Development of Robust Gasoline HCCI Idle Operation Using Multiple Injection and Multiple Ignition (MIMI) Strategy

Engines operating in Homogeneous Charge Compression Ignition (HCCI) combustion mode offer significant benefits of high fuel economy and low engine-out NO_x emissions over the conventional spark ignition (SI) combustion mode. However, due to the nature of HCCI combustion, traditional HCCI combustion can be realized only in a limited operating range. High load is limited by the trade-off between ringing (combustion noise) and stability (COV of IMEP). Low load is restricted by the trade-off between NO_x emissions and combustion stability (standard deviation of IMEP).

The present research is focused on the extension of lo w load limit of HCCI combustion by developing HCCI idle operation. The main obstacle in developing HCCI idle combustion is lack of available thermal energy necessary for successful auto-ignition. The current paper relates to a method for achieving the approriate environment for auto-ignition at idle and the optimal trade-off between combustion stability and NO_x emissions by employing multiple injection and multiple ignition (MIMI) strategy.

HCCI operating range was successfully extended to idle condition. Very low NO_x emissions ( < 1.0 g/kg-fuel) and good stability ( < 10 kPa stdv of IMEP) can be achieved at 800 rpm, 85 kPa NMEP condition. Compared to throttled homogeneous SIDI operation, over 25% fuel consumption benefit can be achieved.