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Engine exhaust flames. Are they realistic?


Terry Dactil

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The exhaust flame effects is very good for when the engine is starting but not yet running.

However, once the engine is running properly and the exhaust gasses / over-rich flame is exiting at high velocity into a fast slipstream, having it looking like a candle flame wriggling in a slight breeze is not at all realistic.

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Thanks. I didn't know that.

 Great - they are more than halfway there then.

This video of a Merlin running at night shows what it really looks like ...

Note that there is nothing to see at a low power, and when something is visible the color is blue not yellow.

Also, individually this is visible for only a very brief period; it is not a flame but more like a miniature explosion

I suspect that it is only when excess fuel is used for cooling at higher power that the exhaust becomes visible.

For comparison this is what we have now ... and it is way overdone and completely unrealistic.

However, there has been a lot of good work put into the coding, as I can see the color and exit velocity changing with rpm. A few tweaks and it could be great!


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It occurs to me that, during WW2, some women workers used to apply radium, i. e. a radioactive lumionous substance, to dials and their pointers to make them glowing at night. (They were instructed to point the tiny brushes used for the task using their lips and therefore they got ill because they ingested that radioactive substance; they were named "radium girls".)

One of the applications was to make instruments of airplanes visible at night without the use of lamps, in order to reduce the possibility that they were spotted.

I've watched the Gream Reapers' cockpit familiarization video for the Mosquito and they show a lamp which is supposed to light the dials with UV light, so that the dials, probably being fluorescent/phosphorescent, reflect/emit visible light at night.

I think it's unlikely that they spent money for that device in order to reduce light emission even though the plane was so visible anyways because of the exhaust flames, so I guess that in reality the flames were not that noticeable.

@Terry Dactil: That real footage is interesting, but I don't know how much we can rely on cameras in cases like this, since their sensitiveness to light intensity and maybe also the range of frequencies that they detect are different from the ones of our eyes.


Edited by BlackLightning
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If I were arranging a night time spectacular of exhaust flames for avo nuts and wasnt too worried about the effects of the engine loosing power of having its sparky bits messed up from a prolonged run, Id run it over lean to produce the biggest blue flames that I could because that is what people want, and have likely paid, to see.  Which is what I think is happening in the spit video. There a lot of restored mossie in-cockpit footage showing the merlin is not a flame spitting monster albeit this is daytime stock.

In low light I beleive there would be some slight to moderate indication of gas and, dependent upon the stack length and design some heat glow on the stacks. The shrouds and covers fitted to many night operating merlin equipped aircraft like the Lancaster,  Hurricane NFs and mossies are testamony to that. 

Geoffrey Wellum talks about loosing night vision because of the glow and gas from the stacks of his aircraft in "first LIght" and theres reference in pilot notes to the colour and type of flame from the exhust as an indication of correctly setting the mixture according to altitude. And theres lots of reference to night fighter pilots homing in on the exhausts of bombers but I take some of that with a pinch of salt given "Cats Eyes" Cunningham apparently ate a lot of carrots!. 

For me its very overdone at present but still a WIP that doesnt especially worry me.

At night, on an unshrouded stack I would expect to see a mild effect. In the day, nothing. 

 

 

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On 10/27/2021 at 5:46 AM, Terry Dactil said:

The exhaust flame effects is very good for when the engine is starting but not yet running.

However, once the engine is running properly and the exhaust gasses / over-rich flame is exiting at high velocity into a fast slipstream, having it looking like a candle flame wriggling in a slight breeze is not at all realistic.

I understand it is not realistic and all, but there are some nice features. Have you tried changing the mixture from rich to poor and watching the flames? It is a cool detail.

This is an amazing sim! 'Nuff said!:pilotfly:

 

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All that demonstrates is that some programmer is completely clueless about how a 4 stroke engine works.

  • the combustion of the fuel gives pressure to drive the piston down on the power stroke
  • then the upward exhaust stroke gets rid of the combustion gasses in preparation for the next (intake) cycle.
  • if there is still fuel burning during the exhaust stroke it cannot provide any power and is just a waste of fuel and shows that the carburetor is not adjusted correctly/.

