Fuels in Transportation - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 25

Table 2.11 Comparison of
alternative fuel's with
kerosene's properties

Kind of fuels Density Specific

energy

Energy
density

Kerosene 1.00 1.00 1.00

Ethanol 1.00 0.50 0.51

Methanol 1.00 0.45 0.46

Liquid methane 0.54 1.16 0.62

Liquid hydrogen 0.09 2.77 0.25

Table 2.12 Most important properties of alternative fuels used in aviation

Substances Physical and chemical characteristics

Ethanol and
methanol

Ethanol and methanol are liquid fuels that can be pumped and metered in
conventional fuel systems in airplanes [ 38 , 39 ]. The heating value of
alcohols is lower than that of kerosene. They have a very low flash point
of only 12-18C (53.6-64.4F) and, respectively, a minimum allowed
temperature of 38C (100F). There are also chemical incompatibilities
associated with materials in the fuel system, although these problems
could be remedied with relatively minor changes

Fatty acid methyl
ester

Adding FAME from vegetable oils, such as soy bean or canola oils to other
biogenic fuels, is starting to be used in aircraft [ 40 ]. In this case, additives
and heated supply systems are needed since more than 2% FAME of soy
bean oil raises the freezing point above the specified maximum. Ethanol
blends with jet fuel and adding FAME of vegetable oils to jet fuel results
in less exhaust smoke and particles in high-power conditions, but
increases the emission of CO and HC during idling, along with the
presence of acids and aldehydes. The emissions of NO and NO 2 increase
with higher flame temperatures

Cryogenic fuel Aircraft gas turbines can be designed to operate with cryogenic fuels such as

methane or hydrogen [ 41 ]. However, conventional fuel systems cannot
handle these fuels. Alternative fuels require additional aircraft fuel
system design, as well as new ground handling and storage systems.
Moreover, cryogenic fuels have to be stored in the fuselage rather than in
the wings to reduce heat transfer. Because methane and hydrogen have
only 65% and 25% of the energy density of jet fuel, fuselages would have
to be considerably larger than current designs, increasing drag and fuel
consumption

Hydrogen For long-range flights, an advantage would be offset by reducing the takeoff

weight because hydrogen and, to a small extent, liquid methane have
higher specific energy than kerosene [ 42 ]. Airplanes with ranges over
10,000 km (5,400 nmi) using hydrogen fuel show a reduction of almost
20% in fuel consumption compared to kerosene. Medium- and short-
range airplanes flying from 3,200 to 5,500 km (from 1,728 to 2,970 nmi)
have a 17-38% higher consumption of fuel. For methane, there is only a
small benefit for long-range aircraft and a 10-28% higher fuel
consumption for medium- and short-range aircraft

kerosene with certification. One expects full official acceptance of biogenic fuel in
aviation in 2012 and 2013. The relevant admittance standards of introduction are
''D 6751'' of the ASTMs and ''Defstan 91-91 for Renewable Fuel'' of the British
Authority [ 43 , 44 ].