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A Two-Stroke Revival, Without the Blue Haze. my research lol


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NO new car marketed in the United States has been powered by a two-stroke engine since Saab phased out its hard-to-housebreak 3-cylinder in the late 1960s, when federal air pollution laws were taking hold. And with images from Eastern Europe of belching Trabants still fresh, there hasn’t been much of a clamor for a two-stroke revival, either.

Simple and inexpensive, yet powerful for their size, two-stroke engines held great appeal in the years before fuel economy and exhaust emissions became primary concerns. But now, with the technology of conventional four-stroke engines quite mature, there is renewed interest in taming the two-stroke to compete with diesels, hybrids and electrics as part of the solution to meeting future mileage standards.

Though two-strokes have largely faded from motorcycles and may be endangered even in applications like lawn trimmers, news of recent progress in research programs has emerged in Europe and the United States. For instance, EcoMotors International, based in Troy, Mich., has had encouraging results in tests of its experimental engines, which the company hopes will be used to power everything from stationary generators to tractor-trailer rigs.

Last year a collaborative effort in Britain of Lotus Engineering, Jaguar and Queen’s University Belfast began developing a two-stroke engine called Omnivore, for its ability to run on a variety of fuels. The direct-injection engine has the ability to vary its compression ratio from 8:1 to 40:1 by changing the volume of the combustion chamber. On Dec. 9, Lotus released test results that it termed successful for fuel economy and exhaust emissions.

And in Chapman, Kan., impressively credentialed scientists, engineers and investors are developing what they call the Grail Engine, a reference to their quest for a power plant beyond current levels of efficiency and greenness.

The Grail Engine differs from two-stroke convention in the use of an intake valve positioned in the top of the piston to admit the fresh charge of air for combustion. It also has an overhead exhaust valve, surrounded by three spark plugs, and a fuel injector at the top of the combustion chamber. The project’s goals are to exceed 100 miles per gallon and 100 horsepower from a clean-burning 1-liter engine. While there is no running prototype, interest in its approach has brought a visit by research engineers from Honda Motor.

In simplest terms, the strength of the two-stroke engine lies in its delivery of a power pulse with every revolution of the crankshaft; the familiar four-stroke piston engine in today’s cars fires each cylinder on every other revolution.

Both types of engines use a four-step combustion cycle that converts fuel and air to power: intake, compression, ignition and exhaust. But the two-stroke does it all with just two sweeps of the piston through the cylinder, one up and one down. The four-stroke design takes twice as many trips of the piston up and down the cylinder, allowing more time for each step and placing less stress on the engine.

Today’s gasoline piston engines trace their roots to Nikolaus Otto, a German inventor. Though patents covering his breakthrough were not issued until 1877, Otto and his partners began manufacturing and selling four-stroke engines in 1864. It was a lucrative business that immediately stirred competition.

A two-stroke alternative was championed by Karl Benz and others. Two-stroke engines have generally been lighter, cheaper and simpler because they did not need an intricate system of valves that open and close to direct air and fuel into the cylinders and to let burned gases exit. Instead, the piston takes on this job, along with a handful of other tasks.

One drawback of the familiar, simple two-stroke engine designs is that some unburned fuel and most of the lubricating oil are swept out the exhaust pipe. Decades ago, the blue clouds trailing a ’60s Saab were deemed tolerable, but no longer.

In spite of its shortcomings, the two-stroke never died. Instead, improved designs, electronic fuel injection and automatic oil-metering systems kept it practical for chainsaws, outboard motors and snowmobiles.

Donald L. Runkle, who was appointed chief executive of EcoMotors last September, spent 31 years at General Motors in top engineering posts. He can barely conceal his enthusiasm for the two-stroke his company is pursuing. “Our OPOC design is the cellphone of power sources,” he said. The two-stroke operating cycle is just one of several unusual aspects of the EcoMotors engine. It also has an opposed-piston, opposed-cylinder layout — the source of its OPOC name — and an electrically assisted turbocharger. The first-generation version runs on diesel fuel.

Peter Hofbauer, chairman and chief technical officer of EcoMotors, conceived this engine in 1997. The idea grew out of his 20-year tenure at Volkswagen, where he developed VW’s first diesel engines and the unusual narrow-angle VR6.

The opposed-cylinder layout — paired horizontal cylinders with a crankshaft down the middle — was the key to the VW Beetle engine’s small size and smoothness. In the late 1970s, while developing a water-cooled version of that engine, Mr. Hofbauer investigated the opposed-piston concept, which had been used in a variety of military, aircraft, marine and industrial engines. The opposed-piston engine has two pistons that move like clapping hands inside each cylinder. Outboard pistons are attached to the crankshaft through long tension rods while the inboard pistons have conventional connecting rods.

