The disclosed invention includes a heat engine where combustion, expansion, and compression are independent, continuous, parallel cycles. The disclosed engine includes a crankcase situated between two axially-aligned, opposed cylinder blocks. Each opposed cylinder block contains zero-clearance cylinders. An oscillating two-headed piston separates each cylinder into expansion and compression chambers. A connecting rod connects the piston heads of opposed cylinder pairs, and articulates with a central, linear-throw, planetary crank mechanism. A single, rotary disk valve mates with each external expander face of the paired, opposed cylinder blocks to regulate expansion and exhaust functions. Controllable intake and outlet valves, integrated within each internal compressor face of the paired cylinder blocks, regulate intake, compression, and regenerative engine braking functions. A separate combustion chamber with heat regeneration capabilities and at least one compressed-air storage reservoir are included.