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134 comments on DrumBeat: February 11, 2008

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goghgoner on February 11, 2008 - 9:47am Permalink | Subthread | Comments top

Seems to me like the airline industry is in serious trouble. Emphasis added to their worries about the lead market -- uh, what about the oil market?

Green fuel, sky-blue dreams

Stirm said the aviation industry has sought an unleaded fuel, but no one has been able to create one that had an octane rating high enough to maintain power.

"There's been a frustration in the industry to come up with a substitute," Stirm said. "What are we going to use to power our airplanes if something happens to the lead market?"

Octane is a scale of how fast fuel burns, Stirm said. The higher the octane rating, the longer it burns and the more energy you get. Lead slows the burning of gasoline, so you can get more power out of it. Stirm said the FAA twice has received permission from the Environmental Protection Agency to keep using leaded fuel, but that extension expires in 2010.

"It's how you use that energy in the engine," he said. "In aviation, the issue has always been power- to-weight ratio. Here we're talking about a fuel that would revolutionize not only the aviation business, but also all our other modes of transportation."
Other solutions to the leaded gas problem have included ethanol, but the Ruseks said the biofuel isn't efficient as a combustible -- and could freeze at high altitudes.

John Rusek said ethanol, when burned in an engine, uses 17 percent of its energy; by comparison, an ethanol fuel cell uses 76 percent of available energy.

E85 gasoline -- the kind many cars and trucks now can burn -- is less efficient, cutting mileage by about 25 percent. "In an airplane, you can't afford to lose 25 percent of your range," he said.

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westexas on February 11, 2008 - 10:08am Permalink | Subthread | Parent | Comments top

Octane rating is really only pertinent to gasoline powered piston engines, so it has almost no effect on airlines, since they almost exclusively use jet fuel in turbine engines.

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RalphW on February 11, 2008 - 10:05am Permalink | Subthread | Parent | Comments top

This is discussing the use of aviation gas in light aircraft. It is a tiny market compared with kerosine as used by jet aircraft. I am amazed that lead is still permitted at all - high octane lead free petrol has been available in the UK for decades. It can only be a price issue. I'm sure a light aircraft operator would accept a 25% reduction in range if the option is not flying at all.

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goghgoner on February 11, 2008 - 10:32am Permalink | Subthread | Parent | Comments top

The article states they use 1.7 million gallons per day of leaded fuel for aircraft, as opposed to 40 million gallons per day of jet fuel being used.

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Black_Dog on February 11, 2008 - 10:52am Permalink | Subthread | Parent | Comments top

From my (now old) internal combustion engines course, I recall that the higher octane fuels allow higher compression ratios in an gasoline engine. It's the higher compression ratio which produces the improvement in conversion efficiency. This also applies to engines with superchargers, which are common on more expensive aircraft. The use of high octane gas used by small general aviation craft might not see much benefit from this fuel, unless it happens to be made of longer chain hydrocarbons. This might produce problems at high altitudes, where temperatures are low.

It's rather well known that cars which are designed to run on "regular" road gasoline do not experience any gain in fuel economy from higher octane grades. There may even be a drop in gas mileage, as some of the higher octane rating may be the result of ethanol added to the blend. There are some cars on the road which are designed for high octane fuel, but are "detuned" to operate on the regular grade. One way to accomplish this is thru the use of a "knock sensor", which detects pre-ignition and retards the spark timing to compensate. These cars would be able to take advantage of the higher octane by operating at optimal spark advance.

E. Swanson

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POBox on February 11, 2008 - 6:43pm Permalink | Subthread | Parent | Comments top

It's more likely a performance issue, not price. Aircraft performance is defined within a stable range of the four opposing forces - thrust, drag, lift, and weight. Change any one of these (like lowering octane) and you reduce the size of the "stable envelope". Pilots don't like that.

Most small aircraft have 4 or 6 cylinder air cooled piston engines, the vast majority designed in the 1950's and early 1960s. It is my impression that FAA certification applies to fuel as well as the engine, and the process of accepting any change is a lengthy one. A small percentage can run on regular unleaded but most private piston aircraft require 100LL which is dyed blue. I guess it's 100 octane low lead, but how low I don't know.

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134 comments on DrumBeat: February 11, 2008

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