Page 289 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Ford Motor Co. - Ford France SA - Ford Werke AG - Ford Motor Co. Ltd. 271

converter, after 5 seconds most of the temperature increase is concentrated at the front end of
the catalytic converter and this front slice is considerably hotter than the remainder of the
converter. On the other hand, in the case of an inefficient converter, the temperature rise at the
front end of the converter after 5 seconds is significantly lower than the temperature rise
deeper within the converter. For efficient converters, the exothermic catalytic reaction is
completed while the exhaust gases are still at the front end of the converter whereas in a less
efficient converter the exothermic reaction takes longer to complete. The exhaust gases also
tend to coof the catalytic converter and the cooling effect is strongest at the front end of the
catalytic converter. As a result after 5 seconds the front end of a converter operating with 60%
efficiency is cooler than the center of the converter.

It is therefore possible measuring the temperature in different slices of the catalytic converter
to determine the conversion efficiency by a comparison of the relative temperatures after a
given time following a step increase in the combustible constituents of the exhaust gases
reaching the catalytic converter.

Fig. 120 (from GB2282467)

The method of GB2282467 (1 995) judges the operability of a catalytic converter during light-
off by determining the time required for the catalytic converter to light off during a cold start-
UP by7

1) propelling a heated air mass through the converter (fig. 120)
2) determining an initial heat transfer rate &,,from the heated air mass to the catalyst material
of the catalytic converter as follows: