Operating Principle Of The Catalytic Converter - Ducati Monster 696 2009 Manual

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Operating principle of the catalytic converter

A
This model is fitted with "three-way" catalytic converters. Catalytic converters are fitted to the exhaust system in order to
eliminate the noxious substances found in exhaust fumes, namely CO (carbon monoxide), HC (unburnt hydrocarbons) and NOx
(nitric oxide). The catalytic converter has a special honeycomb support, coated with aluminium oxide, which creates an irregular
surface thus increasing the surface area exposed to exhaust gas. The aluminium oxide is coated with activated substances that
help to remove harmful components of exhaust emissions. These substances are usually platinum and rhodium. Platinum allows
the oxidation (combination with oxygen) of CO and HC. Rhodium allows the reduction (combination with CO) of NOx contents.
B
To ensure that CO and HC components can oxidise to form water and carbon dioxide and that NOx contents can be reduced
by forming nitrogen and carbon dioxide, there must be a precise amount of oxygen in the exhaust gas. For this reason it
is essential that the air-fuel mixture is correctly proportioned. This result has been achieved thanks to the use of a
sophisticated fuel system designed to meter the air-fuel mixture with absolute precision.
The lambda sensor (Sect. M 3) monitors the oxygen content of exhaust fumes and transmits the relative data instantaneously to
the ECU. To ensure that the catalytic converters in the exhaust system work efficiently, the ECU controls fuel injection to
C
maintain the air/fuel ratio within a tolerance close to the optimal value, achieving the minimum possible emissions of
hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx). The 3 way catalytic converters complete the exhaust
fumes cleaning process by converting residues of CO, HC and NOX in the exhaust gas, thus ensuring exhaust emissions
comply with EURO 3 regulations.
D
How to ensure that the catalytic converter functions correctly
In order to function correctly, the catalytic converter must reach a temperature of around 800 °C and never fall below 300 °C.
The indicated maximum temperature must not be exceeded, otherwise the catalytic converter could be irreparably damaged.
For this reason, it is essential that significant quantities of unburnt fuel do not accumulate in the exhaust gas post-treatment
element, since these would otherwise burn resulting in a sharp increase in temperature. This is why the ignition-injection system
should always be in perfect working order (misfiring is not acceptable). Moreover, the motorcycle should never be pushed
E
with the ignition key and ENGINE STOP button set to ON. In this case, in fact, if the engine fails to start, the unburnt fuel will
enter the exhaust system and deposit in the catalytic converters. Motorcycles fitted with catalytic converters must be used
exclusively with unleaded petrol. Otherwise the lead content of petrol would deposit on the activated substances and limit their
action against the harmful components of exhaust gas.
F
G
H
L
M
N
P
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Fuel/Exhaust System
Monster 696/696+ - M.Y. 2009 - edition 00