Howard

Sleeve valves would work fine to make a four stroke opposed piston engine. Whether four stroke has any advantages in that configuration is different matter. Maybe from pollution control but I'm sceptical.

Professor Timoney did some interesting work on improving the efficiency, economy and peak power output of the TS 3 motor which could usefully be followed up exploiting modern technology. Basic concept was to put the rocker arms connecting the pistons to the crankshaft on eccentric bearings that could turn to vary the piston stroke. Stroke variation was self acting under the control of a simple spring and damper arrangement. The engine was able to operate at near constant BMEP over a wide speed and power range for better economy, especially at light loads, when the stroke was longer. Also gave higher peak power at full throttle but short stroking considerably increased fuel consumption. Timoney later added an exhaust turbine coupled into the transmission drive line to get useful work out of the exhaust. Major benefits under high throttle short stroking conditions. Apparently worked well on the testbed but the relative complexity meant it wasn't considered commercially viable at that time.

Maybe something like the rotary exhaust expender unit proposed for CREEV and similar Wankel based systems would be a better approach than the exhaust turbine. At least the operating RPM would be the same as that of the parent engine making coupling easier. Secondary expansion, with a bit of after burning if need be, also seriously reduces nitrous oxide emissions.

There has long been considerable interest in exploiting the opposed piston motor, Achates being just one relatively recent entrant. But no one has been able to make the push into production.

Clive