Combustion pressure

Explosion Suppression With explosion suppression, an incipient explosion is detected and—within a few milhseconds—a suppressant is discharged into the exploding medium to stop combustion. Pressure and optical detection systems are used suppressors are pressurized and release the suppressants when actuated by an electroexplosive device. 

The assumptions made by the various authors (viz. polytropic efficiencies, combustion pressure loss and temperature ratio, etc.) are all roughly similar to those used in the calculations of uncooled dry cycles. Some modest amounts of turbine cooling were allowed in certain cases [9] but the effect of these on the efficiency should not be large at max 250°C (see later for discussion of more detailed parametric calculations by some of these authors). 

One of the significant innovations in control of pressure oscillations and supersonic mixing enhancement has been very simple, namely using nonaxisym-metric nozzles. Simple triangular, square, rectangular, and elliptic nozzles have been shown to effectively decrease combustion pressure oscillations, as well as increase supersonic mixing [7]. 

Fig. 13.21 shows another example of oscillatory burning of an RDX-AP composite propellant containing 0.40% A1 particles. The combustion pressure chosen for the burning was 4.5 MPa. The DC component trace indicates that the onset of the instability is 0.31 s after ignition, and that the instability lasts for 0.67 s. The pressure instability then suddenly ceases and the pressure returns to the designed pressure of 4.5 MPa. Close examination of the anomalous bandpass-filtered pressure traces reveals that the excited frequencies in the circular port are between 10 kHz and 30 kHz. The AC components below 10 kHz and above 30 kHz are not excited, as shown in Fig. 13.21. The frequency spectrum of the observed combustion instability is shown in Fig. 13.22. Here, the calculated frequency of the standing waves in the rocket motor is shown as a function of the inner diameter of the port and frequency. The sonic speed is assumed to be 1000 m s and I = 0.25 m. The most excited frequency is 25 kHz, followed by 18 kHz and 32 kHz. When the observed frequencies are compared with the calculated acoustic frequencies shown in Fig. 13.23, the dominant frequency is seen to be that of the first radial mode, with possible inclusion of the second and third tangential modes. The increased DC pressure between 0.31 s and 0.67 s is considered to be caused by a velocity-coupled oscillatory combustion. Such a velocity-coupled oscillation tends to induce erosive burning along the port surface. The maximum amplitude of the AC component pressure is 3.67 MPa between 20 kHz and 30 kHz. - ...

As for a rocket motor, the combustion pressure is determined by the mass balance between the mass generation rate and the mass discharge rate according to... 

Field service experience has proved that stop-leak materials cannot be depended upon to correct cylinder head joint leakage due to high combustion pressures at the joint and thermal stresses in the joint metals. 

TQ = flame temp Tj = decomposition temp AHq = heat of combustion AH = heat of explosion PQ = combustion pressure Pj = explosive pressure both at const vol... 

Efforts in LP per se have been largely restricted to improving performance by increasing the combustion pressure, and the developing and testing of exotic mono and biproplnts, such as the NF compounds and Fhiorine-NH3 and Fluorine-H2 biproplnts (See Sect 2). So far there is no mention in the open literature of the practical use of exotic proplnts (Ref 30, p 312)... 

The temperature and composition of propellant combustion products are of interest to those concerned with materials of construction and insulation for the combustion chamber and nozzle of the rocket motor. These values are readily computed from basic thermodynamic data for the specific propellant composition and operating pressure of interest with the aid of today s large-scale digital computers. By way of illustration, however, the products of combustion computed this way for the three typical plastisol propellants given in Table I are shown in Table III for a combustion pressure of 1000 p.s.i.a. Approximate propellant composition is also shown for convenient reference. 

The rates would be much lower for heavier atoms, and increase with the square of the combustion pressure. The half-life of burnup in the most rapid reactions may drop to periods as short as those of chemical fuels. Despite the high temperatures, the radiated... 

Accdg to Mr. R. Baumann of PicArsn, these compds are not catalysts, but rather "modifiers , or additives . They are incorporated into solid proplnts in order to modify or affect their combustion characteristics The compds which affect burning rate include Prussian blues, Aram dichromate, trichromate or tetrachromate, etc). Some compds may be employed to reduce the variability of burning rate with combustion pressure and temperature (Eg Pb stearate or salicylate). Other compds may be used to reduce the tendency toward oscillatory combustion(Eg A1 powder in small quantity), or to affect flash characteristics of exhaust gases [Eg KaS04, Ba(N03)2,... 

S.Nakahara T.Hikita, KogyoKayakuKyo-kaishi 20, 275-79 356-60 (1959) CA 54, 20207 (I960) (Measurements of combustion temp combustion pressure of delay powders)... 

In combustion rockets, the combustion temperature is not directly available as a design parameter but rather is determined by the propellant selection, mixture ratio and combustion pressure. In heat transfer rockets however, the initial temperature of the propellant, that is, the stagnation temperature of the propellant, is available as a design parameter. It is probably sufficient to say that the propellant stagnation temperature should be maximized for maximum performance. 

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