Inaudible Knock and Partial-Burn Detection Using In-Cylinder Ionization Signal

Internal combustion engines are designed to maximize power subject to meeting exhaust emission requirements and minimizing fuel consumption. Maximizing engine power and fuel economy is limited by engine knock for a given air-to-fuel charge. Therefore, the ability to detect engine knock and run the engine at its knock limit is a key for the best power and fuel economy. This paper shows inaudible knock detection ability using in-cylinder ionization signals over the entire engine speed and load map. This is especially important at high engine speed and high EGR rates. The knock detection ability is compared between three sensors: production knock (accelerometer) sensor, in-cylinder pressure and ionization sensors. The test data shows that the ionization signals can be used to detect inaudible engine knock while the conventional knock sensor cannot under some engine operational conditions. Detection of inaudible knock is important since it will improve the existing knock control capability to allow the engine run at its inaudible knock limit.

Partial-burn detection using ionization is also shown in this paper. A comparison of both in-cylinder pressure and ionization sensor signals are used in this analysis. The test results show that some light partial-burn cases can only be detected by ionization signals. The partial-burn information appears to be difficult to observe under some conditions using the pressure trace directly.