Exhaust Aftertreatment System Components and
Selective Catalytic Reduction (SCR)
SCR is an emissions-reduction technology with the ability to deliver near-zero emissions of nitrogen oxides (NOx), a smog-
causing pollutant and greenhouse gas. SCR's performance has been proved in millions of miles of real-world trucks in other
countries, as well as in long-term field tests in the U.S. SCR reduces NOx emissions to very low levels, while at the same
time delivering excellent fuel economy and reliability. The system doesn't change the design or of the basic engine. Rather,
SCR is an aftertreatment system which converts NOx in the exhaust stream into harmless gases. Modern diesels already
use exhaust aftertreatment systems, called diesel particulate filters (DPFs), to control emissions of another pollutant, soot
(also known as particulate matter). SCR works by injecting diesel exhaust fluid (DEF) into the exhaust. DEF is a solution of
ultra-pure water and urea. DEF works with the heat of the exhaust and a SCR catalyst to convert NOx into nitrogen and water
vapor - two harmless and natural components of the air we breathe. The end result is cleaner air, excellent fuel efficiency
and a reliable emissions control system for today's modern diesel engine.
W2031651
System Operation
1. Diesel engine optimized for high performance, low particle emissions and low fuel consumption.
2. Aftertreatment DEF tank.
3. The aftertreatment control module (ACM) continuously monitors and adjusts the DEF dosing rate.
4. DEF is injected into the exhaust gases in between the aftertreatment DPF (5) and the SCR catalyst (6).
5. Aftertreatment diesel particulate filter (DPF).
6. In the SCR catalyst, nitrogen oxides are transformed into harmless nitrogen gas and water.
Notes
Mack Body Builder Instructions
CHU, CXU, GU, TD, MRU, LR
USA139046859
Date 5.2017
Body Builder; Engine, MP7, MP8, and MP10
Page 15 (43)
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