Combustion limits

When an explosion occurs, however, it can directly cause injury. A substantial cloud of gas can accumulate before the combustible limit reache.s an ignition source. The force of the explosion as the cloud ignites can be substantial. 

Annikov, V. E. et al., Chem. Abs., 1983, 99, 73190 MRH Acetone 4.89/18, ethanol 4.73/18, ethylene glycol 4.35/26 The detonation and combustion limits of mixtures of sodium perchlorate, water and ethylene glycol, glycerol, 1,3-butylene glycol, 2,3-butylene glycol, formamide, dimethylformamide, ethanolamine, diaminoethane, acetone, urea and galactose have been studied. 

Stoic Also called Foster Wheeler-Stoic and FW-Stoic. A two-stage, nonslagging coal gasification process, operated under atmospheric pressure and using air as the oxidant. Initially developed by Stoic Combustion Limited Pty, South Africa licensed and further developed by Foster Wheeler Corporation, United States. First used in South Africa in 1950 now widely used in Europe, the United States, and South Africa. 

The amount of explosion overpressure is determined by the flame speed of the explosion. Flame speed is a function of the turbulence created within the vapor cloud that is released and the level of fuel mixture within the combustible limits. Maximum flame velocities in test conditions are usually obtained in mixtures that contain slightly more fuel than is required for stoichiometric combustion. Turbulence is created by the confinement and congestion within the particular area. Modem open air explosion theories suggest that all onshore hydrocarbon process plants have enough congestion and confinement to produce vapor cloud explosions. Certainly confinement and congestion are available on most offshore production platforms to some degree. 

Kubota, N., Role of Additives in Combustion Waves and Effect on Stable Combustion limit of Double-Base Propellants, Propellants and Explosives, Vol. 3,1978, pp. 163-168. 

Both above methods can be used not only for detn of combustion limits, but also for detn of burning rates as will be explained further in this description... 

Combustion Limits (Percentage of Combustible Gases and Liquids in Air)... 

Following values of Table 2 for lower combustion limits of dusts in air and temperatures required for ignition are abstracted from Table 4, p 152 of Ref 14 ... 

Variations in turbojet engine altitude, flight speed, and thrust require combustion to be maintained over a wide range of inlet air and fuel environment. Furthermore, the combustion must be nearly complete in order to achieve maximum aircraft range. Combustion limits and efficiency are, then, two major performance criteria of the turbojet combustion system. Under conditions very favorable to combustion, the influence of operating, design, and fuel variables are minimized, and only in adverse combustion environment is their influence measurable. 

The combustion limit of non-premixed gases is determined by the temperature decrease, which depends on the final chemical reaction rate. 

On the basis of the non-steady theory we predict the combustion limit which is attained when the combustion velocity falls to 37% of the combustion velocity at the boiling temperature. The limit depends on the internal instability of combustion, not on external thermal losses. 

L.H. Caveny et al, Solid Propellant Flammability Including Ignitability and Combustion Limits , BRL-R-1701 (1974), (AD 775795) [The authors found that the use of oxamide with high decompn temp HMX/polyurethane composite propints is effective in reducing flamma-... 

The available diffusion combustion theories can roughly predict the combustion limits for various parameters. Not only ambient oxygen concentration , pressure and flow velocity limits but also sample size , inertial overloads , ambient and material temperature limits have been experimentally determined, and found in accordance with the theoretical predictions. 

The authors of Ref. generalized all the published polymer combustion limits from the viewpoint of the effect of different factors on the cooling of the reaction zone. At the extinction limit of diffusion combustion, the ratio of heat losses from the front edge of the combustion zone to the total heat generation due to the chemical reaction must be proportional to RT, /E here, Tj is the flame temperature at the extinction limit and E the gas-phase reaction activation energy... 

In the case of an intensive laminar flame combustion, oxygen penetration to the surface, across the high-temperature reaction zone, is hindered due to the high rate of its reaction in the zone. A thermal decomposition of the polymer may be expected to take place under these conditions. Near the combustion limit, oxygen is able to penetrate the zone near the surface underneath the flame edge. However, its concentration (1-2 %) is insufficient for a profound oxidation of the condensed phase. The probability of oxygen penetration to the surface increases when the flame becomes turbulent and when the condensed phase decomposition products are less volatile... 

The products of detonation of an underoxidized explosive are themselves fuels. These are normally products such as CO and free carbon. When these expand and mix with air, they eventually reach the lower combustion limit for these materials, and if they are at high enough temperature, or there is some other ignition source present, they will burst into flame. This afterbum or secondary... 

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