Spark plugs fouling

[SH-M]

Spark plugs can clog and eventually foul if the engine is allowed to idle too low for too long. Throttling up an engine with oil-soaked spark plugs can help clear them out.

The engine should be at or above 800 RPM. Failure to do so may cause spark plug fouling. If the plugs do foul (the engine will sound rough), running the engine at a higher RPM will blow them clear within a few seconds by doing so.

Possible to simulate?

[gilbertohasnofb]

This actually sounds like a cool idea! I don't have in mind how to implement it, but I imagine it should be somehow possible. I know for a fact that the payware aircraft A2A Cessna 172 for FSX does simulate this, so why couldn't we? :smile:

[legoboyvdlp]

The stoichiometric ratio is fifteen parts of air for each of fuel (15:1). At peak EGT you’re right there. But when the engine is idling, let’s say below 1000RPMs, mixture full rich, that ratio is way lower, that is, there’s much more fuel than needed.

The lower the air fuel ratio, the colder the combustion and the higher the amount of fuel unburned. As you may know, a cold combustion rich of fuel leads to one thing: carbon.

Some of the carbon is ejected out of the exhaust pipe but a part of it deposits over the spark plugs, fouling them. A fouled spark plug is unable to make the spark that starts the combustion, because the carbon deposits are isolating the two electrodes, thus preventing the spark to take place.

An aircraft piston engine has two spark plugs for each cylinder, one connected to the left magneto, the other connected to the right magneto.

If the RPM drop over a magneto is higher that 125-150 RPM, then one or more spark plugs attached to that magneto are fouling

• a website about a payware x-plane Cessna 172

I think the AFR was exposed in the property tree in a recent jsbsim update. This might require C++ changes to the piston engine code to allow for fouling - not sure if this is currently possible.

[hbeni]

Hi there, this may be helpful: https://www.youtube.com/watch?v=Es69LVZLcYc Also, I compiled alot of information on my issue at the c182 project: HHS81/c182s#439

[hbeni]

Hi there again, it's ready I think: https://github.com/HHS81/c182s/pull/443

[wlbragg]

Cool, I'll take a look soon. I may wait until you get your FDM engine table question answered. I don't know enough about the engine tables to hazard a guess. Although if you could format a row/column for fowling, I don't see why it wouldn't work.

[hbeni]

I played with the tables, and all Tables i could get my hands dirty with had the problem of either MP changing, Fuel flow changing, or both. However, I think with a not-firing plug the ammount of fuel used should be the same. With the friction, the fuel flow oscillates too, but not as widely as the other tries...

I think however that this is irrelevant for the 172, because it has neither a fuel flow gauge, nor a manifold pressure one; so this is probably purely a "it should also be right internally" issue here, nothing affecting the actual simulation.

[wlbragg]

However, I think with a not-firing plug the ammount of fuel used should be the same.

Yes, it should still be drawing the same amount of fuel, its just not burning it.

[hbeni]

Yesterday night I solved that issue :)

[hbeni]

Already implemented in C182s, maybe you can port it easily: https://github.com/HHS81/c182s/issues/439

[wlbragg]

Saw that, on my todo list, thanks!