Environmental Engineering Reference
In-Depth Information
cars, trucks, and buses before WW II and still 60% by
1960.
But Europe matched the U.S. total by 1983 and is
now the world's largest market for new vehicles; China
became the fastest growing new car market during the
1990s. In 2005 there were more than 700 million pas-
senger cars on the roads, and their typical performance
remains unimpressive. The best practical e
1
of the Otto
cycle engine is about 32%; frictional losses bring this
down to 26%, and partial load factors, inevitable during
the urban driving that constitutes most car travel, reduce
it to 19%-20%. Accessory loss and automatic transmis-
sion may nearly halve the total, so the effective e
1
is
no more than 10%-12% and often as low as 7%-8%.
Consequently, the greatest reductions of energy use in
transportation can come from the long overdue radical
redesign of passenger cars.
National differences are clearly discernible in the shares
of final product uses. Gasoline makes up 50% of U.S. de-
mand for liquid fuels, whereas Japan's share of the light-
est fraction is less than 20%, but residual fuel oil accounts
for nearly one-third of Japanese use, whereas the U.S.
share is less than 10% of the total. The U.S. preference
for large cars, decades of declining oil prices, and a tradi-
tion of heavy Detroit design also meant that the perfor-
mance of the U.S. car fleet was actually getting worse.
By 1974, U.S. cars needed roughly 15% more energy per
kilometer than their counterparts of the 1930s. A sharp
turnaround was brought about by OPEC's oil price
increases and by the growing importance of European
and Japanese car imports. Between 1974 and 1988 the
fuel consumption mean for the U.S. car fleet fell by al-
most 50%, to 3.1 MJ/km.
Regrettably, the return of low oil prices and a
decade of economic vigor reversed this trend as pickup
trucks, vans, and the ridiculously named sport utility
vehicles—all used mostly as passenger cars but exempt
from passenger-car strict CAFE standards (minimum of
27.5 mpg or 8.6 L/100 km)—gained nearly half the
U.S. car market. The average performance of these out-
size vehicles in 2000 was only 17.5 mpg. Some of them
weigh more than 4 t and need at least 15 L/100 km in
highway driving. Among 2005 models, General Motors'
Yukon and Chevrolet's Suburban and Tahoe were in this
category. As a result, there has been no improvement in
specific fuel consumption of the U.S. road vehicle fleet.
The average for all passenger cars at the beginning of
the 2000s was just 22 mpg (EIA 2006a). This stagnating
performance was accompanied by a steady increase in av-
erage distance traveled annually. That rate hardly changed
between 1950 and 1975, rising about 3% to 15,400 km/
vehicle, but between 1975 and 2000, it rose 26% to
about 19,500 km/vehicle. Yet there is no shortage of ef-
ficient cars on the market. The best-selling Honda Ac-
cord is highway-rated at less than 6.5 L/100 km, the
Honda Civic at 5.7 L/100 km, and the hybrid Honda
Insight at 3.3 L/100 km.
The high density and portability of refined fuels have
also made them the only practical choice for aviation.
Reciprocating gasoline-powered engines were displaced
in nearly all military uses and all long-distance commer-
cial flying by gas turbines. Kerosene is a much better
fuel for jet engines than gasoline. It has a higher specific
density (0.81 g/L vs. 0.71 g/L) and hence a higher en-
ergy density (35.1 MJ/L vs. 31.0 MJ/L), so more of it
can be stored in tanks. It is also cheaper, has lower evap-
oration losses at high altitudes and a lower risk of fire
during ground handling, and it produces more survivable
crash fires. Jet A fuel, used in the United States, has a
maximum freezing point at
40
C. Jet A-1 fuel, with
