This article was automatically translated from the original Turkish version.
A jet engine is a type of internal combustion engine based fundamentally on Newton’s third movement law, or the action-reaction principle. These engines burn fuel using oxygen drawn from the air and expel the resulting high-temperature, high-pressure gases rapidly from the rear, thereby generating thrust that propels the attached vehicle forward.
Jet engines are also known as reaction engines or gas turbines. In their simplest definition, they operate on the principle of “compressing atmospheric air, mixing it with fuel, igniting the mixture, and ejecting the resulting gases at high velocity to produce thrust in the opposite direction.” This power enables the jet engine to accelerate the aircraft forward.
Jet engines are regarded as one of the most significant inventions in aviation history. Developed since the 1930s, they have become iconic technologies symbolizing power and speed. These engines made the modernization of aircraft possible; jet aircraft, missiles, unmanned aerial vehicles (UAVs), model rockets, rocket engines, and even some high fast black vehicles have employed them. They are also used in industrial gas turbines and the maritime sector.
Jet engines are systems used in both military and civil aviation, enabling powerful, fast, and efficient flight at high altitudes. They are known for being highly complex from an engineering standpoint yet based on a simple and effective principle.
The history of the jet engine is a technological development process extending far beyond the 20th century. The origins of systems operating on gas reaction date back to the Chinese use of fireworks around 3000 BCE. The “aeolipile,” a spherical device developed by Hero of Alexandria in 250 CE, in which steam exiting curved pipes caused rotation, is considered the first mechanical device to operate on gas reaction. In 1232 CE, the Chinese used gas-reactive rockets as weapons during the Battle of Kaifengfu.
Frank Whittle obtained a patent in 1930 for his gas turbine-based engine design. In 1936, he founded the company “Power Jets Ltd.” to begin development. The first engine test was conducted in 1937. Initial technical problems were encountered; however, these were resolved by 1938. The first jet aircraft, the Gloster E-28/39, developed with support from the British government, was flown on 15 May 1941 using the Power Jets W.1 engine. Whittle was awarded the title “Sir” in 1948 for this invention.
Hans von Ohain began his turbojet on research while earning his doctorate at the University of Göttingen in Germany. In 1937, he tested the first prototype powered by hydrogen fuel and achieved successful results. These developments attracted the attention of Ernst Heinkel, who supported the development of the “He S-3” engine for the Heinkel He 178 airplane. On 27 August 1939, this jet-powered aircraft, piloted by Erich Warsitz, completed the world’s first jet-powered flight.
The brief history of jet engines can be summarized as follows:
Jet engines operate according to Newton’s third law of motion, known as the action-reaction principle. This law is expressed as: “For every action, there is an equal and opposite reaction.” In jet engines, this principle is realized when high-pressure hot gases expelled from the rear of the engine push the engine—and thus the aircraft—forward.
The basic operating cycle of a jet engine proceeds through the following steps:
1. Air Inlet: Air entering the engine through the intake at the front of the aircraft is directed through specially shaped inlet ducts designed for subsonic or supersonic flight conditions.
2. Compressor: Air is compressed by rotating disks and blades made of high-strength titanium like materials mounted on the engine shaft. This compression reduces the air’s volume while increasing its pressure and temperature. In Modern jet engines, the compression ratio can reach up to 40:1.
3. Combustion Chamber: High-pressure, high-temperature air enters the combustion chamber. Here, it is mixed with fuel and ignited via spark plugs. The resulting combustion dramatically increases the gas’s temperature and energy.
4. Turbine: High-pressure, high-temperature gases are directed toward the turbine. Turbine, the turbine uses this energy to rotate and drive the compressor and inlet fan via the connected mile.
5. Exhaust and Nozzle: Gases exiting the turbine pass through the exhaust pipe and are ejected at high velocity through the nozzle, generating forward thrust. In some engines, an afterburner (reheat section) is used to increase thrust by injecting additional fuel into the exhaust stream.
This cycle repeats continuously while the engine is operating, ensuring uninterrupted thrust production.
Fuels used in jet engines are typically kerosene-based kerosene and formulated to have a high flash point and low volatility. The main fuel types are:
Each jet engine type and mission profile is designed to operate at maximum efficiency with a specific fuel type. Fuel measurements are typically made in pounds (lb).
Jet engines are complex yet effective systems requiring the coordinated operation of numerous subsystems, from fan geometry and combustion chamber design to turbine blade orientation and exhaust shape.
Jet engines are classified into different types based on their building and operating principles. Fundamentally, these engines are divided into “turbo” and “jet” categories according to whether they contain rotating components.
Turbojet engines are the simplest and earliest developed type of jet engine. In these engines, air is drawn in from the front, compressed by the compressor, mixed with fuel and ignited in the combustion chamber, and then expelled through the nozzle after passing through the turbine. The turbine drives the compressor to sustain continuous operation. Turbojets are efficient at high speeds but suffer from disadvantages such as high fuel consumption, excessive noise, and poor efficiency at low speeds. Today, they are primarily used in military aircraft and missiles.
Turbofan engines are developed by adding a large fan to the turbojet system. This fan at the inlet divides the airflow: part passes through the engine core, while the remainder bypasses the core. This bypass air is also expelled at high velocity, providing additional thrust. Turbofan engines operate more quietly, consume less fuel, and are suitable for long-range, subsonic flight. They are the most common used jet engine type in civil aviation today.
Turboprop engines have a core similar to a turbojet but direct most of the energy from the turbine to drive a propeller. This propeller operates efficiently at low speeds. Fuel efficiency is high at speeds below 800 km/h. They are commonly used in regional passenger aircraft, training aircraft, and military cargo aircraft. The first turboprop engine was developed by Gyorgy Jendrassik in 1938.
Turboshaft engines operate on a principle similar to turboprops; however, their purpose is not thrust but mechanical power generation. The generated power is typically transferred to a helicopter rotor or a generator. The power shaft rotates via a gearbox driven by energy from the turbine. Rotor speed can be regulated independent from the gas generator. This is the most common engine type used in helicopters.
Ramjet engines are the simplest type of jet engine and contain no moving piece. They can operate only while moving forward at sufficient speed to compress incoming air. Therefore, they require an external booster for takeoff. Ramjet engines are preferred in pre-accelerated systems such as guided missiles and hypersonic platforms. While effective at high speeds, they cannot operate at low speeds or when stationary.
Scramjet engines are an advanced version of the ramjet system. Their most important difference is that combustion occurs at supersonic speeds. Like ramjets, they require the aircraft’s speed to compress air and can operate at very high speeds (Mach 5 and above). They have been used in hypersonic flight projects such as NASA’s X-43A. They contain very few moving parts.
Pulsejet engines are simple jet engines that operate through periodic explosive pulses. They come in valved and valveless variants. Their first applications were in German V-1 missiles during World War II. Their construction is very simple, and some models can operate statically. Due to their ease of operation with combustible gases and low cost, they are sometimes preferred in experimental projects or simple UAVs.
Each of these jet engine types has been developed to meet specific requirements of altitude, speed, efficiency, and purpose. Today, most passenger aircraft use turbofan engines, military aircraft use turbojet and turbofan engines, helicopters use turboshaft engines, and missiles use ramjet and scramjet engines.
History of the Jet Engine
Principle of Operation of the Jet Engine
Main Components of a Jet Engine
Fuels Used in Jet Engines
Types of Jet Engines
Turbojet
Turbofan
Turboprop
Turboshaft
Ramjet
Scramjet (Supersonic Combustion Ramjet)
Pulsejet