Sparks

Leaner means cleaner

 By RP Siegel

RP Siegel explains what Carmakers are doing to reduce fuel consumption to meet aggressive US economy goals. Their attention is focusing on a principal area: light-weighting, where new materials and construction techniques, including carbon fiber composites, aluminum and high strength steel are being used to reduce overall weight. It may not seem intuitive that reducing weight would save that much energy, but there is a subtle principle involved here called mass decompounding. In essence, a lighter body, needs less suspension to support it, which then needs a smaller motor to accelerate, which, in turn needs an even smaller suspension, and so on. It’s the snowball effect, in reverse…

In 2009, the Obama administration began raising the Corporate Average Fuel Economy (CAFE) standard for cars and light trucks, to reach 54.5 mpg by 2025 in order to reduce emissions. That’s a very aggressive goal, growing from 30.2 in 2011. According to Margo Oge, former director of EPA’s Office of Air Quality and Transportation, EPA engineers worked with car companies to evaluate numerous technologies in order to understand what was achievable.

Much attention has been focused on alternative fuels and powertrains. Bio-ethanol is already in the national fuel mix. There are 17.4 million flex-fuel vehicles, capable of running on an 83% ethanol mix (E85) already on the road.

Then there is electrification, which takes two forms: battery-electrics and hybrid-electrics. The energy density of today’s batteries is only about one percent that of gasoline. That makes “range anxiety” an issue for long distance driving. Hybrid electrics are essentially a compromise between fuel economy and range. Fuel cell cars are electric vehicles that use a “battery” that can refilled much like a gasoline car, if they have the infrastructure. These cars emit only water vapor.

Most people are familiar with these alternatives. While these technologies all hold considerable promise, it is clear to automakers that these alone are unlikely to provide sufficient reductions to achieve these aggressive targets, at least not in the allowable time frame. In order to move cars and trucks around in the manner that people have become accustomed to, while using that much less fuel, it will be necessary to take the additional step of reducing vehicle weight. Various crash programs have been initiated to find ways to do that.

It may not seem intuitive that reducing weight would save that much energy, but there is a subtle principle involved here called mass decompoundingIn essence, a lighter body, needs less suspension to support it, which then needs a smaller motor to accelerate, which, in turn needs an even smaller suspension, and so on. It’s the snowball effect, in reverse.

Cars today are mostly made of steel, which is strong but heavy. Carmakers have used other lighter alternatives like aluminum and magnesium, but these are more expensive. Can weight reductions be made without raising prices, or will people pay more for better fuel economy?

The fact that the 2015 Ford F-150 pickup, one of the most popular vehicles in America has an all-aluminum body says a lot. The new F-150 lost 700 pounds (316 kg) in the conversion. The trend is clearly accelerating. Says Kevin Anton, Alcoa’s former chief sustainability officer, “Back in the ’70s, the average American car contained approximately 100 pounds (45 kg) of aluminum.” That number has grown to 350 pounds today and is projected to grow to 550 pounds (249 kg) by 2025.”

Improvements in alloying technology have led to a corrosion-resistant, stainless magnesium that is finding its way into cars. VW, Audi, Mercedes Benz, BMW, Ford, Jaguar, and GM now all use magnesium transmission casings.

Perhaps the most dramatic development has been the appearance of carbon fiber reinforced composites. BMW, which had been toying with the materials on roofs and hoods, went all-out on their new electric i3 model in which the entire passenger compartment is carbon fiber. The material is six times stronger than steel and 30 percent lighter than aluminum. In doing so the company has shaved an impressive 770 pounds (349 kg) off the car. Carbon fiber could very well be the material of the future. It is already playing a major role in jet airliners, though the price is still quite high, restricting it to the realm of performance and luxury cars, for now.

Cars today are mostly made of steel, which is strong but heavy. Carmakers have used other lighter alternatives like aluminum and magnesium, but these are more expensive. Can weight reductions be made without raising prices, or will people pay more for better fuel economy?

Meanwhile, steel producers have not been sitting idly by. According to Blake Zuidema, Director of Global Automotive R&D for ArcelorMittal, recent advances in steelmaking have resulted in advanced high strength steels that are 5-6 times stronger than their predecessors. That’s important because it means that thinner sections can now be used that weigh less, but provide the same strength.

These new steels have another “green” benefit.

“Pound for pound,” say Zuidema, “it requires far less energy and far less CO2 to produce steel than aluminum, magnesium or carbon fiber. In fact, each pound of aluminum requires about five times as much CO2, each pound of carbon fiber requires about ten times as much CO2, and each pound of magnesium requires about fifteen times as much CO2.

“So even if these materials could produce a lighter car, with lower carbon emission during the use phase of their life cycle, this would not offset the additional carbon emissions generated during the manufacturing process, starting from raw materials.”

And steel is still the cheapest option, at least today.

As things move forward, you can expect to see a diverse mix of materials, as our cars, not unlike their passengers, watch what they eat, and continue to look for ways to lose weight.

about the author
RP Siegel
Skilled writer. Technology, sustainability, engineering, energy, renewables, solar, wind, poverty, water, food. Studied both English Lit.and Engineering at university level. Inventor.