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Do Modern Piston Engines Have Flames In Exhaust?  
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Posted (7 years 5 months 1 week 4 days 6 hours ago) and read 4429 times:

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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11 replies: All unread, jump to last
 
User currently offlineSoku39 From United States of America, joined Nov 2000, 1797 posts, RR: 9
Reply 1, posted (7 years 5 months 1 week 4 days 4 hours ago) and read 4385 times:

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
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 2, posted (7 years 5 months 1 week 4 days 1 hour ago) and read 4344 times:

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'.


User currently offlineJetfixr757 From Jamaica, joined Jan 2006, 139 posts, RR: 0
Reply 3, posted (7 years 5 months 1 week 3 days 20 hours ago) and read 4244 times:

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


User currently offlineTimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 4, posted (7 years 5 months 1 week 1 day 19 hours ago) and read 4104 times:

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,

User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 5 months 1 week 1 day 18 hours ago) and read 4098 times:

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.

User currently offlineKELPkid From United States of America, joined Nov 2005, 6343 posts, RR: 3
Reply 6, posted (7 years 5 months 1 week 1 day 18 hours ago) and read 4096 times:

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 :-)
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 7, posted (7 years 5 months 1 week 1 day 17 hours ago) and read 4078 times:

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.


User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 8, posted (7 years 5 months 1 week 1 day 17 hours ago) and read 4073 times:

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."


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (7 years 5 months 1 week 1 day 16 hours ago) and read 4064 times:

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.


User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 10, posted (7 years 5 months 1 week 1 day 16 hours ago) and read 4064 times:

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.


User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 11, posted (7 years 5 months 1 week 1 day 5 hours ago) and read 4004 times:

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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