Friday, February 4, 2011

Aviation Fuel Additive to Deliver Stratospheric Aerosols
 Unlike most members of this group I am not professionally involved in climate but my suggestion may be relevant to two proposals already discussed in this group.
--SO2 producing sulphuric acid. By Paul Crutzen.
--Diatoms. From crushed diatomite. Greg Benford and others(diatoms are silica)

I suggest that both the sulphur dioxide and the silica particles could be delivered into the stratosphere by dissolving an additive in jet aviation fuel.

 Different chemicals would obviously be required for the two products but the delivery system would be the same and is therefore described first as follows.

 How to Deliver Products Into the Stratosphere. 
Obviously we would not want to release these products at other phases of the aircraft flight so it is not suggested that an additive should be put generally into aviation fuel.  We would want to burn fuel containing the additive specifically when the aircraft was cruising in the lower stratosphere.

The following information comes from a 747-400 captain flying regularly from the Far East to Europe and the West Coast of United States.  Being near retirement, and having started his career with the RAF, he describes the flight plan provided to him for a long flight now as amazingly comprehensive and accurate.  Such plans rely on detailed knowledge of weather along the whole route including lower stratospheric winds.

In addition he tells me that it is perfectly possible for the pilot to select, for instance, the outer starboard wing tank to feed the outer starboard engine at a particular time during the flight.

It would seem therefore to be perfectly possible to put the additive into one tank only and to use that tank when the plane was defined in the flight plan to be in the stratosphere.  Aircraft cruising altitudes vary between about 30 and 40,000 ft (9 to 12km).  The lower boundary of the stratosphere varies from about 20,000 ft. (6 km) near the pole to close to 55,000 ft. (17km) at times on the equator. 

These heights also vary considerably with weather conditions so careful planning as part of the flight plan would obviously be necessary

Fuel Additive To Produce Sulphur Dioxide on Burning.
 Sulphur dioxide is already present in the combustion products of aviation fuel.  This is because of the organic sulphur compounds naturally present in oil and great trouble is taken to reduce the proportion because of the acid effects of sulphur dioxide in the lower atmosphere.  It should be very easy to use these same sulphur compounds as the additive, which would then only be burned in the stratosphere.  Since these compounds are already present in aviation fuel it is very unlikely that they will cause any problem to the engine.

Fuel Additive to Produce Microscopic Silica Particles. 
At first sight it might seem difficult to produce solid particles from the liquid fuel. It is however perfectly normal chemistry to have a compound which is mainly hydrocarbon like jet fuel but has one or two other atoms in the molecule which have a solid oxide on burning.

I have been experimenting with tetra ethyl silicate.  There is only one silicon atom of the thirty-three in the molecule.  The rest of the molecule is hydrocarbon so it is not surprising that it is a colourless liquid similar to aviation kerosene, which dissolves in kerosene in any proportion.

To simulate a jet engine I have used a paraffin blowlamp.  The solution burns just like paraffin.  At a concentration of 1% a mist or smoke is visible in a spotlight beam.  It is probable that the mist is microscopic crystals of silicon dioxide. This is chemically the same as the diatomite.

 Tetra ethyl silicate is so similar to aviation kerosene that it will probably make no difference to the engine when used in low concentration. Obviously this needs to be tested properly and it is also possible that the microscopic particles will coalesce near the end of the turbine and cause abrasion.

It is also obviously necessary to confirm that the combustion product is silica, to determine the size of the particles, to compare this with the diatomite particles and many other points. 


Assuming satisfactory completion of engine testing, atmospheric testing could be started almost immediately. Greg Benfold has already suggested an atmospheric testing scenario in “Saving the Arctic”

I think this is the only proposal, where satisfactory testing could be transferred into large scale implementation immediately at negligible cost.

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