Exhaust Aftertreatment System Overview - PREVOST H3-41 Maintenance Manual

SECTION 04 : EXHAUST AND AFTERTREATMENT
2. EXHAUST 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
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
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.
PA1615 Maintenance Manual All Series | Section 04 revised September 2016
8
Selective Catalytic
(DOC) and Diesel
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.
2.1 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
damaged or corroded exhaust components
immediately.
Inspect the exhaust system as follows:
•
At vehicle inspection intervals ;
•
Whenever a change is noticed in the sound of
the exhaust system ;
•
When components close to the exhaust
system get unnaturally dirty ;
•
Whenever the exhaust system is damaged.
Replace damaged or corroded exhaust system
components without delay.
When operating the engine in a service garage or
in a closed area, the exhaust must be vented to
the outside. Place the shop vent hose over the
exhaust outlet pipe.
DANGER
Avoid breathing exhaust gases since they
contain carbon monoxide which is odorless and
colorless but harmful. Carbon monoxide is a
dangerous gas
unconsciousness and can be lethal. If, at any
time you suspect that exhaust fumes are
entering the vehicle, locate and correct the
cause(s) as soon as possible.
WARNING
Diesel engine exhaust and some of its
constituents are known to the State of
California to cause cancer, birth defects and
other reproductive harm.
that can cause