Why Not Closed Loop Combustion ??

Bill Pidgeon_2

You're correct.

Before MAFs, speed/density was the ticket. With an absolute pressure sensor for the intake manifold pressure, and knowing engine speed, and a lot of mapping beforehand to provide lookup tables, the airflow could be predicted. So, the feedback carburetor was commanded to trim the mixture appropriately. But that was in the old days of automotive closed-loop systems.

Bill

Brian_18

Here's a question for the boiler manufacturers. Why not take combustion control to the next level? (LP. & Nat. Gas here, oil would be another animal) It would seem to me that something similar to what automotive engine controls do could be used. Why not monitor combustion exhaust (temp & residual O2, or more), and let a microprocessor controlled gas valve regulate mixture to achieve a full closed loop combustion control? That way combustion air density variations due to temperature and barometric pressure, and variations from hydrocarbon content of the supplied gas would be compensated for automatically, and the combustion would ALWAYS be optimum. The mod-con concept seems to take the efficiency & control to a certain level, but it seems to me there's another higher level of combustion control that could be employed. Just thinking out loud here.

Constantin

I can think of a couple of reasons...

... good O₂-sensors are not cheap. Particularly if they're not the on-off type used in cars. Never mind longevity, fouling, and other headaches that most manufacturers would rather not deal with. O₂-sensors used in combustion analyzers are supposed to be exchanged every year and are protected with filters that also have to be changed/dried.

Unlike car engines, the exhaust gases in boilers cannot be relied on to dry the sensors... in fact, the condensate would likely be a big problem.

Car engines can get away with leaning out the mixture until the knocking starts and then they back off. Knock-sensors are cheap, but there is no equivalent in a boiler, is there? I suppose you could use a MAF to meter the air, but they're expensive too and may not be reliable enough.

In a residential setting, it's probably easier to sense temperature on the surface of the burner and adjust the mix from there, which is how I think it's currently done. Simple, cheap, and you need the probe there anyway to prove flame.

Dan Foley

Combustion

Already done! Here is a Webster AutoFlame we worked on last year. It continuously samples multiple parameters to adjust and optimize the combustion process. -DF

Link:

http://www.autoflame.com/EN/index.html

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Ken_40

So...

Dan says its being done already, which I already knew and worked on with larger boiler/burners. And an American company has it.

Connie says it's too expensive, even though he is the poster boy for all things euro, where cost is irrelevant and quality always the basis of existence.

The obvious answer? Webster needs to adopt the only real superiority the euros have a lock on: BETTER MARKETING!

Weezbo

Dan, was this near an aeroport?

there are all kinds of federal rules and regs and it just seems that that would be the most likely placement of superior combustion monitoring boilers.

Al Corelli

Closeed loop combustion.

I believe Weishaupt has such a system.

There. Now thw "Euros" are represented.

Constantin

Al and Dan,

Would you agree that such a control system probably makes most sense on industrial-scale boilers? I.e. would the added cost of the logic, sensors, wiring, maintenance, etc. be better amortized with a high-input burner, not the kind of stuff one would normally expect in a home? I'm just thinking payback here.

I seem to recall at least one manufacturer using the flame temperature and ΔP between the intake and exhaust to adjust their air/gas mixture. Presumably, this is sort of closed-loop control.

Dan Foley

Location

Weezy,

Not near an airport. This was an outbuilding housing three steam boilers feeding a c. 1915 three building apartment complex in Washington, D.C. -DF

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Dan Foley

Controls

I agree that this technology makes most sense with large commercial boilers. I don't know how much this system cost but it looked expensive. I had enough sense to look but not touch. We were there doing some trap work and I wandered into the boiler room to snap a few photos. -DF

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Al Corelli_2

Closed Loop

I agree that it is good for industrial and commercial NOW.

Soon, as in all things technical, the price will trickle down and be semi-affordable for the average homowner.

At least, that is what I am hoping for.

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Constantin

Interesting reading...

... lambda pro control in the Vitodens 300 allegedly adjusts the flame automatically to deal with all sorts of issues.

If the marketing is to be believed, the boiler does not have to be adjusted to run on either natural gas, propane, or whatever combustible gas is being pumped into it... it does it automatically.

Could be a neat feature in areas where the gas quality is very uneven. But, since it's only found in the Vitodens 300 series, we don't have it over here. A technical description I skimmed in German indicates that the changes include a electronic gas and air control combined with the ionization sensor.

This is but one approach, I am sure that there are others. A boiler that adjusts to changing caloric gas content is pretty nifty, however!

Bill Pidgeon_2

Constantin, The Ignition Timing

is retarded when the knock sensors detect knock. Best combustion efficiency on spark ignition engines is attained by advancing the ignition timing. When it becomes too advanced, knock (detonation) occurs. So, the timing is retarded to stop knock. Leaning the mixture adversely affects NOx reduction in the catalyst, and richening the mixture adversely affects oxidation of hydrocarbons and CO in the catalyst. Hence, closed-loop fuel control, to achieve simultaneous oxidation and reduction.

Sorry, not really relevant to the discussion, but I figured you'd want to know.

Bill

Constantin

Awesome!

Thanks for the info, I really appreciate it! So that is the reason then for engines to have a MAF? ... i.e. measure the air mass flow and then meter the injection?

[Deleted User]

I met a man in 1980 who could do this...

His name was Hans Presel, and he was from (you guessed it) Germany.

Hans hired me to install the gas line to this super secret black box heater that he guaranteed the hotel in which it was installed, a 50% reduction on fuel consumption.

When pressed for the super secret, all he would tell me was that his "device" could read the incoming gas calorie content, and incoming airs oxygen content, and could fire the device to optomize combustion to the Nth degree.

I suspect it was probably a mod con boiler predecessor.

So, the technology is out there, and with todays super mini micro computers, it IS a feasible thing.

Obviously, someone just needs to miniaturize the technology and apply it to their mod con's.

Any one care to guess who the first company to come out with it will be? I'm putting my money on a smalll but significant American modcon manufacturer (think donuts...)

ME

Constantin

Thanks for the information!

So if it was up to you to optimize the boiler response in a residential setting, how would you go about it? That is, how would you instrument / control a boiler to optimize its output, perhaps going as far as adjusting to different caloric gas content, wind, low vs. high firing, etc.?

Does the flame ionization sensor approach I mentioned further down make the most sense since it relies on no moving parts other than decoupling the gas and the air metering? Presumably, there are other ways to skin this cat and it could potentially be very interesting for a manufacturer to bring out a boiler that can modulate to below 10kBTU/hr.

Thanks again for the info!

rich pickering

It is available on other industrial boilers. Saskatoon Boiler has it, I think CB has it. No big deal really, if you have the budget to pay for sensors, calibration and maint.

Some customers hate paying 1.00 for a furnace filter.