Ask Kevin: Two-Stroke Innovation Question

Ask Kevin: Two-Stroke Innovation

Ask Kevin: Two-Stroke Innovation

QUESTION (received via Facebook): Can you take a look at this and tell me what you think? Not sure how the port cutout above the ring pack would work out, but it's interesting none the less.

ANSWER: This invention is a one-cylinder displacement machine applicable for compressors, air engines, steam engines and predominantly for small two-stroke internal combustion engines.

What is shown here is rather like a Bert-McCollum sleeve valve turned inside-out. Here, the piston oscillates around its axis instead of the sleeve doing so, to allow ports to be covered and uncovered in proper sequence. The crank with spherical joint used to drive the piston is the same as used in such classic sleeve-valve engines as the Bristol Hercules or Napier Sabre.

I'm sure this could be made to work, at least up to the speed at which the bending of the L-shaped drive piece began to impose a limit. Keeping piston-ring ends out of the ports could be a challenge!

Many two-stroke engines have been built which do not require oil in either the gasoline or above the level of the piston rings. When Toyota researched two-stroke auto engines in the late 1980s/early '90s, it used an inline-Six with four poppet valves in the head, and a separate charging blower. The engine had a sealed crankcase like that of any four-stroke auto engine, with pumped, recirculating oiling.

The classic GM two-stroke truck diesels are also separately charged, using Roots blowers, with a sealed crankcase, exhaust valves in the head and a ring of fresh-charge ports exposed just above the piston crown at BDC.

The Rolls-Royce "Crecy" V-12 two-stroke aircraft engine was prototyped and tested, based upon a concept explored by Harry Ricardo in his E65 test engine. This was a sleeve-valve design in which the sleeve was pulled down to allow exhaust to flow out through four wide ports thus exposed at the top of the cylinder.

There are so many clever ways to perform engine cycles, but only a few have attracted enough funding to permit them to be profitably tooled and produced. Now that the few are in production, any alternative engine would have to be so superior in sales and profitability that a manufacturer could cheerfully scrap existing tooling and start afresh. Pretty much the last time this happened was when the gas turbine replaced the large aircraft piston engine.

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