Thrust, rocket engine

Manned space flight began with the Air Force X-1 airplane, which, like the V-2, was propelled with alcohol and liquid oxygen. The X-1 was the first aircraft in the world to break the sound barrier. The later and more advanced X-15, which was provided with a 254 kN (57,000 Ibf) thrust rocket engine, achieved speeds of over 2km/s (4500 mph)—and altitudes of over 108 km (67 miles) above the earth, or 27 km beyond the arbitrary boundary of space. 

Rocket Engine. A non-airbreathing reaction propulsion device that consists essentially of an injector, thrust chambers) and exhaust nozzle(s), and utilizes liquid fuels and oxidizers at controlled rates from which hot gases are generated by combustion and expanded thru a nozzle(s) (Ref 40a, p 125)... 

The general term for an auxiliary rocket engine specifically used for providing extra thrust to a heavily-loaded aircraft during... 

Choking. A common expression for use of the constricted nozzle(, choke ) to control the flow of gas from a rocket engine thrust chamber by building up pressure inside the chamber until the upper limit of mass flow is reached, or when the speed of sound is reached in the duct... 

From this expression it is seen that the thrust does not depend at all on the combustion temperature Tr. but depends mainly on the dimensions of A , and A . and on the chamber pressure I. . In other words, the thrust that a rocket motor develops does not depend upon the particular choice of propellants, but upon the chamber pressure. The designer controls the pressure level of operation by the amount of propellants choSen to be injected. In fact, if it were not for the slight dependence of y on the combustion products, then the thrust level of a rocket engine could be considered entirely independent of the propellants used. 

Applications. To date, the liquid propellant systems used in chemical propulsion range from a small trajectory control thruster with only 0.2 lbf (0.89 N) thrust for orbital station-keeping to large booster rocket engines with over l. 0 million lbf (4.44 MN) thrust. Bipropellant propulsion systems are the most extensively used type today for... 

Small-orifice injectors are used to atomize and mix the liquid propellants in appropriate proportions. The propellants enter the thrust chamber through the injection manifold and bum inside the thrust chamber. A typical liquid bipropellant rocket engine is shown in Fig. 37.20. 

A more detailed description to derive the thrust or the specific impulse of a rocket is given below In order to propel a rocket, a rocket engine ejects combustion gases with low molecular mass but high velocity z through the nozzle. The rocket has the mass M and initially moves with velocity u. If the rocket ejects combustion gases of the mass of Am within the time At and with the velocity 2 , a decrease in mass M - Am and an increase in the velocity to u + Au results. Due to the conservation of the impulse, the following can be derived ... 

The high temperature gas generated in the combustion chamber of a rocket engine is expanded through a De Laval nozzle to convert a major portion of the enthalpy to mechanical thrust. The thrust F of a rocket engine is defined by the following conservation of momentum equation ... 

Near-equilibrium flow conditions generally yield the maximum thrust for rocket propulsion, because partial recombination of the dissociated atoms, as the temperature falls, releases additional kinetic energy. On the other hand, when the rocket engine is considered for high temperature chemical processing, it is invariably desirable to freeze the composition attained in the combustion chamber. From both theoretical and practical standpoints, it is not always possible to predetermine the flow conditions in the De Laval nozzle as the foregoing discussion indicates,... 

Because of the large number of gaseous molecules produced and the exothermic nature of this reaction, a very high thrust per mass of fuel is achieved. The reaction is also self-starting—it begins immediately when the fuels are mixed—which is a useful property for rocket engines that must be started and stopped frequently. 

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