Theory 124/Engine cycle/Onset phase
Ignition Needs a Compression Ratio
The claim
Combustion begins when the ratio of compressed temperature to fuel ignition temperature exceeds one, so compression ratio sets the ignition timing.
01Mechanism
Compression raises temperature; the ratio determines autoignition.
02Prediction
Ignition timing should track the ratio.
03Refutation
Timing tracking spark advance would remove compression.