NOVELTY - The system has an ECU (28) determining presence or absence of engine knock generation based on in-cylinder combustion state at time of lowering the blend ratio of the second fuel relative to the first fuel. The blend ratio of second fuel is returned to its original value if such knock generation is present or is left as is if the knock generation is absent. The speed of consumption of second fuel is calculated based on the blend ratio and present fuel consumption. The rate of generation of second fuel from first fuel is controlled to match with speed of consumption.    USE - Fuel control system for internal combustion engine, such as in-pipe direct injection gasoline engine capable of homogeneous charge compression ignition and combustion of fuels.    ADVANTAGE - By supplying a proper amount of second fuel with high anti-knock quality to the engine cylinder, discontinuation of homogeneous charge compression ignition and combustion usually due to insufficient supply and occurrence of catalyst degradation due to over-supply can be avoided.    DETAILED DESCRIPTION - The system has an ECU (28) to determine the blend ratio of two fuels when both fuels are injected in the engine cylinder (1). The ECU determines presence or absence of engine knock generation based on in-cylinder combustion state at time of lowering the blend ratio of the second fuel relative to the first fuel. The blend ratio of second fuel is returned to its original value if such knock generation is present or is left as is if the knock generation is absent. The speed of consumption of second fuel is calculated based on the blend ratio and present fuel consumption. The rate of generation of second fuel resulting from modification of first fuel by a fuel reforming reactor (18) is controlled to match with speed of consumption. The second fuel obtains a higher anti-knock quality by having an aromatic content rate higher than that of the first fuel. The reactor relies on dehydrogenation and cyclization reaction to produce the second fuel. An INDEPENDENT CLAIM is also included for a fuel control method.    DESCRIPTION OF DRAWING(S) - The drawing shows the block diagram of a fuel control system. (Drawing includes non-English language text)    Engine cylinder (1)    Piston (2)    Connecting rod (3)    Fuel reforming reactor (18)    ECU (28)