Company: Achates Power
Source: The Virtual Driver
According to Johnson, “Many in the industry said: ‘You can’t have efficient combustion chambers in the void between the two pistons, and all two-strokes have trouble with oil consumption.’ They were historically accurate, but we believed that if we applied the engineering, materials and other improvements made to conventional engines to our motors, we could overcome these obstacles. Plus, in not knowing what couldn’t be done, we did it.” The Achates engine has demonstrated the ability to meet EPA10 and Euro6 emission standards.
Engine mounting, drive system and other features depend on the application, but canting the engine to one side is a possibility.The fuel efficiency gains versus conventional engine designs are not single-digit increases. Johnson claims gains on the order of 10%-20%. That’s significant. And that’s against the most efficient engines in the world. “Typically we show, on average, a 15% benefit,” he says. That number, it should be noted, is against four-stroke diesels of similar output. There has not been an apples-to-apples comparison to a gasoline engine, but Johnson thinks the rule-of-thumb difference would be on the order of 50%.
Achates does not have fully developed engine designs ready for production, though they are working on them with potential customers. “Based on the parts reduction and downsizing that comes with that, and a two-stroke’s greater power density per cc, our forecasts say Achates engines will be less expensive than conventional four-stroke designs,” he says. But Johnson also acknowledges that conventional two-stroke diesels fell out of favor in the 1970s when emissions regulations began to come into effect, and the four-stroke took the lead because each engine event (intake, compression, ignition, exhaust) is discrete, while a two-stroke accomplishes them in half the crankshaft time. However, he points out this was before the advent of modern microelectronics, which made controlling these events a problem, and this accelerated the shift toward four-stroke diesels.