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Turbocharger Technology Gives New Cars More MPG

Once Prized for Power, Now Sought for Fuel Efficiency


  • 2012 Ford Explorer Picture

    2012 Ford Explorer Picture

    Ford's turbocharged 2.0-liter EcoBoost four-cylinder engine produces 240 horsepower and 270 pound-feet of torque while allowing the 2012 Ford Explorer to get 28 mpg while cruising on the freeway. | September 23, 2011

3 Photos

Most of the news about new car technology presented to car buyers recently has centered on hybrid and electric cars, as well as vehicles fueled by such alternative fuels as biodiesel, natural gas and ethanol.

So it's easy to think of the internal combustion engine as old news. But one technology that is giving a boost to the fuel efficiency of the internal combustion engine is turbocharging, something that you might instead associate only with high-performance cars.

As it turns out, the turbocharger demonstrates the way proven technologies are being paired with newer technical developments to deliver not only good performance but also fuel economy that can come close to that of a hybrid.

In fact your next fuel-sipping compact sedan might have a turbocharger under the hood.

First, a Little Science
The turbocharger was originally developed to improve the performance of aircraft engines at high altitudes, where the air is thin. The turbo integrates two wheels. The engine's hot exhaust spins one, and this in turn spins another that charges the engine with more fresh air than it can otherwise inhale. More air plus a little more fuel equals more power.

It's the kind of elegant solution that engineers love to talk about. It's a relatively simple device that rides along without affecting performance, but when you need more zip, it spins into action and packs your engine with more power. It lets you live happily with a small-displacement engine that gets great fuel economy and yet comes through with more power when you need it — while merging onto the freeway, for example.

A turbocharged four-cylinder engine can combine the fuel economy of a four-cylinder with the potential for the power of a six-cylinder. A turbocharged six can deliver the power of an eight. Turbos pack a punch when needed.

Think Small, but Drive Big
"When you're cruising on a highway you may only need 10 or 20 horsepower," says Tom Grissom, director of business development for BorgWarner Turbo Systems, a leading turbo technology company. "But when you need more to accelerate quickly from a stop or to pass or merge onto a highway, a turbo delivers the necessary power as you need it."

Of course, Grissom also reminds us that the point is really to make it possible to use a smaller, lighter and more fuel-efficient engine than might otherwise be practical for overall drivability. Grissom says that turbocharging allows you to increase power using a smaller engine. "That translates into greater efficiency and fuel economy," he says. "A [turbocharged] 3.5-liter engine has the same efficiency today as a 4.0- or 5.0-liter engine had without a turbo."

For example, Ford's turbocharged 2.0-liter EcoBoost four-cylinder engine produces 240 hp and 270 pound-feet of torque in the 2012 Ford Explorer and makes it possible for this full-size, seven-passenger SUV to attain 28 mpg while cruising on the freeway. The four-cylinder turbo improves the Explorer's highway fuel economy by 12 percent compared to a V6, according to Ford.

The Market for Turbos
While hybrids and electric vehicles have commanded most of the headlines lately, the internal combustion engine still owns the vehicle market. Through August 2011, 94 percent of registered vehicles in the U.S. had traditional internal-combustion engines fueled by either gasoline or a flex-fuel (gasoline with a small percentage of ethanol) combination, according to the data accumulated by R. L. Polk. Hybrids had only 2 percent of the market, down from 2.3 percent for the same time period in 2010. Electric vehicles accounted for only 0.1 percent.

Out of 232 million vehicles in operation in the U.S., 217 million are gasoline, 9.2 million are flex-fuel, 5.5 million are diesel, 1.8 million are hybrid and 32,000 are electric cars. For reasons of manufacturing cost, utility and ease of maintenance (not to mention the inertia of a hundred years of history), the internal combustion engine clearly remains the default choice. The significance of the turbocharger is the way it makes this conventional technology more relevant for the fuel-efficient future.

Of course, turbocharger manufacturers are eager to legitimize their product as a device for the goodness of fuel efficiency rather than the evil of pure power. Nevertheless it's true that turbocharging has been popular for decades in Europe, where it made small, fuel-efficient and yet undeniably underpowered diesel engines practical at last for high-speed travel.

