Operating system for internal combustion engine

An operating system for an internal combustion engine, comprising:

• a fuel separation device configured to separate a mixed fuel of a high-octane fuel and a low-octane fuel having a lower octane number than the high-octane fuel to a first fuel having a higher concentration of the high-octane fuel than the mixed fuel and a second fuel having a lower concentration of the high-octane fuel than the mixed fuel;
• an internal combustion engine operating by combusting at least one of the first fuel and the second fuel in a combustion chamber;
• a first fuel injection valve and a second fuel injection valve configured to be supplied with the first fuel and the second fuel separated by the fuel separation device, respectively, and to inject the first fuel and the second fuel to the combustion chamber of the internal combustion engine for combustion separately at a fuel injection amount not less than a prescribed lower injection amount limit, respectively;
• and
• a fuel supply controller configured to variably set a fuel supply ratio parameter defining a desired value of a supply ratio of the high-octane fuel which is a ratio of a supplied amount of the high-octane fuel in the fuels supplied to the combustion chamber of the internal combustion engine to vary according to at least an output torque from the internal combustion engine and to control the fuel injection quantities from the first fuel injection valve and the second fuel injection valve respectively according to the set fuel supply ratio parameter;
• wherein the fuel separation device is configured to separate the first fuel from the mixed fuel to have a concentration of the high-octane fuel not more than a prescribed upper limit, and
• the prescribed upper limit value is defined in such a way that a first high-octane fuel consumption amount is less than a second high-octane fuel consumption amount by a prescribed amount or more,
• the first high-octane fuel consumption amount is a consumed amount of the high-octane fuel which is detected under such a condition that the internal combustion engine is operated at a preliminarily prescribed operation mode including at least an operation state of the internal combustion engine in which the fuel injection amount from the first fuel injection valve is equal to the lower injection amount limit by using the first fuel and the second fuel separated by the fuel separation device, and
• the second high-octane fuel consumption amount is a consumed amount of the high-octane fuel which is detected under such a condition that the internal combustion engine is operated at the prescribed operation mode by using the first fuel having the concentration of the high-octane fuel at 100% and the second fuel having the concentration of the high-octane fuel at 0%.