Nozzle expansion ratio

When the nozzle expansion ratio becomes infinity, the pressure ratio pjpa also becomes infinity. The maximum thrust coefficient Cp then becomes... 

Igp = specific impulse, lb force-sec/lb mass = nozzle expansion ratio g = gravity constant... 

Bedload was sampled during competent flows at the same vertical than suspended sediment. Bedload analysis has been based upon 215 samples, 145 during 2002-2003 and 70 during 2003-2004. At SMS we used a 29-kg cable-suspended Helley-Smith sampler with a 76-mm intake and an expansion ratio (i.e. ratio of nozzle exit area to entrance area) of 3.22 (Fig. 2c). Bedload was measured at... 

Fig. 12.11 shows the structure of a rocket plume generated downstream of a rocket nozzle. The plume consists of a primary flame and a secondary flame.Fil The primary flame is generated by the exhaust combustion gas from the rocket motor without any effect of the ambient atmosphere. The primary flame is composed of oblique shock waves and expansion waves as a result of interaction with the ambient pressure. The structure is dependent on the expansion ratio of the nozzle, as described in Appendix C. Therefore, no diffusional mixing with ambient air occurs in the primary flame. The secondary flame is generated by mixing of the exhaust gas from the nozzle with the ambient air. The dimensions of the secondary flame are dependent not only on the combustion gas expelled from the exhaust nozzle, but also on the expansion ratio of the nozzle. A nitropolymer propellant composed of nc(0-466), ng(0-369), dep(0104), ec(0 029), and pbst(0.032) is used as a reference propellant to determine the effect of plume suppression. The burning rate characteristics of the propellants are shown in Fig. 6-31. Since the nitropolymer propellant is fuel-rich, the exhaust gas forms a combustible gaseous mixture with the ambient air. This gaseous mixture is ignited and afterburning occurs somewhat downstream of the nozzle exit. The major combustion products in the combustion chamber are CO, Hj, CO2, N2, and HjO. The fuel components are CO and H2, the mole fractions of which at the nozzle throat are co(0.47) and iH2(0.24).

Fig. 12.12 shows a typical set of flame photographs of a nitropolymer propellant treated with potassium nitrate. From top to bottom, the photographs represent KNO3 contents of 0.68%, 0.85%, 1.03%, and 1.14%. Each of these experiments was performed under the test conditions of 8.0 MPa chamber pressure and an expansion ratio of 1. Though there is little effect on the primary flame, the secondary flame is clearly reduced by the addition of the suppressant The secondary flame is completely suppressed by the addition of 1.14% KNO3. The nozzle used here is a convergent one, i. e., the nozzle exit is at the throat... 

Fig. 12.17 shows a typical set of afterburning flame photographs obtained when a nitropolymer propellant without a plume suppressant is burned in a combustion chamber and the combustion products are expelled through an exhaust nozzle into the ambient air. The physical shape of the luminous flame is altered significantly by variation of the expansion ratio of the nozzle. The temperature of the combustion products at the nozzle exit decreases and the flow velocity at the nozzle exit increases with increasing e at constant chamber pressure. 

Fig. 12.17 Flame photographs of rocket plumes, showing that the dimensions of the secondary flame decrease as the nozzle expansion area ratio is increased.

Expansion Ratio. In jet propulsion it is the ratio of die nozzle exit section area ro the nozzle throat area. In cartridge actuated device, it is the ratio of final to initial volume in a stroking type of CAD Ref Glossary of Ord (1959), 109-R... 

Fig. 12.13 shows the extent of the secondary flame zone as a function of the concentration of KNO3 at a chamber pressure of 4 MPa and with Dt = 5.0 mm with nozzle area expansion ratios of e = 6.3 and 11.7. No clear difference is seen for the different values of 8. It is evident that the zone shrinks with increasing concentration of KNO3 and thus also with increasing mass fraction of potassium atoms contained within the propellant Fig. 12.14 shows the extent of the secondary flame zone as a function of the concentration of K2SO4 at a chamber pressure of 4 MPa with D, = 5.0 mm and e = 1. Like KNO3, K2SO4 is seen to be effective as a plume sup-... 

The relation between nozzle area ratio and pressure ratios for various combustion chamber pressures, Pc. Equilibrium hydrogen, Tc = 3000°K, equilibrium expansion, vacuum ambient conditions. 130... 

Vacuum specific impulse as a function of nozzle area ratio. Hydrogen/fluorine, Pc = 1000 psia, equilibrium expansion. 130... 

Procedures for calculating the theoretical flame, or product temperature and product composition of a propellant mixture were discussed in the previous section. What remains to be analyzed is the nozzle expansion process. Since most thermochemical performance calculations are made in order to compare various propellants or propellant combinations, certain.ideal assumptions as discussed in Section n. A. are made. These ideal assumptions, however, only relate to the physical processes which actually occur in the rocket motor. As explained, normal dissipative losses such as friction and heat transfer are ignored. The gasses are assumed to enter the nozzle at zero velocity at the temperature and product composition calculated theoretically for the given mixture ratio of the propellant combination. 

Within the limitations imposed by atmospheric operation, expansion to larger expansion ratios allows conversion of additional propellant enthalpy to kinetic energy and higher performance. The employment of high expansion ratio nozzles is a necessary adjunct to the development of higher pressure combustors. 

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