Agriculture Reference
In-Depth Information
Solution
First, we must calculate the tractive power (hp) required to tow the
trailer using equation (2.7):
P
=
F
v
[(50N)(100 kmh
−
1
)(1000mkm
−
1
)]
×
=
[(60 s min
−
1
)(60min h
−
1
)(1000WkW
−
1
)]
−
1
=
.
1
389 kW
1hp
=
0.7457 kW, so
P
=
1.86 hp. Therefore, towing the trailer at this speed
adds 1.86
10 mg, or 18.6 mg of NO
x
to the atmosphere for each kilometer
traveled. This means that at 100 km h
−
1
, the old car is releasing 118.6 mg NO
x
for each kilometer it travels. Indeed, a common challenge to green engineering is
that waste (e.g. NO
x
emissions) accompanies commensurately increased energy
demand. The good news is that reducing waste can have the added bonus of
decreased energy demand.
×
(b) How much can we lower the NO
x
emitted if the old car above produces
90 mg of NO
x
for each mile traveled 50 km h
−
1
and the NO
x
increase from
towing falls to 5 mg km
−
1
for each horsepower expended?
Solution
Once again, we use equation (2.7):
P
=
F
v
[(50N)(50 kmh
−
1
)(1000mkm
−
1
)]
×
=
[(60 s min
−
1
)(60min h
−
1
)(1000WkW
−
1
)]
−
1
=
0
.
695 kW
=
0
.
93 hp
5 mg, or 4.7 mg of NO
x
to the atmosphere for each kilometer traveled. This means that at 50 km h
−
1
,the
old car is releasing 90
Therefore, towing the trailer at this speed adds 0.93
×
94.7 mg of NO
x
for each kilometer it travels. So,
by slowing down, the NO
x
emissions drop 23.9 mg for each kilometer traveled.
+
4.7
=
These examples illustrate that changing even one variable, such as vehicle
weight, can substantially improve energy efficiency and environmental qual-
ity. That is, when the energy efficiency improved, fewer pollutants (i.e., NO
x
)
are released. This demonstrates that pollution is actually a measurement of
inefficiency.
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