Combustion Characteristics Detection for Low Pressure Direct Injection Engines Using Ionization Signal

It is well-known that in-cylinder ionization signals can be used for detecting combustion characteristics of IC (Internal Combustion) engines. For example, engine misfire, incomplete combustion (or partial-burn), knock, MBT (Minimum spark advance for Best Torque) timing and combustion stability can be detected using in-cylinder ionization signals. In addition, closed loop combustion spark timing control strategies have been developed to control engine MBT timing and to manage spark timing advance (knock) and retard (incomplete combustion) limits. In-cylinder ionization signals can also be used for closed loop control of maximum equivalence ratio (lean limit) at a desired combustion stability level. Up to now, most of the ionization applications have been for PFI (Port Fuel Injection) engines. This paper presents ionization detection for gasoline Direct Injection (DI) engines. The test data was obtained using a single cylinder engine equipped with Visteon's LPDI (Low Pressure Direct Injection) system. The test data shows that the ionization signals can be used not only for detecting misfire, incomplete combustion, combustion stability, and MBT timing of gasoline DI engines similar to that of the PFI engines, but also for detecting a wet spark plug tip due to late fuel injection timing. Besides similar closed loop combustion control strategies (spark timing and maximum equivalence ratio) to the PFI case, the ionization signals can also be used for fuel injection timing control of gasoline DI engines.