SECTION 04: EXHAUST AND AFTERTREATMENT SYSTEM
2
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
1.
EXHAUST AND AFTERTREATMENT SYSTEM OVERVIEW
FIGURE 1: EXHAUST SYSTEM
The technology behind clean emissions is
through the immediate aftertreatment of engine
exhaust. The process for reducing NOx via
aftertreatment is called Selective Catalytic
Reduction (SCR). It requires a catalytic
converter into which is injected Diesel Exhaust
Fluid (DEF). The primary component of DEF is
water; the active component is urea. Urea is a
nitrogen compound that turns to ammonia when
heated. When a urea-and-water solution is
injected into the exhaust stream and passed
over a catalyst, the urea reacts with the NOx to
form nitrogen and water vapor – two clean and
harmless components of the air we breathe. The
aftertreatment system primary function is to
capture and oxidize (regenerate) the particulate
matter (soot) in the engine exhaust gases and to
reduce NOx. To achieve this goal, the exhaust
aftertreatment system is split into two main
sections: the exhaust gases first enter the
Diesel Oxidation Catalyst (DOC)
and
Diesel
Particulate Filter
(DPF)
assembly to capture
and regenerate the soot on a regular or passive
basis, then the exhaust gases flow through the
catalytic converter
to reduce NOx to minimum
level. Through constant monitoring of the
exhaust gas temperature and the system back
pressure, the engine management system
(EMS) is able to manage regeneration.
The exhaust aftertreatment system is rubber
mounted to the vehicle structure. This feature
reduces the transmission of vibrations to the
exhaust aftertreatment system thus resulting in
extended life of the system, brackets and also
noise reduction.
1.1 MAINTENANCE
Inspect the exhaust system periodically for
restrictions and leaks. Figure 1 presents the
major components of the exhaust system.
Exhaust leaks are commonly the result of loose
clamp bolts, corroded or punctured pipes. In
addition to excessive noise, a leaking exhaust
system could allow toxic gases to enter the
vehicle. Damage to surrounding components
from hot gases could result as well. Replace
