Carbon buildup completing the circuit on spark ignitors - no spark

[USAeng]

We have spark ignitors that are inserted into a spray of #2 fuel oil and a very turbulent area... the spark ignitors are getting a build-up of carbon on them that is thick enough to complete the circuit so the current travels through the center electrode, through the wet carbon buildup, and back through the outside of the rod --> therefore no spark... This happens after being run for an hour or so

We have pulled the spark rods back slightly to hopefully remove them from being directly in the spray as we think this may have been what was happening... but not for sure

Has anyone ever had this problem of excessive carbon buildup? if so, how did you resolve it? Thank you.

 

[IRstuff]

Isn't this similar to what you might do with fouled spark plugs in a car? Doesn't it mean that you're running too rich and getting incomplete combustion?

TTFN

FAQ731-376

 

[USAeng]

perhaps thats it... I will have to think about that... the funny thing was though that the carbon deposits where harder than any Ive ever seen on anything else... they were rock hard and almost impossible to scrape away with a pick... after a lot of scraping the ignitor would begin to spark again, but I have to figure out how to avoid the scraping as it is a pain and there are 16 ignitors

 

[IRstuff]

It might be worthwhile to get a chemical assay on some of these deposits, as the other possibility is that you're seeing the result of some contaminant in the fuel that has chemically and physically reacted with the hydrocarbons in the fuel.

TTFN

FAQ731-376

 

[danw2]

Long shot since yours is clearly an industrial app with 16 burners, but on my residential oil furnace 25 years ago, the igniter electrodes were located 'behind' the fuel nozzle and the ignition spark was forcibly 'blown' into the fuel/air mix by the combustion air. For reasons never determined, the igniter electrodes worked forward and got too close to the fuel spray and the result was weak spark ignition and hence incomplete combustion, with lots of black carbon. Apparently the physical position of the ignition electrodes was important.

It isn't clear how the position of 16 igniters could change at once, though, so what else has changed over time, as IRStuff alludes to. Is the combustion air flow diminished? Clogged inlet filter?

 

[kongeokin]

In my job we have excessive deposits on spark plugs but in my case they come from the fuel.
If you are sure that the deposits are come from carbon (you can understand them from the color, they must be black) then you have wrong AFR. In case AFR is not correct the exhaust gas temperature is also wrong and if you look the exhaust gases they must be black (when you have new spark plugs).
If your smoke is like very dark blue then you have to check if oil comes into the compastion area.
Also check if the spark plugs that you use are in the correct heat range. The manufacture of the engine can answer this.
To be 100% sure, as IRstuff wrote, a chemical analysis would be useful.

 

[DLite30]

Try experimenting with the the next hotter spark plug. If that doesn't seem to change anything, try a colder plug.