How a Jet Engine Works

This is a picture of how the air flows through a jet engine.
Jet engines move the airplane forward with a great force that is produced by a tremendous thrust and causes the plane to fly very fast.

All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in at the front with a fan. A compressor raises the pressure of the air. The compressor is made up of fans with many blades and attached to a shaft. The blades compress the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward.

The image above shows how the air flows through the engine. The air goes through the core of the engine as well as around the core. This causes some of the air to be very hot and some to be cooler. The cooler air then mixes with the hot air at the engine exit area.

A jet engine operates on the application of Sir Isaac Newton's third law of physics: for every action there is an equal and opposite reaction. This is called thrust. This law is demonstrated in simple terms by releasing an inflated balloon and watching the escaping air propel the balloon in the opposite direction. In the basic turbojet engine, air enters the front intake and is compressed, then forced into combustion chambers where fuel is sprayed into it and the mixture is ignited. Gases which form expand rapidly and are exhausted through the rear of the combustion chambers. These gases exert equal force in all directions, providing forward thrust as they escape to the rear. As the gases leave the engine, they pass through a fan-like set of blades (turbine) which rotates the turbine shaft. This shaft, in turn, rotates the compressor, thereby bringing in a fresh supply of air through the intake. Engine thrust may be increased by the addition of an afterburner section in which extra fuel is sprayed into the exhausting gases which burn to give the added thrust. At approximately 400 mph, one pound of thrust equals one horsepower, but at higher speeds this ratio increases and a pound of thrust is greater than one horsepower. At speeds of less than 400 mph, this ratio decreases.

In a turboprop engine, the exhaust gases are also used to rotate a propeller attached to the turbine shaft for increased fuel economy at lower altitudes. A turbofan engine incorporates a fan to produce additional thrust, supplementing that created by the basic turbojet engine, for greater efficiency at high altitudes. The advantages of jet engines over piston engines include lighter weight with greater power, simpler construction and maintenance with fewer moving parts, and efficient operation with cheaper fuel.

How Rotary Engines Work

A rotary engine is an internal combustion engine, like the engine in your car, but it works in a completely different way than the conventional piston engine.

In a piston engine, the same volume of space (the cylinder) alternately does four different jobs -- intake, compression, combustion and exhaust. A rotary engine does these sam­e four jobs, but each one happens in its own part of the housing. It's kind of like having a dedicated cylinder for each of the four jobs, with the piston moving continually from one to the next.

The rotary engine (originally conceived and developed by Dr. Felix Wankel) is sometimes called a Wankel engine, or Wankel rotary engine.

In this article, we'll learn how a rotary engine works. Let's start with the basic principles at work.­

Inside Engines

Here at HowStuffWorks we have hundreds of articles on a wide variety of topics; each article is grouped together in one of ten super-categories or, as we like to call them -- channels. You can find out all about computers and related technology on the ComputerStuff channel. For information about everything from installing hardwood flooring to learning how your refrigerator works, you can check out the HomeStuff channel. For all of you that find anything from rip currents to radar fascinating, you can find it on the ScienceStuff channel. And, so on ...

Out of all these channels and articles, though, there are a some things that really resonate with our readers. It turns out you're totally revved-up by all sorts of engines! This "Inside Engines" page takes you straight to the power.

How Car Engines Work
It's the reason you can put the pedal to the metal and go from zero to 60 in about 8 seconds. The car engine is a piece of engineering genius and one of the most amazing machines we use on a daily basis. Learn how the four-stroke internal combustion engine works.

How Diesel Engines Work
Ever wonder what the difference is between a gasoline engine and a diesel engine? Diesels are more efficient and cheaper to run than gasoline engines. Instead of using carburetion or port fuel injection, diesel engines use direct fuel injection. Find out what else makes diesel engines different!

How Diesel Two-Stroke Engines Work
A two-stroke engine has the potential to produce twice as much power as a four-stroke engine of the same size. And, diesel, rather than gasoline, is a much better match with the two-stroke cycle. So, take diesel-engine technology, throw in a two-stroke cycle and you've got the basis for the huge engines found in trains and big ships. Learn about the diesel two-stroke engine!

How HEMI Engines Work
The HEMI engine has an awesome design and great performance, and it's pretty unique in operation. With the revitalization of the HEMI in the 2003 Dodge trucks, industry and consumer attention is once again on this interesting configuration. Check out how the HEMI works and see what makes it different from the typical engine design.

How Rotary Engines Work
A rotary engine is an internal combustion engine, but it's not like the one in most cars. Also called a Wankel engine, this type of engine performs intake, compression, combustion and exhaust in a different part of the housing. Learn about the unique rotary setup and how it compares performance-wise to a piston engine.

How Gas Turbine Engines Work
Ever wonder what's happening inside that huge jet engine as you're cruising along at 30,000 feet? Commercial jets aren't the only machines that use gas turbine engines; they're used in all kinds of unexpected places. For example, many of the helicopters you see, a lot of smaller power plants and even the M-1 Tank use gas turbines. Find out how gas turbine engines work.

