In Cycle Pre-Ignition Diagnosis and Super-Knock Suppression by Employing Ion Current in a GDI Boosted Engine 2020-01-1148
In this paper, a low-speed pre-ignition (LSPI) diagnostic strategy is designed based on the ion current signal. Novel diagnostic and re-injection strategies are 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 CompactRIO (cRIO) from National Instruments (NI) is employed. Based on this system, the diagnostic and suppression strategy can be implemented without any adaptions to the regular ECU. Experiments are conducted on a 1.5-liter four-cylinder, turbocharged, direct-injected gasoline engine. The experimental results show two kinds of pre-ignition, one occurs spontaneously, and the other is induced by carbon deposits. Carbon deposits on the spark plug can strongly interfere with the ion current signal. By applying the 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 is early, super-knock can be suppressed effectively; otherwise, continuous pre-ignition might be induced when re-injection 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, fuel re-injection strategy must be carefully calibrated before being used to suppress super-knock.