3.4.4.6 Use of Biofuels
Liquid and gaseous transport fuels derived from a range of biomass sources
are technically feasible (see Section 3.8.4.3.2). They include methanol, ethanol,
di-methyl esters, pyrolytic oil, Fischer-Tropsch gasoline and distillate, and
biodiesel from vegetable oil crops (Section 3.6.4.3). Ethanol is commercially
produced from sugar cane in Brazil and from maize in the USA where it has been
sold neat or blended for more than a decade. Ethanol is blended with gasoline
at concentrations of 5-15%, thereby replacing oxygenates more typically used
in North America such as methyl-t-butylether (MTBE) and ethyl-t-butylether (ETBE)
additives. ETBE production from bio-ethanol is also a promising market in Europe
but the production costs by hydrolysis and fermentation from cereals or sweet
sorghum crops remain high (Grassi, 1998).
In Brazil the production of ethanol-fuelled cars achieved 96% market share
in 1985 but declined to 3.1% in 1995 and 0.1% in 1998. Since the government
approved a higher blend level (26%) of ethanol in gasoline the production of
ethanol has continued to increase achieving a peak of 15,307m3 in the 1997/98
harvesting season. This represented 42.73% of the total fuel consumption in
all Otto cycle engines giving an annual net carbon emission abatement of 11%
of the national total from the use of fossil fuels (IPCC, 2000).
National fuel standards are in place in Germany for biodiesel and many engine
manufacturers such as Volkswagen now maintain warranties (Schindlbauer, 1995).
However, energy yields (litres oil per hectare) are low and full fuel cycle
emissions and production costs are high (see Section 3.8.4.3.2).
3.4.4.7 Aircraft Technology
Several major technologies offer the opportunity to improve the energy efficiency
of commercial aircraft by 40% or more (Table 3.10). The
Aeronautics and Space Engineering Board of the National Research Council (NRC,
1992, p. 49) concluded that it was feasible to reduce fuel consumption per seat
mile for new commercial aircraft by 40% by about 2020. Of the 40%, 25% was expected
to come from improved engine performance, and 15% from improved aerodynamics
and weight. A reasonable preliminary goal for reductions in NOx emissions
was estimated to be 20%–30%.
| Table 3.10: Energy information administration
aircraft technology estimates |
 |
| Technology |
Year of
introduction
|
% gain in
seat-km per kg
|
| |
| Ultra-high bypass engine |
1995
|
10
|
| Propfan engine |
2000
|
23
|
| Hybrid laminar flow |
2020
|
15
|
| Advanced aerodynamics |
2000
|
18
|
| Material substitution |
2000
|
15
|
| Engine thermodynamics |
2010
|
20
|
| |
An assessment of breakthrough technologies by the US National Research Council
(1998) estimated that the blended wing body concept alone could reduce fuel
consumption by 27% compared to conventional aircraft, assuming equal engine
efficiency. The NRC report also identified a number of breakthrough technologies
in the areas of advanced propulsion systems, structures and materials, sensors
and controls, and alternative fuels that could have major impacts on aircraft
energy use and GHG emissions over the next 50 years.
Noting that the energy efficiency of new production aircraft has improved at
an average rate of 1-2% per year since the dawn of the jet era, the IPCC Special
Report on Aviation and the Global Atmosphere concluded that the fuel
efficiency of new production aircraft could improve by 20% from 1997 to 2015
(Table 3.11), as a result of a combination of reductions
in aerodynamic drag and airframe weight, greater use of high-bypass engines
with improved nacelle designs, and advanced, “fly-by-light” fibre
optic control systems (Penner et al., 1999, Ch. 7). Advanced future aircraft
technologies including laminar flow concepts, lightweight materials, blended
wing body designs, and subsystems improvements were judged to offer 30%-40%
to 40%-50% efficiency improvements by 2050, with the lower range more likely
if reducing NOx emissions is a high priority. The purpose of these
scenarios was not to describe the technological or economic potential for efficiency
improvement and emissions reductions, but rather to provide a “best judgement”
scenario for use in assessing the impacts of aviation on the global atmosphere
through 2050. A number of alternatives to kerosene jet fuel were considered.
None were considered likely to be competitive with jet fuel without significant
technological breakthroughs. On a fuel cycle basis, only liquid methane and
hydrogen produced from nuclear or renewable energy sources were estimated to
reduce greenhouse gas emissions relative to jet fuel derived from crude oil.
In operation, aircraft seat-km per kg is also influenced by aircraft size,
and overall passenger-km per kg efficiencies depend on load factors as well.
Industry analysts (Henderson, 1999) have forecasted an increase in global load
factors to 73% by 2018, but foresee only a small potential for increasing aircraft
size, however, since most additional capacity is expected to be supplied by
increased flight frequencies. If average aircraft size could be increased, perhaps
as a strategy for reducing airport congestion, further reductions in energy
intensity could be achieved.
Table 3.11: Historical and future improvements
in new production aircraft energy efficiency (%)
(Lewis and Niedzwiecki, 1999, Table 7.1). |
| |
| Time period |
Airframe
|
Propulsion
|
Total
|
percent per year
|
| |
| 1950 to 1997 |
30
|
40
|
70
|
1.13
|
| 1997 to 2015 |
10
|
10
|
20
|
1.02
|
| 1997 to 2050 |
25
|
20
|
45
|
0.70
|
| |
|