Problem running diesel on biogas

Discussion in 'Designing, building, making and powering your life' started by erawan, Feb 24, 2009.

  1. erawan

    erawan Junior Member

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    Hi

    I am new to this so bear with me.

    I'm with Engineers Without Borders doing a biogas project for a remote community hospital in Laos, we have a biodigestor which is running of cow poo and is generating biogas to run the burners in the kitchen and gas lights. They have a single cyclinder 10.5 hp diesel generator which is a chinese copy of a kubota diesel and I have been trying to run that on the biogas as well. To test I ran the engine on Propane and it worked well by just feeding into the air inlet, the biogas is diffrent it doesn't work at all, the engine runs eratically and then cuts out. The engine is old and in bad state of repair I suggest that it is down to about 13:1 or14:1 compression. Any pointers would be useful.

    cheers


    G
     
  2. trimnut2

    trimnut2 Junior Member

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    Re: Problem running diesel on biogas

    erawan

    I assume that you are not changing any of the fuel settings. Meaning that all you are doing is just feeding the biogas into the air intake. Are you using the same pressure "regulation" for the biogas supply as you used for the propane? I would try cutting the biogas amount/pressure? back and then slowly increase the amount/pressure and watch what happens. Keep in mind that ignition will only happen when the biogas oxygen ratio is suitable and the diesel can ignite the both the gas mixture and the diesel itself. My guess from the description is the engine progressively starved of oxygen. Let me know how you get on.
     
  3. erawan

    erawan Junior Member

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    Re: Problem running diesel on biogas

    Thanks for your reply

    I rely do appreciate the help.

    The facilities here are very crude, the propane was just a test last year as they did not ahev any biogas when I was there. It was just a small cyliner and a torch ( for brazing ). I stuck the nozzle in the top of the air filter and then engine just went ( ran 100% propane although the engine didn't like that. The only regulation I have of gas pressure is what is coming out of the digestor which is a good 300 M away and feeds by 1/2" pipe, as a 1/2" ball valve on the new infeed I have put into the air filter. I have spoken to someone else bout this and he says that the water vapour is are red herring the problem is the mix prior to the engine inlet. Our thought are moving towards removing the air filter and fitting a mixing chamber with the gas infeet to that. this will be something like a 4 litre paint tin, which will be placed where the air filter fits on the intake and the air filter fitter on top on the mixing chamber.

    Would you concur that this could be the way to go ?.


    erawan
     
  4. RobWindt

    RobWindt Junior Member

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    Re: Problem running diesel on biogas

    My first guess would be to limit the gas with a tap, open slowly and see how it goes.
    Is it a drum biodigestor? If so, you can raise pressure (if need be) by adding weights on top of the drum.
    Let us know how you go
    Cheers
    Rob
     
  5. trimnut2

    trimnut2 Junior Member

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    Re: Problem running diesel on biogas

    erawan I would do just as Rob says. Let us know the result.
     
  6. MonteGoulding

    MonteGoulding Junior Member

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    Re: Problem running diesel on biogas

    Hi

    I'd love to see some pictures of your experiments. I have a Petteroid engine hooked up to an alternator for battery charging and have been contemplating either biogas or woodgas conversion one day.

    Cheers

    Monte
     
  7. erawan

    erawan Junior Member

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    Re: Problem running diesel on biogas

    Many thanks for all the suggestions

    I will try to figure how to get photo's on this blog.

    The digestor is an underground brick construction and does not have any pressure regulation, what you see is what you get. I tried crack the valve very slightly just to allow some gas through remember it was only at 10 Kpa. The smart thinking is that unlike the propane the biogas needs to be mixed more before entering the inlet. The plan now is to build a mixing chamber from 4" dia exhaust pipe the mixing chamber will have a fixed impeller to create a vortex. The plan is remove the air filter, fit the mixing chamber to the inlet and stick the airfilter on top with an inlet to the mixing chamber. The biogas will have a seperate inlet coming in the side of the inlet and pertruding into the centre to get the most from the vortex effect. I will keep you posted.

    E
     
  8. RobWindt

    RobWindt Junior Member

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    Re: Problem running diesel on biogas

    Hi Erawan -

    I fit lpg to diesels via a simple nipple in to the intake tube - the 10 mm nipple is closed at one end and has only a 1mm hole in it - to tune it to different motors i raise the revs to 1600 rpm and then turn the gas on and look for the rev's to rise by another 200 rpm - i drill out the hole in small steps to achieve this. Try an inlet nipple with a 3 or 5 mm hole for starters as biogas has less energy than lpg

    The lpg is off at idle and comes on as the rev's go up (via a switch on the throttle) but with woodgas generators the gas is always on (they idle faster to keep producing the gas)
    Is it possible to limit or modify the injector rack so that it idles on diesel (for ignition) and uses gas for power? My knowledge of diesels is limited to lpg vehicles but i know this is often done with old generators, modern vehicles automatically limit the diesel as the lpg is introduced.

