Page 37 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Introduction 19

because the electrical load on the vehicle battery during the period required may exceed the
rated battery output. Also, there is a measurable delay between the time the operator places the
ignition switch in the "on" position and the time the heater brings the converter to the light-off
temperature. An alternator powered electrically heated catalytic converter (APEHC) still
requires a 5 to 10% increase in battery capacity to cope with the EHC start-up scenario.

The development target is to obtain an electrical power consumption of 1 kW. Up to now this
target has not been reached and electrical power of 3-4 kW is still required for larger engines.
This leads to an unacceptable increase in size of the engine generator system or else in the
battery (see [2]).
An alternative solution is to expose the upstream part of the catalytic converter to an
alternating magnetic field or to electromagnetic radiation having such a frequency that the
washcoat of the converter and the particles dispersed in the washcoat are heated to light-off
temperature without a corresponding increase in the temperature of the entire converter. A
magnetron producing microwave radiation can be used for this purpose (see W09014507
( 1990)).

Afterburners

An afterburner can be also installed upstream of the catalytic converter. In this case during cold
engine start up, the engine operates with a rich aidfuel mixture and air is introduced in the
exhaust pipe (fig. 99. An ignition plug ignites the produced air/fLel mixture upstream of the
catalytic converter and the heat produced warms up the converter. Such a method is described
in [ 131. The solution of an afterburner can produce smoke and the combustion is not very
reliable.

Fuel burners

In the case of fig. 9g, a fuel burner is positioned parallel to the exhaust pipe and near the
converter. The burner consists of a burning chamber with a fLel/air mixing system and ignition
device. Contrary to the afterburner chamber of fig. 9f, this heating system operates in principle
independently of the engine's current running mode. During cold engine start up, the fuel
burner burns the air/fuel mixture provided in its combustion chamber and the hot exhaust gas
produced heats fast the catalytic converter. Heating rates exceeding 40 "C/s are common for
systems that are heated electrically or by means of fuel burners.