Engine control systems

A method of engine control, characterised by the steps of firing a weak spark through a spark gap between two electrodes of a spark plug in a combustion cylinder of an internal combustion engine, measuring a current through or a voltage across the electrodes following the weak spark, analysing the voltage or current to derive a prediction of a flame propagation speed in the combustion cylinder and subsequently firing a stronger spark through the spark gap to ignite a combustion charge in the combustion cylinder, the stronger spark having an ignition timing varied in dependence upon the prediction of the flame propagation speed, and further including the step of firing several weak sparks in a single engine cycle to obtain several gas velocity readings, the readings being processed to provide by extrapolation an estimate of the gas velocity at the instant of the ensuing stronger spark.