As the outboard piston nears the end of its motion away from the crankshaft, it uncovers ports — essentially the window opening of a passageway in the cylinder wall — that admit fresh air to the cylinder. When the twin pistons move toward each other, two injectors deliver fuel to the cylinder, initiating combustion. The rising pressure drives the pistons apart. EcoMotors calls the process inside each cylinder a Direct Gas Exchange Cycle, because the air and fuel mixture moves in only one direction.

Mr. Hofbauer says the EcoMotors engine has twice the power density — the output on a per-pound, or per-cylinder-displacement basis — of conventional engines. The production cost is 20 percent less, he said, because the engine has only half the parts of a conventional power plant. Ganging modules together and using an electric clutch to shut down one module when its power isn’t needed yields a 45 percent gain in efficiency over conventional engines. Mr. Hofbauer said a hybrid configuration, with two power modules assisted by a motor-generator, would raise efficiency an additional 10 percent.

According to Mr. Runkle, the OPOC engine has already cleared two big hurdles in its initial development: it is capable of meeting future gas and diesel emission standards while operating more efficiently — by 15 to 60 percent — than conventional engines. Mr. Runkle has his eye on a shuttered factory in Livonia, Mich., not far from the EcoMotors headquarters. His dream is to put the Motor City back on the map as the world’s pre-eminent source of clean, cost-effective and fuel-efficient engines.





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Is it just me, or is a complicaed 2 stroke not very attractive for some reason? especially for motor cycles, I'm sure we'd all love a new generation of fast, light 2 strokes, but if they're as complicated as they sound, then I'm sceptical.

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The idea layout is a big bang V4 500CC motor with the dytech system (basically a 500cc gp motor with direct injection). Thats it, nothing more complicated it'll be hard enough like that, still have a powerband and go link stink. When will manufacturers realise this?

They had it working on an RS250 ande believe in a GT750 aswell. I think the only reason we haven't seen a new sports stroker is percieved public opinion, maybe the 250 marker is dead but I definatly want a 500cc stroker and I'm convinced that I am not alone.



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What if you could get a motor with nearly all of the characteristics of a 4-stroke and the lightweight and power of a 2-stroke rolled into one? Eyvind Boyesen may just be onto something with his revolutionary design.

Ski-Doo introduced the E-TEC motor this year with direct injection and very low emissions while keeping the power and responsiveness, plus increasing the fuel efficiency. Ski-Doo, using the acquired direct injection from their outboard division, accomplished this task using electronics and computer chips. Boyesen, on the other hand, has built prototype engines that accomplish this using mechanical means and the old-fashioned carburetor.

We talked with Joe Nocentino at Hay Days and he was eager to share the Boyesen engine with us. At first we weren’t sure what we were looking at; after all we’ve seen a lot of engines and prototypes that never seem to make it to the market. However, Joe assured us that this prototype is being developed along with a University and a manufacturer and it could show up in future sleds, as well as in Asia, where 2-stroke engines are more of the norm in most transportation.

There’s no denying that 2-stroke engines have a few advantages over 4-strokes; some being lighter weight, more compactness and a power stroke on every cycle. Where the 2-stroke falls short is longevity, efficiency, and emissions. These are changing with the advent of the E-TEC from Ski-Doo to be sure, but Boyesen has developed a system that increases the efficiency and decreases the emissions, similar to that of a 4-stroke.

2-Stroke Basics

We’re all familiar with the exhaust valve on a modern 2-stroke motor. This valve acts to raise or lower the exhaust port depending upon the RPMs of the engine to get the most power it can. This shuts off the exiting fuel charge so that fuel charges will combust more completely. The valves work in combination with a tuned exhaust pipe, which sends a sound wave back toward the ports to push unburned fuel back into the cylinder. If the timing of the valves or the pipe isn’t tuned with the motor or any of its modifications, the power is off, efficiency is low and emissions are high. The charge of fuel that is pushed back into the cylinder is also mixed with spent fuel, degrading some of the power that could be achieved with a fresh charge. Basically it would be like breathing fresh air, but mixing the exhaled air with it, and breathing it in again. Yes, we’ve all done it, but don’t your lungs feel better breathing fresh clean air?

With the E-Tec motor, the fuel charge and air charge are more controlled, and the tuned pipe and exhaust valves all work in sync to provide the most efficient power/emissions/economy combination. A carbureted motor doesn’t’ have the same advantage as an EFI or Direct Injected motor. But Boyesen may have solved part of the equation with a low-cost solution that can be used in conjunction with a carb and without the need for a tuned pipe.


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only a nuter poking his nose in ,but if a reed vale sorts the inlet charge,why not an axhaust reed system,surly this can be done....hi.ho.hi.ho,its off to the shed we go... :eusa_whistle:

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only a nuter poking his nose in ,but if a reed vale sorts the inlet charge,why not an axhaust reed system,surly this can be done....hi.ho.hi.ho,its off to the shed we go... :eusa_whistle:

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