Ignition process

The initial conditions vary with time because the physicochemical process of ignition varies according to the ignition energy supplied to the ignition surface of the energetic material. A typical example of a radiative ignition process is shown below  

and 3 -are the surface temperatures at t , tg, and tp respectively. During the time tp t tjs, ignition is completed, combustion occurs without external heating, the surface temperature reaches T, and the bunting rate attains a steady-state value with regression velocity at t, Fig. 13.4 shows a schematic diagram of the ignition process expressed by Eqs. (13.17)-(13.21). 

Real ignition processes are rather complicated and heterogeneous because igniters contain various types of metal particles and crystalline oxidizer particles. The metal particles are oxidized by the gaseous oxidizer fragments and produce high- 

When heat is transferred to a gaseous mixture of oxidizer and fuel components, i.e., a premixed gas, an exothermic reaction occurs and temperature increases. The reaction continues and proceeds into the non-reacted portion of the mixture even after the heat is removed. The amount of heat transferred to the mixture is defined to be the ignition energy. However, when the reaction is terminated after the heat is removed, ignition of the mixture has failed. This is because the heat generated in the combustion zone is not enough to heat up the unreacted portion of the mixture from the initial temperature to the ignition temperature. 

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From these many considerations, the propellant formulator is often faced with preparing a propellant with rather precise 7sp and burning-rate characteristics. As a result, there is considerable interest in understanding the basic propellant combustion and ignition processes and in developing the capability to prepare from theory propellants with the desired burning-rate and 7sp characteristics. 

The results of the studies.discussed in Section II,C permit calculations to be made of the time required for the flame to spread to the entire propellant surface. Once this phase of the motor-ignition process has been completed, the time required to fill the combustion chamber and establish the steady-state operating conditions must be computed. This can be done by the formal solution of Eq. (7). Because this equation is a Bernoulli type of nonlinear equation, the formal solution becomes... 

Kadota, S., et al.. Numerical analysis of spark ignition process in a quiescent methane-air mixture with ion-molecule reactions. The 2nd Asia-Pacific Conference on Combustion, p. 617, 1999. 

Nakaya, S., et al., A numerical study on early stage of flame kernel development in spark ignition process for methane/air combustible mixtures, Trans. Jpn. Soc. Mech. Eng.(B), 73-732, 1745,2007 (in Japanese). 

Side view of the ignition process in an SCSI engine showing the spark arc and early flame development. 

Aqueous cyanide effluent containing a little methanol in a 2 m3 open tank was being treated to destroy cyanide by oxidation to cyanate with hydrogen peroxide in the presence of copper sulfate as catalyst. The tank was located in a booth with doors. Addition of copper sulfate (1 g/1) was followed by the peroxide solution (27 1 of 35 wt%), and after the addition was complete an explosion blew off the doors of the booth. This was attributed to formation of a methanol vapour-oxygen mixture above the liquid surface, followed by spontaneous ignition. It seems remotely possible that unstable methyl hydroperoxide may have been involved in the ignition process. 

The ignition process for FRC materials can be described in terms of the relationship between time to ignition and heat flux. A technique developed by FMRC using its Small-Scale Flammability Apparatus (2-6) was used for the quantification. 

Zhong H-H, Zhou X-L, Liu X-Q, and Meng G-Y. Synthesis and electrical conductivity of perovskite Gd1 ICaICr03 (0Sx 0.3) by auto-ignition process. Solid State Ionics 2005 176 1057—1061. 

It is obvious, then, that only the H2—Cl2 reaction can be exploded photo-chemically, that is, at low temperatures. The H2—Br2 and H2—12 systems can support only thermal (high-temperature) explosions. A thermal explosion occurs when a chemical system undergoes an exothermic reaction during which insufficient heat is removed from the system so that the reaction process becomes selfheating. Since the rate of reaction, and hence the rate of heat release, increases exponentially with temperature, the reaction rapidly runs away that is, the system explodes. This phenomenon is the same as that involved in ignition processes and is treated in detail in the chapter on thermal ignition (Chapter 7). 

In many practical systems, one cannot distinguish the two stages in the ignition process since To> t, thus the time that one measures is predominantly the chemical induction period. Any errors in correlating experimental ignition data in this low-temperature regime are due to small changes in rt. 

The ignition process was modeled as an energy release in a relatively small volume inside the vessel with the power as a given function of time. 

Fig. 12.7 Light attenuation and pressure profile of the ignition process of a micro-rocket motor with the BK igniter.

Since initiation of the decomposition is dependent on the heat flux supplied by the high-temperature gas flow, the ignition process is dependent on the various gas-flow parameters, such as temperature, flow velocity, pressure, and the physicochemical properties of the gas. 

When the ignition process occurs under conditions of constant pressure, the momentum equation is expressed by... 

Equations (13.7)-(13.13) are used to evaluate the ignition processes of energetic materials with appropriate initial and boundary conditions. In general, the conditions in the thermal field for ignition are given by... 

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