Method and system for engine control

A method for a hybrid vehicle, comprising:

• propelling the vehicle via an engine using a first fuel selected based on driver demand;
• and
• in response to a change in driver demand,
• comparing, for the change in driver demand, a first value of fuel cost for operating with the first fuel with a first amount of stored power offset to a second value of fuel cost for operating with a second, different fuel with a second, different amount of stored power offset;
• and
• maintaining usage of the first fuel when the first value is lower than the second value;
• and
• transitioning to usage of the second fuel when the first value is higher than the second value to deliver the changed driver demand.

A hybrid vehicle system, comprising:

• a motor powered via an energy storage system;
• an internal combustion engine including a cylinder;
• a first fuel injector for injecting a first fuel into the cylinder;
• a second fuel injector for injecting a second fuel into the cylinder;
• vehicle wheels propelled via one or more of motor torque and engine torque;
• a pedal position sensor for receiving an operator torque demand;
• and
• a controller with computer-readable instructions stored on non-transitory memory for:
• responsive to a first change in operator torque demand, maintaining injection of the first fuel while changing a state of charge of the energy storage system by a first amount to meet the torque demand;
• and
• responsive to a second, different change in operator torque demand, shifting to injection of the second fuel while changing the state of charge of the energy storage system by a second, different amount to meet the torque demand.