Jet Engines
What is the Jet Engine
Jet engines are types of engines that use the thrust generated by the ignition of the compressed air-fuel mixture. These engines, which are used for aircraft to fly in the air, are also called gas turbines and all turbine engines work on the same principle.
History of Early Engines
- In the 18th century, Sir Isaac Newton theorized that a rearward-channeled explosion could propel a machine forward at a great rate of speed. This theory was based on his third law of motion. As the hot air blasts backwards through the nozzle the plane moves forward.
- In mid 1800s, Henri Giffard built an airship which was powered by the first aircraft engine, a three-horse power steam engine. It was very heavy, too heavy to fly.
- In 1874, Felix de Temple, built a monoplane that flew just a short hop down a hill with the help of a coal fired steam engine.
- In 1894, American Hiram Maxim tried to power his triple biplane with two coal fired steam engines. It only flew for a few seconds.
- The early steam engines were powered by heated coal and were generally much too heavy for flight.
- American Samuel Langley made a model airplanes that were powered by steam engines. In 1896, he was successful in flying an unmanned airplane with a steam-powered engine, called the Aerodrome. It flew about 1 mile before it ran out of steam. He then tried to build a full sized plane, the Aerodrome A, with a gas powered engine. In 1903, it crashed immediately after being launched from a house boat.
- In 1903, the Wright Brothers flew, The Flyer, with a 12 horse power gas powered engine.
- From 1903, the year of the Wright Brothers first flight, to the late 1930s the gas powered reciprocating internalcombustion engine with a propeller was the sole means used to propel aircraft.
- In 1930, Frank Whittle, a British pilot, designed and patented the first turbo jet engine.The Whittle engine first flew successfully in May 1941. This engine featured a multistage compressor, and a combustion chamber, a single stage turbine and a nozzle. Picture is from The Gloster E.28/39, the first British aircraft to fly with a turbojet engine.
- At the same time Hans von Ohain was working on a similar design in Germany. The first airplane to successfully use a gas turbine engine was the German Heinkel He 178, in August, 1939. It was the world’s first turbojet powered flight.
- General Electric built the first American jet engine for the US Army Air Force jet plane . It was the XP-59A experimental aircraft that first flew in October, 1942.
- By the 1950s, the jet engine was used in combat aircraft, with the exception of cargo, liaison and other specialty types.
- By this point, some of the British designs were already cleared for civilian use, and had appeared on early models like the de Havilland Comet and Avro Canada Jetliner.
- By the 1960s, all large civilian aircraft were also jet powered. Piston engines start used in the low-cost jobs such as cargo flights.
- By the 1970s, the efficiency of piston engines still better than turbojet engines.But, with the advent of high-bypass turbofan jet engines fuel efficiency was about the same as the best piston and propeller engines.
The parts of the Jet Engine
Jet engines are generally divided into parts as follows; Fan, Compressor, Combustor, Turbine, Nozzle;
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Fan : A turbofan is the first component of the engine and has the task of sucking in the outside air. The blades of these big fans are titanium, and they divide the air they absorb into two, transmitting half of them to the engine core inside, and spraying the other half tangentially to the outside of the engine.
Compressor : The compressor, which is the first component of the engine core, has a multi-blade structure. Thanks to the shaft it is connected to, it rotates rapidly and compresses the air drawn inside by the fan. The pressure of this compressed air increases and is transferred to the next part, the combustion chamber.
Combustor : Compressed air coming into the combustion chamber mixes with the fuel through nozzles. The jet fuel sprayed from the nozzles is combusted, creating a high-energy airflow of the compressed air-fuel mixture. Since these parts of turbine engines can reach up to 2700–3000 degrees, they are produced from heat resistant ceramic material.
Turbine : The high-energy hot air coming out of the combustor section of the engine enters the turbine part of the engine core, enters the turbine blades located here, and enables the compressor shaft to rotate. This allows jet engines to spin at idle speed.
Nozzle : Nozzles are the exhaust outlet of the engine. In some engine types, warm air from the inside and cold air from the outside is combined. The combination of hot air and cold air is expelled from this nozzle and the engine is provided with thrust.
Working principle of Jet Engines
The working principle of all jet engines is the same, and the thrust force is created by burning the compressed air. In these engines, the air is sucked into the interior of the engine with the help of a fan in the front. The pressure of this air is increased with the help of a compressor in the next section.
The many blades in this compressor rotate quickly, thereby compressing the air. This compressed air is injected with fuel, the fuel is ignited by the ignition system and the high-pressure air expands by burning. In this way, the high-temperature air that gains energy is sprayed out, and the thrust direction gains a high force in the opposite direction of the spraying air.
Types of Jet Engines
Turbine Powered, Gas turbines are rotary engines and they extract energy from a flow of combustion gas. They have an upstream compressor coupled to a downstream turbine with a combustion chamber in between. In aircraft engines, those three core components are called the gas generator. There are many different variations of gas turbines but they all use a gas generator system of some type.
Turbojet:
A turbojet engine is a gas turbine engine. It works by compressing air with an inlet and a compressor mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high pressure air through a turbine and a nozzle.
The turbojet engine is a reaction engine. In a reaction engine, expanding gases push hard against the front of the engine. The turbojet sucks in air and compresses or squeezes it. The gases flow through the turbine and make it spin. These gases bounce back and shoot out of the rear of the exhaust, pushing the plane forward.
Turbofan:
Turbofans have an additional fan at the front of the engine and it accelerates air in a duct bypassing the core gas turbine engine. Turbofans are used in medium and long range flight aircrafts.
Turboprop:
A turboprop engine is a jet engine attached to a propeller. The turbine at the back is turned by the hot gases, and this turns a shaft that drives the propeller. Some small airliners and transport aircraft are powered by turboprops.
Turboshaft:
Turboshafts working principle is very similar to turboprop engines. Turboshafts are also gas-turbine engine. Turboshafts does not drive a propellor. Instead, it provides power for a helicopter rotor.
Ramjet:
The ramjet is the most simple jet engine and has no moving parts. The speed of the jet rams or forces air into the engine. Ramjets are airbreathing engines and similar to gas-turbine engines. It is simply a turbojet which rotating machinery has been skipped.
