Page 475 - Air Pollution Control Engineering

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Emerging Pollution Control Technologies 447

ulates, and 0.6% sulfur found in typical gasoline supplies in the United States. Heat emis-
sion rates of large automobiles traveling at high speeds are also enormous and reach val-
ues of 750,000 Btu/h per vehicle—over 500 times that required to maintain a comfort-
able temperature in a typical room or office.
In terms of fuel consumption, these transportation devices use about 140 billion gal
of motor fuel in the United States each year. The only more abundantly used liquid is
water. Seventy-four percent of motor fuel is consumed in highway use, of which cars
account for 52%, trucks 21%, and buses and motorcycles 1%. Off-highway consump-
tion breaks down as follows: aviation 13%, industry and construction 4%, and lawn and
garden equipment 1.5%.
Motor fuels consist of gasoline, diesel, jet fuel, and liquefied petroleum gas (LPG),
which is mainly butane. Cars use essentially only gasoline, whereas trucks use mostly
gasoline (85% gasoline and 15% diesel on a consumption basis). Because gasoline
accounts for about 75% of the total fuel consumption, most of this vehicle section dis-
cussion is related to gasoline engines. The current trend toward reducing the quantity of
automotive pollutants is to encourage the use of smaller vehicles, which can give more
miles per gallons, and to develop new nonpolluting vehicles using fuel-cell technology.

3.2. Standards
The August 8, 1977 Clean Air Amendments established the following emission stan-
dards, given in Table 1, to be met by automobiles in the United States. Depending on
automobile size and type, these emissions in grams per miles may be equivalent to
approximately
1.5 g/mile HC ≅ 120 ppm by volume
15 g/mile CO ≅ 6400 ppm by volume
2 g/mile NO ≅ 550 ppm by volume
x
No particulate emission limits have been set for automobiles, but opacity limits do
exist for jet aircraft and diesel trucks. McKee (1) presents a general discussion on air
quality and control, and Nevelle (2) presents some winning strategies for air pollution
control using emerging technologies.
3.3. Sources of Loss

The maximum thermal efficiency of internal combustion engines (ICEs) is about
40%, making the overall actual automobile efficiency about 10%. In comparison, a
large stationary boiler may have thermal efficiencies of over 70%, with an overall
electrical generation efficiency of about 35%. From this, it is obvious that internal com-
bustion engines could be replaced by more thermally efficient devices, but problems
with mobility requirements would still exist.
In addition to the substantial thermal losses, the following list suggests other losses
expressed as percent of overall efficiency. These values vary, depending on driving
conditions, vehicle size and type, maintenance, and road and wind conditions:
1. Air filter element: Excess dirt can waste 20%.
2. Spark plugs misfiring can waste 12%.
3. Tires: Stiffer tires can save 5%.
4. Air conditioning can add 2–15% waste.