A system includes a controller operable to communicate with at least one sensor and an engine. The controller responds to one or more signals received from the sensor and influences engine operation based on determined engine operation threshold limits and information regarding a first fuel and a second, different fuel. The controller is configured to change or maintain engine operation based on the one or more signals compared to the threshold limits, and to change or maintain an engine fuel supply to control specific fuel consumption of at least one of the first and second fuels and to achieve values for the one or more signals in a determined range relative to the threshold limits. The one or more signals indicate an exhaust emissions parameter or at least one of pre-turbine temperature, fuel injection pressure, turbocharger rotational speed, peak firing pressure, rate of pressure rise, or knock intensity.