Optimization of a steady-state and hybrid transitions in a diesel engine

A method of selecting an engine operating point in a powertrain system having multiple modes comprises that a desired axle torque is monitored based on a torque demand of an operator and a vehicle speed. an engine-torque range, and an engine-speed range are received and accessed more fuel losses as well as a plurality of emission losses for each available combustion mode of the diesel engine, each of the fuel and emission losses of each of several engine operating points corresponding to inside of the engine-torque region and the engine-speed range. The respective fuel and emission losses are compared to each of several possible engine operating points with the engine-torque region and the engine-speed range of the available combustion. A desired engine operating point in one of the available combustion modes is selected, which corresponds to one of the possible engine operating points, which comprises, based on the compared respective fuel and emission losses a lowest power loss.