In Cycle Pre-ignition Diagnosis and Super-knock Suppression by Employing Ion Current in a GDI Boosted Engine 2020-01-1148
A low-speed pre-ignition (LSPI) diagnostic strategy is designed based on the ion current signal. A novel diagnostic and additional fuel injection strategy is proposed to suppress super-knock induced by pre-ignition within the detected combustion cycle. A parallel controller system that integrates a regular engine control unit (ECU) and NI CompactRIO (cRIO) was employed. Based on this system, the diagnostic and suppression strategy can be implemented without any adaptions to the regular ECU. Experiments were investigated in a 1.5-liter four-cylinder, turbocharged, direct-injected gasoline engine. The experimental results show two kinds of pre-ignition, one occurs spontaneously, and another is induced by carbon deposits. Carbon deposits on the spark plug can strongly interfere with the ion current signal. By applying ion current signal, approximately 14.3% of spontaneous and 90% of carbon induced pre-ignition cycles can be detected. Moreover, among detected carbon induced pre-ignition cycles, 91.4% of them can be detected earlier than crank angle at 50% heat release (CA50), providing ample time for super-knock suppression. The results also show that additional fuel injection (re-injection) after the detection of pre-ignition in the current combustion cycle can be used to suppress super-knock. The re-injection timing is a crucial parameter of the suppression strategy. When re-injection timing is early, super-knock can be suppressed effectively; however, continuous pre-ignition might be induced when the re-injection timing is too late, e.g., later than CA90. Furthermore, the duration of re-injection is also essential because too little fuel has a limited effect on suppression, yet too much fuel will produce more carbon deposits, thereby aggravate pre-ignition in the following cycles. Therefore, re-injection strategy must be carefully calibrated before been used to suppress super-knock.