How is a turbofan started?

Question

if the compressed air from the compressor that has been passed the combustion section propels the turbine and that drives the compressor then what starts the compressor

Answer 1

I'm an old guy, but back in the day the engine works just like a compressor, thats enough to get it started, then the purpose of the turbo comes into play. More power than previously could be had from an engine of that size.

Answer 2

This is laymans basic terms:
their is a starter/generator mounted on the engine.
It has to be cranked most of the time by tractor on the ground
It aint like cranking a car
basically start fuel nozzles spray a fine mist into the combustion chamber
the starter /generator (thats right the starter becomes the generator after ignition)turns over the engine causing compression in the forward compartment compressing the air to a tremdous amount of pressure, this then goes to a diffuser, which speeds up the air by over a 1000 times faster than the already compressed air ,at this point the engine has not started but is building up to it it is going zzzzzzzzzrrrrrrrrrr at this point the ignitors are switched on in the combustion chamber POW ignition! and the start fuel ignites cause the compressor to turn even faster then the main fuel nozzles kick in FFFFFrrrrrroooomm and get the plane up to what we call take off speed through a turbo fan jet that has a shaft going back to that compressor. to keep the engine from running away and blowing up, the throttle has a linear actuator that can be tweeked by the pilot.only to a certain rpm.their is a bleed band around the area between the combustion chamber and the diffuser that allows the engine to bleed off air and maintain the RPMs under different altitudes and weather.For a real burst of speed some engines have after burners which can spray nozzles of aviation fuel directly into the jet exhaust and make a roman candle out of an already swift bird.

Answer 3

in a turbofan engine there have a starter to drive the compressor. there is 3 type of starter using nowadays. first, electrical. it using electrical motor to drive the compressor. when the compressor have compress enough air into the combustion camber. the electrical motor will disengage and combustion will happen in the combustion camber. second, using air turbine starter. an air turbine starter utilize a small turbine wheel to convert the velocity energy of a moving air stream into mechanical energy to turn the compressor. it will disengage when the turbine accelerate to the idle speed. third, combustion starter. it is a completely - self contained starter consisting of the same component found in typical free turbine engine. as soon as the free turbine begins rotating, the main engine is also rotated through a series of reduction gears. there are many type of stater. u can find it in many ways such as book, internet, and etc. the starter are used to crank the compressor. then the compressor will suck all air coming to it to support the combustion camber. this story are finish if you read more. that all.

Answer 4

A jet engine, including a turbo fan, runs on one shaft. The compressor is at the front, with a combustion chamber in the middle and an exhaust fan at the back.

To start a jet engine, an external starter motor starts the engine turning. Once the engin is at high enough RPM the fuel pump is turned on and the igniters are activated. The igniters are similar to spark plugs and create the flame in the combustion chamber. Once this process is underway, the hot gases pass through the exhaust fan, turning the engine. The starter motor is turned off and the engine runs with the igniters to heat up. Once the heat is high enough, the fuel air mixture ignites on it's own and the igniters are turned off.

At this point the fuel burns and passed out the back of the engine, turning the exhaust fan, which in turn spins the compressor fan at the front. This pulls in more are, which is mixed with fuel and burns in the combustion chamber. A nice little loop of mutual support. For more power, they just add more fuel.

Answer 5

Nope. Two wrong answers out of two answers. A turbo fan has an accessory gearbox, sometime two, that is driven by the turbine shaft. One of the accessories attached to one of the gear boxes is a starter, either electrically or pneumatically driven. Other gear driven accessories such as generators, alternators, fuel pumps and hydraulic pumps also mount to the gear box. When the starter is engaged, it turns the gear box which in turn drives the turbine shaft and rotates the turbine rotors. This begins an air flow which now windmills the fan disc, and also mechanically turns the compressor. When enough rotation is available, fuel is injected into the combustion chamber and the ignitors are energized which lights off the combustor and provides additional rotational force to the turbine and further drives the compressor and accelerates the fan. When the proper turbine speed is reached, usually about 40% N2 the starter is disengaged and the fire in the combustion chamber will now sustain rotation to idle.

Answer 6

John N the water injection is not for starting but is used at take off where the mix of water and methanol is sprayed into the intake in order to cool the air so that it becomes denser and in order to regain power when operating in hot conditions.
Otherwise the normal methods of starting are: Starter generators (electrical [TFE731]), Pneumatic (bleed air from anouther engine, APU or ground cart spins a starter motor [CFM56, PW4000]), Cartridge (an explosive charge creates a charge of air that spins a motor ), Finaly liquid IsopropylNitrate is injected in a unit which when burned produes air agin to drive the motor side of the unit inorder to spin the engine.

Answer 7

Well, on the KC-10, we used bleed air from the APU to start our engines. Once one engine is started, we use the crossfeed valves to start the other two. If the APU is not operational, we used a HUFFER cart which was an enormous V-8 Detroit diesel that turned a huge fan that created the airflow to get one engine turning, after that engine was started, we would disconnect the cart, and start the other two with bleed air. (We used the apu as little as possible during the war because it overheat in the desert.)

We use 18%N1 for the 10's

Answer 8

Info to John N. You are correct. Some of the early DC-8"s powered by the JT3D3 and D7 engines and JT4 engines had water injection. Also some of the early 747's with JT9 engines had provisions for water injection although I don't think it was ever used.

Answer 9

Initially that lady who posted above me is right . But now a days that compressor is started by a huffer. portable energy's supply that provided the power for the planes engines to get fired up . Most of the time the compressor is turned by electricity then when the engines actually mix the fuel and air and become stable then the huffer is no longer need. This process is sued for major aircraft technically the planes engines can be started from its batteries but it is not practical because of the vast amount of power needed to start them.

Answer 10

Huffer Cart