N231YE
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Do Modern Piston Engines Have Flames In Exhaust?

Mon Feb 19, 2007 1:07 am

I know that old radial engines used to put out a nice flame display from the stacks when running normally; something old timers enjoyed and young people like me can only dream of...but I was just thinking, do modern piston engines (like the Lycoming IO-360s on my university's C172s  smile  ) put out flames in the exhaust too? To date, I have never seen flames (when the engine operates normally), although it would be interesting.


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Soku39
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Mon Feb 19, 2007 3:00 am

As far as Cessnas and Pipers etc. are concerned, If you overprime the engine and get a start (it might not if the cylinders are too flooded) flames will come out the exhaust... and the cowling.

Thats definately not normal operation though.

[Edited 2007-02-18 19:01:30]
The Ohio Player
 
411A
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Mon Feb 19, 2007 5:38 am

There is a difference.
So-called 'modern' piston engines, those of the opposed design fitted to most general aviation single engine aircraft have mufflers (sound suppressors/heat exchangers) which preclude the sight of 'flames' out of the exhaust.
On the other hand, piston powered airliners of yesteryear had no such devices in the exhaust, so 'flames' out of the exhaust was a regular sight.
Next time you are riding in an early model Cessna 401/402 (1968 vintage) at night, have a look down through the top of the cowling louvers, as the turbo and associated exhaust can be seen to be glowing a dull to bright cherry red.
IF the tailpipe was short enough (which it isn't) you would see 'flames'.
 
Jetfixr757
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Mon Feb 19, 2007 11:01 am

I have seen flames out of a Navajo PA-31-350 at night, and they also have the turbos glow at night along with 402's like melons glowing.
Jet
 
TimT
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 11:57 am

Every piston engine has flames coming out of the exhaust ports. ALL of them. It's just that with the length of the stacks and mufflers, you just don't see it. The combustion process is somewhat incomplete even at peak efficiency and continues to burn especially after the exhaust valve opens and it gets a shot of fresh air, We don't see the acyual flames because the exhaust goes into the muffler(s), completes burning and is passed on as the gases. The older engines had really short stacks and were operated rich- more flame, If an engine is really rich, like the Navajo in an earlier post, there is so much fuel in the exhaust stream that you see flames,
 
N231YE
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 12:22 pm

Thanks for the response guys. I remember reading in a prior thread about how older engines used to really flare when the mixture was rich and at high power settings...I just thought that maybe on takeoff (or anytime the C172 is at full power with full rich) one could see flames poking out of the exhaust stack.
 
KELPkid
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 12:24 pm

Didn't the Early Cessna 310's, the ones with the "Augmented" exhaust, produce visible flames out the stacks?
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
411A
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 1:13 pm

Older piston engines of the radial variety used on airliners operated at best power (R2800's) or LOP (turbocompound R3350's) during cruise and as a result, still produced flames out of the short stacks.
The color was often a blue/white on the turbocompound series, and indicated a proper mixture for the selected power setting, which was on the order of 45% BHP.

General specific fuel consumption for these engines:

R-2800, .47 pounds fuel/hp/hr.
Turbocompound R-3350, .36 pounds fuel/hp/hr.
The latter type was very economical, but suffered from PRT short life, if not operated properly.
Average oil consumption, 1 gal/hr per engine.

Both types has two speed superchargers, and the blowers (superchargers) were shifted to HIGH at about 13,000 ft.

The R-4360, used on the Boeing Stratocruiser was a hi-bred, it had a supercharger and a turbo supercharger.
A VERY complicated piece of machinery.
 
N231YE
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 1:59 pm

I do recall reading somewhere that the color of the flames changed throughout the flight, based on the mixture settings.

After seeing many pictures, I noticed the Constellation is very good at spitting out flames...more so than many other airliners of the period. Did the R-3350's Power Recovery Turbines contribute to the glorious flames, or was it the just the design of the exhaust system?

Quoting 411A (Reply 7):
The R-4360, used on the Boeing Stratocruiser was a hi-bred, it had a supercharger and a turbo supercharger.
A VERY complicated piece of machinery.

Possibly one of the reasons that at the time the model 377 was referred to the "best three-engined airliner of the pacific."
 
411A
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 2:30 pm

Just the design of the exhaust system.
These engines had three exhaust stacks.
Three PRT's, driven by six cylinders each.
Now, when a PRT failed, the torching was something to behold....flames often twenty feet long, followed by a BMEP decrease of 20, followed by engine shutdown.
 
Fly2HMO
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Wed Feb 21, 2007 2:31 pm

Quoting TimT (Reply 4):
If an engine is really rich

Apparently if its really lean it works too...


I had an instructor on a night xc to Needles, CA in a PA-44 show me how to get flamin' Lycomings (Yes he was that bored Big grin ). So he grabbed the mixture on the left engine (the one I could see the easiest, if that aint obvious enough) and told me to look at the exhaust. He leaned the mixture to peak EGT and even a little bit further, and then I saw a very faint but constant whiteish-blue flame coming out of the exhaust. There's no way you would see this during the daytime.

Not the smartest thing to do IMHO, unless you want to clean the spark plugs in the air, though you should do that on the ground.
 
N231YE
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RE: Do Modern Piston Engines Have Flames In Exhaust?

Thu Feb 22, 2007 1:45 am

It is interesting to note that many WWII aircraft had flame arresting systems in the exhaust to protect the aircraft from being spotted over enemy territory at night.

Quoting 411A (Reply 9):
Now, when a PRT failed, the torching was something to behold....flames often twenty feet long, followed by a BMEP decrease of 20, followed by engine shutdown.

Now that would have been a sight to see...despite any mass panic and safety concerns it may have induced.

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