Linked Questions

5 votes
4 answers
6k 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 ...
mins's user avatar
  • 73.2k
6 votes
3 answers
2k 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 ...
Martin's user avatar
  • 169
-1 votes
1 answer
1k 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!
Dominykas Kruopis's user avatar
2 votes
2 answers
191 views

Why does a jet's combustion energy propel the engine forwards rather than acting equally in all directions to create zero thrust? [duplicate]

I'm a novice. I have high school physics and I've seen many explanations of how a jet engine works. To paraphrase: Fans compress air into a chamber where combustion energy is created, which spews ...
jay613's user avatar
  • 121
61 votes
4 answers
39k 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, ...
Dylan's user avatar
  • 1,115
27 votes
7 answers
33k 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 ...
fooot's user avatar
  • 73.2k
18 votes
3 answers
12k 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)
Regmi's user avatar
  • 925
20 votes
2 answers
26k 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 ...
Anarach's user avatar
  • 393
10 votes
5 answers
7k views

Why do jet engines have a maximum speed?

What's the scientific background behind a jet engine's top speed? Jet engines increase efficiency at higher airflow rates, so why does the efficiency stop increasing at some point?
thebiggay's user avatar
  • 109
8 votes
3 answers
12k 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 (...
albin's user avatar
  • 677
17 votes
2 answers
9k 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?
Remz's user avatar
  • 173
11 votes
2 answers
31k 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 ...
Fabrizio Mazzoni's user avatar
8 votes
5 answers
10k views

Why is there a pressure drop in the combustion section of a jet engine?

This image, referenced in this question, shows in green the pressure value in a jet engine: The combustion section between compressor and turbine is where fuel is injected, mixed with air, and ...
mins's user avatar
  • 73.2k
6 votes
2 answers
12k 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 ...
Eylan's user avatar
  • 61
21 votes
1 answer
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 ...
Manu H's user avatar
  • 16.5k

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