‘Every action has an equal and opposite reaction’ – Newton enunciated this principle long ago which is commonly known as Newton’s third law of motion. And a jet engine works on this principle. Its working can be compared to the action of a swimmer who swims forward by pushing water backwards. To put it in the Newtonian law, here the action is pushing of the water backwards and the opposite reaction is the forward movement of the swimmer. In a similar fashion a jet engine ejects (pushes backward) gases at the rear with a great speed and the resulting opposite reaction to this action is the moving of the aircraft in the forward direction in an equal speed. But where does this gas come from and how is it released with such a great force?
All jet engines have fuel inside them which when burnt in the engine produces a great amount of hot gases almost instantly. It is like an explosion. These hot gases blast out of the back with a great force and the engine reacts by being pushed forward with an equal force. This forward force is called thrust. To get an idea of this movement, we can observe the motion of an air-filled balloon when the air is released suddenly. The balloon zips away rushing out the air in one direction. The rushing out of air is responsible for pushing the balloon in the opposite direction with a thrust.
The rockets also work on the same principle. The main difference between jets and rockets is the source of oxygen to burn the fuel. A jet engine takes in oxygen from the air around it through an intake nozzle. But a rocket carries its own oxygen which may be in the form of Liquid oxygen in a tank or may be part of a solid fuel the rocket burns. The jet engines have compressors to compress or squeeze the sucked air together before it is mixed up with the fuel and burned in the combustion chamber thereafter. The compression is done to increase the force of explosion within the engine.
There are four main kinds of jet engine: turbojets, turboprops, turbofans, and ramjets. Jet engines are increasingly used in place of propeller-driven piston engines for they have several advantages. Firstly, jet engines weigh less than the piston engines. Secondly, malfunctioning occurs less in jet engines. Thirdly, their moving parts spin instead of moving to and fro which stops the shaking of the plane. Fourthly, the fuel used in jet is kerosene or cheap paraffin instead of petrol and hence cost-effective. Last but not the least is that jet engines can move the plane faster and higher than the piston engines. Some jet engines can even travel at 3400 km/h.
Going back to its history it can be said that with the first flight of a jet plane in 1939, a new era began in the history of flying. It was the culmination of the efforts of Frank Whittle, a British engineer, who had been working on the theory of jets since 1930s. And since then there have been continuous improvements in it over the years.
