Process parameters ignition conditions

In addition to the main variables already considered, other parameters also influence the combustion synthesis process. These include the ignition conditions, initial temperature of the green mixture, sample dimensions, and their effects and they are discussed next. 

We now consider the dependence of the stationary-state solution on the parameter d. To represent a given stationary-state solution we can take the dimensionless temperature excess at the middle of the slab, 0ss(p = 0) or 60,ss-With the above boundary conditions, two different qualitative forms for the stationary-state locus 0O,SS — <5 are possible. If y and a are sufficiently small (generally both significantly less than i), multiplicity is a feature of the system, with ignition on increasing <5 and extinction at low <5. For larger values of a or y, corresponding to weakly exothermic processes or those with low temperature sensitivity, the hysteresis loop becomes unfolded to provide... 

A distinction must be made between chemical and physical stability. While physical stability is important, particularly in the evaluation of solid propellants, the chemical stability is of prime importance in the estimation of the course of decomposition of nitrate esters. The nitrate esters which are processed for use as propellants - unlike nitro compounds, which are relatively stable under these conditions - undergo a steady decomposition, which is due to imperfect purification of the starting materials and to the effect of other parameters such as temperature and air humidity. The rate of this decomposition is auto-catalyzed by the acidic decomposition products and may in certain cases produce spontaneous ignition. In order to reduce the decomposition rate as much as possible, suitable stabilizers are added to the powders, which are capable of accepting the acid cleavage products with formation of the corresponding nitro compounds (- Stabilizers). The stability is controlled by means of several tests (- Hot Storage Tests). 

A stochastic description of explosion phenomena is set up, both for isothermal and for exothermic reaction mechanisms. Numerical simulations and analytic study of the master equation show the appearence of long tail and multiple humps in the probability distribution, which subsist for a certain period of time. During this interval the system displays chaotic behavior, reflecting the random character of the ignition process. An estimate of the onset time of transient bimodality is carried out in terms of the size of the system, the intrinsic parameters, and the initial condition. The implications of the results in combustion are discussed. 

The start-up of methane-fueled, catalytic, channel-flow microreactors has been investigated numerically with a transient code that included full elliptic flow description, detailed hetero-Zhomogeneous chemistry, and all relevant heat transfer mechanisms in the reactor. Of particular interest were operating conditions pertinent to microturbine-based microreactor systems. Parametric studies have been carried out to identify the effect of various operations parameters, such a pressure, equivalence ratio, solid material properties and radiation properties on the transient process leading to ignition and finally to steady state operation. The following are the key conclusions of this smdy. 

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