An engine control unit of a multi-fuel is provided. The engine consumes a mixture of a first combustion fuel and a second combustion fuel. The engine control unit includes hardware circuitry that includes one or more processors configured to calculate an autoignition delay of the mixture of the air and the second combustion fuel based on current operating conditions of the multi-fuel engine. The one or more processors also are configured to calculate an upper limit on an amount of the second combustion fuel that is supplied to the multi-fuel engine based on the autoignition delay that is calculated.