Patent ID: 7059281

Claim:
A method of operating a four-stroke controlled auto-ignition combustion engine having at least one cylinder with direct fuel injection and containing a piston reciprocably connected with a crank and defining a variable volume combustion chamber including an intake valve controlling communication with an air intake and an exhaust valve controlling communication with an exhaust outlet, the mcthod comprising: operating the engine with two sequential pairs of expansion and contraction strokes during two revolutions of the crank; opening both the intake and exhaust valves during terminal portions of the expansion strokes and initial portions of the contraction strokes; and injecting fuel directly into the combustion chamber for mixing with retained gases and igniting the fuel near the ends of the contraction strokes; whereby combustion gases are expanded to produce power during major portions of the expansion strokes when the valves are closed, combusted gases are blown down intothe exhaust outlet and the air inlet as the valves are opened and the combusted gases are partially redrawn into the cylinder with fresh air during the terminal portions of the expansion strokes, such that the air and exhaust gas charges are heated by the hot exhaust gases; and portions of the charges are expelled into the exhaust outlet and the air intake during the initial portions of the contraction strokes and the remaining portions of the charges and injected fuel are compressed during major portions of the contraction strokes, after closing of the valves, for ignition of the resulting compressed charges of the dilute fuel/air and exhaust gas mixture.