Environmental Engineering Reference
In-Depth Information
and publisher of international standards, networking 170 countries and approving
international norms in all technical areas.
What is the energy efficiency potential in transportation?
The transportation sector as a whole was responsible for 27% of the world's energy
consumption in 2008 (up from 23% in 1971). For the OECD it was 33% in 2008
(up from 24% in 1971). For non-OECD countries it was 18% in 2008 (up from
13% in 1971).
Increased mechanical efficiency (currently 40%) could be achieved by decreas-
ing the power required of the engine. This can be done by reducing air drag, rolling
resistance, weight, friction in the transmission gears, and vehicle accessory loads.
Increasing the actual average mechanical efficiency to approximately 65% percent
seems an achievable goal. In contrast, thermal efficiency is limited by the laws of
thermodynamics to less than 40%.
The mechanical efficiency of typical US automobiles is roughly 35%, on aver-
age, for urban driving and about 50% for highway driving. The overall mechanical
efficiency averages about 40%. It is lower for high-powered automobiles and high-
er for low-powered automobiles.
Improving mechanical efficiency at a given load requires that the power neces-
sary to operate the engine be reduced, particularly the energy used for pumping,
overcoming friction, and driving engine accessories. There are many strategies for
achieving this: engine size, sources of friction themselves, and engine speed. The
Otto spark ignition gasoline engines in use today have a low cost and high power-
to-weight ratio and are, therefore, difficult to replace with other types of engines.
Working against improvements in the present transportation system is the fact
that advances in designing better automobile engines and vehicles to guarantee
higher energy efficiency are inhibited by other factors of customer acceptance.
These include visual attractiveness, safety, capacity, performance, and comfort
(even luxury). Safety is also one of the key features that must be taken into account
in energy-efficient designs, and it has been repeatedly argued that smaller and more
efficient automobiles increase highway fatalities.
For such reasons, the maximum power of new automobiles has increased in re-
cent years: the average new-automobile power/weight ratio has risen from a low 70
HP/1,000 kg to 90 HP/1,000 kg, although high power is only required in unusual
driving conditions such as acceleration at high speed and on mountainous roads.
Some governments have tried to counteract such trends by imposing taxes on gas
Search WWH ::




Custom Search