Chapman-Jouguet combustion waves

HMX and RDX are heated, deflagration combustion occurs with a burning rate of about 1 mm s" at 1 MPa. However, when these nitramines are ignited by primers giving rise to shock waves, detonation combustion occurs with a burning rate of more than 7000 m s . The characteristics of combustion wave propagation are determined by the Chapman-Jouguet relationship described in Refs. [1-5]. 

From the previous classification of combustion waves, the region 0 < M <1 corresponds to deflagrations and the region M > 1 to that of detonations. Point B at which M = 1 is the Chapman-Jouguet point. It is seen from the above that detonativc combustion... 

In detonation, the temperature behind the wave is not limited to the adiabatic flame temperature, since there is an initial temperature increase across the shock besides the increase due to combustion. Figure 12 (42) presents some temperatures computed from the experimental data presented in Figure 5, assuming chemical equilibrium was attained behind the Chapman-Jouguet wave. Temperatures as high as 1200° K. greater than the adiabatic flame temperatures are thus attainable with detonation waves. 

The most important new conclusion of the theory turned out to be the fact that in front of the zone of reaction products, whose state is determined by the Chapman-Jouguet rule, there is a certain amount of initial combustible material compressed by the shock wave. In this compressed material the pressure is approximately twice as high as the final pressure. The significance of the existence of a zone of such increased pressure is obvious not only for the theory, but also for accident prevention. Many studies are devoted to experimental proof of the existence of this zone. Perhaps still the most convincing and practically useful is a paper written by Ya.B. in collaboration with S. M. Kogarko which confirmed the conception of an increased pressure zone (28). Concrete perceptions of the conditions of the chemical reaction have changed substantially (see the commentary to 28). However, Ya.B. s... 

It was shown in Section 2.2 that the downstream Mach number is unity for Chapman-Jouguet waves. When interpreted correctly, this result applies to any combustible gas mixture. However, a possible source of ambiguity for multicomponent systems is the fact that more than one sound speed a can be defined. Since there are iV - - 2 independent thermodynamic variables in an AT-component gas mixture, N parameters besides s must be specified as constants in computing dp/dp to evaluate... 

An example of calculation of a shock tube flow with combustion and detonation were presented in Ref. 5. It was found that "/i>-layer aflfects dramatically transition to detonation of the Chapman-Jouguet type. This transition occurs after formation of the p-layer, and secondary local explosion in the re on of p-layer takes place. The space-time pressure diagrams and variation of the detonation wave velocity in time are presented schematically in Fig. 2. 

Chapman-Jouguet detonation velocity (CJDV) Ideal detonation velocity that satisfies Chapman-Jouguet condition at the end of the reaction zone a gas moves at the velocity equal to the difference between the detonation velocity and the sound speed in the combustion products. CJDV in a stationary moving detonation wave is calculated from the thermodynamic equilibrium condition of the reaction products and the mass, impulse, and energy conservation laws. CJDV for typical hydrocarbon fuel + air mixtures lies in the range from 1,400 to 1,900 m/s. 

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