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What breaks down burnt carbon deposits?

  1. Jul 12, 2016 #1
    I have an aerosol based 'oven, and chimney cleaning' product.
    Here are the contents:
    Propylene Glycol
    Cocamide DEA
    Sodium Hydroxide
    Sodium Laureth Sulfate
    Xanthan Gum

    From the list, it appears that the only active ingredient is Sodium Hydroxide.
    The rest is either foaming agent, propellant, filler, and perfume.

    From a chemistry perspective... is Sodium Hydroxide the best chemical to dissolve carbon?

    For myself, I'm interested in cleaning spark plugs, when testing jetting.
    The idea is that one starts rich, and then go progressively leaner.

    To clean up the plugs for the next test, the oven cleaner and toothbrush works, but I'm wondering what is the best solution.
  2. jcsd
  3. Jul 12, 2016 #2


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    Staff: Mentor

    NaOH alone won't work. You definitely don't need a pleasant smell, but must of other compounds present play some important role making the mixture thick yet penetrating.
  4. Jul 15, 2016 #3
    The best way to clean off carbon deposits is in a muffle furnace at 550 C. However, salt and isopropanol may work. Can you go from lean to rich? That would require less cleaning in between runs.
  5. Jul 15, 2016 #4


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    I believe Carbon Tetrachloride (CCl4) is a specific solvent for Carbon. The trouble is that it's carcinogenic and not as readily available as it used to be. Automotive repair shops used to have "Spark Plug Cleaners" that were very compact sand blasters. "Put the plug in and push the button." They were used as a normal part of a Tune Up to save the cost of of new plugs. Don't see 'em these days.

    EDIT: Starting at lean would be risking engine damage due to the high combustion temperature created.
  6. Jul 16, 2016 #5
    Yes, I do accept that.... I was lazy in my wording :oops:
    The need to 'wet' the surface, and provide a detergent due to potential oiliness is important.
    I have used a butane torch in the past, to burn off any residual oiliness.
    Which leads to:
    I had a read up on isopropanol and salt.
    That was interesting... a bit too interesting :smile:
    I ended up reading about how it can make water soluble in fuel, and how salt can remove water from it.
    I did note its effect on non-polar molecules and its ability to dissolve oils.

    On an abrasive note... I thought perhaps the salt would act as grit, to disrupt the surface.
    I only had it in its oxidised form - acetone.
    It certainly left the plug very dry; therefore it could be a useful first stage, if dealing with an oily plug.
    (and as Tom noted... carburation setup should always be carried out from a rich position)

    I had a look at Carbon Tetrachloride, and read the safety notes.... yes, it doesn't look like a good candidate, when one's nose is two inches away from the electrode :wink:

    The spark plug sand blaster remains an open topic, all be it apparently closed by the major plug companies.
    The official line taken is: 'the electrode surface is returned in a non-ideal condition'.
    Hence garages stopped using them, hence manufacturers stopped making them.
    However... I once had reason to send a spark plug to NGK for analysis.
    I received a very detailed report back, and in it, this was explained.... but I felt, without conviction.
    Something along the lines of 'current thinking.............'
    And the technician returned the spark plug back to me 'sandblasted' (lightly he said) :biggrin:

    Because of this, I am of a mind to think that by getting rid of the spark plug cleaner, they all sell many more spark plugs.

    But back to the chemistry.
    Perhaps the best solution is to first degrease the plug and then use the oven cleaner, with a bumped up NaOH content.
  7. Jul 16, 2016 #6
    .... continuing on...

    I decided that the first test should be without detergents and surfactants.
    What I had was a drain de-blocker:
    Sodium Hydroxide
    Sodium Chloride
    Aluminium Granules

    I'm not sure of the role of the NaCl.
    It could be as a water softener, or perhaps to bring water into contact with the NaOH as I noted that when left outside the container, the small quantity of materials began to get wet, presumably taking moisture from the air.
    Perhaps it is involved in the chemical reaction.

