Method and apparatus for controlling fuel reforming under low-load operating conditions using exhaust recompression in a homogeneous charge compression ignition engine

Method for operating an internal combustion engine in a controlled auto-ignition combustion mode, comprising:

• determining a preferred engine operating point;
• determining a fueling rate, a preferred air/fuel ratio and a preferred mass air flow based upon the preferred engine operating point;
• measuring an air/fuel ratio of the exhaust gas feedstream;
• measuring mass air flow of engine intake air;
• determining an actual air/fuel ratio based upon the measured mass air flow and the fueling rate;
• controlling engine valve timing to achieve a preferred negative valve overlap period based upon the preferred air/fuel ratio;
• and
• controlling timing of a pre-injection fueling during the negative valve overlap period to achieve a preferred amount of fuel reforming.

Method for controlling fuel reforming in a direct injection spark ignition internal combustion engine operating in a controlled auto-ignition combustion mode, comprising:

• determining a preferred engine operating point based upon an operator torque request;
• determining a fueling rate, a preferred air/fuel ratio and a preferred mass air flow based upon the preferred engine operating point;
• measuring an air/fuel ratio of the exhaust gas feedstream;
• measuring mass air flow of engine intake air;
• determining an actual air/fuel ratio based upon the measured mass air flow and the fueling rate;
• and
• controlling timing of a pre-injection fueling during the negative valve overlap period based upon a difference between the actual air/fuel ratio and the measured air/fuel ratio.