How jet engines work

Pratt & Whitney's web site has a simple tutorial about how jet engines work. Also, its web site recounts the company's long history in airplane engine design and manufacturing.
Written by John Dodge, Contributor on

Today's new family of GE GenX engines for Boeing's new 787and 747-8 produce upward of 70,000 pounds of thrust compared to the 5,000 pounds for the early jet power plants.

Ever wonder how that happens? Jet engine maker Pratt & Whitney (P&W) has one of the best and simplest jet engine basics tutorials I've seen. And P&W's site does a marvelous job recounting the company's storied history of airplane engine design and manufacturing.

As best as I paraphrase, propulsion (or thrust) is created by large amounts of air sucked into the engine's front fan, the one you can see when you're at the airport. From there, about 15% known as primary air travels through a series of compressors and shortly thereafter into a combustion chamber where it is heated to about 2,000 degrees F. and compressed 30 times.

As it blasts out from there, the primary air hits the rear turbines on the same shaft as the front fan (that's how they turn...the compressors rotate on a separate shaft...see illustration below). The primary air provides thrust by its increased weight and its acceleration through the narrowing channel walls of the thrust nozzle.

The other 85 per cent called bypass air and is pulled through by the spinning fan and turbines. Bypass air is cooler and goes around the compressors and combustion chamber instead of through them, providing the lion's share of the thrust.

Turbofan jet basics. credit: Rolls Royce

From front to back, a jet engine's five main components are the front fan, compressors, combustion chamber, rear turbines and thrust nozzle.

This, of course, is a crude explanation and Pratt & Whitney which has been making airplanes engines since 1925 is better at it than me.

P&W claims to have made more than a half million airplane power plants across 30 engine families. For example, P&W says it made 21,186 J57/JT3 jet military and commercial engines which powered everything from the F-100 Super Sabre fighter to the Boeing 707 which ushered in the age of commercial passenger jetliners. It also made 125,334 R-2800 Doublewasp twin row radial piston engines in many of WWII's most famous fighters such as the Grumman F6F Hellcat and Vought F4U Corsair.

P&W made more than 120,000 Doublewasp piston engines. credit: P&W

Today, the company's P&W2000, 4000 and 6000 can be found on just about any narrow or wide body passenger jetliner you can name. However, P&W has been somewhat ecliped with the 787 Dreamliner, Boeing's latest jetliner which flew for the first time last week. Just Rolls Royce and GE are getting those lucrative orders which together are well north of 1,600 units at the moment.

At the same time, P&W has partnership deals with both GE and Rolls to power both Airbus A380s and A320s respectively. Going it alone in jet engines is virtually impossible given huge capital requirements and long development and testing lead times (jet engines are a tough business, witness P&W's dispute with machinists about moving 1,000 jobs out of its home state of Connecticut. Arguments started being heard in court today on whether the move is legal.).

P&W is hoping to add some lustre with its new PurePower 1000G engine which through innovative gearing promises to lower fuel consumptions, emissions, noise and cost of operation on commuter and medium size jetliners.

PurePower 1000G. credit: P&W

PurePower engines are scheduled for military and commercial deployments in the 2013-14 timeframe.

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This post was originally published on Smartplanet.com

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