CONTROLLER FOR HYDROGEN ENGINE

A controller for a hydrogen engine controls a hydrogen engine including a selective catalytic reduction (SCR) device installed in an exhaust passage and a urea addition valve that adds urea to exhaust gas flowing through a portion of the exhaust passage upstream of the SCR device. Processing circuitry of the controller executes a reduction process that causes a urea addition amount of the urea addition valve to be smaller when a urea deposition amount of the SCR device is greater than or equal to a prescribed value than when the urea deposition amount is less than the prescribed value. The processing circuitry executes a lean-burn limiting process that sets an air-fuel ratio of an air-fuel mixture to be burned in the hydrogen engine to a value less than or equal to a prescribed lean-burn limiting value while the reduction process is reducing the urea addition amount.