The patented D-cycle (differential-stroke cycle) is a 2-/4-cycle hybrid, which is by splitting ring section from its skirt to be operated via a (valvetrain-like) piston-train to pump gases (Breathe) during the exhaust and intake strokes and to reunite with skirt for the heavy compressing and power strokes (Run) to completes 4 strokes (different in both displacements and periods) per revolution.

The piston-train is synchronized with the crankshaft, eliminating the reduction gear system. It can retrofit existing engines for >2.5 times more power (torque); or new engines with 20% fuel efficiency and >2.5-times torque gains from the D-cycle retrofit.

D-cycles can also make a hybrid of diesel’s-compression and gasoline’s-spark ignitions combustion - for diesel’s power and efficiency and gasoline’s clean exhaust - by port injection of stoichiometrically charged air and fuel mist (using exhaust heat) into the cylinder to avoid soot formation. The combustion gases contain no extra (fresh) air but about 1/3 to ½ of burnt exhaust, called BGR (Burnt Gas Retention) from previous stroke cycle to avoid the NOx formation. (The BGR can regulate the ignition timing and burn rate which is somewhat like EGR). This piston-train air pumping can be controlled via ECU for cycle-to-cycle transient operations. This is compression ignition followed by the low temperature combustion of the gasoline type stoichiometrically charged intake to avoid the harmful NOx exhaust. This BGR-controlled dilution can also be assisted by EGR.