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Lean condition = Idle hang, why, the scientific reasoning ?

thread71-491925

Lean condition = Idle hang, why, the scientific reasoning ?

Lean condition = Idle hang, why, the scientific reasoning ?

(OP)
Hello,
Why does usually a lean idle causes the rpm to drop very slowly when you shut the throttle ?

Rather than very quickly when it is too rich ?

Is it because it burns hotter and 100%of the fuel is burned ?

Thanks

RE: Lean condition = Idle hang, why, the scientific reasoning ?

Lean doesn't burn hotter, it burns later. This reduces the effective expansion ratio so the exhaust is hotter.

RE: Lean condition = Idle hang, why, the scientific reasoning ?

Whether that's the case or not, depends on the reason for being lean. Vacuum leaks tend to do that. Vacuum leaks can be variable depending on what else is going on.

RE: Lean condition = Idle hang, why, the scientific reasoning ?

I can imagine a few mechanisms that could be going on, but no point speculating on such limited information. If it is really important to figure out, you either need to get a system engineer looking at it, or become one yourself.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Lean condition = Idle hang, why, the scientific reasoning ?

To a certain point lean flames are hotter, the average cutting torch shows that. If you go super lean then yes it cools, and that is how the TC-18 aircraft engine could obtain such a good BSFC.

RE: Lean condition = Idle hang, why, the scientific reasoning ?

That chart shows acetylene and CO hottest when rich - not lean.

je suis charlie

RE: Lean condition = Idle hang, why, the scientific reasoning ?

Quote:

To a certain point lean flames are hotter, the average cutting torch shows that
Actually, what an average cutting torch shows, is that intense heat plus a strong jet of pure oxygen allows the cutting of metal via oxidization.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Lean condition = Idle hang, why, the scientific reasoning ?

NOx formation needs excess oxygen molecules, and high temperature, so maximum NOx formation is just lean of Lambda 1.0.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

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