The Two-Stroke Engine's Expected Revival

Don Sherman

Conventional wisdom suggests that our faithful internal combustion (IC) engines are heading the way of the buggy whip. The lithium-ion battery has arrived, emissions standards are tightening, and machinery which converts hydrocarbons to horsepower will have no role in the future some pundits say.

This point of view assumes that the 148-year old IC engine is tapped out and lacks potential for improvement. Actually, conventional engines and the cars they drive are recording notable gains in efficiency and cleanliness on a daily basis. The rise of two-stroke engines from their near-dead status is the latest evidence that internal combustion's best days lie ahead.

The four-stroke engine that powers all of today's cars and trucks (except for the Tesla Roadster) was the brilliant invention of German Nikolas Otto who wisely realized that compressing the fuel and air mixture before igniting it was the way to go. This idea came to him in 1861; three years later he and his backers were building and selling four-stroke engines that were vastly superior--mainly more fuel efficient--than alternative designs missing the compression stroke.

Naturally there were competitors with alternative designs and hopes of skirting Otto's patents not issued until 1877. Karl Benz and others had two-stroke engines running successfully by 1870 which delivered one power pulse per crankshaft revolution versus the two turns required in four-stroke engines.

The most common form of two-stroke requires no valvetrain resulting in major cost, weight, and complexity savings. That leaves the piston with a laundry list of responsibilities: pumping air and fuel into the combustion chamber, metering the lubricating oil, compressing the mixture, delivering power to the crankshaft, and ushering the spent gasses out of the cylinder. All of this occurs every 360-degree rotation of the crankshaft. The inevitable result is that some of the unprocessed fuel and all of the lubricant is swept out the exhaust pipe.

While the blue smoke trailing sixties-era Saabs, the last two-stroke cars in America, was tolerable in the day, noxious emissions are no longer socially acceptable.

Nevertheless, the compelling advantages inherent in two-strokes kept them going all these years. Two-stroke Trabants manufactured in the former East Germany lasted until 1991. And, thanks to the implementation of effective oil metering systems, improved piston and port designs, and direct electronically controlled fuel injection, two strokes are still powering many marine outboards, off-road motorcycles, and snowmobiles. Simple versions are the engine of choice for chainsaws, weed trimmers, some lawn mowers, and nearly all radio-controlled models.

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When will it go to production? I would like to see it powering the soon to arrive "Synergy Aircraft"!
Well, if that isn't the most annoying thing. We designed a oil-less, efi 2 stroke based on production parts for PWCs, but couldn't get exemptions from laws that prevent 2-stroke Jet Skis on certain lakes and waterways.This design is obviously designed to be a patent farm rather than a simple, reliable design. Has about 3x the necessary parts. EFI 2-strokes are already pretty clean, and oil-less 2 strokes without all the extra gingerbread have been around for 60 years...Like I said, annoying.

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