In an embodiment, the invention provides an internal combustion engine, including a first fuel injector that supplies a first fuel to a first predetermined region in a combustion chamber, and a second fuel injector that supplies a second fuel to a second predetermined region in the combustion chamber. The second fuel has an octane number that is different than an octane number of the first fuel, and the second predetermined region is different from the first predetermined region. An ignition device is configured to start ignition of one of the first and second fuels based on an ignition signal. An operation condition detector detects at least one engine operating condition. A controller is configured to provide the ignition signal to the ignition device and to determine which one of the first and second fuels to ignite by the ignition device based on the engine operation condition.