Automotive
The air-polluting effects of internal-combustion engines were not recognized until the early 1960s. Up until that time, improvements in power output and exhaust noise were the main areas of development.1 The driving force for change originated in the first measures to control air pollution, which were introduced in the smog-bound city of Los Angeles, USA. Controls for exhaust gases from motor vehicles were introduced in Japan and Europe soon afterwards. These early measures were focused on carbon monoxide (CO) and unburned hydrocarbon (HC).
The use of oxidizing catalysts to convert HC and CO has been mandated
under exhaust gas regulations in the USA and Japan since 1975. The main
components of the early catalysts were base metals such as Co, Cu, Fe, Ni, and Cr.2 However, these were found to degrade over time, and precious metal catalysts were introduced to address problems of sulfur poisoning and metal evaporation. Unleaded petrol was developed because it was found that the lead in petrol coated the catalysts and made them ineffective.
An exhaust gas recirculation (EGR) system was introduced to decrease NOx emissions, but catalysts to remove NOx were not legally required until 1978. Regulations introduced in Japan (1978) and the USA (1981) required a further decrease in NOx emissions, and although the oxidizing catalyst system addressed HC and CO requirements, various controls in the engine were necessary to decrease NOx. As a result, power output fell and fuel consumption increased.
The first vehicle with a three-way catalyst was marketed in 1977, although it was not introduced for European cars until 1993. A system combining a three-way catalyst with electronic fuel injection (EFI) and oxygen sensors has now become the standard in petrol engines for cars. The three-way catalyst system reduces exhaust emissions after warming up, but recent legislation on emissions now requires a further decrease in pollutants, and reducing emissions at cold start is an important issue.
The science and technology of materials in
automotive engines
Hiroshi Yamagata
Woodhead Publishing and Maney Publishing
on behalf of
The Institute of Materials, Minerals & Mining
CRC Press
Boca Raton Boston New York Washington, DC
WOODHEAD PUBLISHING LIMITED
Cambridge England
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