Page 251 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter 2

Catalytic Converter Functionality Diagnosis by Means of
Tern peratu re Measurements

This chapter comprises methods of diagnosing degradation of the functionality of catalytic
converters by measuring the temperature of the exhaust gases. The measurement can be direct
by making use of one or more temperature sensors placed upstream, downstream or inside the
catalytic converter or the measurement can be indirect by estimating the temperature from
other engine parameters. The methods are based on the useful information received fi-om the
heat release caused by exothermal reactions in the catalytic converter, which is an indication of
catalyst light-off.

In the case of an efficient catalytic converter, the chemical reactions taking place within the
catalytic converter generate heat so that the temperature of exhaust gases leaving the converter
should be greater than the temperature of exhaust gases entering the converter. The
temperature difference between inlet and outlet of the catalytic converter becomes then an
important criterion for diagnosing the fhctionality of the catalytic converter.

The deterioration of a catalytic converter usually occurs at the front face of the converter
(reaction zone). This aging reduces the temperature gradient from the front face of the
converter and undesirably increases the inlet temperature needed for maximum conversion

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