- #1
KleptoBear
- 5
- 0
Hello everyone,
Long time follower, first time user here. I have got a Q about propulsive efficiency.
My understanding of the jet engine in a nutshell is that air is compressed in the compressor (pressure and temp go up), energy added in the combustor (large increase in temp), work extracted by the turbine (pressure and temp decrease) and then the air goes out the exhaust with a velocity higher than inlet velocity.
Now I thought that the higher the difference between inlet and exit velocities of air, the more engine thrust there is. However, I read this line in Mattingly's book "Elements of Propulsion": "The turbofan also accelerates a larger mass of air to a lower velocity than a turbojet for a higher propulsive efficiency". I am little puzzled by this. According to this statement, the ideal jet engine would be one that actually has zero exit velocity, wouldn't it?!
Surely that can't be right. Any help is appreciated.
Thx in advance
Long time follower, first time user here. I have got a Q about propulsive efficiency.
My understanding of the jet engine in a nutshell is that air is compressed in the compressor (pressure and temp go up), energy added in the combustor (large increase in temp), work extracted by the turbine (pressure and temp decrease) and then the air goes out the exhaust with a velocity higher than inlet velocity.
Now I thought that the higher the difference between inlet and exit velocities of air, the more engine thrust there is. However, I read this line in Mattingly's book "Elements of Propulsion": "The turbofan also accelerates a larger mass of air to a lower velocity than a turbojet for a higher propulsive efficiency". I am little puzzled by this. According to this statement, the ideal jet engine would be one that actually has zero exit velocity, wouldn't it?!
![Bug Eye :bugeye: :bugeye:](https://www.physicsforums.com/styles/physicsforums/xenforo/smilies/oldschool/bugeye.gif)
Thx in advance