Measuring Air/Fuel Mix In an Oil Burner

Discussion in 'Burners and their construction' started by Melterskelter, Jan 29, 2018.

  1. Melterskelter

    Melterskelter Gold Banner Member

    In another thread the question of determining optimal air/fuel mixture in an oil burner has been touched upon.

    I got to wondering about using an automotive O2 sensor as a means of accurately determining if my fuel /air mix was right as performance of the furnace is highly dependent on this mix. So, I started searching on available automotive O2 sensors following leads where they took me. I got increasingly convinced that a wide-band automotive sensor could be a practical solution. Then I stumbled across this device which is indeed a wide-band automotive O2 sensor coupled with a power supply and Bluetooth connection for a smart phone. It looks like this should work with the only accomadation being a means of cooling a portion of the exhaust gas stream ( could be a simple pipe inserted into the exhaust stream with enough travel to the sensor to ensure cooling of the gases to maybe 400 to 600 degrees F) so as not to burnout the sensor.

    https://www.amazon.com/PLX-Devices-...show_all_btm?ie=UTF8&reviewerType=all_reviews

    Do folks see factors that might prevent this type of device from being useful? Has anyone any experience with such a device?

    160 bucks is a fair bite. But it could reduce guesswork. Looking forward to comments.
     
    Last edited: Jan 30, 2018
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It was discussed a number of times at AA. Try a keyword search there and you should get multiple threads. I remember one fella was building a close loop control to vary fan speed/combustion air on a fixed orifice propane burner.

    On a somewhat related topic, I also remember a couple threads and YouTube videos with fellas using automotive injectors, pump, and ECU to manage the whole sha-bang on a foundry furnace.

    Best,
    Kelly
     
  3. Melterskelter

    Melterskelter Gold Banner Member

    A search of AA does certainly return a pile of speculative threads and I do not doubt there is useful experience-based information in some thread there, but actually finding it has proven challenging. That may be because threads and their subjects often migrate mid-thread ( I am as certainly guilty of causing this as anyone) making it difficult to actually retrieve useful info. That is one of the reasons I started a new thread with a clear title dedicated to the question in hopes that useful information on the subject would be easily retrievable in the future as a search would surely find it. The other reason was to make sure there weren’t hidden confounding factors I was not considering.

    So, if anyone remembers a thread that did not just speculate about the possible use of a wide-band O2 sensor but actually reports on how they worked out in practice, I would really appreciate a link.

    If anyone has any experience with actual use, a report pro or con on that experience would be very helpful.

    Pointing out theoretical problems which one might encounter would also be helpful.

    Denis
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

  5. PatJ

    PatJ Silver

    I think the O2 sensor idea could be a good thing, but I would want to verify it at least once with thermocouples to get a definite relationship established between O2 levels and furnace shell temperature.
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    Thanks, I will look closely at that thread. The problem was not finding a thread it was weeding out the many threads that did not have much useful content.

    The modern wideband O2 sensors are generally heated so you don’t have that concern. The one I linked is such a sensor. The attraction for me of the linked sensor is that it is reputedly plug-and-play Bluetooth syncing with your smartphone or pad to provide an information display without having to worry about power supplies, pinouts, and display interfaces. I initially thought I would have to do all that until I found this unit.
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There was a time when I was going to use one of my automotive EFI Engine Control Units to build a variable output burner. I had a fuel pump and was going to use diesel/kero and 4 injectors, then use the throttle position sensor coupled to speed control on the feed air blower to provide the input signal to throttle up and down. You can program the fuel MAPS using the wideband O2 sensor to tune for whatever output you want within the feed air supply........step on the pedal and throttle up, off pedal back down. You could go closed loop if you like but the ECUs typically only do that at low speed and incorporate an idle air control motor for that. I decided it was fun to think about but over complicated and the expensive equipment when simple and inexpensive would do just fine. I suspect you'll lose interest in the sensor once you become more familiar with your burner.

    Best,
    Kelly
     
  8. Melterskelter

    Melterskelter Gold Banner Member

    I do not doubt that there will come a time when I will have become familiar enough with my furnace that I will be able to tell by sight, sound, and smell when it is set at an optimal mix. Until then (and probably even occasionally after that I will want to measure to confirm) I will feel a lot more confident that I am on the right track if I can reliably measure the air/fuel mix. The only down-side I can see to doing so is the expense of the sensor and plugin unit. But unknowingly running the furnace too lean or too rich and at inconsistent settings has big penalties in terms of frustration and time and material wasted.

