameter to the core diameter was also plotted against the maximum tangential velocity. 

Prediction 4 overestimates the lean methane flame speeds (Figure 4.2.7a), however, it considerably predicts the flame speeds of the stoichiometric (Figure 4.2.7b) and rich propane mixtures (Figure 4.2.7c) as long as the value of is <10m/s. On the other hand, predic-... 

Figure 5.1.7a shows a side view of a lean propane flame, 10 cm in diameter, propagating downward in a top-hat flow. The flame speed is 9cm/s, below the stability threshold, and the flame is stable at all wavelengths. Figure 5.1.7b shows a near stoichiometric flame in the same burner. The flame is seen at an angle from underneath. The mixture is diluted with nitrogen gas to reduce to flame speed to the instability threshold (10.1 cm/s), so that the cells are linear in nature. The cell size here is 1.9 cm. Figure 5.1.7c shows a flame far above the instability threshold, the cell shape becomes cusped, and the cells move chaotically. 

Botha, J.P. and Spalding, D.B., The laminar flame speed of propane-air mixtures with heat extraction from the flame, Proc. Royal Soc. London, Ser. A., 1954, 225, 71-96. 

Figure 9. Variation of normal flame speed with logarithm of pressure for propane-air Bunsen flames with four burner sizes...

Flame speeds and quenching distances in the perfluoroethane—perfluoror propane and perfluorocyclobutane—chlorine trifluoride systems have been measured. Perfluoroethane burns much more weakly than perfluoropro-pane, while perfluorocyclobutane burns very vigorously [148]. 

The presence of propylene and butylenes in liquefied petroleum gas used as fuel gas is not critical. The vapor pressures of these olefins are slightly higher than those of propane and butane and the flame speed is... 

A series of 17 tests was carried out by the ICT with ignition of pancake-shaped, free, homogeneous, near-stoichiometric methane-air or propane-air gas clouds of up to 13,000 m volume. The generation of additional turbulence due to obstacles or entries/exits was observed to result in locally higher flame speed (up to 80 m/s) and overpressures (up to 8 kPa) compared with undisturbed clouds with respective figures of 6 - 8 m/s and 0.1 -0.2 kPa [90]. 

---