Page 35 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Introduction 17

the combustion chamber that does not allow the formation of NO,. Water also reduces the
flame temperature inside the diesel engine cylinder and contributes to reduction of NO,.
However, both methods complicate considerably the control of the engine and a lot of
additional components and instrumentation must be added to the engine system [33].

As already shown in Table 1, the main pollutant of diesel engines is the particulate matter
(soot). Particles are captured in filters or traps. The accumulated particulate raises filter
backpressure, i.e. the pressure difference across the filter or trap which is necessary to force
the exhaust through it. The filters are cleaned periodically by oxidizing the collected particulate
(regeneration of filter) to decrease the high backpressure. In modem diesel engines catalytic
coated filters and oxidation catalysts are used to eliminate particulate matter from the exhaust
gas.

Table 2 summarizes the application of catalytic converters in different technology engines
..
([91).

Pdlutnnt 1 Spark-ignition engine Lean-burn spark- Diesel engine
ignition engine
co Precious metal loaded Precious metal loaded oxidation catalytic
three-way catalytic oxidation catalytic converter
converter converter
HC three-way catalytic oxidation catalytic oxidation catalytic
converter converter converter
NOx three-way catalytic lean zeolite based or lean NO, reduction
converter precious metal loaded catalytic converter
NO, reduction
catalytic
converter
Particulate Filter regeneration aid
(catalytically coated
filters, fuel additives to
lower filter regeneration
temperature)

TABLE 2: Application of catalytic converters in different technology engines