Page 184 - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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168 Automobile mechanical and electrical systems

2.4 Air supply, exhaust and emissions

2.4.1 Air pollution and engine combustion

Atmospheric pollution has become a serious problem to the health of people and
to the environment. Many urban areas are heavily polluted, with people suffering
Key fact medically from the effects of vehicle exhaust pollution. There have been many
The rapid burning of fossil fuels changes in climatic conditions in the world. Many of these have occurred over
during the past century increased a long period and animals and plants have adapted to the changes naturally.
carbon dioxide levels in the However, the rapid burning of fossil fuels during the past century has increased
atmosphere.
carbon dioxide (CO 2 ) levels in the atmosphere.
Carbon dioxide allows the sun’s heat in, but reduces the ability of the heat to
radiate outward, causing the Earth to warm up. Many studies of the warming
process indicate that the rate of Earth warming is increasing too quickly and
preventing animals and plants from adapting. Vehicle exhaust gas also includes
other toxic components ( Fig. 2.177 ). Environmental regulations are now in
place to fi nd safer alternatives, or to reduce the production and use of the most
harmful pollutants. Other regulations and agreements are seeking to reduce the
production of carbon dioxide by improving the effi ciency of fossil fuel burners.

Lead was at one time used as an additive in petrol to slow down the combustion
process. This was to eliminate knocking or pinking in the engine. It made engines
more effi cient but the lead did not burn and was, instead, passed into the
atmosphere from the exhaust and produced airborne concentrations that were
capable of causing many physical disabilities, including brain damage. For this
reason, lead additives are no longer used and modern engines are now designed
to run on lead-free fuel.
Another naturally occurring substance in fossil fuels, particularly diesel, is sulphur.
This does not burn but, during combustion, chemically reacts with oxygen in the
). This passes from the engine exhaust into the
air to form sulphur dioxide (SO 2

atmosphere, where it combines with water to form sulphuric acid (H SO ) and
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falls back to Earth as acid rain, which destroys trees, plants, other vegetation and
Oxygen & Carbon
Inert gases Dioxide
Water 1% 18% Pollutants
9% 1%

Nitrogen
71%

Pollutants (1% of total) Solids Nitrogen
1% Oxides
8%
Hydro-
carbons
5%
Carbon Monoxide 86%

Figure 2.177 Approximate composition of vehicle exhaust gases