It is a special type of heat engine that causes a forward propulsion when hot gases are exhausted from the rear of the Jet engine (Newton’s Third Law of Motion). Nowadays these engines are widely used in the manufacturing of fastest aircrafts used for both military and commercial purposes.
The Main Components of a Jet Engine are:
Intake Fan: Its function is to suck the atmospheric air and transfer it to the compressor for further processing. The blades of the fan are generally made of stainless steel, titanium or Aluminum.
Compressor: It increases the air pressure by compressing the air sucked by the intake fan. The compressed air is then forced into the combustor. The compressor is generally made of cobalt, iron or Nickel based alloys.
Combustor: In this chamber, jet fuel like kerosene is mixed with the compressed air. The air-fuel mixture is then ignited. This combustion of air-fuel mixture produces hot expanding gases. The combustion chamber is generally made of superalloys with refractory metals such as molybdenum, tungsten, tantalum, niobium, ceramics and ceramic-metal mixes.
Turbine: The hot compressed air from the combustor is passed through the turbine. The expansion of high pressure hot compressed air in the turbine causes the rotation of the turbine blades. The turbines are generally made of Nickel-based superalloy
Nozzle: It is the exhaust duct of the engine. Nozzle produces the actual thrust (Forward Force). The exhaust nozzle is generally made of stainless steel alloys, Nickel Inconel.
Afterburner: It is located just behind the turbine in the jet engine. Around one-fourth of the total air entering the jet engine is normally utilized to assist the combustion of fuel taking place within the jet engine. Afterburner consists of a series of tubes from where the fuel is sprinkled over the hot exhaust gases exiting the tubes resulting in the combustion of exhaust gases in the afterburner, providing the jet engine with the additional thrust i.e. Forward Force.
Types of JET Engines:
Turboprop: A Turboprop engine comprises of an air intake, a combustor, a compressor, a propelling nozzle and a turbine. In this type of engine, a traditional propeller is connected to the turbine of the jet engine. The Turboprop engine draws air into the intake which is further compressed using the air compressor. The mixing of fuel with compressed air takes place in the combustor followed by the combustion of the air-fuel mixture. The expansion of hot gases produced during the combustion process takes place in the turbine that results in the generation of power. These hot gases further expand in the propelling nozzle and thereafter the gases are finally exhausted at the atmospheric pressure. By using this combination a very high propeller speed could be achieved in comparison to the ordinary piston-driven propeller plane. However, these propellers are not effective at higher airspeeds. The maximum suitable range at which a turboprop airplane can fly is less than 724 Km/hr.
Ramjet: Ramjet is a simple air-breathing jet engine which has a long metal tube (cylindrical in shape and open from both sides). This cylindrical tube is designed in such a way that it is narrow at both the ends and wide in the middle. When a ramjet is driven forward at a very high speed, it produces a high-pressure region upstream. This high pressure forces the air into the tube where it gets compressed automatically. The combustion of a jet fuel like kerosene results in the heating of the compressed air. The hot gases generated are then discharged out through the nozzle exit. The engine is propelled as the exhaust gases leave the nozzle exit. A ramjet that combusts the air-fuel mixture in a supersonic airflow is called a Scramjet. Ramjets are extremely helpful in applications that require a simple mechanism for a high-speed application, like missiles. In order to boost the range of artillery shells, several weapon-designing experts have planned to assist artillery shells with the ramjet technology. For example, a mortar shell (120mm), if assisted by a ramjet, is expected to achieve a range of 35 kilometers.
Turbojet: It is a type of an airbreathing jet engine (propelled by a jet of hot exhaust gases). It comprises of a gas turbine to which a propelling nozzle is connected. In this gas turbine, there is an air inlet, a combustion chamber, a turbine and a compressor. The air is compressed in the compressor. The combustion of fuel takes place in the combustion chamber resulting in the heating of the compressed gas. The heated compressed air is then passed through the turbine where it expands and the power is generated. In slower aircrafts, turboprop has replaced turbojet because of its better range and specific fuel consumption. Also, at normal speeds, the propeller is not efficient and hence turbofans are used instead of turboprops. In comparison to the turbojet, turbofan has an even better range and specific fuel consumption. Turbojets are still common in normal range cruise missiles, because of its simplicity, high exhaust speed, and smaller frontal area.
This is a brief explanation of the Jet engine. For a better understanding of physics related concepts, students can subscribe to our Byju’s YouTube Video channel-