Page 18 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Introduction

In order to meet increasingly stringent restrictions on the emissions of certain polluting gases
by automotive internal combustion engines, it is common nowadays for the exhaust systems of
such engines to include catalytic converters. The exhaust gas from the engine passes through
such converters and pollutant gas constituents are converted into less undesirable gases by the
catalytic action of the catalyst within the converter for venting to the atmosphere.

Catalytic action in general is the action of certain materials to provoke with their presence in a
suitable environment chemical reactions, without themselves being modified by this reaction. In
exhaust systems noble metals play the role of these catalytic materials (cutufysts).
The dramatic evolution of catalytic converters in the last 30 years was a result of a need
worldwide to reduce pollution created by the exhaust systems of internal combustion engines.
Pollutants like nitrogen oxides (NO,), carbon monoxide (CO), hydrocarbons (HC) and
particles (e.g. carbon) are produced from the incomplete combustion of the aidfuel mixture in
the engine. These, in combination with the atmospheric conditions can lead to photochemical
reactions which generate smog and contribute to the production of acid rain.

Studies in the United States have shown that about 10 per cent of vehicles are responsible for
50 per cent of the CO emissions at the sites studied. Besides, experience has shown that a
desired durability (80000 Km) of anti-pollution systems of gasoline cars cannot be guaranteed
with high confidence levels. Therefore, special emphasis is given to tailpipe inspections and
maintenance programs ([ 1 I). Environmental concerns have led American, Japanese and
European Union (EU) legislation to pose continuously stricter emission limits for gasoline
engines over the last decades.

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