Peak Cheap Oil, Peak Dollar, but no Peak Gold

[GRG55]

Re: NatGas

A little background is in order:

1. I'm a military pilot, have been for the last ten years.

This does not appear to be correct, unless I am misunderstanding what has been written.

First, although volume is important in aircraft applications, weight is the governing design limitation. Energy density expressed as combustion energy per unit of mass is more important for aircraft fuels than volume.

2. "Although volume is important in aircraft applications"

You miss the argument completely. It is HOW fuel is stored on an aircraft typically (in the wings) that makes volume so important. The type of storage vessel for GTL (a pressurized storage container) mandates locating fuel stowage in the fuselage vs a typical aircraft installation where fuel is stored unpressurized in the wings for the majority of the fuel supply. (Yes there are body tanks, but these are either hard tanks or even in many cases simple flexible fuel bladders that forgo cargo space). It is the weight and complexity of the installation as well as the requirement that all fuel storage be relocated in the fuselage that makes this technology incompatible with the existing aircraft fleet and makes retrofit highly unlikely. Hence the need for purpose built aircraft.

Missed the argument completely did I? Please allow me the indulgence of a second attempt:

GTL at STP is a relatively stable liquid with boiling point properties very similar to diesel (Initial boiling point greater than 150 C vs about 170 for typical diesel, final boiling point generally greater than 350 in both cases). Typical diesel/GTL RVP is about 2 kPa compared with motor gasoline (summer) RVP about 50 kPa.

What is it about GTL that makes you think that pressurized storage in the fuselage is necessary?

3. Interestingly, GTL is considered a diesel, not kerosene, substitute. Compared with conventional crude based diesel, GTL's energy density is typically 4% higher because it's highly paraffinic (lower aromatic/higher paraffin content). Volumetric density is lower at about 0.76 kg/l for GTL vs about 0.83 kg/l for conventional diesel because paraffins have a higher hydrogen to carbon ratio than aromatics. GTL can be burned directly in compression ignition engines.

"Volumetric density is lower at about 0.76 kg/l for GTL vs about 0.83 kg/l"
"(lower aromatic/higher paraffin content)"


You said it not me. When the Air Force switched from JP-4 to JP-8 (a fuel with lower volitility and higher volumetric density) our flight duration increased by 15-25% depending on aircraft type! This is an apples to apples comparison of two kerosene based fuels. It also caused huge problems with our engine fuel controls because of the viscosity differential. (we also had to implement special procedures to reduce the risk of flaming out our engines during certain flight regimes).

Speaking strictly as a civilian pilot, I would have thought that increased flight duration would be a highly desirable outcome.

Especially if the fuel management systems and engine characteristics can be engineered to overcome the problems caused by the viscosity differential between the fuels.

GTL has a lot of issues that need to be solved before it will ever become a widely used substitute liquid fuel (in any application), but energy density is not one of them.

Maybe, but that does not invalidate the points addressed. And, fuel storage installation on-board aircraft is certainly an issue.

This is the point I am trying to understand. For decades much more volatile avgas was used routinely in Otto cycle engines at high altitudes without the need for specialized fuselage pressure vessel fuel tanks.

Why can't GTL, a liquid at STP and similar in characteristics to diesel and kerosene, be used in conventional wing tanks?

call me nuts but isn't an airplane the last place you'd put these fuels?

Mike: I would agree with you in normal circumstances. But these are anything but "normal" times. I don't know what's happening in North America in this regard, but in Europe the climate change cohort have recently been particularly zealous targeting the airlines and Airbus (an easy target with its government sponsorship) over carbon emissions, green practices, environmental responsibility, and so forth.

The airlines are scrambling around trying to come up with politically correct responses. Last year Virgin Group's Richard Branson proposed using tugs to tow aircraft between ramps and runways to lower CO2 emissions (smart man...this would save him fuel and transfer the cost to the airport authorities, where they could argue forever about landing fee increases). The Shell-Qatar-Airbus GTL flight (some GTL blended into conventional jet fuel) was a nice promotion for Shell's Pearl GTL project in the State of Qatar, but not much else. Expect more PR stuff and stunts, as the airlines and manufacturers try to prevent their reputations from being trashed as environmental pariahs.

In the meantime, the search for suitable substitutes for crude based aviation fuels will be an interesting challenge that should soak up untold amounts of alternate energy government subsidies. And as cheap oil becomes scarcer, there is the possibility that flying once again becomes the exclusive purview of the financially well off gin and Jaguar set, and the business/government/UN expense account groupies (how else are they going to get to Davos and all those climate change conferences?).