HOW to DESIGN, BUILD and TEST SMALL LIQUID-FUEL ROCKET ENGINES

ROCKETLAB /

CHINA LAKE, CALIFORNIA

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NOTICE
ROCKETLAB cannot assume responsibility, in any manner whatsoever, for the use readers make of the information presented herein or the devices resulting therefrom.

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COVER PHOTOGRAPH
Exhaust plume from small 75-lb thrust water cooled liquidfuel rocket engine. Propellants are gaseous oxygen and methyl alcohol. Official U. S. Navy photograph.

Note: …ver más…

The chamber must also be of sufficient length to ensure complete combustion before the gases enter the nozzle. The function of the nozzle is to convert the chemicalthermal energy generated in the combustion chamber into kinetic energy. The nozzle converts the slow moving, high pressure, high temperature gas in the combustion chamber into high velocity gas of lower pressure and temperature. Since thrust is the product of mass (the amount of gas flowing through the nozzle) and velocity, a very high gas velocity is desirable. Gas velocities from on to two miles per second (5,000 to 12,000 feet per second) can be obtained in rocket nozzles. Nozzles which perform this seemingly amazing feat are called DeLaval nozzles (after their inventor) and consist of a convergent and divergent section, as shown in Figure 2. The minimum flow area between the convergent and divergent section is called the nozzle throat.

Figure 2 DeLeval Nozzle
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The flow area at the end of the divergent section is called the nozzle exit area. The nozzle is usually made long enough (or the exit area is great enough) such that the pressure in the combustion chamber is reduced at the nozzle exit to the pressure existing outside the nozzle. If the rocket engine is being fired at sea level this pressure is about 14.7 pounds per square inch (psi). If the engine is designed for operation at high altitude the exit pressure is less than 14.7 psi. The drop in