Detonation wave time profile

The laser interferometry technique is widely used for the study of the detonation wave time profile and structure due to its exceptionally good time resolution. The laser interferometry operating principle is based on the Doppler effect. The technique records the position and time dependence of the interferometric fields obtained due to the Doppler shift in wavelength of the reflected laser beam, resulting from the thin metal shim motion. The metal shim, 15-25 pm thick, is placed between the explosive charge and windows that are made of an inert optically transparent material, such as water, lithium fluoride, or polymethylmethacrylate. On the basis of the velocity of the explosive/metal shim interface as a function of time, it is possible to calculate the values of detonation parameters of the explosive (Gimenez et al., 1985, 1989 Hemsing, 1985 Leeetal., 1985). 

The induction time data and density profiles pf detonations in oxy-hydrogen and oxy-methane mixtures were analyzed on the basis of the kinetic data obtained by the reflected-wave technique and similar methods. A plot of the ignition delay vs 1/T in oxy-ammonia mixtures gave a straight line with a slope corresponding to an activation energy of 42.5 kcal/mole. In these mixtures the induction zone is not uniform, but the shock front is flat and end of the reaction zone is clearly discernible. Onedimensional detonation waves of low Mach number but relatively stable were obtained in a gas preheated to 600-1800°K ahead of the shock front... 

According to the ZND model of detonation, a steady-state plane detonation wave has the pressure-time profile shown in Figure 4.32. 

Figure 4.32. Pressure-time profile for the steady-state detonation wave...

The advant e of such continuous viewing of the flow of the detonation products lies in the possibility of observing the positions of the wiiole metal foil as a function of time. The smaller mass of a single foil (compared with several foils in the case of the previously described test) and the pc ibility of recording the detonation products flow vs. the time profile behind the ctetonation wave front enable the stu[Pg.144]

The dependence of the pressure wave profile on the HAM volume (Fig. 9.7) and the unavoidable transition from the compression phase to the rarefaction phase attract attention. For defiagration, the pressure wave amplitude depends on the HAM cloud linear dimensions, in the near zone it is ten times less than for detonation (Fig. 9.8). The reduced impulse value is less than that of the detonation and it is practically the same for different volumes. Such a result is important for expert assessments of targets behavior depending on a HAM explosion type. Assessments of the effects based only on a pressure amplitude level might contain subjective errors. 

---