Head-End Pressure

It is evident that erosive burning occurs only in the inihal stage of combustion and diminishes about 0.5 s after ignition in each of the cases shown in Fig. 14.19 the burning pressure then returns to the designed pressure, For example, the head-end pressure reaches more than 3.5 times the designed pressure of = 5 M Pa just after ignition at L/D =16, but the pressure decreases rapidly thereafter and the propellant continues to burn at constant pressure, p,..  

Since the initial port area of the propellant grain, A, is small, the flow velocity becomes large because the velocity at the nozzle throat is always at sonic level. Furthermore, when K is kept constant. Ay and Aj increase simultaneously with in- 

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Since the specific heat raho of the combushon gas, y, lies between 1.2 and 1.4, the ratio of the discharge coefficients, Cd, j/Cd,>> is 0-80 for y = 1.2 and 0.78 for y = 1.4. This result indicates that the mass flow rate from the port exit is approximately 20 % lower than that from the isentropic nozzle exit used for a convenhonal rocket motor when the head-end pressure is equal to the chamber pressure in the rocket motor.[5]... 

Tail rods are dummy rods that protrude from the head end of the cylinder (see Figure 3-9). The purpose of the rod is to pressure-balance a piston or to stabilize a particular piston design. Because of the personnel hazard, a guard must be specified and provided. In a tandem cylinder arrangement, the outboard cylinders are driven with a rod similar to the tail rod... 

A single-acting, head end cylinder will not have load reversal if suction pressure is applied to the crank end. Similarly, if discharge pressure is applied to the head end of a single-acting, crank end cylinder, load reversal will not occur. 

Figure 12-2M. For low compression ratios, designed for 1,000 psi discharge pressure equipped with hand-operated crank and head-end fixed clearance pockets for capacity control. Air-cooled, cast semisteel, double-acting. (Used by permission Dresser-Rand Company.)...

By examining the curve for the initial compression with no unloaders, it shows that the horsepower requirement crosses the +3% overload line about one-third of the way through the suction pressure range. Figure 12-32 shows the effect of adding first one unloader and then a second one. The simplest way to handle this is a head-end unloader on each of the two parallel cylinders. 

Beyer (B8) has recently reported experimental data obtained in small test motors under atmospheric and altitude conditions. At atmospheric pressure, his results showed the observed ignition delay to be a function of the delivery rate, as shown in Fig. 10. Additional data obtained in small test motors by Fullman and Nielsen (F6) are shown for comparison. These latter investigators conducted studies on the effects of various injectors, with delivery from both the head end and the aft end. Their results indicate that the hollow-cone injector is the most efficient. This subject has been treated in more detail by Miller (M7). 

Fig. 14.19 shows a typical set of pressure versus time curves obtained from tests on a rocket motor. When the I/D ratio defined in Fig. 14.19 is increased, the head-end chamber pressure is increased drastically immediately after the ignition stage. These grains are seven-pointed-star-shaped neutral-burning grains (diameter D = 114 mm), and are made of an AP-Al-CMDB propellant with the composition nc(0-25), ng(0-31), Ita(0-08), ap(0-27), and ai(0 09). The ratio of the initial burning surface area (Ayg) to the nozzle throat area (Aj), = AygjAp and the ratio of the... 

The pressure peaks observed in the combustion tests shown in Fig. 14.19 are computed as a function of L/D as shown in Fig. 14.20. The peak pressures computed by means of the Lenoir-Robillard empirical equation are confirmed by the measured pressure at the head-end of the motor. It is evident thatp values predicted without erosive burning are significantly lower than the measured maximum pressures. Fig. 14.21 shows the erosive ratio, 8 = r/to, as a function of the mass flow rate per unit cross-sectional area in the port, G. The erosive ratio increases with increasing Mach number in the port at constant L/D. 

In hydrodynamic columns, there are spools of coiled tube that rotate on themselves and around a central axis. These combined rotations create a planetary motion with a highly variable centrifugal field that produces mixing zones followed by decanfafion zones (Figure 7.3). The stationary phase is partly retained inside the coils if fhe mobile phase is flown the right way. The coil rotation produces an Archimedean force that pushes the liquid phases toward one end of the coil called the head (higher pressure). 

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