Pre-ignition is defined as ignition of the charge by some means other than the normal spark before ignition is timed to occur.

• A. Ignition caused by the normal spark at the proper timing
• B. Ignition of the charge by some means other than the normal spark before ignition is timed to occur
• C. Ignition of the charge after scheduled time
• D. No ignition occurs

Answer: (B)

Pre-ignition happens when the fuel-air mixture starts burning before the spark plug is supposed to fire, due to heat sources in the cylinder rather than the planned spark. The statement you’re selecting describes ignition of the charge by some means other than the normal spark before ignition is timed to occur, which is exactly what pre-ignition is. Ignition by the normal spark at the proper timing is normal operation, not pre-ignition. Ignition after the scheduled time is late ignition, not pre-ignition. No ignition occurring is simply no ignition at all, not pre-ignition.