    The Aluminium Granules, I am thinking, are present to create an agitating fizz, perhaps also to raise the temperature of the reaction.

    I placed a teaspoon of the granules in a 2.5L plastic container, and added water until the granules dissolved.
    There was hot reaction taking place.
    When that had died down, with the container at an angle, an old spark plug was placed into the liquid, with the tip submerged.

    It was left for ten minutes, then careful downward brushing of the tip.
    The plug was deep, and there would be a problem of an air pocket, therefore ultimately I used a longer bristled brush to agitate around the base of the ceramic core.

    Here's the result compared to a plug of similar condition:

    It was certainly a success.
    I'm now testing with the plug upright.
    I placed a few granules (without aluminium) around the electrode gap, then dropped droplets of water on them.
    The liquid expanded.
    It is sat there now with a bubble of black liquid set to burst, being held in place only by surface tension gripping around the top electrode.
    I'll leave it for a few hours.

    Edit: For some reason, the images are not showing.
    Perhaps because they are png, or the wrong size.
    Last edited by a moderator: Apr 19, 2017
  8. Jul 22, 2016 #7
    The experiment was interesting, with the plug left upright overnight in the black gel.
    I think the problem is that the black gel seems to stain the ceramic core slightly

    The best solution, to deal with the inner base of the plug, is a stiff 'thin flat' brush, and oven cleaner, to agitate out the worst of the gunk.
    Then place the tip of the plug in the bath as described above.

    The carbon then falls as it fizzes.
    A brush off with a toothbrush on removal takes the plug back to full clean condition.
    The plug also gains lovely clean threads as well.

    I did try a 'gel' drain de-blocker, which also contained Ammonia.
    It didn't really work, so I presume that the NaOH content was not sufficient.

    Therefore the answer to the question:
    What breaks down burnt carbon deposits?

    Sodium Hydroxide & Sodium Chloride, dissolved in H2O
  9. Jul 22, 2016 #8


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    Don't discount the Aluminium. That and the NaOH react strongly generating the heat. Perhaps some Chemist here can report what the reaction product is and if it is contributing to the cleaning.
  10. Jul 23, 2016 #9
    I know Tom.... I've also been wondering about that.
    The thing is.... when I did the 'upright' test... there was no aluminium content, yet it still fizzed up to create the gel.
    However, the gel stained the ceramic OR the ceramic stain was simply not removed.

    This leads us to the potential re-deposition of carbon.
    It perhaps brings us back to Boreks original response:
    The tests continue... but in context :

    1st phase testing


    After phase 1 tests, the results show the impact of NaOH + NaCl + H2O when applied to spark plug electrodes.
    The results can be summarised:
    Combustion deposits are broken down, and can be removed by brush agitation with water.
    Where excessive deposits existed, either the ceramic insulator was stained, or the original stain was not removed.
    However, the surface presence of 'combustion deposits' were removed..... the plug became cleaned, but for the ceramic staining (IE. it was not white).


    Anybody wishing to repeat these tests... I would recommend a careful choice of plugs.
    4 stroke plugs meet with little oil during combustion.
    The ceramic begins life 'white'... the remaining stain after cleaning is shown here

    2 stroke plugs do meet with oil during combustion AND that oil can be of coloured synthetic type.
    This oil 'paints' the plug, making 'combustion colour identification' extremely difficult.
    Here can be seen a B9ES run with 'blue' (literally) 2T oil, after cleaning.
    The plug is clean of all deposits, but the ceramic is far from white.

    There are two questions that arise from this:
    1. Can the engine combustion finish the job, and either clean the plug, OR, deposit a new layer
      IE. Has the chemical cleaning done it's job?
    2. Must the search continue, to return the ceramic insulator to a white condition?
    The answer to point 1..... baseline tests have been completed - the comparative tests will be done tomorrow.

    Point 2... the tests continue.

    Thinking of Boreks comment, I mixed dishwashing liquid with the water, before adding NaOH + NaCl + Al
    What was utterly remarkable was that no odour was emitted.

