Various embodiments of the present invention are directed toward a 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, each piston
assembly including a spring rod and a piston comprising a
solid front section adjacent the combustion section and a hollow back section comprising a
gas spring 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 the engine includes a variable
expansion ratio greater than 50:1.