Environmental Engineering Reference
In-Depth Information
Minimal energy consumption requires careful braking and accelerating when
changing gears. Since the combustion engine operates most efficiently with
relatively high loads at a low number of revolutions, minimum consumption is
achieved with short and strong acceleration. In cars, it is useful to switch into third
gear at 25-30 km h
-1
(15.5-18.6 mph), into fourth gear from 35 to 40 km h
-1
(21.8-24.9 mph), and into fifth gear at approximately 50 km h
-1
(31.1 mph) [
5
].
In compact and mid-size cars, fuel consumption can be decreased by changing
from a simple manual to an automatic transmission with a suitable switching
program. In the upper mid-size and full-sized cars, automatic transmissions can be
best adapted to the higher efficiency of the engine.
Vehicles with spark ignition engine should always be driven with the lowest
possible number of revolutions, since their efficiency depends on the load and the
speed of the engine. The efficiency increases in a high gear compared to driving at
the same speed in a low gear.
The automatic transmission and the adaptive driving assistance system save
most of the fuel, and improve road performance and comfort, e.g., with the
automatic mechanical transmission that is widely applied in heavy commercial
vehicles.
8.2.2 Auxiliary Equipment
The auxiliary equipment consists of the power steering, the brake booster, the air
conditioning system, the alternator, the windscreen wiper, the radio, the seat
heating and the air heating etc. which are usually directly powered by the engine
and significantly affect its fuel consumption.
The use of the air conditioner has the greatest effect on the fuel consumption in
a mid-size car. The amount and the energy demand of equipment is rapidly rising
in all means of transportation:
• Air conditioning system increases consumption from 0.5 to 2.5 l h
-1
(from 0.13
to 0.66 gal h
-1
), depending upon the manufacturer and the cooling demand;
• Headlights increase consumption from 0.1 to 0.2 l h
-1
(from 0.03 to 0.06
gal h
-1
);
• Rear window heating increases consumption from 0.1 to 0.2 l h
-1
(from 0.03 to
0.06 gal h
-1
); and
• Other electrical consumers, e.g., windshield wipers, stereo boxes, cooling boxes,
electrical windows, electrically adjustable seats, etc., increase the fuel con-
sumption from 0.2 to 0.5 l h
-1
(from 0.06 to 0.13 gal h
-1
)[
6
].
It is predicted that the air conditioning system will remain the main source of
increased consumption. Currently, it consists of a compressor directly powered by
the engine, which requires a high amount of generator capacity. In the future, it
may be that other solutions, e.g., the application of phase changing materials
(PCM) can be used for more economical and ecological air conditioning. A few
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