    I agree that the idea of automating control of fuel flow and blower with an electronic control driven by a sensor is a clever thought experiment, but is far too complex and expensive for my tastes and perceived needs. I just want to be able to tune my setup.

    Once I have done a bit more reading and listening, I think I will most likely plunk the money for the unit I linked unless there is a better option.
     
  9. master53yoda

    master53yoda Silver Banner Member

    when you get to that point your are looking for a 2% O2 reading that should give you. roughly 10% excess air.

    Art b
     
    Melterskelter likes this.
  10. Melterskelter

    Melterskelter Gold Banner Member

    Art,

    So, the target Lambda is .9 or an air/diesel mix of 13.14 and not 1.0 and 14.6 respectively?


    On this page

    http://www.plxdevices.com/Wideband-O2-Air-Fuel-Ratio-Sensor-Module-p/897346002726.htm \

    For anyone interested there is a decent user manual link which will download the two-page manual.
    The link is just under the book symbol. Since the manual is itself a PDF, I cannot give a direct link to it.
     
    Last edited: Jan 30, 2018
  11. master53yoda

    master53yoda Silver Banner Member

    from my reading i think that you will want a lambda # 1.026 which would be a air fuel ration of 14.8 :1 this is an extrapolation of stoichoimetric ratio of 14.6 : 1 with a 2% oxygen in the flue gas.

    these sensors are completely different from what is used in combustion analysis so I'm somewhat guessing. it is possible that my calcs are inverted. if so the lambda # would be .975

    Art B
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    Your numbers are in close agreement with those printed in the user manual supplied by the manufacturer of the gauge I am considering. It is helpful to know what number to target for a furnace which is somewhat different from the target of the usual users, hot rod tuners.
     
  13. Melterskelter

    Melterskelter Gold Banner Member

    Couple more melts yesterday using an unmeasured A/F mix but using some of the tips generously offered here. Both a 5 pound and 8 pound melt proceeded nicely with very fluid free-flowing water-like molten iron. With each firing I gain more ability to sense what takes to get high heat. But, though the results have been fairly good, I still don't know if I am operating at optimal efficiency or taking more time and fuel than needed.

    I did receive my automotive O2 sensor and Bluetooth interface device late today. I will be anxious to give it a try in the next few days. One challenge I have been mulling over is how to set up a reliable sampling system that will allow me to "sniff" the exhaust but ensure that the exhaust temp is down around 600 C or less at the sensor and that will not melt the intake to the sensor system. Most likely the system will have to be setup to swing into the exhaust and "inhale" for a while and make the reading and then swing back out of the stream. It can make a reading in only a few seconds (or even less), I believe. This system should be relatively blunder-proof so that it does not require babysitting or else there is a risk of becoming distracted and cooking the sensor.

    I would welcome any brainstorms you folks might have in regarding design options for the system.

    [I accidentally posted this same message initially in another thread on Furnace Break-in. My apologies for the double post]
     
  14. Melterskelter

    Melterskelter Gold Banner Member

    A way to cool the exhaust stream prior to it entering a measuring chamber where the sensor would be located might be to draw the exhaust through a heat sink consisting of a section of pipe filled with steel BB’s. For scale, I am thinking an inch or so diameter and maybe 3 inches or so length. The BB’s would provide high surface area and a fair bit of mass. Such a heat sink would be cheap and easy to fabricate. It would not allow continuous sampling, but that is OK. After a sample is pulled through it, the BB’s could be cooled by pulling environmental air through it. As a means of aspirating exhaust and, subsequently air, I am thinking sucking air using a compressed air stream blown across a relatively small diameter pipe much as an atomizer lifts fluid into the atomizer or use a crude Venturi to do the same. Since the sensor has a very short response time (less than a secondary since my intuition tells me that the heat exchanger would tolerate 10seconds or so aspiration cycles, such a system might work. Other ideas?

    Another idea for a heat exchanger could be a plug in a pipe where the plug would be bored with an array of small holes running its length. Just for scale, maybe 1 inch in diameter with twenty 1/16th holes drilled for n inch or so length inmild steel. But, this is more labor intensive to fabricate and is not as easily scaled up as need for adequate cooling.

    Lots of idea churning around....
     
  15. Peedee

    Peedee Silver

    W3? built a unit based on perstylatic (sp??) pump with a lambda sensor feedback using a arduino as I recall. It was a very effective furnace and he poured a lot of metal using it for a small commercial venture making CNC kits. Well worth finding the thread if you can.
     
  16. Peedee

    Peedee Silver

  17. Peedee

    Peedee Silver

  18. Melterskelter

    Melterskelter Gold Banner Member

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