Linked Questions

5
votes
4answers
4k views

How is the correct air speed for fuel combustion obtained at the inlet of the combustor? [duplicate]

Many jet aircraft travel at speed of about Mach .8 which at an altitude of 11 km represents an airspeed of about 300 kt or 150 m/s. If fuel was injected into air at this speed, the mix would just ...
6
votes
3answers
1k views

How is combustion directed in one direction in a jet engine? [duplicate]

The answer here explains how jet engines work. During the BOOM phase air expands, however, the expansion would be in both direction, say toward the turbine blades as well as towards the compressor ...
-1
votes
1answer
389 views

How is pressure kept nearly constant in jet engine burner? [duplicate]

How do engineers make sure the pressure doesn't rise, but velocity does. I have no idea how that can work, please help!
59
votes
4answers
29k views

Why can't jet engines operate with supersonic air and how do they slow it down?

Typically jets cannot operate when intake airflow is supersonic relative to the engine. Why is this so? Also, why are scramjets able to use supersonic air? To slow down the air to subsonic speeds, ...
24
votes
7answers
24k views

Why are adjustable area jet engine nozzles mostly limited to military use?

It seems that only jet engines with afterburners use adjustable area nozzles (this means adjusting the area of the nozzle but not necessarily the direction). This includes most fighter jets, as well ...
18
votes
3answers
11k views

Why would a jet engine that runs at temps excess of 2000°C burn when it crashes?

Airline engines are designed to work at very high temperatures. Yet, when a plane crashes they're burnt (see below). Is it something in their design? (bostonherald.com)
16
votes
2answers
20k views

Why do military turbofan engines use a low bypass ratio?

I know that the most civilian engines use a high bypass ratio which is good for fuel economy and noise reduction. What prevents military engines from using the same technology instead of opting for ...
8
votes
3answers
10k views

How is combustion flame maintained in the combustion chamber after igniters are switched off?

During start phase of a jet engine, igniters in the combustion chamber create sparks to initiate combustion. As far I know, when the engine reaches self sustaining speed, igniters get turned off (...
16
votes
2answers
6k views

Why do jet engines sometimes spit out flames after ingesting birds?

After seeing this video of a 757's engine catching fire because of a bird, I wonder: What happens to the engine? Why does it periodically exhaust fire? Is this some safety feature?
9
votes
2answers
22k views

What is a normal EGT range of a jet engine?

Out of curiosity at what temperatures are the exhaust gasses are expelled from jet engines? A normal reciprocating engine from what I recall should be in the 700 - 1100 degrees Celsius range. Does ...
20
votes
1answer
6k views

How are temperature differences handled in a jet engine?

Given the graph in this answer, the temperature are quite high inside a jet-engine, even greater that many metal's melting point. I understand high core temperature are efficient. A jet engine is ...
6
votes
2answers
9k views

Why do turbofan engines have low pressure compressors?

In my understanding turbofan engines usually have 2 stages of compressors: one low pressure compressor followed by a high pressure compressor But it looks like the high pressure compressor ...
6
votes
4answers
8k views

How is engine thrust measured in flight?

When aircraft engines are evaluated in a test flight, how is the thrust of the engine measured? You would need accurate thrust numbers to calculate the real-world specific fuel consumption (i.e. not ...
1
vote
6answers
3k views

WHY does a jet engine work?

Maybe this isn't the right forum for this question but anyway: WHY does a jet engine work? I know how it works: compress Air -> inject fuel -> ignite -> expand -> thrust But why does this work? ...
9
votes
3answers
4k views

Where does turbine vane and blade cooling air come from?

Some large jet engines have a high combustion temperature to increase maximum thrust. First vanes and blades of the turbine must be cooled to prevent them from melting. One method is to circulate cold ...

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