Encyclopedia of Environmental Science and Engineering, Volume I and II

MOBILE SOURCE POLLUTION 709

are engine refi nement, fuel additives, catalytic conversion

and reduction of peak combustion temperature.

Gas Turbines

The exhaust of gas turbines contains perhaps less pollutants

than that of any other internal combustion process. The

high airport traffi c density makes the problem a real one,

however. Sulfur dioxide emissions are low, but the smoke

and odor producing compound levels are high. For auto-

mobile use, the total mass of gas turbine exhaust is many

times greater than that for the gasoline engine of equivalent

power. Hydrocarbon and CO mass emissions are known to

be low and diffi cult to reduce. A greater deal of the pollu-

tion control work underway is in the engine modifi cation

area. In aircraft the turbofan engine is largely replacing the

turbojet. Turbofans bypass some of the air past the engine

and rejoin it with the burner gases at the exhaust tailpipe.

Modern dry NO x combustion systems can obtain emissions

of 25 ppm at 15% O 2. 36,37

The airplane is a much more effi cient carrier (pollu-

tion wise) than the automobile, on a people × miles basis.

Aircraft engine research has been concerned primarily with

smoke reduction. Fuel type, fuel additives and combustion

chamber design have been the primary variables studied.

PARTICULATE EMISSIONS

The particulate matter emitted from automobiles has been

characterized^25 as consisting of “lead salts, alkaline earth

compounds, iron oxides, soot carbonaceous material, and

tars. This material ranges in size from large fl akes to submi-

cron particles and varies in consistency from hard and brittle

particulate to oil mists. Some of the particulate material is

generated in the engine combustion chamber and nucleated

and agglomerated in the vehicle exhaust system before it

passes out the tail pipe. On the other hand, a large portion of

the particulate material generated in the engine subsequently

deposits on various surfaces of the exhaust system. At some

later time, this deposited material fl akes off and becomes

reentrained in the exhaust gas to be emitted from the vehicle.

Obviously, opportunities exist for various types of chemi-

cal and physical processes to take place and, as a result, the

overall particulate emission process for a vehicle is quite

complex and diffi cult to defi ne.”

CYCLE LIFE

2004

2000

2000

1998

2002

USABC long-term goal

USABC

midterm

goal

Nickel- Lead-acid

cadmium

Nickel-

metal

hydride

Lithium-

ion

Sodium-

sulfur

Sodium-

nickel

chloride

2500

2000

1500

1000

500

0

FIGURE 4: Performance Parameter Comparison for Electric Vehicles as a Function of Advanced Battery Type (After Moore^38 ).

C013_005_r03.indd 709C013_005_r03.indd 709 11/18/2005 10:42:30 AM11/18/2005 10:42:30 AM