A method of operating an internal combustion engine, the method comprising: passing a first fuel and a second fuel into a combustion chamber of an engine cylinder to form a fuel mixture, the engine cylinder comprising a cylinder head and cylinder sidewalls, wherein the first fuel comprises a greater octane rating than the second fuel, and wherein the combustion chamber is defined at least partially by the cylinder head, the cylinder sidewalls, and a piston; and combusting the fuel mixture with a spark plug to translate the piston housed in the engine cylinder and rotate a crank shaft coupled to the piston; wherein: the combustion chamber comprises an end gas region and a central region; the end gas region is positioned furthest away from the spark plug in an area at or near a corner of the combustion chamber defined by an edge of the piston and the cylinder sidewalls; the central region more near to the spark plug than the end gas region; the first fuel and second fuel are passed into the combustion chamber such that: the first fuel is injected into the end gas region; the second fuel is injected into the central region; and the end gas region has a greater concentration of the first octane fuel than the central region, and the central region has a greater concentration of second octane fuel than the end gas region. passing a first fuel and a second fuel into a combustion chamber of an engine cylinder to form a fuel mixture, the engine cylinder comprising a cylinder head and cylinder sidewalls, wherein the first fuel comprises a greater octane rating than the second fuel, and wherein the combustion chamber is defined at least partially by the cylinder head, the cylinder sidewalls, and a piston; and combusting the fuel mixture with a spark plug to translate the piston housed in the engine cylinder and rotate a crank shaft coupled to the piston; wherein: the combustion chamber comprises an end gas region and a central region; the end gas region is positioned furthest away from the spark plug in an area at or near a corner of the combustion chamber defined by an edge of the piston and the cylinder sidewalls; the central region more near to the spark plug than the end gas region; the first fuel and second fuel are passed into the combustion chamber such that: the first fuel is injected into the end gas region; the second fuel is injected into the central region; and the end gas region has a greater concentration of the first octane fuel than the central region, and the central region has a greater concentration of second octane fuel than the end gas region. the combustion chamber comprises an end gas region and a central region; the end gas region is positioned furthest away from the spark plug in an area at or near a corner of the combustion chamber defined by an edge of the piston and the cylinder sidewalls; the central region more near to the spark plug than the end gas region; the first fuel and second fuel are passed into the combustion chamber such that: the first fuel is injected into the end gas region; the second fuel is injected into the central region; and the end gas region has a greater concentration of the first octane fuel than the central region, and the central region has a greater concentration of second octane fuel than the end gas region. the first fuel is injected into the end gas region; the second fuel is injected into the central region; and the end gas region has a greater concentration of the first octane fuel than the central region, and the central region has a greater concentration of second octane fuel than the end gas region. <EOS>