| abstract |
Method for operating an engine having a piston reciprocable in a cylinder, an intake port for admitting air, an exhaust valve controlled by a valve actuator independently of crankshaft position, spark ignition, and fuel injection. During a first stroke the piston moves from BDC to TDC, the intake port is closed, the exhaust valve is closed, and fuel is injected. During a second stroke (TDC to BDC) the exhaust valve remains closed, lowering the pressure and causing some evaporation of the fuel-air mixture. During a third stroke (BDC to TDC), the pressure of the fuel-air mixture is again increased and finally ignited. During a fourth stroke (TDC to BDC) the ignited mixture expands, followed by opening the exhaust valve and the intake port. The second and third strokes enhance evaporation thus permit ignition of low vapor pressure fuel in a cold engine. Once the engine is hot, the valve actuators permit transition to a two-stroke-cycle. |