Gas Rocket Engine
Gas rocket engine — a rocket engine, the working body of which is gas. Most gas rocket engines run on compressed gas coming from a high—pressure cylinder through a reduction gear (pneumatic rocket engines); the gas pressure is lowered from 10-40 to 0.1-1 MPa. As the gas is consumed, the thrust of the gas rocket engine decreases. Gas rocket engines on “cold” gas (with a temperature of.
20 °C) are simple and reliable in operation, but their specific impulse is small (350-700 m/s), since gases with a large molar mass (nitrogen, refrigerants, argon, krypton, neon, etc.) are used to obtain an acceptable mass of the propulsion system.
The reduction in the mass of the propulsion system is achieved by using gas rocket engines running on a vaporized working body. The initial working substance is a liquid (for example, liquefied ammonia) or a solid (for example, ammonium bicarbonate, ammonium hydrosulfide, lithium hydride), which are gasified before being fed to the rocket engine by heating from an electric, radioisotope energy source or from warmer elements of the spacecraft structure. Gas rocket engines that run on solid-state sublimation products are called sublimation rocket engines. Their advantage is that the low vapor pressure of the sublimating substance (less than 0.1 MPa) allows you to use thin-walled containers of any convenient shape for storing the working fluid. This advantage can be realized, however, only at very low thrust, typical of sublimation rocket engines (up to several N).
A gas rocket engine on a vaporized working body slightly exceeds a gas rocket engine on a “cold” gas in terms of specific impulse. This parameter can be significantly increased by additional heating of the working fluid from an electric or radioisotope energy source placed in front of the rocket engines or in the rocket engine itself (which becomes an electric or radioisotope rocket engine, respectively). When heated to 1100 K, the specific impulse of a gas rocket engine on compressed gas increases approximately twice. A slightly larger specific impulse-1500 m / s-of a gas rocket engine based on the products of the catalytic decomposition of hydrazine, in which (unlike a hydrazine liquid rocket engine) the catalyst package is placed in a separate gas generator and the gas produced first enters the receiver tank.
Schemes of propulsion systems with gas rocket engines: a-propulsion system with pneumatic rocket engines; b-propulsion system with rocket engines on a vaporized working body; c-propulsion system with sublimation rocket engines; d-propulsion system with rocket engines on the products of catalytic decomposition of liquid monopuels; d — propulsion system with rocket engines on the products of catalytic decomposition of gaseous monopuels; e-propulsion system with rocket engines on the products of water electrolysis; 1 — control valve; 2 — drainage and safety valve; 3-pressure sensor (relay); 4 — compressed gas; 5 — filling valve; 6 — filter; 7 — pressure reducer; 8 — jet nozzles (chambers); 9 — gas receiver (steam); 10 — evaporator — heater; 11-liquid fuel (working fluid); 12 — separation diaphragm; 13 — temperature — controlled throttle; 14 — sublimating solid; 15 — heat — sensitive element; 16 — catalyst; 17-electrolytic plant.
The gas rocket engines described above are essentially jet nozzles that are equipped with control valves. There are also gas rocket engines running on gaseous monofuel and two-component fuel, similar in design to liquid rocket engines . A monofuel can be a mixture of gases, for example,” Tridyne ” (Tridyne): 85% N 2, 10% H 2, 5% O 2 — by volume), reacting in the catalytic chamber of a rocket engine. The two-component fuel of a gas rocket engine can be, for example, the products of evaporation of the primary liquid oxidizer and fuel, or the products of water electrolysis (i.e., gaseous oxygen and hydrogen). Gas rocket engines with two-component fuel are comparable in specific impulse to liquid rocket engines.
The thrust of a gas rocket engine ranges from a few mN to hundreds of N, and most of them belong to rocket micro-engines. The main application of gas rocket engines is jet control systems and individual rocket propulsion systems, where they operate mainly in the pulse mode.