How a Liquid Propellant Rocket Works

The idea of liquid rocket as understood in the modern context first appears in the book “The Exploration of Cosmic Space by Means of Reaction Devices”, by Konstantin Tsiolkovsky.

Liquid Oxygen is the most common oxidizer used. Other oxidizers used in liquid propellant rockets including: hydrogen peroxide (95%, H2O2), nitric acid (HNO3), and liquid fluorine. Of these choices liquid fluorine, given a control fuel, produces the highest specific impulse (amount of thrust per unit propellant). But due to difficulties in handling this corrosive element, and due to the high temperatures it burns at, liquid fluorine is rarely used in modern liquid fueled rockets. The liquid fuels often used include: liquid hydrogen, liquid ammonia (NH3), hydrazine (N2H4), and kerosene (hydrocarbon). Most of the propellant combinations listed are dangerous, toxic, and expensive.

Liquid propellant rockets are the most powerful (in terms gross thrust) propulsion systems available. In a liquid rocket, stored fuel and stored oxidizer are pumped into a combustion chamber where they are mixed and burned. The combustion produces great amounts of exhaust gas at high temperature and pressure. The hot exhaust is passed through a nozzle which accelerates the flow. Thrust is produced according to Newton's third law of motion. The amount of thrust produced by the rocket depends on the mass flow rate through the engine, the exit velocity of the exhaust, and the pressure at the nozzle exit. All of these variables depend on the design of the nozzle. The smallest cross-sectional area of the nozzle is called the throat of the nozzle.

A cooling jacket permits the circulation of a coolant, which, in the case of flight engines is usually one of the propellants. However, for static tests and for amateur operation, water is the only coolant recommended. The cooling jacket consists of an inner and outer wall. The combustion chamber forms the inner wall and another concentric but larger cylinder provides the outer wall. The space between the walls serves as the coolant passage. The nozzle throat region usually has the highest heat transfer intensity and is, therefore, the most difficult to cool.

Control of valves during engine ignition and steady-state operation should be by remote means.

Separating of fuel and oxidizer storage reduces the fire and explosion hazard and limits the amount of propellant stowed in any one area.

Date: 2015-02-28; view: 1699