Turbojet Engine

Turbojet engines are the first jet engines used in aviation and are propulsion systems that operate using gas turbine technology. Their fundamental operating principle is based on compressing airflow, mixing it with fuel, igniting the mixture, and producing high-velocity exhaust gases. When these exhaust gases are expelled rearward from the engine, they propel the engine forward in accordance with Newton’s action-reaction principle. Turbojet engines are powerful thrust systems that enable aircraft to fly efficiently at high speeds and high altitudes.

The history of turbojet engines extends back to the early 20th century. The earliest principles of jet propulsion encompass an evolution spanning from ancient times to the present, but the foundations of modern turbojet engines were laid particularly in the early 1930s.

• 1930s – Initial Research: British engineer Frank Whittle and German engineer Hans von Ohain independently began developing jet engines. Whittle patented a turbojet engine in 1930 and used it in the Gloster E28/39 aircraft in the United Kingdom in 1939. During the same period, Hans von Ohain from Germany achieved the world’s first successful jet flight in 1939 with the Heinkel He-178 aircraft.
• World War II: Jet engines rapidly advanced for use primarily in military aircraft. In 1941, Germany introduced the Messerschmitt Me 262, becoming the first nation to fly a jet-powered combat aircraft. These developments solidified the importance of turbojet engines in military aviation.
• Subsequent Developments: In the 1950s, turbojet engines began to be used in commercial aircraft. However, their efficiency decreased significantly at low speeds. Nevertheless, turbojet engines delivered high speed and performance for military aircraft and supersonic flight. From the 1960s onward, the development of turbofan engines led turbojet engines to gradually be replaced by more efficient propulsion systems.

^{Turbojet Engine Schematic}

^{Subaşı Hilal, Eren Türkoğlu, Kerim Yazıcı, Sefer Çelik, and Özge Erdoğan. PID Control of the Radial Fan of a Turbojet Engine. Master's thesis, Karabük University, 2019. Advisor: Dr. Öğr. Üyesi Cihan Mızrak.}

A turbojet engine consists fundamentally of five main components:

Air Intake (Inlet): This section draws air from the atmosphere into the engine. The design of the air intake varies depending on whether the aircraft is flying subsonic or supersonic. The air intake is an important component that affects the engine’s efficiency and performance.

^{Turbojet Engine Air Intake (}Source: Freepik/jannoon028⁾

Compressor (Compressor): Air is compressed in the compressor section of the engine. Compressors are typically either axial-flow or centrifugal type. Compression increases air pressure and temperature. This stage determines the engine’s efficiency and power output.

Combustion Chamber (Combustion Chamber): The compressed air is mixed with fuel and ignited here. As a result, high-temperature and high-pressure gases are produced. These high-energy gases are directed toward the engine’s turbine section.

^{Turbojet Engine Combustion Chamber (}Source: DefenceTurk.net⁾

Turbine (Turbine): The turbine uses the high-energy gases from the combustion chamber to drive the compressor and other components. The turbine ensures the continuous operation of the engine’s cycle.

^{Turbojet Engine Turbine Section (}Source: Levtems⁾

Exhaust Nozzle (Exhaust Nozzle): Gases passing through the turbine accelerate as they exit through the nozzle, pushing against the atmosphere to generate forward thrust. The nozzle optimizes gas velocity and pressure to maximize thrust output.

^{Turbojet Engine Exhaust Nozzle Section (}

Turbojet engines first compress incoming air, then mix it with fuel and ignite it, directing the resulting gases to a turbine to generate energy. The turbine provides the necessary energy to sustain the engine’s operation. Finally, the combustion gases are expelled at high speed through the nozzle, generating thrust.

The fundamental principle of the engine is that the high-speed combustion of the fuel-air mixture releases energy that accelerates gases rearward. This rearward thrust propels the aircraft forward.

Turbojet engines are categorized into several types, each with distinct applications and performance characteristics:

1. Turbojet: This is the basic type of jet engine. Air is compressed, mixed with fuel, and ignited to produce thrust. Turbojet engines are inefficient at subsonic speeds and are typically used in military aircraft and cruise missiles.
2. Turbofan: Similar to a turbojet engine but features a large fan at the front. This fan generates additional thrust and improves engine efficiency. Turbofan engines, which are more efficient at subsonic speeds, are widely used in commercial aircraft.
3. Turboprop: This engine type uses a propeller instead of direct jet thrust. It operates on the same fundamental principle as a turbojet engine, but the exhaust gases drive a propeller to generate thrust. Turboprops are used in smaller aircraft and short-haul flights.
4. Ramjet: A ramjet is a simple jet engine with no moving parts. Air enters the engine due to the aircraft’s speed, is compressed, mixed with fuel, and ignited. However, this engine type requires a minimum speed to begin operation and is only efficient at high speeds.
5. Scramjet: A variant of the ramjet, the scramjet compresses and combusts air at supersonic speeds. These engines are suitable for hypersonic flight and achieve extremely high velocities. NASA’s X-43A, powered by a scramjet, reached record high speeds.

1. High Speed and Performance: Turbojet engines operate effectively at high speeds and are ideal for supersonic flight. They are an ideal choice for military aircraft and certain high-speed commercial aircraft.
2. Simple Design: The structure of turbojet engines is simpler than that of more complex engine types. This simplifies maintenance and repair processes.
3. High Efficiency: At high flight speeds, turbojet engines are highly efficient because thrust is generated by accelerating exhaust gases to high velocities.

1. Low Efficiency at Low Speeds: Turbojet engines are inefficient at low speeds, which is why most civilian aircraft prefer more efficient turbofan engines.
2. High Noise Levels: Turbojet engines can produce high noise levels, especially at low speeds. This is a significant environmental concern in civil aviation.
3. High Fuel Consumption: Turbojet engines consume more fuel, particularly at low speeds, increasing operational costs.
4. Long Takeoff Distance: Turbojet engines require longer takeoff distances compared to other engine types. This can be problematic at airports with short runways.

In line with its goals of domestic production and technological independence in the defense industry, Türkiye has taken several important steps in recent years. The development of turbojet engines has emerged as a significant milestone in this process. The “Development of Turbojet Engines Project,” carried out by Kale Arge and the Presidency of Defense Industries, has achieved a major success in advancing Türkiye’s indigenous missile propulsion systems.

^{KTJ-3200 Turbojet Engine (} Source: Defence Turkey⁾

The KTJ-3200, Türkiye’s first national turbojet engine, was developed by Kale Jet Engines and has been deployed in indigenous missile systems. Designed to power the ATMACA and SOM missiles, this engine is entirely produced using domestic resources. The development of the KTJ-3200 represents a significant step for Türkiye’s defense industry. Its domestic production has reduced the country’s dependence on foreign suppliers and provided a critical solution to various export restrictions.