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Saturday, May 23, 2009

Less carbon in the skies

Today there was an interesting op-ed in the WSJ on three approaches for lowering carbon emissions from commercial aviation, signed by the president of Boeing Commercial Airplanes.

Scott Carson started at the obvious takeoff point — better fuel efficiency:
There's plenty of incentive to develop more efficient airplanes. Historically, fuel has been the airlines' second-biggest operating expense next to labor. Last year, with oil reaching $140 a barrel, fuel costs even outstripped labor costs, rising to 40% of total airline operating expenses. So airlines have demanded increased efficiency from airplane and engine manufacturers. And manufacturers have responded big time. Over the past 50 years, the efficiency of commercial jets has risen an astounding 70%. This means that carbon emissions per mile flown have dropped 70% -- all without a regulatory requirement for greenhouse gas emissions.
That said, Boeing with GE (and others?) wants to encourage fuel efficiency standards for new airplanes — sort of like a CAFE in the skies.

Carson listed two other ideas for reducing carbon emissions. One is more efficient routing — a plan to shift from the 1950s-era traffic corridors to GPS-enabled point-to-point routing (NextGen). The idea of flying point to point is welcomed by all segments of the aviation industry, but the question is how to pay for the huge capital costs: private pilots welcome the idea of fuel/ticket taxes while airlines oppose it.

Surprisingly, Carson suggested that biofuels could also reduce carbon emissions:
Third, we have been testing various advanced, sustainable biofuels with the goal of finding renewable fuels for aviation that don't compete with food crops for land and water and that emit 50%-80% less carbon than petroleum. We have conducted test flights using mixtures of standard jet fuel and several different sustainable biofuels, among them fuels made from algae and camelina (a plant that produces seeds that aren't used for food).
However — as with other cleantech efforts — Carson requests government subsidies to get the new fuels off the ground.
One proposal is that government could provide loans to refiners to make biofuels competitive when the price of petroleum is low and get repaid when the price of petroleum is high. We hope government officials will seriously consider such ideas because biofuels, in our view, are the ultimate answer to aviation's carbon-emissions challenge.
Looking further out, ATAG (an industry trade association) has an interesting overview of near-term and long-term fuel alternatives that argues that hydrogen is the long-term solution.

As it turns out, this week I received (from a NASA historian) a copy of the NASA book Taming Liquid Hydrogen. The book is about how NASA’s Lewis Research Center and industry researchers learned in the 1950s and 1960s how to create safe and reliable hydrogen-fueled rockets, at a time when rival groups said it couldn’t be done.

Researchers at Lewis (now Glenn) co-authored a 2006 report evaluating all the aviation fuel alternatives. Ironically, they are more pessimistic about hydrogen as an aviation fuel:
Liquid hydrogen (LH2) not only presents very substantial airport infrastructure and airplane design issues, but because of the need for heavy fuel tanks, a short-range airplane would experience a 28 percent decrease in energy efficiency while on a 500-nautical-mile (nmi) mission. However, because airplanes need to carry much more fuel for a long range flight, and Liquid Hydrogen (LH2) fuel is quite lightweight the lighter takeoff weight of the airplane results in an energy efficiency loss of only 2 percent while on a 3,000-nm mission.
As they note, the key driver of hydrogen is that it’s not an energy source, but a way of converting ground-based electricity generation into a portable fuel. If there is (someday) enough electricity generating capacity that doesn’t produce carbon emissions — nuclear, hydro, solar, wind, tidal —then a use of hydrogen-based fuels is the one solution that would eliminate commercial aviation’s carbon footprint.

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