Encyclopedia of Environmental Science and Engineering, Volume I and II

ENERGY SOURCES—ALTERNATIVES 319

alternative power plants are illustrated in Figure 7 which

indicates the range of specific power in watts/lb and specific

energy in watt-hr/lb available with these devices. The pro-

pulsion system requirements for a 2000 lb vehicle propelled

with a 500 lb power source at speeds of 20, 40, and 60 mph,

and for vehicle ranges of 50, 100, and 200 miles are also

indicated. From these characteristics it may be seen that the

gas turbine and external-combustion engine are the systems

most competitive with the current I-C engine. Various types

of battery systems are shown and these as well as fuel cell

systems may be applicable to limited-purpose vehicles. The

sodium–sulfur and lithium–chlorine systems may approach

the performance of combustion engines but are still in the

development stages. Introduction of a battery driven vehicle

will shift the emission problem from the automobile to a

central station power plant where the electrical energy

required to recharge the battery would be generated (see

section: The Problem of Transport).

Emissions from automotive power plants are variable

and depend upon engine, load, level of maintenance, and

individual driving habits. To allow for variable engine loads,

emission standards are often related to a given driving cycle

involving specified warm-up, acceleration, deceleration,

cruise, and idel periods. The hydrocarbon, CO, and NO x

emission standards now in effect in California and those

established by the EPA for 1974 concurrent are shown in

Table 18 along with emissions from a representative uncon-

trolled gasoline fueled I-C engine as well as alternative

power plants. The pollutants from current I-C engines have

been reduced from uncontrolled levels by control of gasoline

evaporation sources and by crankcase ventilation systems

that recirculate cyclinder blow-by gases back to the com-

bustion chamber. Further reductions of CO and hydrocar-

bon releases, especially NO x , will involve high temperature or

catalytic reaction of exhaust gases in unregulated or regulated

catalysts, which are more and more applied in Gasoline I-C

engines. The advantages of the gas turbine and external com-

bustion engines, which can operate on distillate fuels such as

kerosine, over the I-C engine lie in the better control of com-

bustion conditions that can be achieved by separating the fuel

combustion chamber from the working parts of the engine.

The emission figures for a battery driven electric vehicle indi-

cated in Table 18 were developed by Agarwal^58 on the basis

that the electrical energy is provided from a central station

Range (miles): 50 100

20 mph

40 mph

200

Lead–acid

battery

60 mph

Nickel–cadmium

battery

Internal–combustion

engine

Sodium–sulfur

battery

Gas turbine

External–

combustion

engine

Lithium–chlorine

battery

1

1

10

10

100

100

1000

1000

Specific energy (watt–hr/lb)

Specific power (watts/lb) Fuel

cells

FIGURE 7 Vehicle requirements, and characteristics of mobile power plants for a 200 lb vehicle with a 500 lb power source.

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