How Radial Engines Work
Radial engines reached their zenith during WWII. But today they are not that common. One place where you can still see the radial engine's influence is in the two-cylinder engine of a Harley-Davidson motorcycle. This remarkable engine can be thought of, in a way, as two pistons from a radial engine. Find out about radial engines.

How Quasiturbine Engines Work
The quasiturbine engine takes the Wankel concept and improves on it: Instead of three combustion chambers, it has four, and the setup of a quasiturbine allows for continual combustion. That means greater efficiency than any other engine in its class. Learn about the quasiturbine and why it might be the most promising internal combustion engine yet.

How Steam Engines Work
Steam engines were the first engine type to see widespread use. They powered all early locomotives, steam boats and factories. It can be said that they powered the Industrial Revolution. Learn how the steam engine produces power.

How Two-Stroke Engines Work
What do leaf blowers, chain saws, dirt bikes, mopeds and jet skis all have in common? Two-stroke engines, of course! A car engine uses a four-stroke cycle -- how can two strokes accomplish the same tasks? Learn all about the two-stroke engine and how it compares to a four-stroke.

How Rocket Engines Work
One of the most amazing endeavors man has ever undertaken is the exploration of space. The hardest part of space exploration is getting a spaceship off the ground. Explore the basics of propulsion and learn about both solid-fuel and liquid-fuel rocket engines.

How Stirling Engines Work
Right now, stirling engines are used only in some very specialized applications, like in submarines or auxiliary power generators for yachts, where quiet operation is important. But it may have some new, high-tech uses; a few very high-power inventors are working on it. Learn about this unusual heat engine!

How NASCAR Engines Work
The original NASCAR races were run on dirt tracks in regular street cars. Today, almost every piece of a NASCAR race car is handmade. Get a behind-the-scenes look (with lots of photos and videos!) at how these amazing machines come together.

How Champ Car Engines Work
Champ Cars have carbon fiber bodies, 900-horsepower engines and top speeds of over 230 mph. With the help of the Motorola PacWest Racing Team and CART, go behind the scenes to learn about the car, its engine and the team and driver.

How an Atkinson Cycle Engine Works

For over a hundred years, engines got bigger, faster, and meaner, with more horsepower and torque. Exhaust belched from the tailpipes like a dragon awoken from its slumber to roar at potential thieves of its treasure. At least, that's what the guy with the wide tires and the airbrushed flame job wants you to think.
Then came the twentieth century, when we realized that fire-breathing engines were slaying more than red-light drag racing opponents. Turns out, all that belching was changing the climate and creating nasty smog. Too many dragons were making the planet more like Mordor than the Shire.

Who can save us from these exhaust-belching dragons? Who can tame their gas-guzzling ways with his sword of science and engineering? Who carries the one true ring of fuel efficiency? One man: James Atkinson of Hampstead, Middlesex, England. Also of 1887.

That's right -- the latest in green engine technology comes from the dawn of the automotive age. The Atkinson cycle engine was patented in the United States in 1887 (Atkinson filed for U.K. and European patents a couple years earlier). But the uneven strokes of the piston in his gasoline-powered combustion engine fit our modern hybrid systems pretty neatly.

The Atkinson cycle engine used in so many hybrids these days works on the same principle as the original -- with the obvious advantage of a century of technological advances. But in order to understand where we're at today, we first have to know where we've been. Set your time machine for 1887!

How Sleeve-valve Engines Work

During World War II, engineers within the Nazi regime devised some of the best and most-advanced aerial weaponry of the era. One German fighter plane, the Focke-Wulf Fw 190, for a time outperformed anything the Allies could put in the air.
Fortunately for the Allies, engineering on their side eventually swung the air superiority pendulum to their advantage. A rugged, unconventional engine that many people today have probably never even heard of helped to neutralize the Fw 190 and the rest of the Luftwaffe. In its own way, an engine helped propel the Allies to victory [source: Rickard].
The sleeve-valve engine, which has been used on both automobiles and airplanes, powered speedy British fighters such as the Hawker Typhoon and Hawker Tempest. With their brute horsepower, they helped the Allies control the skies, provide air support for ground forces and eventually win the war.

But what exactly is a sleeve-valve engine, and what's with the funny name? And why don't we see or hear much about them today?
The engine gets its name from the thin-walled, metal sleeve that slides up and down within each cylinder during the combustion process. Typically, holes in the sleeve and in the cylinder containing it line up at predictable intervals to expel exhaust gases and suck in fresh air.

Despite its honorable armed services record, the complex sleeve valve setup lost out to what we use in internal combustion engines today, tappet valves. In airplanes, of course, piston-driven powerplants of all types largely gave way to jet engines.

But hold on -- don't dismiss the sleeve valve as a useless historical relic just yet.
At least one company is seeking to bring the venerable sleeve valve engine back into action, but with a few modern twists.

In the next few pages, we'll take a look at just what makes the sleeve-valve engine turn. We'll also examine why it fell out of favor, along with the reasons it's being called up now, more than a century after its invention, to serve in a different kind of "fight."