Spark plug electrode wear rate determination for a spark-ignited engine

An ignition system for an internal combustion engine, comprising:

• at least one spark plug,
• an ignition coil for the at least one spark plug,
• a control unit electronically connected to the ignition coil and configured to perform a method for determining a wear rate of the spark plug electrode of the ignition system, the method comprising:
• determining a risetime number indicating the time required for raising a primary current and hence an ignition energy which is supplied to an ignition coil of the spark plug from an inactive level to a predetermined level;
• determining an operating condition indicator indicating an operating condition of the ignition system;
• and
• determining a wear rate of the spark plug electrode based on a difference of a first spark plug state indicator indicating the spark plug electrode state at a first time instance and a second spark plug state indicator indicating the spark plug electrode state at a second time instance, wherein:
• the first time instance and the second time instance are separated by a predetermined time interval,
• the spark plug state indicator is determined as a value based on the determined risetime number and the determined operating condition indicator,
• the wear rate comprises the difference between he first spark plug state indicator at the first time instance and the second spark plug indicator state at the second time instance divided by the predetermined time interval;
• and
• the risetime number is determined based on a risetime mean value and a risetime standard deviation.

An electronic control module configured to perform a method to determine a wear state of a spark plug electrode of an ignition system, comprising:

• determining a risetime number indicating the time required for raising a primary current and hence an ignition energy which is supplied to an ignition coil of the spark plug from an inactive level to a predetermined level;
• determining an operating condition indicator indicating an operating condition of the ignition system;
• and
• determining a wear rate of the spark plug electrode based on a difference of a first spark plug state indicator indicating the spark plug electrode state at a first time instance and a second spark plug state indicator indicating the spark plug electrode state at a second time instance, wherein:
• the first time instance and the second time instance are separated by a predetermined time interval,
• the spark plug state indicator is determined as a value based on the determined risetime number and the determined operating condition indicator,
• the wear rate comprises the difference between he first spark plug state indicator at the first time instance and the second spark plug indicator state at the second time instance divided by the predetermined time interval;
• the operating condition indicator corresponds to an ignition density (ρip) of a fuel-air-mixture at an ignition time;
• and
• the ignition density (ρip) is determined based on an initial density (ρi) of a fuel air-mixture and an ignition angle.