In the U.S., turbochargers haven't been newsworthy since the 1980s, and they accounted for no more than 4 percent of the vehicles on the road a handful of years ago because large-displacement engines were in fashion. Today that number is 10 percent and growing.

"We expect penetration of turbo to grow to 23 percent of the light-vehicle market by 2016," says Michael Stoller, director of communications for Honeywell. "Forecasters at IHS Global Insight predict it will grow to 80 percent by the end of the decade."

What's Behind the Pickup in Popularity
Better performance and consumer demand for better fuel economy aren't the only reasons for broader turbo adoption, however.

Carmakers are under pressure from the government to deliver higher fuel economy in their overall vehicle fleets. By 2016, the U.S. car and light-truck fleet must reach an Environmental Protection Agency goal of 35.5 mpg. That figure rises to 54.5 mpg by 2025. Since vehicles for the 2016 model year are in design studios right now, the pressure is on and the turbo is helping automakers succeed by permitting the use of smaller engines for fuel efficiency while providing the power for all-around drivability that Americans demand.

Sources including IHS Global Insight Automotive and BorgWarner predict that 98 percent of total global engine growth from 2011-'16 will be in two-, three- and four-cylinder engines. In the U.S. and Canada, the growth will primarily be four-cylinder engines, while some three-cylinder engines will come to the market as well. And when the engine must be small but the vehicle must be big, there you'll find an opportunity for a turbocharger.

More Money
No technology is perfect, and it should be no surprise that turbocharging has negative consequences as well as positive ones. To begin with, a turbo adds cost to a car. It is hard to pin down exactly how much more a turbocharged vehicle costs, but estimates range between $500 and $2,000.

Grissom, of BorgWarner Turbo Systems, says that's cheaper than adding a battery pack to a car in order to improve fuel economy, which is what hybrids do. When the payback period for some of the hybrids on the road today can extend to as much as a decade, this is an important point. Moreover, battery packs entail a significant weight and packaging penalty that turbochargers sidestep.

Historically turbo engines generally required high-octane fuel, which has an associated higher cost.

"Manufacturers are aware of the resistance of the American consumer in the bread-and-butter price range," says Jason Kavanagh, engineering editor for Edmunds.com. "Consumers are very sensitive to this octane issue. They are not big on paying more for higher octane. It's a real factor for consumers."

Thanks to ever more sophisticated electronics (and a new set of priorities), many turbo engines can run low-octane fuel. It's not a cut-and-dried issue, however. As an example, Kavanagh says, "We tested the Chevrolet Cruze out in the desert heat on 87 octane and did notice that the heat had an impact on both the performance and the fuel economy," he says. "We got 15 percent better fuel economy as well as improved performance and drivability when we switched from 87 octane to 91."

You might also look for an argument to break out when turbocharging is stacked up against electric or hybrid technology. An electric vehicle emits no CO2 from the vehicle, only from the "upstream" source — the plant where the electricity is made. Emissions from hybrid vehicles vary, but a 2012 Toyota Prius, for example, emits 3.8 tons per year of CO2. By comparison, the turbocharged 2012 Chevrolet Cruze emits 6.2 tons annually. It's a relatively close call, especially when you figure in the carbon footprint of the manufacture and disposal of batteries.

Turbocharge Your Shopping List
We'd tell you to keep an eye out for turbocharged vehicles when you next go car shopping, but the truth is that they'll increasingly be in evidence in the next few years. Check out their impact on the cost of a car, as well as the cost of fueling it, and remember that a higher price at the pump may well be canceled out by better fuel economy.

Of course, once you take a test-drive, it's likely that you'll be persuaded. But even though it's the performance feeling that will clinch the deal, remember that there's an associated benefit at the gas pump. A turbocharger is not the exotic, hyper-expensive and finicky technology for pure performance that you might once have believed, yet it is still the kind of technology that combines performance with fuel economy — just as you have always hoped.

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