Ducati Monster 796 - Operating Principle of the Catalytic Converter; Removal of the Exhaust System

Exhaust system
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33 LH heat shield
34 Washer
35 Guard
36 Cable
37 Exhaust valve motor
38 Washer
39 Clamp
40 Clamp
41 Spacer
42 Screw
43 Screw
44 Spacer
45 Circlip
46 Clip
47 Spacer
48 Washer
Spare parts catalogue
796
EXHAUST SYSTEM
796 ABS
EXHAUST SYSTEM
Important
Bold reference numbers in this section identify parts not shown in the figures alongside the text, but which can be found in
the exploded view diagram.
Operating principle of the catalytic converter
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. 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. 6 - 8) monitors the oxygen content of exhaust fumes and transmits the relative data
instantaneously to the ECU. The control unit (through injection) keeps the air-fuel ratio as close as possible to optimum
value (with a certain tolerance) in order to ensure top performance of the catalytic converters in the exhaust pipes. In
terms of emissions, this means achieving minimum hydrocarbon (HC) and carbon monoxide (CO) emissions as well as
minimum nitrogen oxide (NOX) emissions. 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.
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,
never push-start the motorcycle (with key and ENGINE STOP button set to ON). In this instance, if the engine does not
start, any unburnt fuel would enter the exhaust system and stay 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.
Removal of the exhaust system
Operations Section reference
Remove the RH footrest bracket 7 - 15, Removal of the footrest
brackets
Remove the seat 5 - 3,
Removal of the seat
Remove the retaining spring (10) of the LH silencer (8) from the centre exhaust pipe (5).