Originally Posted by
cmulder
My car has a ignition system where 2 coils provide spark for a 4 cylinder engine. So one plug gets fired when the piston is at the botom and as result there is no ignition there.
Actually, no, that is not how that works... The two plugs at the same coil are basically a plug, coil and 2nd plug in series, and both fire at the same time, and both fire with the piston in top. One cylinder is in its firing position (both valves closed), the other one in its scavenging position (both valves slightly opened), so one spark is actually igniting something, the other spark is the so called "wasted spark".
Check it if you don't believe me: Cyl 1 and 4 are on the same coil, and cyl 2 and 3 on the other coil. Pull the plugs of 1 and 4 and check piston position, and you will see that they are both in TDC at the same time.
Originally Posted by
cmulder
If this engine can be seen as 2, 4 cylinder engines combined?
That is correct, but...
Originally Posted by
cmulder
Then one coil could fire 4 plugs at once and the other coil the other 4? This assumes 2 cyclinders fire at the same time and there are 2 other cylinders at 180 deg.
To simplistic or might work?
this is not, and indeed just a touch too simplistic.
Regardless of how many cylinders a multicylinder has, if it is a fourstroke, the maximum number of plugs on a coil is 2, and if the bank angle is not 90 degrees, or the crank interval is not evenly spread around the 360, then only 1.
In this case it is just a matter of luck that the bank angle is 90 and the crank division also is 90. That makes for an even division of 90 degrees per ignition and 4 pairs of sychronous running pistons. Therefore 4 coils. I can opt between 4 twin ignitions, or 2 fourcylinder ignitions. I prefer the latter.