The Two-Stroke Lives (cleanly, too)

Evinrude's E-TEC engines have done the seemingly impossible: saving the air-cooled two-stroke from oblivion

 About 10 years ago, Chrysler’s Joe Goulart was singing the praises of the two-stroke engine as an automotive powerplant. His dream, however, couldn’t pass muster with the EPA. As a result, the automotive two-stroke engine died. Environmental concerns dogged the recreational two-stroke, as well. After years of doing nothing, the EPA set strict pollution limits for recreational vehicles (personal water craft, snowmobiles, etc.), which called into question the two-stroke’s continued viability. Fortunately, no one told George Broughton, director of Engineering, Boats and Outboard Engines Div. for Bombardier Recreational Products (Sturtevant, WI). He and his team created the Evinrude E-TEC family of two-strokes; engines that are clean and darn-near worry free.

Fuel Injection That Sings
“The trick was to make an engine that would idle at 500 rpm and make 1 hp, and run 6,000 rpm and make 250 hp while meeting the emission standards,” says Broughton. Part of the solution involved using a Lorentz coil. Better known as the voice coil that drives loudspeakers, a Lorentz coil is made up of a permanent magnet and coil winding, and produces a force proportional to the current applied to the coil. Which makes it perfect for devices requiring high acceleration, high frequency application, and a flat force vs. displacement output. Another big advantage is that it can push or pull, so it can be reset between injection events very quickly.

“The strength and duration of the injection pulse determine fuel droplet size,” says Broughton, “which varies to meet the unique needs of an air-cooled two-stroke.” At low engine speeds, small droplets offer the greatest atomization, and the most homogenous mixture. This is sprayed over the spark plug, and ignited as a stratified charge. At high speed, larger droplets are used to cool the top of the piston. (Cooling also is helped by use of a NASA-developed alloy three times stronger than conventional alloys at temperature. Broughton’s team found it while searching the Internet.)

A swirl-nozzle fuel injector with 0.046-in. tangential slots is another key to clean combustion. “It’s made through metal injection molding,” says Broughton, “and starts as a piece about three or four times bigger than the final product. Then it’s shrunk to size in an oven like a new pair of blue jeans in the dryer.” The fuel rail is pressurized to 30 psi, and the Lorentz coil amplifies this to 600 psi (1,000 psi is possible, but as yet unnecessary) under wide-open throttle conditions.

No Battery, Plenty of Spark
The E-TEC’s electrical system is based around a magneto – like a Model T – for a simple reason: recreational vehicles are put into storage at the end of each season, then pulled out when the weather turns favorable. Batteries die in storage, so relying on one to drive the fuel injection system and engine controller only adds to customer frustration. “The magneto produces from 150 to 300 volts,” says Broughton, “but that is reduced to 55 volts to drive the oil and fuel pumps and the fuel injectors. It’s further reduced to 14.7 volts to charge the battery, if the boat has one.”

Evinrude promises an E-TEC engine will start within one revolution, something most two-stroke owners will find hard to believe, especially for an engine that’s been in storage. The key is the sealed injection system. Though the fuel in the gas tank may oxidize over time, no air can enter the fuel system itself. The gas stays fresh. As the flywheel starts to turn, the magneto sends current to the engine controller, which determines where the piston is, when to inject the fuel and fire the spark plug – all inside of one revolution. At the end of three year’s use, and except for greasing the lower drive unit because of its constant immersion in water, Broughton insists the only item that may need service is the spark plug. “The E-TEC is designed to go three years without any dealer interaction,” he says.

Oil and Catalysts
But what if the regulations get tighter, won’t two-strokes be at a disadvantage because of their propensity to burn oil? “Oil isn’t a big player,” says Broughton, “because the amount burned is about 1% of the total intake charge, and it never mixes with the gasoline.” (The average user of a 50-hp E-TEC will go through two quarts of oil per year.) Hydrocarbons are the predominant pollutant, a portion of which are scavenged and burned in the next combustion cycle. When emission standards tighten, Broughton will be ready with a simple reduction catalyst he terms, “1970’s technology.” Right now, the engine is clean enough to pass California’s 2008 standards.

Broughton doesn’t claim E-TEC technology might have saved the automotive two-stroke, but he does suggest Detroit’s obsession with preventing the lubricating oil from being burned during combustion sent them down the wrong path. “Their concentration on retaining an oil sump, oil scraper rings, and relying on plain bearings instead of roller bearings,” he theorizes, “increased the amount of oil burned, which harmed emissions performance.” And it may be another reason why automotive two-stroke emission performance degraded over time. “The E-Tec actually gets cleaner as it progresses through the EPA test,” he says. “And we never have to worry about the potential for secondary pollution when changing the oil.” Maybe not, but try selling that to the EPA when discussing emission tradeoffs.