Controller for internal combustion engine and method for controlling internal combustion engine

A controller for an internal combustion engine, the internal combustion engine being mounted on a vehicle and including a fuel injection valve configured to inject fuel so that the fuel is supplied to a combustion chamber of the internal combustion engine, a delivery pipe configured to supply fuel to the fuel injection valve, and a sensor provided at an upstream side of the delivery pipe and configured to detect a physical quantity correlated with a density of the fuel, wherein

• the delivery pipe includes a supply area and is configured to supply the fuel from the supply area to the fuel injection valve,
• when a posture of the vehicle is horizontal, the supply area is located at a position biased toward one of an upper side or a lower side of the delivery pipe in a vertical direction, and
• the controller comprising processing circuitry, wherein the processing circuitry is configured to execute
• an estimation process that estimates a density parameter of fuel in an upper layer portion of the delivery pipe and a density parameter of fuel in a lower layer portion of the delivery pipe in the vertical direction based on a detection value of the sensor, and
• an operation process that includes acquiring a density parameter of the fuel injected from the fuel injection valve based on at least one of the estimated density parameter of the fuel in the upper layer portion or the estimated density parameter of the fuel in the lower layer portion and operating an operation unit of the internal combustion engine based on the acquired density parameter,
• the density parameter of one of the upper layer portion or the lower layer portion located closer to the supply area has a higher degree of contribution to the density parameter of the fuel injected from the fuel injection valve, and
• the estimation process includes a process that assumes that when the density of the fuel flowing into the delivery pipe is high, a greater proportion of the fuel flowing into the delivery pipe flows into the lower layer portion than when the density of the fuel flowing into the delivery pipe is low.