Alternative fuels and green aviation - Biomass as Energy Source: Resources, Systems and Applications - page 176

Figure 11.1. Chronological patterns in air traffic, including passenger and cargo traffic, from 1960-2006,
overlaid with relevant events. Air traffic is shown in terms of revenue tonnes per kilometer
(RTK). Predicted growth in jet fuel demand is shown from 2006 through 2025 (solid line),
which includes expected efficiency gains from technology development (dotted line) and logis-
tics improvements (dashed dotted line). Adapted from Chèze et al . (2011), with permission
from Elsevier, Inc.
can arise due to incomplete access to all the relevant data or processes, or they can be due to
real statistical variation (e.g., variation in fuel sulfur content depending on whether the fuel was
extracted from shale or more conventional petroleum reservoirs). Either way, it is useful to develop
an understanding of how much variation can be expected in any given factor. Now, let us dig into
some of the details.
Over the last several decades, air traffic has increased by about 5% annually. As shown in
Figure 11.1, itsmomentumwas slowed only briefly through 2006 bymajor events such as the attack
on the World Trade Centre in 2001, wars, the SARS epidemic, and gloomy economic conditions.
Since the global economic crisis in 2008-2009, the airline industry has recovered to pre-recession
levels and is expected to grow at or above historical levels (Boeing, 2011). However, even when
accounting for technology advancements (dashed line) and logistics optimization (dash-dotted
line), jet fuel demand is expected to increase for the foreseeable future. In other studies that
attempt to predict energy demand for the aviation industry during the coming decades, the details
may vary somewhat, but the fundamental conclusion is that the demand for jet fuel will continue
to increase. Better air traffic management could provide a potential fuel consumption savings
up to 15% (Blakey et al. , 2011), such as separation distance control and speed optimization.
With the right infrastructure on the ground, continuous descent approaches could improve fuel
efficiency over the current stepped approaches.Although there is some ongoingwork in alternative
modes of propulsion, such as fuel cells (Novillo et al. , 2011; Renouard-Vallet, et al. , 2012), this
technology will not be commercially viable for decades, at best. The major efforts at reducing fuel
consumption in engine and airframe design include increased efficiency through new turbofan
designs, e.g., high pressure-ratio cores and super high bypass-ratio fans, reduced drag airframes,
and advanced materials in ceramic composites. The recently unveiled Boeing 787 delivers a 20%
fuel reduction relative to similarly sized planes through the use of advanced materials, new engine
design, and improved fuselage integration. Aircraft lifetimes are typically in the range of 20-30
years or more (Moavenzadeh et al. , 2011), so that it will be some time before there is a complete
turnover to more efficient aircraft designs. To work with the fleet as it exists, some aircraft can be
retrofit with winglets to improve aerodynamics, but this is only an aid, not a fix to the problem.
In addition, airport supply chains and infrastructure are currently set up for petroleum-based
fuels. The automobile industry is well-suited take advantage of all-electric and hybrid engines to
reduce overall fuel consumption. However, the aviation sector has no practical alternative to the
internal combustion engine in the coming decades, and in spite of technological and logistical
improvements, jet fuel demand will continue to grow.