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Exhaust flames - running lean or just high temp?

General engine tech -- Drag Racing to Circle Track

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Circlotron
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Exhaust flames - running lean or just high temp?

Post by Circlotron »

This YouTube vid of a burnout car, note how there’s flames continually exiting the end of the pipes even though the pipes are perhaps 2-1/2 metres long. At idle, yeah, okay, it’s just unburnt fuel catching alight as it hits the atmosphere, but what about when it’s going full noise? Does the type of fuel affect this? Disregard nitro of course. Can exhaust gases have a flame-like appearance and be incandescent simply because of their temperature even though they have quit burning?

Start at 3 min 10 sec.

https://m.youtube.com/watch?v=51VCGaGtSKk
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Re: Exhaust flames - running lean or just high temp?

Post by David Redszus »

Circlotron wrote: Wed Sep 09, 2020 5:47 pm This YouTube vid of a burnout car, note how there’s flames continually exiting the end of the pipes even though the pipes are perhaps 2-1/2 metres long. At idle, yeah, okay, it’s just unburnt fuel catching alight as it hits the atmosphere, but what about when it’s going full noise? Does the type of fuel affect this? Disregard nitro of course. Can exhaust gases have a flame-like appearance and be incandescent simply because of their temperature even though they have quit burning?

Start at 3 min 10 sec.

https://m.youtube.com/watch?v=51VCGaGtSKk
An orange or yellow flame indicates a rich mixture. A correct mixture burns with a blue flame. Check out your Bunsen burner flame colors.

What the video is showing is an engine that is experiencing excessive shortstopping. Combustible mixture is being blown into the exhaust and is burning in the pipes. Examine the exhaust pipes under the car. Driver needs Nomex boots.
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Re: Exhaust flames - running lean or just high temp?

Post by hoodeng »

Pretty much as David said,, also the driver getting on and off the gas is going to load the pipe, the fuel won't burn unless there is oxygen available, as there is none in the consumed charge in the pipe it burns at the outlet. [The sparks in the exhaust suggest consumption of metal].

In some turbo applications fuel is also injected post exhaust valve to wind up boost.

The picture is of what a pilot or crew chief could observe on a Allison V1710 and their diagnosis.

Cheers.
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Re: Exhaust flames - running lean or just high temp?

Post by englertracing »

I'm guessing that's an alcohol getup with mechanical injection.

Lots of part throttle.
They aren't really meant to be ran that way, and the mixture will mostly be greatly effected by barrel valve settings
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Re: Exhaust flames - running lean or just high temp?

Post by steve cowan »

englertracing wrote: Wed Sep 09, 2020 10:01 pm I'm guessing that's an alcohol getup with mechanical injection.

Lots of part throttle.
They aren't really meant to be ran that way, and the mixture will mostly be greatly effected by barrel valve settings
These style of burnout competitions are pretty standard here in Australia, the heavy hitters all run blown alcohol engines and turn them hard,I personally could never do that to my own car or never have the budget either,a lot of cars catch on fire etc,its crazy really lol.
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Re: Exhaust flames - running lean or just high temp?

Post by n2omike »

I could see those burnout guys intentionally producing flames out the exhaust... just for show. It doesn't take much power to melt tires. The spectacle is what it's all about. Noise, rpm, FLAMES, flash and dazzle are what it's all about. If they knew how to shoot flames out the exhaust without killing the engine or breaking the rules, they WOULD.
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Re: Exhaust flames - running lean or just high temp?

Post by 1972ho »

That Is INSANE is all I have to say the engine is damn near as big as the car.
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Re: Exhaust flames - running lean or just high temp?

Post by Belgian1979 »

Exhaust is red hot indicating late ignition timing. Probably due to too much boost and trying to prevent detonation. Combine that with too rich a mixture to equally prevent detonation and that is what you get.
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Re: Exhaust flames - running lean or just high temp?

Post by naukkis79 »

Belgian1979 wrote: Thu Sep 10, 2020 2:56 pm Exhaust is red hot indicating late ignition timing. Probably due to too much boost and trying to prevent detonation. Combine that with too rich a mixture to equally prevent detonation and that is what you get.
They are burning rubber - so retard ignition timing is from soft rpm limiter. Without soft limiter it would need to use hard limiter - cutting fuel or ignition or both.
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Re: Exhaust flames - running lean or just high temp?

Post by Truckedup »

hoodeng wrote: Wed Sep 09, 2020 9:03 pm Pretty much as David said,, also the driver getting on and off the gas is going to load the pipe, the fuel won't burn unless there is oxygen available, as there is none in the consumed charge in the pipe it burns at the outlet. [The sparks in the exhaust suggest consumption of metal].

In some turbo applications fuel is also injected post exhaust valve to wind up boost.

The picture is of what a pilot or crew chief could observe on a Allison V1710 and their diagnosis.

Cheers.
That chart is from V's For Victory, a great book!!!
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Re: Exhaust flames - running lean or just high temp?

Post by MadBill »

naukkis79 wrote: Fri Sep 11, 2020 8:44 am
Belgian1979 wrote: Thu Sep 10, 2020 2:56 pm Exhaust is red hot indicating late ignition timing. Probably due to too much boost and trying to prevent detonation. Combine that with too rich a mixture to equally prevent detonation and that is what you get.
They are burning rubber - so retard ignition timing is from soft rpm limiter. Without soft limiter it would need to use hard limiter - cutting fuel or ignition or both.
If the limiter cuts sparks, which is likely, it would load the exhaust with an ideal air fuel mix. Retarded timing would drive up EGT, promoting light-off. He also might be using a spark plug in each collector for the purpose: https://www.thevehiclelab.com/exhaust-f ... n%20flames.
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Re: Exhaust flames - running lean or just high temp?

Post by naukkis79 »

MadBill wrote: Fri Sep 11, 2020 10:54 pm If the limiter cuts sparks, which is likely, it would load the exhaust with an ideal air fuel mix. Retarded timing would drive up EGT, promoting light-off. He also might be using a spark plug in each collector for the purpose: https://www.thevehiclelab.com/exhaust-f ... n%20flames.
You can hear from sound when that engine hits hard limiter( which in modern engine control systems are made by cutting both fuel and spark) and see that from pulsing fires from exhaust and cracking sound, most of time it's in soft limiter firing all cylinders and fire coming from exhaust is steady. Yes, soft limiter will drive up EGT and that is very well seen in video from glowing exhaust. With soft limiter mixture is usually over rich to keep in cylinder temp in control, which is also seen in that video from color of exhaust flames.
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Re: Exhaust flames - running lean or just high temp?

Post by Firechicken »

Can't help with the flame question but wow watching that is like trying to look away from a car accident. To each his own I guess.
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Re: Exhaust flames - running lean or just high temp?

Post by Truckedup »

Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
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