Environmental Engineering Reference
In-Depth Information
achieved by putting nuclear weapons in submarines powered by nuclear
reactors, and therefore capable of staying at sea for long periods.)
But biofuels are now being tried out for aviation. In the past two years
there have been several commercial trials: Virgin Atlantic flew a Boeing
747 with one of its four engines running on a mix of coconut and babassu-
nut oil; Air New Zealand used a fifty/fifty mix of jatropha oil and ordinary
jet fuel in one of a 747's four engines; Japan Air Lines used a fifty percent
mix of jatropha, camelina and algae in one of a 747's four engines, and
Continental Airlines put a mix of fifty percent of jatropha and algae in one
of a Boeing 737's two engines.
Apart from coconut oil - which Virgin openly admitted is not an eco-
logically desirable fuel-source due to deforestation issues - the other feed-
stocks look commercially and technically viable. Jatropha can be grown
on very marginal land and camelina in temperate climes, while algae,
which grows continuously, requires little land (see p.137). One absolute
requirement for biojet fuel is that it does not freeze at high altitudes; some
early biofuels had a higher freezing-point than conventional fuel, which
was an obvious and alarming flaw, but one that is being overcome.
The aviation industry is very keen that any biojet fuel should be “feed-
stock agnostic”, so that whatever source is used produces the same grade
of biojet fuel. The industry is also insistent that biojet fuel should be capa-
ble of being used as a “drop-in” replacement for ordinary jet kerosene: in
other words just dropped into the existing fossil-fuelled system without
modifications to jet engines, or to the transport and storage of fuel.
Of course, the other way of reducing aviation emissions is to reduce the
amount of fuel that planes burn. But this is proving increasingly hard to
do as today's turbo-fan engines approach the limit of their potential. One
technology, the so-called open-rotor engine, could save a lot of fuel, but
is intrinsically noisier.
Emission trading
By deciding to include airlines in its Emission Trading Scheme, the
European Union has devised a form of charging for the use of the airways
over and around Europe. The aim of governments and of the EU is not
to reduce air travel directly. Such a reduction would obviously be a plus
for the climate, but it would run counter to aviation liberalization in
North America and Europe, which has made flying cheaper (and, until
9/11, easier) on both sides of the Atlantic. The goal is rather to pressure
airlines, aircraft makers and aero-engine manufacturers into reducing
