Page 41 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Introduction 23

Other systems io. faciliiate light-ofltemperature qf catalytic converters

Another way to make a catalytic converter effective for cold engine start-up is to keep it hot
with some kind of heat storage system while the car is parked. This device might be similar to a
thermos bottle or air-gap pipe that fits over the converter. The problem with this technique is
releasing the heat once hot exhaust starts pouring in so the contents do not overheat ([14]).

An alternative approach is to heat the main catalytic converter by means of a cross-flow
catalytic converter-heat exchanger combination like the one of fig. 10d. The exhaust gas
leaving the engine and passing through the converter heats the part of the converter that is on
the far downstream side, thus reaching the light-off temperature to oxidize the HC released for
example by a HC adsorbent.

Combinations of the above mentioned approaches as well as other methods not described in
this book may be also found in the literature. An example of such combinations is given in fig.
10, where a HC adsorbent, an electrically heated catalytic converter (EHC), a close-coupled
converter, a main catalytic converter and a heat exchanger are combined in the exhaust pipe of
an internal combustion engine (see W09508702 (1995)).

exhaust gas flow HC Main catalytic
Engine , 'adsorben' EHC converter
A

Engine Main catalytic HC EHC
converter ' adsorben

Main catalytic
Engine EHC converter

catalytic converter
Engine + HC
-.c( EHC~-~k exchanger dsorbe
heat
I I

Fig. 10 (fiom W09508702)