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Wednesday, November 4, 2015

demise of airliners

Appreciable research is under way in an endeavor to determine a viable alternative to the jet fuel derived from oil. This research is driven by the requirement to reduce emissions from the exhausts of jet engines in aircraft as well as the fact that the availability of oil is expected to decline in the future. There is a vast airline industry operating something like 200,00 airliners. An airliner consumes around 150,000 litres of jet fuel per flight. For example, a Boeing 747 consumes 4 litres/sec  So something like 3 x 10exp10 litres per day of jet fuel is being used.
Bio fuels are being promoted as a viable alternative. Fundamental energy relations show that these fuels cannot possibly meet the demand for jet fuels so the demise of most airline (and other aircraft) operations this century is certain.
Sunshine powers the production of the bio mass needed for bio fuels. About half of the amount of sunshine energy producing the biomass is available in the bio fuel produced. This means that about 15 hours of sunshine on a square metre of plant are required to produce the amount of energy in a litre of fuel. That is, about 3 square metres of plant are required to each day supply the energy provided by a litre of fuel. Plants do not have anything like the energy density of oil. The energy in jet fuel is about 35 MJ/L so airliners use abut 10exp12 MJ/day of energy in the fuel consumed in their operations. So something like 10exp11 square metres (10exp5 square Km, about 1 per cent of the area of USA) would be required of bio fuels to meet the present airliner demand. This would have to be in addition to the amount of land used for other purposes, including food production.
Research into using hydrogen as an alternative jet fuel decades ago did not get very far because it has such a low energy density in its gaseous form that the necessary fuel tanks would have been enormous. Cooling it to its liquid form was not technically practical on an aircraft.
Energy issues alone do not determine what is reasonable or even feasible. The extraction, transportation and processing of oil to yield jet fuel entails the use of energy and materials in technological systems that irrevocably age so need maintenance. In the main, these systems exist around the globe.
The growing, processing and transportation of bio mass to provide bio jet fuel entails the future installation of a massive eco costly, aging system. Yet it can only meet only a small portion of the demand. So airliners (and other aircraft) are a doomed species!

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