Oxygen analyzer

[Solomon]

Has anyone tried to put an exhaust oxygen meter on a RMH? There are many standalone wideband oxygen sensors on the market that are not terribly expensive. The readouts are generally in fuel/air ratio.

I originally came upon this idea when I was building a wood gasifier, needing an automatic fuel air mix for an engine using an Arduino.

I  have built a core in the back yard and have been playing around with it trying to figure out how to tell how efficiently it is burning by sound and other indicators.

I've also seen the videos with Peter Vandenberg's gas analyzer, which would be optimal, but is very expensive. I was wondering if there were a way to do a similar thing cheaper.  I have found oxygen sensors that could handle up to 400F that might be good for measuring the exhaust after the mass.

I'm interested in other thoughts.

[Solomon]

I guess the reason I'm thinking about this is for reasons of efficiency. A highly "rockety" stove may be burning lean and not getting the best BTU per pound. And a stove may be burning rich, producing lots of CO but no smoke.

If we had a reasonably inexpensive way to monitor our stoves, a basic oxygen sensor for instance, we could adjust our habits for the best efficiency, which is good for everybody.

[hallinen]

I spent some time using a zinc air battery and an arduino as an oxygen sensor. It used Pr44 hearing aid batteries, about $1 each. Basically, you short the battery for 30 seconds then watch the voltage recover. The higher the oxygen, the steeper the slope. You calibrate the sensor using room air before every run. I didn’t test it using calibration gasses, but I tested it using oxygen depletion sachets and it seemed accurate and reproducible. I used a syringe to manually remove the flue gas and injected it into a Mylar bag that had an injection port. I think it can differentiate between low, optimal and excessive oxygen, maybe with + or - 2% accuracy, at least above 6%. Lower than 6% oxygen the voltage has a slow recovery time. There is a thread under experiments regarding this work. I can dig up the schematics and code if you want to play with it. If you have an arduino and the parts it is really cheap.

[hallinen]

docs.google.com/document/d/1UaVK4XO46G51LYe6Pd3v5tCrHtLteAPdmCEX-vHgfBk/edit?usp=sharing%C2%A0 Is the link to a document that has the circuit and code that I wrote. I’m sure if can be improved. If you experiment with the project please post what you discover here. I found the pr44 to be superior to the smaller zinc air hearing batteries.

[Solomon]

This is great stuff, thank you.

I was thinking about starting with an off the shelf wideband oxygen sensor for a car. Testing with what you're talking about is an interesting idea, but we need gauges, continuously monitoring so we can make adjustments on the fly. An oxygen sensor can handle temperatures in the range we are working with, though not in the core, it could be mounted somewhere in the barrel or chimney. And it would last for quite a number of years. many also have outputs and could be interfaced with an Arduino for other fun things.

Just by looking at the graphs from Peter's work, it seems like we start getting elevated CO when oxygen drops to around 3-5%. That's not terribly useful, but it's better than nothing.

Unfortunately, the units I have found have gauges that indicate air/fuel mix. Need to figure out how to relabel the gauge.

[gadget]

Yes you would want a wide band type and a way to control the heater so it stays active. This would require a computer monitoring activity level and adding more power to the heater when response time drops. There are 2 types, zirconia and titania. One produces a voltage when there is an imbalance of oxygen(lean), the other has a change of resistance so needs a reference voltage. The resistive type is the wide band. Most automotive upstream O2 sensors are wideband though some are dual element. I forget which ceramic type is the wideband

I was going to try it then I come to the conclusion there is way to many variables to try and get a perfect burn. Just moving a piece of wood can completely change your levels.

It could be useful if you get a run away burn that over pyrolysises(?) the fuel and you want to add an oxygen boost via a blower or some sort of secondary air injection.

Other then that, I think it is a fool errand, spin off from to much gov. regulation. Just look for smoke, no smoke = your doing pretty good. Your biggest challenge would be it clogging fairly quickly and the corrosive exhaust stream. But never say never right?

[Solomon]

I don't know what this has to do with government regulation. It's good practice to burn as efficiently as possible and prevent pollution floating over your neighbor's fence.

I'm not really concerned with any automated controls at this point, just want to monitor the burn. I've noticed playing with my core in the back yard that certain conditions cause smoke or flames in the wrong places. If wood is stuck in the feed and not falling to the bottom, it will smoke. If it is not getting enough air and running rich, the flames will extend well up the heat riser and it will smoke.

I think a well designed burner will be efficient and unlikely to cause problems even if conditions are not optimal but without an objective measure, people just don't know.