    Running your biogas through a sealed bucket of wood chips or charcoal would filter out a lot of impurities (in near the bottom and out at the top)

    Cheers
    Rob
     
  9. ppp

    ppp Junior Member

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    Re: Problem running diesel on biogas

    sure it isn't a LACK of gas?
    If it it the type of gas producer I am thinking of, can you increase the pressure by putting some bricks on / some one standing on the upside-down tank?

    just an idea.. I would suggest that the trial you did, was with quite compressed gas in a bottle, and this is very low pressure.
     
  10. erawan

    erawan Junior Member

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    Re: Problem running diesel on biogas

    Many thanks for all the suggestions I like the charcoal filter one, might give that a shake when after I tried the mixing chamber. Just to clarify, the digestor is a brick built construction of fixed volume, there is no standing on or putting weights on to increase the pressure, the pressure is generated by the level of the biomass in the chamber and the amount of gas that is produced.

    Thanks all

    Erawan
     
  11. erawan

    erawan Junior Member

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    Re: Problem running diesel on biogas

    Hi Rob
    thanks for your advice however this whole problem has started with the fact that Propane worked fine but the biogas doesn't, thanks for the gen on the filter.
     
  12. RobWindt

    RobWindt Junior Member

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    Re: Problem running diesel on biogas

    I would try a 5-10mm pipe in to the intake first, pick the narrowest spot between the air cleaner and intakes and insert the pipe half way in.

    Have the end of that pipe cut at a 45-60o angle, with the angled opening facing the motor, this will mix and flow the gas as well as any mixer that we can purchase or fabricate.

    Some diesel or light vegetable oil will be required for reliable igntion, which ever way you choose to go.

    Cheers
    Rob
     
  13. dgriffith

    dgriffith Junior Member

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    Re: Problem running diesel on biogas

    Are you sure you're actually getting something combustible out of the digester and to your engine? Your 300m of pipe might be full of CO2 or something if it's at a low point.....

    Mixing shouldn't *really* be an issue - if you're bleeding it into the air filter/intake manifold, there's plenty of mixing going on once you pass the gas through inlet valves and squeeeeeze it in the cylinder.
     
  14. erawan

    erawan Junior Member

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    Re: Problem running diesel on biogas

    Results of experiment

    There is a short video on the blog www.erawan-biogas.blogspot.com

    We are contemplating the results of the test, we believe we were burning the biogas but probabaly putting too much in, unlike the propane the biogas needs the desiel to ignite.

    If you watch the video there is plenty of bluegrey smoke when the biogas is opened and a lot of black smoke as the rack returns to the original position with an inrush of desiel. We ran plenty of other experiments it is just that we only have 2 mins of video on the camera.

    Our next test is to try to quantify if there is less diesel being used when the biogas is turned on

    Cheers

    Erawan
     
  15. dgriffith

    dgriffith Junior Member

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    Re: Problem running diesel on biogas

    Looks like too much gas going in from that video, but it's hard to tell when someone's just yankin on a 1/2" valve :)

    Can you measure the flow? How quickly will it fill an inverted bottle underwater?

    Going from 10.5HP for your engine, I would guess 300CC or so displacement?

    Working backwards from that at 1500RPM, you're drawing in roughly 0.3 x 1500RPM / 2 = 225 litres/min or so of air (cylinder filling ignored). Googling indicates about 9.5 - 10:1 air/fuel ratio for biogas, but that's dependant on how much methane you've got in your mix.

    Using 225L/min at 9:1 AFR gives 25 litres/min of biogas and 200L/min of air going in. This doesn't include the air needed for the diesel to ignite, so I'd probably aim for somewhere near 12:1 AFR, or about 15 litres/min.

    Try lowering gas flow to around that amount and see how things go.
     
  16. erawan

    erawan Junior Member

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    Re: Problem running diesel on biogas

    I have run some more experiments at the site and you can see the results on

    www.erawan-biogas.blogspot.com

    I still have some work to do but I am returning to Australia for now.

    I am looking for a piece of equipment that can analyse biogas on site
    does anyone have any suggestions ?

    Cheers

    Erawan
     
  17. permasculptor

    permasculptor Junior Member

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    Re: Problem running diesel on biogas

    a canary :D
     
  18. RobWindt

    RobWindt Junior Member

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  19. eco4560

    eco4560 New Member

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    Re: Problem running diesel on biogas

    That's an expensive canary :wink:
     
  20. dgriffith

    dgriffith Junior Member

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    Re: Problem running diesel on biogas

    Hmmm. That *is* pricey.

    Perhaps you could talk to a chemist (not the pharmaceutical kind) and see if they can offer a solution.

    For example volumetric measurement of CO2 is relatively easy (Expose known volume of gas to an aqueous solution of potassium hydroxide, CO2 is drawn out of gas into solution to form potassium carbonate, reducing gas volume proportionally). If CO2 is the issue, then you can easily check the % CO2 and assume that something combustible makes up the bulk of the remainder. All you need is a couple of bits of glassware and KOH. Easy enough to get out on a remote site,right? :D

    Or perhaps check about for an cheap "personal safety" detector that does CO2/CH4/O2 - coal mines use them a fair bit.

    (I'm not sure what else apart from CO2 would choke a diesel engine like that. Excess air won't, and in theory you shouldn't have any other sort of inert atmosphere left in your digester if it's been running for any length of time)
     

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