To determine an upper limit quantity of an injection quantity of fuel for combustion at which excessive noise caused by HCCI (Homogeneous Charge Compression Ignition) combustion can be suppressed in a fuel injection quantity control device adopted to an internal combustion engine capable of injecting fuel for HCCI combustion and fuel for diffusion combustion at the same cycle.

This fuel injection quantity control device determines the upper limit quantity of the fuel injection quantity qhcci for HCCI combustion as a smaller value by using a linear function funcqhccimax assuming that a temperature in a cylinder becomes higher as a total demand fuel injection quantity qfin is larger, and controls the fuel injection quantity qhcci for HCCI combustion so that a fuel concentration in a homogeneous charge air fuel mixture becomes smaller. Noise by the HCCI combustion becomes higher as HCCI combustion reaction speed becomes higher. Accordingly, a reaction speed of HCCT combustion is presented from exceeding upper limit reaction speed corresponding to an upper limit of a range in which the noise is not excessively high since fuel injection quantity qhcci for HCCI combustion is controlled as above.

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