Fuel mixtures obstacles

Fuel-pair mixtures, in soap bubbles ranging from 4 to 40 cm diameter and with no internal obstacles, produced flame speeds very close to laminar flame speeds. Cylindrical bubbles of various aspect ratios produced even lower flame speeds. For example, maximum flame speeds for ethylene of 4.2 m/s and 5.5 m/s were found in cylindrical and hemispherical bubbles, respectively (Table 4.1a). This phenomenon is attributed to reduced driving forces due to the top relief of combustion products. 

Flame velocity versus fuel concentration for H2/air mixtures in the 10 m long tubes of 5, 15, and 30 cm internal diameter with obstacles (orifice plates) BR = 1 - d /D - blockage ratio, where d is the orifice diameter and D is the tube diameter. (From Lee, J.H., Advances in Chemical Reaction Dynamics, Rentzepis, P.M. and CapeUos, C., Eds., 246,1986.)... 

Methanol synthesis from waste C02 streams has the potential to contribute to the limitation of worldwide C02 emissions and to serve as an alternative carbon source to fossil fuels if a renewable source of hydrogen is available (see Section 5.3.1). The main obstacle to methanol synthesis from C02-rich streams is thermodynamics. The equilibrium yield of methanol from 25% C0/C02 75% H2 mixtures of varying C0/C02 ratio is shown in Figure 5.3.5. For pure CO, a one-pass methanol yield of nearly 55% can be obtained at 525 K, while pure C02 would only yield 18%. Besides the addition of CO, this equilibrium limitation can be overcome by operating at lower temperatures (an option that requires more active catalysts), implementing higher recycle ratios, or product extraction (an option that requires higher capital investment) [8]. 

Oxygen difluoride (OF2) is an attractive oxidizer for many fuels (II, 16), especially hydrocarbons, because it provides the optimum O/F ratio for hydrocarbon oxidation. Since it is denser than the equimolar 02-F2 mixture (Flox), it should be easier to handle and should perform better. However, OF2 has been expensive to make because the usual preparation from F2 plus base (18) converts half the F2 to F . Consequently, the less attractive but lower cost Flox mixtures have received more attention. A better synthesis for OF2 would remove this obstacle and justify a more thorough investigation of its performance. 

This paper centers on the problem of turbulent flame acceleration by obstacles and the prediction of the dynamic detonation parameters of fuel-air mixtures. 

A vapour cloud explosion may occur after the release of a flammable gas. The condition is that a cloud with a sufficient quantity of a mixture of fuel and air between the explosion limits is accumulated before ignition. The rich mixture portion of the cloud contributes to the fire following the explosion. Additionally there must be a certain degree of turbulence. This may result from the release process itself or be caused by obstacles to cloud spreading. If these conditions are not fulfilled a flash fire or a fireball are to be expected. 

Compared to Fig. 7 the measured flame velocities are essentially higher, the maximum values are here between 75 m/s and 135 m/s for the same fuel-air-mixtures. Hence, the acceleration effect of the obstacle structure depends strongly on the shape parameters of the grid, i.e., the induced turbulence intensities and macro length scales obviously play an important role in the propagation process. 

This fact becomes more evident using another correlation for the data. On the basis of the wind tunnel experiments, the turbulence intensities (u ) and the macro length scales (L) are estimated for the different obstacle structures and fuel/air-mixtures used in the experiments in the near field of the grids and are taken as characteristics for all distances due to the lack of the real local data. 

Fig. 6 Maximum rate of pressmre rise in the 1.86-m closed tube as a function of fuel content, with and without obstacles a) methane-air mixtures b) comstaich-air mixtures.

In 1943 the CWS began to develop a 2.36-inch incendiary rocket for the bazooka. Chemists filled shells with various thermite and PT mixtures and tested them. The missiles were not stable ballistically, and the fuel would not always ignite upon impact. While these problems might eventually have been solved, there was another obstacle that proved insurmountable. The rocket cavity held so little filling that it was practically... 

Flame acceleration caused by turbulence promoting obstacles is especially efficient in tubes or closed vessels. In open volumes, obstacles met in the path of the flame are most often surface pipelines, plants, or building structures. In industrial zones, fuel-air mixture (FAM) combustion has caused the generation of powerful shock waves, which proves the practicability of fast local combustion of a partial or even total volume of FAM. The possibility of combustion transition to detonation in a woodland area has been verified in practice. 

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