Fuel tolerant combustion engine with reduced knock sensitivity

A supplemental cylinder head assembly mountable to an engine cylinder, said engine having a power piston movable within a combustion chamber and adapted to transfer power to a drive train during operation of said engine comprising:

• an accumulator piston housing having an internal volume;
• a combustion accumulator piston movable within said housing;
• means on said combustion accumulator piston for dividing said internal volume of said housing into a first volume and a second volume;
• means for providing fluid communication between said first and said second volumes during movement of said combustion accumulator piston within said housing;
• means for guiding movement of said combustion accumulator piston within said housing during operation of said engine;
• means for loading a predetermined force on said combustion accumulator piston to urge said combustion accumulator piston and said means for dividing said internal volume to a resting position during operation of said engine;
• and
• means for mounting said assembly to said engine cylinder whereby said engine is operable on any fuel having an octane value between zero and 130;
• wherein said means for providing fluid communication between said first and said second volumes further comprises a first multiplicity of depressions in a first interior wall surface of said accumulator piston housing.