[gadget]

Jan 22, 2021 11:27:34 GMT -8 Solomon said:

I don't know what this has to do with government regulation. It's good practice to burn as efficiently as possible and prevent pollution floating over your neighbor's fence.

I'm not really concerned with any automated controls at this point, just want to monitor the burn. I've noticed playing with my core in the back yard that certain conditions cause smoke or flames in the wrong places. If wood is stuck in the feed and not falling to the bottom, it will smoke. If it is not getting enough air and running rich, the flames will extend well up the heat riser and it will smoke
I think a well designed burner will be efficient and unlikely to cause problems even if conditions are not optimal but without an objective measure, people just don't know.

If you spend anytime on the internet it seems like everyone is hell bent on saving the planet at any cost. Now I'm a conservationist but even I have my limit. So many people out there trying to make sure every single molecule is accounted for. Its insanity, so you never know now a days. If they only knew how much "pollution" a single forest fire put out, and yet nature keeps chugging along. Yet, its the gov thats got everyone programmed in fear. Don't get me started on CO2. Sad part is its distracted everyone from the real problem of all the chemicals put in our soils and lawns. Anyway....a little bit of smoke isn't going to hurt anyone if its from a high temp burn chamber. There is worse things in there home they are breathing.

If you build a good heater it will be fine. There is the fire triangle - Fuel / Oxidizer / Heat, but there is also the efficiency triangle - Time / Temperature / Turbulence. Focus on those 3 and you will have a nice heater thats plenty clean. Time under residency is the most difficult in a heater. Acetic acid needs about 1400F for 2 seconds to decompose 98% efficiency. No way you will see 2 seconds in a wood heater so you increase the heat and turbulence to make up for it.

Carbon smoke is fine for me, smoke with turpins, acetic acid, and other volatiles is where you get your nasties. If your temp is high enough(insulated burn chamber), You will not have those - even if you see smoke it will just be carbon. Its all about the molecule size, if your breaking it down small enough (high temp), nature will recycle them rapidly if they don't oxidize(burn) in your heater. The classic metal box wood stove does not get high enough temps to completely break down the complex molecules, they certainly are a problem. If they did, they would get bright red. Its not uncommon for a RMH bricks in the burn chamber to get bright red or orange.

I still think is a neat idea, like I said I was working on it also. Had you been a couple weeks earlier, I could of sent you some electronic throttle bodies I was saving for the project. Sadly, they have been scrapped.

Good luck!!!

[Solomon]

Old-people-government-whining is political and off topic in my book, I don't recall the rules. But I'm not interested. So I respectfully request that it not be brought up again.

I just like to know what's going on with my machines. Efficiency is always high on the list of priorities. I'd like to know a little of what's going on inside.

That's one reason why I'm going the ceramic fiber route. I guess one downside is that turbulence is reduced.

[gadget]

Jan 23, 2021 6:04:31 GMT -8 Solomon said:

Old-people-government-whining is political and off topic in my book, I don't recall the rules. But I'm not interested. So I respectfully request that it not be brought up again.

I just like to know what's going on with my machines. Efficiency is always high on the list of priorities. I'd like to know a little of what's going on inside.

That's one reason why I'm going the ceramic fiber route. I guess one downside is that turbulence is reduced.

Consider this example, some people can't burn wood due to gov regulations. People with clean burning RMH get wrapped up in laws that came about from dirty burning metal box wood stoves. Some day the chimney cops will come to your town. Its just a matter of time. Its probably one of the most important "political" subjects we could talk about on this forum since it affects us all. Good changes can't come if we don't talk about it. Anti wood burning is spreading so don't be surprised when it gets banned in your town some day. Trying to silence another member over a subject thats uncomfortable is like putting ones head in the sand. Accepting bad science is the same thing, putting ones head in the sand. If thats the forum rules then that would say allot about this forum. They will take us down one town at a time. Its not politics, its survival. We need to stop calling science politics when we don't agree. Science is science. If we don't correct the bad science, we all lose.

I was just trying to save you time and money that I have wasted before. I was also working on that idea years ago. I learned that it is 95% effort for 5% gain. Its just not worth it for small fuel saving/(science)emissions. A well designed heater burns plenty clean! If your getting enough smoke to worry about there is a design problem with your heater. Now for a hobby I think the control system its very intriguing.

Ironically full spectrum wood smoke may be very healthy for plants and trees. The phenols, carbonyls and other compounds are very anti bacterial and anti fugal. Nature is expecting it from time to time.

[Solomon]

Well, fortunately members can be blocked. So that solves that problem.