Combustion speed flames

Experimental research has shown that a vapor cloud explosion can be described as a process of combustion-driven expansion flow with the turbulent structure of the flow acting as a positive feedback mechanism. Combustion, turbulence, and gas dynamics in this complicated process are closely interrelated. Computational research has explored the theoretical relations among burning speed, flame speed, combustion rates, geometry, and gas dynamics in gas explosions. 

Similar behavior was observed for LNG clouds during both continuous and instantaneous tests, but average flame speeds were lower the maximum speed observed in any of the tests was 10 m/s. Following premixed combustion, the flame burned through the fuel-rich portion of the cloud. This stage of combustion was more evident for continuous spills, where the rate of flame propagation, particularly for LNG spills, was very low. In one of the continuous LNG tests, a wind speed of only 4.5 m/s was sufficient to hold the flame stationary at a point some 65 m from the spill point for almost 1 minute the spill rate was then reduced. 

Ishizuka, S., Murakami, T., Hamasaki, T., Koumura, K., and Hasegawa, R., Flame speeds in combustible vortex rings, Combustion and Flame, 113, 542-553,1998. 

Choked flame (CJ deflagration)—high-speed flame propagating with the velocity close to sound speed in the combustion products (600-1200 m/s)... 

The high-speed flames propagate in a tube with repeat-able obstacles with the steady-state velocity, which is maintained for the rest of their passage over the obstacles. In some cases, the steady-state flame propagation velocity of the combustion products may approach the... 

A related term is flame speed. Flame speed is the speed with which a flame appears to move relative to a stationary observer. The flame speed can be much larger than the burning velocity due to expansion ofthe combustion products, instability and turbulent deformation ofthe flame. Flame speeds of 30-300 ft/sec (9-90 m/sec) are commonly observed for hydrocarbon-air mixtures. A gas phase detonation occurs when the flame speed exceeds the speed of sound in the burning vapor air mixture. 

To be detected by AAS, the analyte must be presented to the optical beam of the instrument as free atoms. The process of converting analyte ions/molecules, dissolved in a suitable solvent, to gaseous atoms is accomplished by the nebuliser flame assembly. The nebuhser (from the Latin nebula meaning cloud) creates an aerosol (a fine mist) of the hquid sample which is mixed with an oxidant gas and a fuel gas (to support the flame combustion). The mixture is ignited above the burner assembly. The liquid droplets are desolvated, the resulting microcrystals are melted and vaporised and finally the gaseous products are thermally dissociated to produce free atoms. The combustion speed of most flames is such that the conversion from liquid droplet to free atoms must be accomplished within a few milhseconds. 

Major Pathways and Reactions Effects. As seen above the experimental data (flame speeds, flame widths and NO concentrations) are well described by the kinetic mechanism. A schematic of the whole kinetic chain for the combustion of the nitrogeneous species is shown in Figure 4. The relative influence of reactions on a species are determined by a flux analysis (13, ). This is a flame averaged analysis, but it typically gives results similar to a comparison of net reaction rates in the reaction zone. To further test the effect of the specific reaction changes we recalculate selected flames. 

Plantier KB, Pantoya ML, Gash AE (2005) Combustion wave speeds of nanocomposite Al/Fe203 The effects of Fe203 particle synthesis techniques. Combustion and Flame 140 299. 

Miller, D. Evers, R. Skinner, G. (1963). Effects of various inhibitors on hydrogen-air flame speeds. Combustion and Flame, Vol. 7, pp. 137-142, ISSN 0010-2180... 

Mechanical load values depend on the combustion regime. In the case of slow combustion, when flame propagation velocity is much less than the sound speed, a quasi-static pressure rise is observed. Overpressure values depend on the mixture composition and the initial conditions. Resultant pressure values can be estimated by Aicc - maximal pressure at adiabatic combustion in a confined volume. 

Detonation. In a detonation, the flame front travels as a shock wave, followed closely by a combustion wave, which releases the energy to sustain the shock wave. The detonation front travels with a velocity greater than the speed of sound in the unreacted medium. 

The balanced equation for turbulent kinetic energy in a reacting turbulent flow contains the terms that represent production as a result of mean flow shear, which can be influenced by combustion, and the terms that represent mean flow dilations, which can remove turbulent energy as a result of combustion. Some of the discrepancies between turbulent flame propagation speeds might be explained in terms of the balance between these competing effects. 

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