Anything you get is a side benefit of reliability. There are two separate ignition systems for flight safety. They are also not connected to or dependent on the electrical system - some airplanes don’t even have them - since they run either on magnetos (ask your great grandfather about his Model T sometime) or solid-state systems.
An airplane engine has room for 2 plugs per cylinder since they have separate air-cooled jugs covered with fins, like a motorcycle engine, instead of having them all jammed together in a single block with coolant passages getting in the way of things.
They’re generally exempt from any pollution standards. The main concern is lead, and that appears to be on its way to finally being removed from aviation gasoline.
Oooh… learned some stuff today without having to dig through thousands of posts.
It seems that two plugs matter if the benefit out-weighs the cost. The benefit being power or efficiency or emissions. But, there’s going to be that trade-off in cylinder head being used for valves versus spark plugs.
Would some or all of this be why BMW came out with laser ignition? Is that ignition system on the cylinder head smaller than a spark plug so you can have two or more lasers causing spark allowing for greater spark coverage?
I don’t think laser ignition is in production. IIRC the main benefit to it is that it doesn’t require as much power/current to operate than an electro-magnetic ignition coil. I think some of the reporting on it is misconstruing the efficiency claims; as I read it it would potentially be 27% more efficient than coils/spark plugs, and some sites seem to have misinterpreted that as making the engine 27% more efficient.
They didn’t have two plugs per cylinder, the exhaust stroke mentioned was on another cylinder. I had one of those cars. Firing two cylinders at once simplified the ignition system somewhat.
Toyota did produce a lot of twin plug 4 cylinders back in the late 70s, though.
Both of my current vehicles have 5.7 liter Hemi V-8s (Chrysler and Dodge) and both have two plugs per cylinder. I do not know for what particular reason, just pointing out at least one manufacturer does make them currently.
Can’t believe nobody’s brought up Splitfire spark plugs yet. Those came out when I was a kid, but I thought I smelled a scam even at that age.
Hemis have emissions problems because the hemispherical shape has areas where unburnt fuel can hide. The dual plugs are for getting a more complete combustion and lowering emissions. In other words, it made sense for them financially.
My Hemi Challenger had dual sparkplugs. It was for emission reasons, not power.
But, 16 plugs at about 8 bucks each was a turn off. It also was not a 4 valve engine.