Excess air and smoke.

MikeAmann

Quick question - assuming that nothing is broken or way out of whack, is it possible to have smoke if the combustion analysis reveals extra air (>31%)? For a fuel oil burner.

EBEBRATT-Ed

If the combustion is good you shouldn't have smoke but it is always possible.

EdTheHeaterMan

Before Flame retention burners were popular, (1960s and 70s) it was not uncommon to find a number 2 (or more) smoke with 50% excess air. You can have a bad nozzle, or a bent or clogged air handling part, that causes the left side of the flame to burn poorly while the right side of the flame has too much air. After adding 40% excess air the flame may be lean on top and rich on the bottom. By looking at the flame thru the inspection port, it will look fine but that inspection opening may not show the full picture.

So try to see if a different nozzle of the same specification will correct the problem, or maybe even a different fuel pressure, spray angle or spray pattern will get you a better outcome.

Steamhead

Too much excess air can chill the flame to the point where poor combustion will make smoke (and CO). But 31% doesn't sound like you've reached that point.

What exactly is going on here?

MikeAmann

@EBEBRATT-Ed , @EdTheHeaterMan , @Steamhead

I am doing a combustion analysis tonight on Mom's boiler, and with everything functioning properly, I noticed during previous tests that the ZERO smoke point correlates to about 32% excess air. If this is somewhat true, then I should be able to skip the smoke test and adjust the air band to that target. Yes, I know, not the total and complete proper way - it's just that by the time I find the zero smoke adjustment, the boiler is hot and then I am done testing for the night. I am just trying to get in the ballpark as fast as I can and then I can fine-tune over the next few days.

I will be updating last year's thread with all the details within a few days. Please watch for it.

EdTheHeaterMan

Ah Yes, The old short warm up time to the limit shut off. That has always been a problem when doing combustion testing on oversized boilers and furnaces.

I feel your pain.

Steamhead

I think there might be some air leaks between the flame and the exhaust outlet- but it's probably not worth stripping the jacket off to look for them. On a new unit the EA at zero smoke is considerably lower- around 20% or so.

MikeAmann

The new baffles went in last night. No soot anywhere!
Tonight - new electrodes and a slightly larger nozzle.
Hopefully this improves on last year's numbers and doesn't take me in the wrong direction.
My fingers are crossed that I get better numbers with no adjustment changes.

STEVEusaPA

I would 'get in the ballpark' by doing this.
https://fueloilnews.com/2005/02/01/a-setup-wakeup/
Then come back when it’s colder and you have more time to do a complete test. Maybe even have her shut the burner off a few hours before you get there so you can get a longer run time.
Overall, I wouldn’t recommend just trying to hit any one number on an analyzer and calling it good. All numbers are important.
IIRC, Beckett (I think) publishes guidance on CO2 targets based on outside temperature and shows how they change. IOW, on a 90 degree day, you might have a CO2 of 12.8%. If you try to hit that target on a 30 degree day you'd be looking for trouble.

MikeAmann

Thanks @STEVEusaPA
Well, unfortunately this went in the wrong direction. I was trying to improve on last year's numbers.
Also something I did last year proved that the combustion chamber was not leaking air into it.
So I had a little excess air to use up and I wanted to make the new baffles slightly more restrictive to lower the stack temperature a little bit and use a slightly larger nozzle. I thought for sure that I was going to hit a home run with this, but the stack temperature went up to over 500 degrees, which lowered the efficiency. However the Xair went down slightly after I closed the air shutter more than it was before. CO2 slightly up and O2 slightly lower. Comparing the numbers says to me, (if I understand correctly) that the slightly larger nozzle was a step in the right direction. I did try lowering the pump pressure to 100 psi (was 145) and the numbers went all to hell. But that gave me good data.

The problem is my new baffles. I designed for 6 tongues (or tabs), more restrictive right?
WRONG. It actually opens up another mouth for hot flue gas to go up the tube (less restrictive). I was concentrating on the tongues, trying to make the heat scrub the walls of the tube more and get better heat transfer and a little lower stack temperature. Now I have to figure out what I can do with the baffle to go back in the other direction.





I have 1 more set to play with. I can block hot gas by tack welding on an additional tab, or close a mouth, or not bend out 1 or 2 tabs on the last set. And where would make more sense to restrict - tabs at the top or at the bottom?

