Various embodiments of the present invention are directed toward a two-piston linear combustion engine, comprising: a cylinder having a cylinder wall and a pair of ends, the cylinder including a combustion section disposed in a center portion of the cylinder; a pair of opposed piston assemblies adapted to move linearly within the cylinder, each piston assembly disposed on one side of the combustion section opposite the other piston assembly; a pair of driver sections, each driver section comprising a compression mechanism that directly provides at least some compression work during a compression stroke of the engine; and a pair of linear electromagnetic machines adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke, wherein each linear electromagnetic machine is located distal to an end of the cylinder; wherein the engine includes a variable expansion ratio greater than 50:1.