Disclosed are model-based combustion timing systems and control logic for engine assemblies, methods for making/operating such engine assemblies, and motor vehicles with spark-ignited engine assemblies implementing model-based combustion timing. A method for controlling torque output of an engine assembly includes receiving a requested torque demand for the engine, and determining a current fuel command and valve timing for the engine's power cylinder(s). A first math model is used to determine a desired CA50 based on the requested torque demand, a power cylinder indicated mean effective pressure (IMEP), an expander cylinder IMEP, and the current fuel command/valve timing. A second math model is used to determine a maximum brake torque (MBT) CA50 based on power cylinder and expander cylinder IMEPs, and current fuel command/valve timing. An engine control unit determines a final spark timing based on a correlation between the desired CA50 and MBT CA50, modified by a spark timing gain.

A combined slip based driver command interpreter for a vehicle is provided which may be communicatively coupled to a steering wheel angle sensor, an acceleration pedal position sensor and a brake pedal position sensor, the combined slip based driver command interpreter including, but not limited to a memory configured to store a non-linear combined lateral slip model and a non-linear combined longitudinal slip model, and a processor, the processor configured to determine a driver's intended vehicle lateral velocity and a driver's intended vehicle yaw rate based upon the angle of the steering wheel, the position of the acceleration pedal, the position of the brake pedal, a longitudinal velocity of the vehicle, the non-linear combined lateral slip model and the non-linear combined longitudinal slip model.

An internal combustion engine is operated at fuel-rich conditions by adjusting one or more operating parameters such as, for example, a throttle, an ignition timing, a load coupled to the engine, a fuel pressure, power to a supercharger, and power to a preheater to maintain a specified engine speed and a temperature of an exhaust gas. Operating the engine under these conditions allows the engine to function as a reformer producing a synthesis gas comprising hydrogen and carbon monoxide.