I will put all the details in the other thread. Unfortunately, my cheap digital camera died, so no pics.

retiredguy

Why all the fuss trying to get just slightly more efficiency out of your unit. Remember this, if it is perfect it is just a hair away from going the wrong way. What if an adjustments moves just slightly, or the next batch of oil is from another refiner or supplier and has a different BTU content, you could have a mess on your hands. Now, if you are in a lab, then I can see going for the maximum. But in a home getting it "right" has the best outcome. My 2 cents.

MikeAmann

Because the original baffles were burned away, giving me a 900 degree stack temp. So I took the baffles out of my boiler and put them in Mom's. I ended up with very good CA numbers, but my baffles need to go back where they belong.

MaxMercy

EdTheHeaterMan said:

Ah Yes, The old short warm up time to the limit shut off. That has always been a problem when doing combustion testing on oversized boilers and furnaces.

I feel your pain.

And it's worse for guys like me who are amateurs and use a wet kit on a boiler that short cycles even on pretty cold days...

MaxMercy

Make sure there's no flame impingement anywhere.

MikeAmann

For now, until you experts chime in with any good ideas, it looks like I will have to swap the baffles back until I come up with a solution. But I will leave the nozzle alone and do another analysis.
The forecast says it will be going down into the 30s at night, so I need the heat.

Right now my idea is to reduce the size of the mouth at the top of each baffle.
Only the mouth at the top - the ones below it will not matter.
The new set has mouths that are a good deal larger than the other set of baffles.
I just have to calculate how much I need to reduce that hole to and tig weld (tack) a piece
of stainless steel in that opening. I suppose that I could use a plate with small SS screws
and nuts until I get it dialed in.

Robert O'Brien

MaxMercy said:

Make sure there's no flame impingement anywhere.

This would give you smoke at proper excess air levels

MikeAmann

Another question: stack temperature - should I be reading GROSS or NET?
I can set my UEI analyzer for either.
What temperature do I need to make sure I don't have flue gas condensation?
And wouldn't a temperature reading where the pipe enters the 3 sides exposed
chimney be more meaningful?
I am targeting a temp of 400F in the breach. But that 70 degree ambient temp in
the basement could mean the difference between condensation and no condensation.

EBEBRATT-Ed

Net. 330 net is about as low as you would want to go. And the stack temp will vary a little with the water temperature.

You want to measure the temperature between the boiler and the barometric damper but I am sure you know this

MikeAmann

Thanks @EBEBRATT-Ed , that clarifies that.
I was wrong about the setting - I can choose GROSS or NET for efficiency.
So I tried changing it to GROSS and got 90% on tonight's test.
I'm not that good, so I changed it back to NET.
This is a UEI analyzer. What the heck is the difference between the two settings?

I put the old baffles back in and at a water temp of about 120 F, I read a 420 stack temp.
So if I am displaying GROSS, then net would therefore be 350 - right where I want to be.
With a higher water temp, the stack temp does rise, as you said and basically tops out at 455.
And the barometric damper was actually about 25% open, not just sitting there doing nothing.

Looking at the flame thru the viewport, IMO it's dancing around a little too much.
How do I calm it down? Carlin 100CRD burner. I know it's the retention ring setting.
Despite what the picture below might show, I am at ZERO. .77 FR and air band closed. Air shutter = 3.





EBEBRATT-Ed
EBEBRATT-Ed Member Posts: 14,117
October 2022
The retention ring setting is variable. Close the gap gives you more velocity and a short hard noisy fire. Opening the gap gives you a quieter longer less intense fire. It will work differently with different nozzles and boilers needs to be adjusted when testing. The book settings are not always right...they are a range.

Do I want to move it IN or OUT?

MikeAmann

Retention ring setting was at zero. I changed it to 3/32" and the flame seems a little more stable.

EBEBRATT-Ed

Pulling the retention ring back closes the gap between the retention ring and the blast tube and will give you a short intense hard noisier fire because it drives more air around the nozzle and less around the outside of the retention ring. Moving the retention ring back reduces the air and you usually have to open the air band/ shutter to get more air.

Pushing the retention ring foreword tends to give you a softer, quieter fire.

I usually start with what Carlin says and work with it if I don't like the results with the factory setting

DawsonArnold

excess air can cause a fuel oil burner to smoke. It's like a breezy campfire that smokes because of too much wind. Adjusting the air-to-fuel ratio could fix it.

MikeAmann

@EBEBRATT-Ed I am currently set to the book specs and am working posting the CA numbers right now in this thread: https://forum.heatinghelp.com/discussion/189353/nearly-900-degree-stack-temp-carlin-100-crd-oil-burner-and-original-steel-boiler#latest