Engine block and a process for hybrid ignition of an engine

An engine block comprising a combustion chamber, an inlet for introducing a fuel/air mixture into the combustion chamber and an outlet for expelling combusted fuel/air mixture from the combustion chamber, a piston that reciprocates within the combustion chamber to compress the fuel/air mixture therein, and a reciprocating separator that separates the combustion chamber into a primary chamber and a secondary chamber, wherein the primary chamber is provided with an ignition source to initiate combustion in the primary chamber, which moves the reciprocating separator to compress and spontaneously combust the fuel/air mixture in the secondary chamber to drive the piston, wherein the reciprocating separator contains an aperture through which fuel/air mixture communicates between the secondary chamber and the primary chamber and the piston supports a closer that seals the secondary chamber by engaging the aperture.