I recently had an idea about the design of an internal combustion engine. Normally, the spark must be timed using some kind of circuit, but if there was a "spike" on the piston:
then would there be no need for a specialized ignition system?
Of course, there would have to be some kind of insulation between the spike and the casing, and between the spike and the piston.
Well, you'd still need something to generate the high voltage for the spark, so there isn't much overall simplification. A magneto driven by points is about as simple as it gets.
But more importantly, the spark does not always occur at TDC — in fact, in most operating regimes for most engines, it never does. In order to get the best efficiency, the ignition timing must be variable relative to the piston position.
Normally, at idle, ignition occurs a few degrees before TDC. But as the speed goes up, or under hard acceleration, the ignition might be advanced by as much as 40°-50°. Back when we used mechanical points for ignition timing, these were known as "centrifugal advance" and "vacuum advance", respectively.