As a side note:    The problem of WW2 aircraft being seen at night was not because of flames from the exhaust, but because the exhaust gasses are hot enough (>1000C) to cause the stubs to become red-hot and this glow was visible.  You can see a lot of photos where the bombers have a metal shield over the exhausts to hide the glow.

Here is an example:

lanc_02.jpg


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19 hours ago, Terry Dactil said:

All that demonstrates is that some programmer is completely clueless about how a 4 stroke engine works.

  • the combustion of the fuel gives pressure to drive the piston down on the power stroke
  • then the upward exhaust stroke gets rid of the combustion gasses in preparation for the next (intake) cycle.
  • if there is still fuel burning during the exhaust stroke it cannot provide any power and is just a waste of fuel and shows that the carburetor is not adjusted correctly/.

As a side note:    The problem of WW2 aircraft being seen at night was not because of flames from the exhaust, but because the exhaust gasses are hot enough (>1000C) to cause the stubs to become red-hot and this glow was visible.  You can see a lot of photos where the bombers have a metal shield over the exhausts to hide the glow.

Here is an example:

lanc_02.jpg

 

Petrol engine are not as perfect as you think, flame comes out from exhaust port, i have seen this my self as well.

Petrol engine are not working at stochiometric fuel air mixture , actually AFR have to be lower to fuel be able to provide cooling, so there is excessive fuel and oxygen to be burned in exhaust pipe, when you run engine at high power ratings.

At day time is not a big issue, but at blind night it flashes so hard that it blinds you completely.

 


Edited by grafspee
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1 hour ago, grafspee said:

Petrol engine are not as perfect as you think, flame comes out from exhaust port, i have seen this my self as well.

Petrol engine are not working at stochiometric fuel air mixture , actually AFR have to be lower to fuel be able to provide cooling, so there is excessive fuel and oxygen to be burned in exhaust pipe, when you run engine at high power ratings.

At day time is not a big issue, but at blind night it flashes so hard that it blinds you completely.

 

All the videos show engines with very short stacks. The effect of the stack length/design is especially apparent on the 605 test run where simplified items are used. The mossie has much longer stacks which may help reduce the flash. 

This is  a Merlin XX with short stacks (I think its from a Beaufighter) which again shows little in the way of gas discharge in daylight. 

Im not saying you wouldnt see anything but I doubt youd see anything approaching the night run videos above from a mossies merlin. Here is a night run from NZ. There are flames but not in huge quantity and not from every stack (despite the dramatic still). 

Whats interesting on this video is how the engine seems to be manipulated in order to acheive the flames effect. Id be tempted to say its being over leaned given the lack of anything at the start (full rich??) but I dont know. 

As a point of thinking....given you could technically make a stack and pipe quite long, wouldnt you just make the stack as long as it needed to be to dampen the flame and avoid dazzling the crew in order to save weight and material? This, to me, would be a sensible thing in terms of vision but also a very good visual reference for the crew (if you can see the blue flame you are over lean)


Edited by Boosterdog

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Yes . We see engines being test run and there are pretty flames out the exhaust.

Why are the engines being test run?

Probably to adjust the carburetor.

Exhaust flames do not produce power and are just wasting fuel.

To be fair, there is one way that there may be some combustible mixture in the exhaust stubs. These are supercharged engines which is why they do not have tuned  exhaust / collector pipes. There is some brief valve overlap at the end of the exhaust stroke where both intake and exhaust valves are open at the same time and the pressurized intake charge helps scavenge and helps the exhaust on its way. However, the spark plugs are not firing here so there should be no ignition source to produce a flame. If there is, it means there was combustion still occurring on the exhaust stroke (or perhaps a large glowing carbon build-up) and the mixture control is grossly in error.

Sorry /rant off.

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@Boosterdog you can't see flame from every stack only because of frame rate of video not capturing every flame.

7 hours ago, Terry Dactil said:

Exhaust flames do not produce power and are just wasting fuel.

Yes engines are already doing this all the time, blowing unburned fuel in to the air 🙂

If you adjust carb to provide exactly amount of fuel needed to burn all oxygen in combustion chamber engine will be much weaker and it may end up with engine fatal failure.

14.7 ratio is exact spot but no petrol engine runs on this mixture, most common is 12 and for very high power settings it can go to 10, so there is plenty of fuel in exhaust stroke to continue to burn.

