The typical tradeoff for a greener powertrain is higher cost. Electric vehicles, plug-in hybrids, Prius-type hybrids -- all come at a price premium.
But imagine an engine that promised a 30 percent increase in fuel economy and cost less. Automakers would race to get that kind of paradigm-buster into their cars, right?
Well, not exactly.
Three companies developing opposed-piston engines say they can produce the magic combination of sharply increased efficiency and lower costs. The trio -- EcoMotors International, Pinnacle Engines and Achates Power Inc. -- are refining a pre-World War II internal combustion scheme in which two pistons operate in a single cylinder.
But automakers remain wary, saying that use of opposed-piston engines on high-volume programs is years away.
For one thing, the EcoMotors and Achates engines are two-strokes, which characteristically have high hydrocarbon emissions and high oil use. The engine companies are trying to convince automakers that they can meet emissions standards. And they are starting to make inroads on the fringes of the industry.
Don Runkle, CEO of EcoMotors, points to a development deal with truckmaker Navistar International for a turbodiesel engine as establishing credibility.
"They obviously think our claims are real, and we are in the process of running test engines for them," he says. "This is not a theory."
But major automakers are a tougher sell. That's because big automakers plan powertrain programs in terms of billions of dollars of investments and a decade or more of lead time, says Dan Kapp, Ford's director of powertrain research and advanced engineering.
"When someone says, 'I've got a game-changing development,' you've got to understand what changing the game means to us in terms of time and investment," Kapp says.
But, he adds, Ford is not dismissing opposed-piston engines as an option.
"We do some deep internal technical vetting of these concepts," Kapp says. "We do take them very seriously."
The three competitors have their own takes on opposed-piston technology. But for all, improved fuel economy is central. Because of the engine design, that's linked to lower cost.
Opposed-piston advocates say that the engines can use many of the same parts, materials and tooling as today's internal combustion engines -- a piston's a piston, in other words. So there's no need to create a new supply chain.
Fewer parts, lower cost
But because two pistons run in a single cylinder, they don't use all the parts that today's engines use. No valvetrain, no cylinder head. That cuts costs. It also reduces heat loss, friction and weight, giving the engines an advantage in power-to-weight ratio.
The engine companies' efforts represent a renewal of interest in a technology that the automotive industry previously rejected. Opposed-piston engines were invented in the early 1900s and probably are best known for powering Junkers airplanes in Germany. They also have been used in maritime applications.
But automakers in the past have dismissed the technology, particularly because of emissions.
"It took someone who didn't know it couldn't be done to figure out how it could be done," says Dave Johnson, CEO of Achates. "The first reaction is almost universally to say, 'That won't work. We tried that, and it won't work.'"
Pinnacle CEO Ron Hoge says the company is focusing on small vehicles in Asia as a way to get to market faster. He said the company expects to announce a deal soon to put its engine into a two-wheeler for "a major Asian vehicle manufacturer." Pinnacle plans to power other two-, three- and four-wheelers in Asia.
Says Hoge: "We would love to be in Detroit and have the right partnership, to be in Stuttgart and elsewhere in Europe. But we've got to build some credibility first."
Other observers see large, fuel-hungry vehicles like semi tractor trailers as the likely initial use. But the engine companies say opposed piston engines can work on anything from a lawnmower to a semi, including passenger cars.
The engine companies say that they are willing to license technology or supply engines. Their engines can be made in various sizes and can run on a variety of fuels, they say.
"It's an internal combustion engine," Runkle says. "It runs on the fuel you stick in it, and you can make it the size that you need, powerwise. It'll just be half the size of the four-stroke that you would have designed and half the weight."
And they're optimistic that they will start getting automaker deals within two or three years. They say their products are ready.
"No one ever concludes the r&d phase, but we have done enough research," says Achates' Johnson. "We were founded in 2004. We didn't just wake up yesterday and start working on this."
Automakers, on the other hand, see penetration coming slowly, if at all.
One automaker powertrain engineering executive who asked not to be named said the technology would have to be completely proved out today to be in cars by 2017. He sees opposed-piston engines as a post-2020 technology.
"There's too much risk here to bet on," the executive says. "But there's enough promise to keep looking at it in our r&d space to get it sorted out."
Part of the uncertainty, he adds, is whether modifying the engines for emissions would diminish fuel economy: "We haven't seen any data that we could put it into production and still produce the benefits."
Tougher U.S. fuel economy standards might seem likely to make automakers snap up new technologies. But Ford's Kapp says the opposite is true: The need, under pressure, to make steady, year-to-year improvements gives Ford less flexibility and leads planners to stick with familiar, proven technology.
"We certainly have a technology strategy and development plan in place," he says. "It's how we're going to evolve and keep deploying our EcoBoost engine. I have a line of sight of how we're going to get to that with our existing and limited resources."
Others say automakers tend to resist powertrain changes.
Gary Rogers, CEO of engineering giant FEV Inc., says that institutional inertia can be a barrier. But, he adds, sheer industry scale means that change takes a long time.
For example, Rogers says, the move from carburetors to port fuel injection was slow: "It took about 20 years until we rolled all the cars over to fuel injection."
Research analyst Greg Schroeder at the Center for Automotive Research says automakers may farm out design and subsystems but are territorial about powertrains.
"In my opinion, the automakers really see themselves as having their core competency in powertrains," Schroeder says. "For someone outside to come in and sell a new powertrain, it's difficult."