<p>General Electric CF6 high-bypass turbofan engine on display at the Smithsonian Air and Space Museum in Washington, D.C.
</p><p>When Nazi Germany first developed the jet engine in World War II, it was a simple device.  A large fan spun up and pushed air toward a series of smaller fans in a tunnel.  These smaller fans compressed the air.  Compression also heated the air.  The hot, compressed air then moved into a combustion chamber.  Gasified fuel was mixed with the hot, compressed air.  The heat from the air ignited the fuel -- creating very hot, very highly compressed gas.  The exploding gases passed another fan (a turbine) on their way out of the engine, generating electricity.   This electricity was fed back to the main fan and main compressor, keeping the entire system going.  The ignited, high temperature, highlyl compressed gas then exited out a nozzle -- which provided propulsion.
</p><p>After World War II, two-stage compressors were developed.  This allowed for greater throttle control over the engine, and also provided much more compression, heat, and power.  These were called "turbofans".
</p><p>Not all the air from the first compressor goes into the second one in a turbofan.  Some flows over and around the second compressor.  When the amount of air bypassing the second compressor is high, this is known as a "high bypass" turbofan.
</p><p>In 1964, the U.S. Air Force contracted with Lockheed and General Electric to begin development work on high-bypass turbofan engines.  The engine that GE developed was the TF39 -- which had an 8-to-1 bypass ratio, boosted fuel efficiency by 25 percent, and provided one-third more power.
</p><p>The TF39 entered military service in 1968.  In 1971, GE began offering the engine to civilian customers.  Called the CF6, it proved to be one of the most popular civilian jetliner engines of all time, flying aboard the Boeing 747, Airbus A300, Airbus 310, Airbus 330, Boeing 767, and McDonnell Douglas MD-11.
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The CF6 has had problems, however.  The U.S. National Transportation Safety Board has warned in 2000 that the high pressure compressor could crack and cause the engine to fly apart or fail.  The failure of a CF6 led to the Sioux City, Iowa, crash of United Airlines Flight 232 in 1989.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/23165290@N00">Tim Evanson</a> from Cleveland Heights, Ohio, USA
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/timevanson/7276904338/">General Electric CF6 high-bypass turbofan engine - Smithsonian Air and Space Museum - 2012-05-15</a>