EcoMotors’ OPOC program enters combustion-optimization phase
The architecture and component design of the OPOC engine provides perfect primary- and secondary-order balance. Note long and short connecting rods in this recent CAD rendering.
EcoMotors International’s development of an innovative lightweight, multifuel engine aimed at diverse vehicle applications has entered its combustion-optimization phase, after the two-year-old startup company received $23.5 million in new funding from its primary investor, Vinod Khosla, and Microsoft Chairman Bill Gates.
“The sixth generation of our opposed-piston opposed-cylinder (OPOC) engine is on the dyno now,” EcoMotors CEO Don Runkle told AEI. “The Series B financing [from Khosla and Gates] will support our combustion work and testing, which I expect will conclude about half way through next year,” he said.
Runkle expects the direct-injected, turbocharged, two-stroke OPOC could be ready for production within two to three years, given the current development plan. The program is based on a modular architecture supporting a range of cylinder bore diameters—currently 100-, 75-, 65-, and 30-mm (3.93-, 2.95-, 2.56-, and 1.18-in diameters, respectively).
Each “power module,” as Runkle calls them, includes a pair of horizontally-opposed cylinders with two pistons in each, operated via pairs of short and long connecting rods by a common crankshaft. The opposing pistons share a combustion space in each cylinder. Power can be multiplied by adding another cylinder set.
Extensive dynamometer testing of diesel variants of the EM100 (100-mm bore) has given the company’s engineers “compelling data” showing the engine’s emissions, efficiency, and power are on track to achieve targets, Runkle said. A gasoline-fueled version is also in the works.
The OPOC’s two-stroke combustion cycle, low internal friction levels, and less heat rejection make it capable of producing twice the power density of a comparable conventional four-stroke; Runkle said the EM100 has exceeded one horsepower per pound in dyno testing. And the engine’s sophisticated engine-management and turbocharger controls give it superior cylinder scavenging and exhaust-recirculation capability, he added.
Early tests have shown the OPOC capable of delivering up to 50% greater fuel efficiency than a comparable conventional ICE. While EcoMotors initially targeted the commercial and military vehicle sectors—the engine is capable of running on JP-8 in addition to diesel fuel—the company also has had requests from light-duty vehicle OEMs. They are interested in smaller-displacement OPOC units for use in extended-range electric vehicle (E-REV) powertrains, Runkle explained.
The aerospace industry also perceives benefits in the OPOC’s high power density, lower mass, potential fuel economy, and reduced bill of materials. Eurocopter, the rotary-wing division of European aerospace giant EADS, installed two diesel versions of the OPOC in its hybrid-electric “bluecopter” concept aircraft unveiled at the recent Berlin Air Show.
“EADS chose our engines because of their power density and light weight,” Runkle said. “It’s a six-passenger helicopter, with a five-blade rotor—a very futuristic design. They want to fly it next year and when they do, I’ll be in it!”
The combustion optimization phase of development now underway on a diesel EM100 includes creating engine-control maps and working through a myriad of design and engineering details—including final piston-crown geometries, the number of fuel injectors to be fitted per cylinder, and injection spray angles, patterns, and pressure.
“We’re addressing all the parameters we can adjust during optimization in making sure the engine passes the emissions required, and that we’re getting the efficiency and specific power we deserve from this design,” Runkle noted.
Regarding diesel emissions, Runkle said the goal is “to control NOx in the combustion chamber.” He explained that EcoMotors’ electrically-controlled turbocharger (developed by company founder and technology chief, Peter Hofbauer) provides “significant benefits” in meeting increasingly stringent emissions standards below the current U.S. EPA Tier2 Bin5 levels with minimal aftertreatment.
“We can pump very high levels of EGR to keep combustion temperatures below the point which NOx forms. That is our primary approach, to do it in the cylinder. And we’re cooling the EGR big time,” Runkle said.
Hofbauer’s development engineers also are keeping selective-catalytic reduction (SCR) aftertreatment as a back-up strategy, Runkle noted, should they “find it more difficult to reduce NOx where it ought to be done—in the combustion chamber. Our primary approach is high rates of EGR—and we have a few tricks with how we use EGR.”
Regarding the OPOC for light-duty vehicle applications, Runkle noted that the engine’s “flat” layout, similar to a conventional “boxer” four- or six-cylinder unit, is ideal for a conventional transverse fwd application—“it fits nicely in a fore-aft arrangement with the crankshaft oriented in the same direction as the halfshafts,” he said.
The OPOC architecture has another benefit—90% of the combustion loads go into the crankshaft and not into the crankcase, allowing design engineers to optimize lightweight materials for the crankcase construction.
The more than two dozen EcoMotors engineers working in the company’s development centers near Santa Barbara, CA, and Livonia, MI (a facility owned by Roush Industries) are evaluating solutions for higher power applications, such as some OEMs are requesting for commercial and military versions. According to Runkle, these would be created by “stacking” the OPOC power modules horizontally.
“We’d put an electric clutch between the two modules’ crankshafts,” he explained. “Once the clutch engages, the second engine starts and the two modules are synchronized very quickly, within one revolution.
“One engine would be running all the time, but when you needed additional power the other engine would clutch-on and you’d have double the power available. That would be controlled basically by the gas pedal,” Runkle said.
He added that the configuration would “allow us to run an EPA city and highway cycle on just one of the two engines.”
EcoMotors’ focus for the OPOC in the next 12 months will be “getting the engine mapped at various required emission levels,” Runkle asserted. Developing a demonstration vehicle is not a priority; all work will be done on dynamometers.
The company is still awaiting word on its request for a $200-million U.S. Department of Energy loan, which would enable low-volume engine builds at a former GM Powertrain plant near Detroit. And its development of intellectual property and patents, a key to Khosla and Gates’ interest in the company, is moving swiftly.
“We’ve got a ton of IP,” Runkle beamed.
[For more detailed information on OPOC engines, check out the new SAE International book, Opposed Piston Engines: Evolution, Use, and Future Applications, by Martin L.S. Flint and Jean-Pierrre Pirault. A link to the book’s web page can be found at http://books.sae.org/book-r-378].
Lindsay Brooke
Original article: http://www.sae.org/mags/AEI/8613