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The road to better gas mileage isn't as difficult as it seems (© Andria Patino / Corbis)

Good-bye, Gas Guzzlers

What will it take for automakers to deliver a fleet of fuel-sippers?

smithsonian.com

Giant leaps of vehicle technology are the stuff of dreams: flying cars, sunmobiles that run solely on solar power or two-wheeled helicars held in balance by gyroscopes. But the path toward cleaner cars will be walked in tiny steps. There’s a place for all-electric and even semi-autonomous vehicles, but tweaks to designs that burn gasoline will deliver much of the fuel-economy gains expected in the coming decades.

Guzzlers are on their way out. This spring, the average fuel economy of all newly purchased cars climbed as high as it’s ever been, to 24.6 miles per gallon, according to an analysis from the University of Michigan Transportation Research Institute (UMTRI). Fuel economy will surely climb even higher: By 2025, national standards demand that automakers achieve a fleet average of at least 54.5 miles per gallon for cars and light trucks.

Better fuel economy can help reign in oil consumption and the more than 1.5 billion tons of greenhouse gas emissions coughed out annually by U.S. highway vehicles. And although cars and trucks with the best fuel economy often sell at a premium, improved gas mileage can help motorists save money at the pump, where a typical American household now spends about 4 percent of its annual income.

When gasoline prices exceed $4 per gallon, fuel economy tends to rise to be one of the top things people consider when purchasing a vehicle, says Bruce Belzowski, a research scientist at UMTRI. Prices have hovered around that mark nationally—though the national average has not crossed it since 2008--and shoppers are showing an appetite for better fuel economy. “Consumers may be saying, ‘We gotta get more outta this tank,’” Belzowski says.

A recent report from the National Research Council finds that it’s technically feasible to reduce petroleum use and greenhouse gas emissions from automobiles by 80 percent by 2050, compared to 2005 levels. Improving the efficiency of conventionally powered vehicles, however, will not be enough on its own to deliver such dramatic reductions. Cars would have to average upwards of an astonishing--and extremely unlikely--180 miles per gallon to reach that target based on efficiency gains alone. That’s where alternative fuels and all-electric vehicles will come into play. 

All vehicles, no matter their power source, must become much more efficient if those goals are to be realized, but improving the efficiency of those that run on petroleum could have the biggest impact in the near term. These cars make up the vast majority of vehicles on the road today, consuming roughly one-third of all oil used in the United States. And there’s plenty of room for improvement, with as little as one-quarter of the energy in fuel for today’s cars actually being used to move them down the road. Most of the rest is lost as heat in the engine. Minimizing the amount of work that a gas engine must perform is one of the easiest and least costly ways to save fuel. Scientists, researchers and automobile manufacturers believe this can be accomplished through multiple strategies, many of which are catalogued below:

New Tire Technology

Tweaking tire designs can also deliver gains by cutting rolling resistance, or the force caused by the flattening of a tire as it rolls along the road. Cyclists know that a flat tire demands noticeably more legwork to roll along at a respectable clip. Similarly, minimizing the amount of flattening or deformation of a car tire through advanced materials and design can reduce the amount of energy required just to keep it rolling.

Engine Innovations

The most dramatic improvements, though, will probably come from changes to the engine transmission, says Alan Crane, a senior scientist for the National Research Council’s Board on Energy and Environmental Systems and the study director for the NRC report. Transmissions with a higher number of speeds, dual-clutch transmissions and friction-reducing coatings could help engines run at higher efficiency and cut energy loss. 

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