    Normally, you can't approach the tub, due to the vapours.
    Add a touch of dishwashing liquid, and all you can smell is soap.
    A really strong smell of soap like Savon de Marseilles.

    I approached the tub with my nose very carefully, until it was right in the tub.... and nothing.
    I washed the mix down the sink, and started again.

    I couldn't get near the tub.
    Added a small squeeze of detergent... mixed it in... and no vapour.

    Did I just screw the chemical reaction, or have I fallen upon a nice safety feature?

    Anyway, I'm leaving a stained plug in the bath overnight.
    Tomorrow I'll try the oven cleaner, added with NaOH + NaCl + Al.
    The reason being that we know the oven cleaner has a correct detergent formula, and yet perhaps it requires an increase in the active ingredients.

    Tomorrow should be interesting on all fronts.
  11. Jul 24, 2016 #10


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    Staff: Mentor

    marcophys, at google drive look around to see whether you can get the direct URL for your images. It will make your future posts more convenient for most readers.

    I think this two-year old google forum post discusses the problem, though surely it has been fixed by now. https://productforums.google.com/forum/#!topic/drive/Xm_mnQ1RYZo;context-place=topicsearchin/drive/url$20for$20google$20drive$20imsges

    EDIT. Following the information in that article I was able to fix your images. I took the "random string" file ID from your URL and appended it to this: http://drive.google.com/uc?id= [Broken]

    Suggest you make a note of this for future posts.
    Last edited by a moderator: May 8, 2017
  12. Jul 26, 2016 #11
    Oh!....... that's good work.
    Thank you for figuring that out.
    One wonders why this is not a standard option.
    Let me try it using https://drive.google.com/uc?id=0B9HHPLN8L5MxeVY2NTd3Y2xTZlk

    Note: This code is generated after creating a sharing link.


    Great.... it works.
    This is really first class advice and probably should go into the 'help file' for images.

    I've just tested it for a big 4Mb png image, for the next post in this thread.
    It allows members to zoom in on the electrodes, and can be loaded in a new tab.

    I really need to share this information (crediting Physics Forums of course) :wink:
    Thanks again for taking the time to figure this out.
  13. Jul 26, 2016 #12
    Back to the testing results

    The first thing to note is that there was no 'apparent' further improvement in efficacy, either by adding detergent, or oven cleaner.
    To be honest, my stock of plugs was now down to 'nicely burned' two-stroke plugs...... you'll see how nicely burned they were.

    Adding dish-washing liquid seems to be the big win, from a chemistry perspective.
    It seems to dramatically impact upon noxious gas production/emittance, reducing it to the point of making it smell quite nice (if you like Savon de Marseilles).

    The problem with my remaining stock of plugs, was that they had been 'painted metallic grey' by the semi-synthetic 'blue' two-stroke oil.
    The NaOH + NaCl + H2O solution had no real impact upon this surface staining.

    So again.... from a chemistry perspective.... the solution is perfect for the title of this thread.
    It has no impact on the 'semi-synthetic oil' colour deposits.

    We could leave it at that.
    For me, it's a big win.

    However, I thought that I'd share the final results pictorially, and in video format, for members who are particularly interested in engines and tuning.

    Here's the photo of 4 spark plugs..... all are cleaned in the solution except the new plug, shown as a control.
    The second control is a plug that has been cleaned, but not run.
    Read the text in the photo.... it should explain everything.

    The video....... maybe I should have made two videos..... one short vid showing the cleaning method and safety etc..... and another showing plug colours.
    But for me the whole subject is intertwined.
    So it ended up being a 22 minute video (as usual), providing all the details.

    Maybe I'll do a quick three-minuter just for the YouTube generation.

    Highly Zoomable Image of Four Spark Plugs



    Fouled Spark Plugs - cleaning and testing (definitive method)

    Last edited by a moderator: Apr 14, 2017
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