Analysis of the ion current in misfiring and firing cycles during the cold starting of a compression ignition engine

Compression ignition engines will continue to power heavy-duty, long-haul vehicles, and heavy machinery in the future, while batteries become more prevalent in powering light-duty vehicles. However, compression ignition engines face problems when started under severe cold conditions. These problems include combustion instability, misfiring, and higher emissions of unburnt hydrocarbons. Feedback of an engine’s performance to its control unit can be used to improve the fuel injection strategy in real time and mitigate these problems. The ion current signal, being reflective of the combustion and emissions characteristics, has already been proven as a reliable feedback signal under warmed-up conditions. This paper investigates the ion current signal as potential feedback during the cold starting and the warm-up period. Cold starting experiments were conducted in a VW’s 2.0-L, direct injection, four-cylinder compression ignition engine at ambient temperatures of −10°C, 0°C, 10°C, and 20°C. The engine experienced misfiring cycles at the ambient temperatures of −10°C and 0°C. In some misfiring cycles, the ion current was detected even though the pressure trace did not show a distinct combustion event, indicating that the autoignition occurred but the combustion failed to sustain. This means the ion current can identify un-sustained combustion events in misfiring cycles. In firing cycles, an ion current characteristic could well predict the combustion phasing at ambient temperatures of 10°C and 20°C. The real-time feedback of (1) un-sustained combustion events in misfiring cycles and (2) combustion phasing in firing cycles at various ambient temperatures can be utilized to mitigate cold starting problems in compression ignition engines.