A direct injection spark ignition multi-cylinder internal combustion
engine operative in a controlled auto-ignition combustion mode includes a
direct fuel injection system, a spark ignition system and a controllable
engine valve system. The air/fuel ratio in the exhaust gas feedstream and
an intake mass air flow are measured and an actual air/fuel ratio is
calculated based upon the intake mass air flow and engine fueling.
Magnitude of a negative valve overlap period between an exhaust valve
closing and an intake valve opening is adjusted based upon the measured
mass air flow. Timing of pre-injection fueling is adjusted during the
negative valve overlap period based upon the measured air/fuel ratio.