Figure B Piston position approximately half way on downstroke. Combustion chamber (3) expanding previously ignited air/fuel/air/egr combination. Middle chamber (2) compressing air only scavenge air. Inlet valve for middle chamber (2) is closed. Upper chamber (1) draws fuel and air mix through its’ open valve in the top of the upper chamber. Injection tube (4) holds a compressed fuel air mixture received from the upper chamber (1) on the previous upstroke. A static condition exists; as both valves, the pressure controlled one-way valve on top and the cam actuated valve in the head at the bottom are closed. 

Figure C Piston near Bottom Dead Center (BDC) on downstroke. Combustion chamber (3) exhausting burnt gases. Exhaust ports in lower cylinder open by piston. Middle chamber (2) scavenging with air only scavenge air. Inlet valve for middle chamber (2) is closed. Upper chamber (1) continues to draw fuel and air mix through its’ open valve in the top of the upper chamber. Injection tube (4) holds a compressed fuel air mixture received from the upper chamber (1) on the previous upstroke. A static condition exists; as both valves, the pressure controlled one-way valve on top and the cam actuated valve in the head at the bottom are closed. 

Figure D Piston position approximately half up on upstroke. Combustion chamber (3) compressing air/fuel/air/EGR combination. Exhaust ports closed. Middle chamber (2) draws in air only scavenge air. Inlet reed valve for middle chamber (2) is open. Upper chamber (1) compresses fuel and air mix . Injection tube (4) delivers a compressed fuel air mixture into the combustion chamber (3). The pressure controlled one-way valve at top is closed and the cam actuated valve in the head at the bottom is open. The evaporated fuel/air mixture rushes under pressure, into the combustion chamber, mixing with scavenge air. 

Figure E Piston near Top Dead Center (TDC) on upstroke. Combustion chamber (3) ready for ignition. Exhaust port closed. Middle chamber (2) approaching maximum intake. Inlet reed valve about to close. Upper chamber (1) nearing maximum compression, opens top valve into injection tube. Injection tube (4) pressure controlled one-way valve is open in response to pressure from upper chamber (1). Lower cam actuated valve is closed.

All the true functions of a four-stroke - in two strokes!

Operational Cycle

The middle chamber introduces its’ scavenge air Fig. B, (absent fuel to preclude fuel loss out the exhaust port) across the bottom of the head, in the upper most zone of the combustion chamber. Shaping and baffling the delivering passages allows delivery to be prioritized to the ignition zone. Properly optimized, this delivery will prioritize even when the quantity varies, enabling the scavenge air to become a controlled operating (combustion) variable. This feature (throttled scavenge air) is critical to emissions control as it makes it possible to avoid overly lean mixtures. 

The S2S throttles both scavenge air and fuel/air mix separately and delivers a locally prioritized charge of each in sequence, Fig. D. Working from the ignition zone outward, the scavenge air strongly dilutes and replaces the exhaust gases in the zone, followed by a rich mix of fuel/air into the same area, both according to demand. The two mix to form a zone of homogenous stochiometric overall mixture. Ignition is assured regardless of inducted quantity as the spark takes place in this zone. 

Air throttled into the upper chamber is compressed past a one-way valve Fig. E, into injection tube and held for timed delivery into the combustion chamber. An increase in combustion chamber air of up to 110% is possible; equal to a 50% increase over a typical two stroke of the same major bore diameter. Projected power using current performance levels would result in a two-stroke that could produce more than twice the power of a four stroke! 

Fuel may be added to this air at any appropriate point and time; upper chamber intake, upper chamber, or injection tube, using inexpensive metering devices. Fuel/air mixture undergoing compression in this manner is termed “pre-evaporated”, achieving the smallest droplet size possible, smaller than from the most expensive direct fuel injectors. This results in very stable, rapid combustion and low emissions.

CYCLE The chart below – depicts the sequence of events in the cycle of the SUPER TWO-STROKE tm.

© Primary Motion 2005