Planar combustion fronts

The model envisions a planar combustion front propagating through an infinite isotropic combustible porous medium. Figure 1 depicts the situation and the assumed temperature, O2 and pressure profiles. Important assumptions in the model are described below, and are discussed in more detail in a later section. 

Harmonic corrugation of planar combustion front in stability analysis... 

The low NO production for combustion in a refractory tube apparently results from the short residence times of 2-5 msec at high temperature and from the minimal back-mixing caused by the planar fiame front and the absence of acoustical oscillations. Bernstein and Churchill showed that the observed decrease in NO. and increase in CO with decreased residence time are consistent with kinetic considerations. 

LINEAR STABILITY OF A PLANAR REVERSE COMBUSTION FRONT PROPAGATING THROUGH A POROUS MEDIUM GAS-SOLID COMBUSTION MODEL... 

The above models do not address the question of the stability of the planar RC front or the evolution of channels. Physically an RC front can be viewed as an unstable displacement front, where the thin combustion zone separates a region of low permeability... 

A laminar flame propagates through a combustible mixture in a horizontal tube 3 cm in diameter. The tube is open at both ends. Due to buoyancy effects, the flame tilts at a 45° angle to the normal and is planar. Assume the tilt is a straight flame front. The normal laminar flame speed for the combustible mixture is 40 cm/s. If the unbumed gas mixture has a density of 0.0015 gm/cm, what is the mass burning rate of the mixture in grams per second under this laminar flow condition ... 

Such diffusion-driven instabilities have been observed earlier in combustion systems. As early as 1892, Smithells reported the observation of cellular flames in fuel-rich mixtures [40]. An example is shown in figure A3.14.14. These were explained theoretically by Sivashinsky in terms of a thermodifflisive mechanism [41]. The key feature here involves the role played by the Lewis number, Le, the ratio of the thermal to mass diffusivity. If Le <1, which may arise with fuel-rich flame, for which H-atoms are the relevant species, of relatively low thermal conductivity (due to the high hydrocarbon content), a planar flame is unstable to spatial perturbations along the front. This mechanism has also been shown to operate for simple one-off chemical wave fronts, such as the iodate-arsenite system [42] and for various pH-driven fronts [43], if... 

In premixed combustion, the characteristic laminar speed, Uf, is the laminar flame propagation speed and the characteristic length scale, Lp, corresponds to the flame thickness. The laminar flame regimes are confined to regions (1) and (2P), where in the latter the turbulence intensity, u, is less than the laminar flame speed, Mp. Region (1) is defined by Rct< and the flame front is essentially a thin planar... 

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