Page 23 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

6 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

The current European exhaust emissions standards for heavy duty diesel vehicles over 3.5 tons
(EURO stage 11, effective October 1996) are:

CO 4.0 gkWh,
HC 1.1 gkWh
NO,7.0 g/kWh and
particles 0.15 g/kWh.

The German government has introduced incentives to encourage early adoption of the 2000
limits. It recently brought in tax incentives for the retro-fitting of existing vehicles with closed-
loop three-way catalytic converters (petrol) or oxidation catalytic converters (diesel).

Similar standards like the ones of Europe and the USA have been adopted by Japan. However,
the testing cycles in all three regions differ from each other, because the authorities try to
reproduce conditions more typical of their own traffic patterns.
Emission standards like the ones of EC96 can be met only by making use of catalytic
converters and especially three-way catalytic converters.

As shown in Table 1, compression-ignition or diesel engines produce smaller amounts of CO
and HC than petrol engines, their main problem being particulate emissions. The NO,
emissions are comparable for the two engines, however the diesel engines emit significantly
fewer hydrocarbons than the petrol engines. The different composition of pollutants of the
exhaust gases for petrol and diesel engines has led to a different catalytic converter technology
for each type of engine.
Before handling the problem of monitoring of catalytic converters, a few elements concerning
the technology of catalytic converters will be presented below. Most of the technology
described in this book refers to spark-ignition (petrol) engines. However a few elements
concerning diesel engines are also described.