But flames in dcs are way far fetched right now.


Edited by grafspee

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1 hour ago, grafspee said:

@Boosterdog you can't see flame from every stack only because of frame rate of video not capturing every flame.

 

Thats a very good point. Living near to East Kirkby in Lincolnshire I have attended a couple of night runs of the lancaster and one of the mossie there. The mossie has a very different exhaust than the standard MkVI.  I cannot recall the Lanc, whos exhaust are not shrouded as many wartime aircraft were, producing the type of vivid blue flame seem in some videos above. Id go as far as to say those expecting that would be sorely dissappointed. There were traces however but there were quite slight.  The mossie produced no lighting effects but the exhaust stack is very different and appeared to be more of a damper in design (2 outlets at the front leading from an enclosed shroud). 

My feeling is still very much that public night time runs can be "enhanced" by running the engine over lean for brief periods and that the overall effect is affected by the length and design of the stack (short stacks allowing for more visiable effects).  I do agree with you that the effects are currently overdone in DCS. I think something should be visible in low light but the effect should be subtle. I do not think flames should be spouting from the ports every start. 

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This one much better

Flames change shape, because pilot move throttles, i can hear that props are unsynced and wof wof sound changes frequency 


Edited by grafspee

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29 minutes ago, grafspee said:

This one much better

Flames change shape, because pilot move throttles, i can hear that props are unsynced and wof wof sound changes frequency 

 

If the above was what eventually got settled on in the game - I wouldnt be unhappy. 

This is quite an interesting article 

http://www.clubhyper.com/reference/mosquitocowlingsjh_1.htm 

Blue and snappy - its the future

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24 minutes ago, Boosterdog said:

If the above was what eventually got settled on in the game - I wouldnt be unhappy. 

 

Me as well.

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On 12/13/2021 at 1:53 PM, Terry Dactil said:

Yes . We see engines being test run and there are pretty flames out the exhaust.

Why are the engines being test run?

Probably to adjust the carburetor.

Exhaust flames do not produce power and are just wasting fuel.

To be fair, there is one way that there may be some combustible mixture in the exhaust stubs. These are supercharged engines which is why they do not have tuned  exhaust / collector pipes. There is some brief valve overlap at the end of the exhaust stroke where both intake and exhaust valves are open at the same time and the pressurized intake charge helps scavenge and helps the exhaust on its way. However, the spark plugs are not firing here so there should be no ignition source to produce a flame. If there is, it means there was combustion still occurring on the exhaust stroke (or perhaps a large glowing carbon build-up) and the mixture control is grossly in error.

Sorry /rant off.

Have you never watched a drag race in your life ???

 

 

Cheers.

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59 minutes ago, Weta43 said:

Have you never watched a drag race in your life ???

Yes I have, and I have also operated aircraft engines for more than 40 years.

Aircraft engines are not designed to give extreme amounts of power, run on exotic fuels and have 30 second overhaul life.

Yes. That is very impressive, but I bet you have never seen a drag racer engine running for many hours like an aircraft engine has to.

That is not a valid comparison.


Edited by Terry Dactil
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On 12/13/2021 at 12:44 PM, Boosterdog said:

If the above was what eventually got settled on in the game - I wouldnt be unhappy. 

This is quite an interesting article 

http://www.clubhyper.com/reference/mosquitocowlingsjh_1.htm 

Blue and snappy - its the future

It has improved, the flames don't seem be as lazy now, but could still do with a bit of tweaking imho. They could definitely do with a bit of sharpening up, multiple very short flashes instead of the seemingly constant flame, and maybe randomise it a bit between cylinders. 
They are still a bit too bright though I think, they should be rarely visible during daylight hours, even dawn and dusk to an extent.

Heading in the right direction, but not quite there yet for me.

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  • 5 months later...

id like to see the option to add the exhaust covers that were fitted to some mosquitos.

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Trying to bump this thread since it still has been ignored for all the piston aircraft. 

Still no improvement to this in the sim, with any of the aircraft (especially the merlin powered ones).  The flames are not realistic and that can be seen in the mossie night run videos above(not massively visible at night so certainly not visible in the daytime). 

Once this is resolved then smoke should be looked into, on startup and various power settings (ie.  Running at low idle). 

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