A jet engine is a machine that produces forward thrust by sucking in air, compressing it, mixing it with fuel, igniting the mixture, and blasting the hot exhaust gases out the back at high speed. That rearward blast of gas pushes the engine (and the aircraft attached to it) forward, a direct application of Newton’s third law: every action produces an equal and opposite reaction. It’s a beautifully simple concept that, in practice, involves extreme temperatures, precisely engineered components, and some of the most demanding material science on the planet.
How a Jet Engine Produces Thrust
The core process inside every jet engine follows four steps, known in engineering as the Brayton cycle. First, air enters the front of the engine and passes through a compressor, which squeezes it into a much smaller volume. This dramatically raises both the air’s pressure and temperature. Second, that compressed air flows into a combustion chamber where fuel is sprayed in and ignited. The burning happens at constant pressure, and the temperature spikes depending on the fuel type and how much is injected relative to the air.
Third, the superheated gas rushes through a turbine, a set of fan-like blades mounted on a shaft. As the gas pushes past these blades, it spins the turbine, which is connected back to the compressor at the front. This is what keeps the compressor running without an external power source: the engine sustains itself once started. Fourth, the exhaust gas accelerates through a narrowing nozzle at the rear, converting heat and pressure into a high-speed jet of gas. The force of that gas shooting backward is what pushes the airplane forward.
The amount of thrust depends on two things: how much air moves through the engine per second and how fast it exits. A larger mass of slower-moving air can produce the same thrust as a smaller mass of very fast air, and this tradeoff is central to why different types of jet engines exist.
Key Components Inside the Engine
The compressor is the workhorse at the front. Most large jet engines use axial compressors, where air flows parallel to the engine’s central shaft through alternating rows of spinning and stationary blades. Each row squeezes the air a bit more, and a modern engine may have a dozen or more stages stacked in sequence. Axial compressors are compact and lightweight for the amount of compression they deliver, which is why they dominate commercial aviation. Smaller engines, particularly those on business jets or helicopters, sometimes use centrifugal compressors instead, which fling air outward from a spinning disc to build pressure. These are simpler but bulkier for the same airflow.
The combustion chamber sits between the compressor and turbine. Fuel injectors spray a fine mist of kerosene into the compressed air, and the mixture burns continuously once ignited. Temperatures here can exceed 2,400°F, which creates an engineering challenge: the metal and ceramic parts surrounding the flame must survive conditions that would melt most materials.
The turbine section extracts energy from the hot gas to drive the compressor (and, in some designs, a fan or propeller). Turbine blades operate in the hottest part of the engine and are typically made from nickel-based superalloys, often with tiny internal channels that pipe cooler air across the blade surfaces. Newer engines are introducing ceramic matrix composites, materials made of ceramic fibers embedded in a ceramic shell. These can withstand temperatures 300 to 400°F hotter than metal alloys, reducing the need for cooling air. The LEAP engine, one of the most widely used commercial engines today, uses a ceramic composite turbine shroud that operates at up to 2,400°F. That reduced cooling demand is part of a package of technologies that cut fuel consumption by 15 percent compared to the previous generation.
Types of Jet Engines
Turbojets
The turbojet is the original design. All the air entering the engine passes through the compressor, combustion chamber, and turbine before exiting as exhaust. This makes turbojets efficient at very high speeds but noisy and fuel-hungry at the lower speeds where most flying happens. They powered early jet fighters and airliners but have largely been replaced in both roles.
Turbofans
The turbofan is what powers nearly every commercial airplane flying today. It adds a large fan at the front of the engine that moves a huge volume of air around the core, bypassing the combustion process entirely. This bypass air still produces thrust, just at a lower velocity. The ratio of air going around the core versus through it is called the bypass ratio, and higher ratios generally mean better fuel efficiency and less noise. A modern airliner engine might have a bypass ratio of 10:1 or higher, meaning ten times more air flows around the core than through it. These engines cruise most efficiently between Mach 0.7 and 0.85, the typical speed range for commercial flights.
Military fighter jets use a different flavor: low-bypass turbofans with bypass ratios between 0.3 and 0.9. These sacrifice fuel efficiency for the ability to produce enormous thrust, especially when equipped with afterburners that inject extra fuel into the exhaust stream for short bursts of power. This is what allows fighters to go supersonic.
Turboprops
A turboprop uses its turbine to spin a conventional propeller through a gearbox. About 95 percent of the thrust comes from the propeller, with only 5 percent from the residual exhaust. This is effectively a jet engine with an extremely high bypass ratio, and it’s very fuel-efficient at lower speeds, typically up to about Mach 0.6. Regional airlines flying shorter routes at lower altitudes rely heavily on turboprops because the fuel savings outweigh the speed penalty.
What Fuels a Jet Engine
Commercial jets burn kerosene-based fuels, most commonly Jet A or Jet A-1. These fuels pack about 43 megajoules of energy per kilogram, roughly 40 percent more energy density than car gasoline by weight. Jet A-1 has a freezing point of minus 47°C (minus 53°F), which matters because fuel in wing tanks can get extremely cold at cruising altitude. The global average for commercial jet fuel actually freezes even lower, around minus 52°C, because refineries tend to exceed the minimum specification.
Kerosene was chosen decades ago for good reasons: it’s energy-dense, relatively stable, and liquid at a wide range of temperatures. But burning it produces carbon dioxide, and aviation accounts for roughly 2 to 3 percent of global CO₂ emissions. This is driving interest in alternative fuels, including hydrogen.
Hydrogen and the Next Generation
Hydrogen burns much faster than kerosene and produces more compact flames, which changes how a combustion chamber needs to be designed. Engineers at ETH Zurich and GE Aerospace are currently testing hydrogen injection nozzles as part of an EU-funded project called HYDEA. One of the trickiest challenges is thermoacoustic vibration: the interaction between sound waves and flame inside the combustion chamber. Kerosene engines took years to get these vibrations under control, and switching to hydrogen resets that problem because the fuel’s burning characteristics change how sound and flame interact.
Meanwhile, the open fan design being developed under the CFM RISE program represents a nearer-term leap. These engines eliminate the enclosed casing around the fan, essentially creating a visible set of large spinning blades on the outside of the engine. The goal is to cut fuel consumption and CO₂ emissions by more than 20 percent compared to today’s best engines. The main engineering hurdle is noise: without a duct to contain sound, the larger rotor blades are inherently louder, and the design must still meet certification requirements. Airbus and CFM are running wind tunnel tests on a demonstrator to study how the open fan interacts with the wing’s aerodynamics and how to manage its acoustic footprint.
A Brief Origin Story
The jet engine was invented independently and almost simultaneously in Britain and Germany in the late 1930s. Frank Whittle, a Royal Air Force officer, patented his design in 1930 and spent nearly a decade refining it. His W.1X engine produced 1,240 pounds of thrust at full speed. In Germany, Hans von Ohain developed a separate design that powered the Heinkel He 178, which made the world’s first jet-powered flight on August 27, 1939. Whittle’s engine flew two years later in the Gloster E.28/39. Within a decade, jet engines had transformed both military and commercial aviation, and the basic architecture those two inventors established remains recognizable in every jet engine flying today.