Method and system for controlling water injection

A method for an engine coupled with a continuously variable transmission (CVT), comprising:

• for a driver demand,
• estimating a first efficiency associated with operating the engine with water injection disabled and a second efficiency associated with operating the engine with water injection enabled while operating with a knock-adjusted and friction-adjusted engine speed-load profile;
• and
• in response to the second efficiency being higher than the first efficiency, and a water availability being higher than a threshold, enabling water injection and transitioning to the knock-adjusted and friction-adjusted engine speed-load profile via adjustments to a speed ratio of the CVT.

A vehicle system, comprising:

• an engine;
• a fuel injector for delivering fuel from a fuel tank to the engine;
• a water injector for delivering water from a water reservoir to the engine;
• a continuously variable transmission (CVT) coupling the engine to vehicle wheels, the CVT having a plurality of speed ratios;
• and
• a controller with computer readable instructions stored on non-transitory memory for:
• estimating a first efficiency associated with operating the engine with the water injector deactivated and a second efficiency associated with operating the engine with a first modified engine speed-load profile and the water injector activated;
• if the second efficiency is higher than the first efficiency, and a water level in the water reservoir is higher than a threshold, activating the water injector while selecting one of the plurality of speed ratios of the CVT to provide the first modified engine speed-load profile;
• and
• if the second efficiency is lower than the first efficiency, or the water level in the water reservoir is lower than the threshold, deactivating the water injector while selecting another one of the plurality of speed ratios of the CVT to provide a second modified engine speed-load profile, different from the first modified engine speed-load profile.