Jet propulsion is based on newton’s second law and third law of motion. Newton’s second law states that the rate of change of momentum in any direction is proportional to the force acting in that direction. Newton’s third law of motion states that for every action there is an equal and opposite reaction. A type of jet engine is explained below.
A rocket does not depend upon the oxygen in the atmosphere for its operation. It carries all its supply of oxygen in addition to fuel with it.
Principles of working: In rocket engine, a large amount of gases are produced by the combustion of oxidizer and fuel. High pressure gases are created by burning the oxidizer and fuel in the combustion chamber. The gases emerge out of the exit nozzle with a supersonic velocity producing a thrust to propel the rocket.
Solid propellant rockets
In this rocket, the total mass of fuel is stored and burned within the combustion chamber. No separate fuel supply system is provided. It consists of a seamless tube made of steel. The one end of the tube is closed and the open end holds the nozzle. These rockets are classified as the following.
Restricted burning type Rocket: In this type, the propellants are burnt on only end surface and the burning of propellant takes place progressively to the other end. The burning of propellant takes place similar to that of a cigarette.
Unrestricted burning type rocket: In this type, propellant is burnt freely on all surfaces at the same time. Washers provided at the ends to prevent the ends from burning.
Nitrocellulose, ammonium nitrate, ammonium perchlorate are some of the solid propellants used in rockets.
Liquid Propellant Rockets
Liquid propellant rockets use liquid propellants. The propellants are stored in separate containers outside the combustion chamber. It consists of
· A fuel tank,
· An oxidizer tank,
· A fuel injection system,
· A combustion chamber and
· An exit nozzle.
The oxidizer and fuel are pumped into the combustion chamber. In the combustion chamber, burning of fuel and oxidizer takes place at high pressure and at high pressure, high temperature gasses are produced. These gases expand through the exit nozzle. In the nozzle, pressure energy is transformed into kinetic energy and the gases are emerging from the nozzle to the atmosphere with a very high velocity. As a result of the increased velocity of gases coming out of the nozzle, a reaction or thrust is produced in the opposite direction. This thrust propels the rocket engine.
Application of rocket engines
· Signaling and fireworks – small solid fuel rockets are used for sending distress signal from ships and signals from the ground army. They are also used for fire work display,
· Long range artillery – rockets are used in long range artillery enemy countries may be attacked by rocket assisted shells.
· Lethal weapon – naval ships and ground forces are equipped with short and long range missiles. Rocket propelled missiles are used in modern fighter aircrafts.
· Satellites – satellites are sent by rockets into outer space.
· Space ships – these are driven out of the earth with the help of rockets.
· Future expectation-rockets may be used to carry passengers from one place to another.
· JATO – jet assisted take off enables interceptor, fighters, bombers, etc. to climb vertically rapidly