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Turbocharger Technology Gives New Cars More MPG

Once Prized for Power, Now Sought for Fuel Efficiency


  • 2014 Ford Explorer

    2014 Ford Explorer

    The 2014 Ford Explorer EcoBoost uses turbocharging to deliver V6 power with four-cylinder fuel efficiency. | May 15, 2014

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Much of the news about new car technology presented to car buyers recently has centered on hybrid, plug-in and hydrogen fuel-cell cars, as well as vehicles fueled by such alternative fuels as biodiesel and natural gas.

But there's one technology (turbocharging) that is giving a boost to the fuel efficiency of the gasoline internal-combustion engine. Turbochargers might be something that you associate only with diesels and high-performance gasoline-fueled cars. But they increasingly are being used by automakers to make it possible to use downsized gas engines that are less thirsty but still deliver the power of the larger-displacement engines they replace.

As it turns out, the turbocharger demonstrates how 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.

That fuel-sipping compact sedan you've been eyeing just might have a turbocharger under the hood.

First, a Little Science
The basic turbocharger is a deceptively simple-looking device that compresses fresh air and forces it into the engine's cylinders, increasing the amounts of both air and fuel in the combustion chamber. Turbos originally were developed to improve the performance of aircraft engines at high altitudes, where the air is thin. Combustion of gasoline (or aviation fuel) is improved when it is mixed with cold, dense air.

The turbocharger itself is a device that integrates two bladed wheels. The engine's hot exhaust spins one, the turbine, which in turn spins the compressor wheel that charges the engine with more fresh air than it can otherwise inhale. An incredibly complex set of valves and computerized controls make turbochargers work at peak efficiency at various levels of power demand. Some applications — typically those with two banks of cylinders — often use two turbochargers.

In addition to increasing power, turbos make use of the exhaust gases that otherwise would spew from the tailpipe as wasted energy. Turbos and superchargers both reduce the amount of work the engine has to do to breathe in the fresh air, increasing its efficiency. But while turbochargers restrict exhaust flow, making the engine work a little harder to completely empty each cylinder after combustion, they do not sap as much mechanical power from the engine as do superchargers, making them more appropriate for smaller, less-powerful engines.

It's the kind of elegant solution engineers love to talk about. It's a relatively simple device that rides along without diminishing performance when it's not needed, but spins into action and packs your engine with more power when you need more zip. 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.

When operated with an eye toward efficiency, a turbocharged four-cylinder engine can combine the fuel economy of a four-cylinder with the power of a six-cylinder. A turbocharged six can deliver the power of a V8 while gulping a lot less fuel.

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 of turbocharging in most cases these days is 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 power today as a 4.0- or 5.0-liter engine had without a turbo, Grissom says.

For example, Ford's turbocharged 2.0-liter EcoBoost four-cylinder engine produces 240 horsepower and 270 pound-feet of torque in the 2014 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 16 percent compared to a V6, according to Ford. Combined city-highway mileage is up 15 percent to 23 mpg from 20 mpg.

A Heavy Foot Can Defeat the Turbo's Purpose
The key to great fuel efficiency lies in the driver's approach to using the turbo's power.

"In the real world — in the hands of real drivers and not an EPA [Environmental Protection Agency] test cycle — these designed-for-efficiency turbo cars often fall far short of their EPA ratings," cautions Edmunds.com Senior Editor Josh Jacquot.

"Usually their numbers miss the EPA mark by a much larger percentage in our testing than their non-turbo counterparts." The lesson from this, Jacquot says, is that when the power is there, many drivers will use it.

Automakers and turbocharger system developers overcome some of that tendency by matching the turbocharger to the job, making smaller, less powerful turbos for systems designed predominately for fuel economy than for those designed for maximum power. Downsizing the vehicle's engine also helps maximize efficiency, although lead-footed acceleration will typically result in lesser fuel economy than will a more moderate manipulation of the gas pedal. Of course, that's true in any type of vehicle, turbocharged or not.

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. In 2013, 93.4 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. That's a substantial share of the market, but down from 95.1 percent in 2010. Hybrids had 3.4 percent of the market, up from 2.4 percent in 2010, while diesels' share rose to 2.8 percent from 2.4 percent. Plug-in electric vehicles accounted for 0.3 percent of registrations last year, up from 0.012 percent in 2010.

Out of 247.5 million vehicles in operation in the U.S. through January 2014, 219.8 million were gasoline, 16.6 million were flex-fuel, 7 million were diesel, 2.9 million were hybrid and 98,000 were 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. That's because large-displacement engines were in fashion.

Today, about 17 percent of all new commercial and passenger vehicles being sold in North America are turbocharged, and the number is expected to increase to 31 percent of total sales by 2018, says Michael Stoller, communications director for Honeywell Transportation Systems, a major developer and manufacturer of turbocharger systems.

The EPA recently projected that 90 percent of new vehicles in the U.S. market could be turbocharged by 2025.

What's Behind the Pick-Up 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 EPA goal of 35.5 mpg. That figure rises to 54.5 mpg by 2025. Because vehicles for the 2016 model year are in the final design and engineering stages 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 through 2016 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 are coming to the market as well. Ford, for instance, introduced a turbocharged, 1.0-liter, three-cylinder EcoBoost engine option with the 2014 Ford Fiesta. And a turbocharged three-cylinder gas engine provides a key element of the new BMW i8 plug-in hybrid sports car's powerful gas-electric drive system.

Audi, General Motors and Volkswagen also have three-cylinder engines either in development or in production in European models. 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. Because turbo models often come with additional equipment and special sporty trim packages, it is hard to pin down exactly how much the turbocharging system itself adds to the cost of a vehicle, but estimates range between $500 and $2,000.

Grissom, of BorgWarner Turbo Systems, says that's cheaper than adding a battery pack and electric motor 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 long 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 of today's turbocharged engines can run low-octane fuel. It's not a cut-and-dried issue, however. Some turbocharged engines are more octane-sensitive than others, says Kavanagh. A few years ago, Edmunds.com tested the turbocharged Chevrolet Cruze in the desert heat on 87 octane fuel, "and did notice that the heat had an impact on both the performance and the fuel economy. We got 15 percent better fuel economy as well as improved performance and drivability when we switched from 87 octane to 91," Kavanagh recalls.

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 you won't have to look very hard; they'll increasingly be in evidence in the next few years. Edmunds.com's list of future fuel-efficient vehicles includes almost 30 turbocharged models, half of them diesels and half gasoline-powered.

Still, it is always wise when shopping to check out the turbo's impact on the cost of the models you are considering, as well as the cost of fueling a turbo model versus a conventionally aspirated engine. But remember that even if premium is required, the higher price at the pump may well be canceled out by the better fuel economy the turbocharged engine delivers.

Of course, once you take a test-drive, the turbo model's performance kick may well persuade you. But even though it's the power boost 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 it once was: It has morphed into a technology that combines performance with fuel economy.

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