An internal combustion engine is disclosed in which at least one cylinder is adapted to run in homogeneous-charge compression-ignition (HCCI) combustion mode and at least one cylinder is adapted to run in spark-ignition (SI) combustion mode with the HCCI cylinder having a compression ratio at least 2 ratios higher than the SI cylinder. The intakes and exhausts of the HCCI and SI cylinders are separated with a throttle valve disposed in each intake and exhaust aftertreatment devices tailored to each combustion mode disposed in the exhausts.