Our previous article talks about careful planning in order to
save unnecessary trips, adopting carpooling to share out the
costs, avoiding traffic jams at peak hours to avoid
unproductive burning of fuel, avoiding carrying unnecessary
loads and other tips that will help in some way or another to
save on fuel consumption.
I did touch a bit on more efficient smaller cars that are
lighter and do not have to carry excess and unproductive weights
in their frames, chassis and body. However, very often, these
smaller and lighter cars are not as comfortable to ride compared
to the heavier ones.
So, in this article, I won't compare lighter cars with heavier
cars. I will explore with you the kinds of efficiency losses
that are quite typical even within the same class of cars.
If you look through the sales brochures of new cars, very often
you can find figures that indicate the fuel efficiency of the
car. With that information, you can compare and find out the
most fuel efficient vehicle that will meet your needs. Even
within a specific size class, there is a tremendous range of
MPG (miles per gallon) performance that you can find.
Just for example, for the same model year compact cars, we can
find fuel efficiency ranges from 21 to 48 MPG. If you choose
the 48 MPG car, you could be saving hundreds of dollars in fuel
costs each year. I think that should be an important point to
note when buying a new car.
Having decided on the model that fulfils your needs, you might
be interested to know where the energy goes.
Idling losses could account for as much as 17.2% of all the
losses. In urban driving, this much of energy is lost to idling
at stop lights or in the traffic. There are technologies
available such as integrated starter / generator (ISG) systems
that help to reduce this type of losses. It does this by
automatically turning off the engine when a vehicle comes to a
stop and restarting it instantly when the accelerator is pressed.
Another very significant loss is through the engine itself. The
internal combustion engine of gasoline-powered vehicles is very
inefficient. Over 62.4% of the fuel's energy is lost through the
engine combustion process of converting the fuel's chemical
energy to mechanical energy. Energy is lost to engine friction,
pumping of air into and out of the engine, and removing the
wasted heat.
Advanced engine technologies have been developed to address
these losses. Some of them are: variable valve timing and lift,
turbocharging, direct fuel injection, and cylinder deactivation.
Diesel engines are about 30~35% more efficient than gasoline
engines. New advances in diesel technologies and fuels are
making these vehicles more attractive.
Accessories like air-conditioning, power steering, windshield
wipers, and others use the energy generated from the engine.
These use up to 2.2% of the energy. Efforts in developing more
efficient alternator systems and power steering pumps can
improve the fuel economy by up to 1%.
Driveline losses can account for up to 5.6% of the total. The
energy is lost through the transmission and other parts of the
driveline. To reduce these, technologies such as automatic
manual transmission (AMT) and continuously variable transmission
(CVT) has been developed.
Next comes the shape of the vehicle. Aerodynamic drag accounts
for 2.6% of the energy losses. As the speed of a vehicle
increases, the drag caused by expending energy to push air out
of the way increases. By designing the shape of a vehicle for
smoother air flow, significant drag reduction can be achieved.
Rolling resistance is another loss encountered in a vehicle. It
accounts for 4.2% of the losses. This rolling resistance is a
measure of the force necessary to move the tire forward. To
counter this, tires technologies like thread and shoulder
designs, and the use of improved materials on the tire belt and
traction surfaces are being developed.
For passenger cars, a 5~7% reduction in rolling resistance
increases fuel efficiency by 1%. However, these improvements
must be balanced against traction, durability and noise.
Related to the driver's behavior is braking loss. This can
account for as much as 5.8%. Each time a vehicle moves forward,
the vehicle's drivetrain must provide enough energy to overcome
the vehicle's inertia. This inertia is directly related to the
weight of the vehicle. So for lighter vehicles, less energy is
expended to overcome the inertia of the vehicle compared to a
heavier vehicle. The less a driver brakes, the less energy is
expended to move the vehicle again.
As you can see, there are many factors that can affect the fuel
efficiency even of similar vehicles. Factors like the vehicle
condition, tire pressures and design, driver's habit, planning
trips, reducing excess loads, avoiding drag, idling at peak
traffic and many others can affect the efficiency.
With a better understanding of the measures you can control, you
should be able to achieve the best optimum efficiency in your
vehicle and save money in the process.
More information on engineering at Marine and M & E Engineer websites.
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