1. SCR Aftertreatment

2. SCR (Selective Catalytic Reduction) technology
SCR technology uses a liquid mixture of urea and deionized water. The U.S. on-highway trucking industry has begun to call this fluid “Diesel Exhaust Fluid (DEF)”. A premix DEF solution is available from Cummins Filtration under the brand name StableGuard. Urea is a stable, chemical substance containing ammonia. The aqueous urea DEF mixture is injected into the exhaust gases before they pass through an SCR catalytic converter. In the catalytic converter, the nitrogen oxides are turned into harmless nitrogen gas and water vapor.
DEF is stored on the machine in a separate tank. StableGuard and other common DEF premix solutions such as AdBlue have a urea concentration of about 32% corresponding to DIN standard
The chemical process; DEF: (NH2) 2CO (urea) + H2O (water). Warm exhaust and water are needed to decompose urea into ammonia and carbon dioxide: (NH2) 2CO + H2O => 2NH3 + CO2. Reduction of nitrogen oxide by ammonia in the presence of oxygen: NOx+NH3+O2 => (catalytic reaction) => N2 + H2O. This process and the Cummins Euro 4 SCR system is shown graphically on the following slide.

3. SCR System Schematic System function lamps
Aqueous Urea Solution (aka Diesel Exhaust Fluid (DEF)) storage tank
DEF Pump
Compressed
Air supply
Dosing Unit
N2 + H2O
Nox Sensor
Urea
Injection
Temperature Sensors
Tailpipe
Decomposition
Area
Turbo
Exhaust
SCR Brick

4. Diesel Exhaust Fluid Usage Projections
Fluid usage is estimated to be 1% to 4% of fuel burned.
Fluid usage increases with load factor on the engine
Engine-out NOx is higher
SCR bed temperature is higher which allows for more total dosing.
Fluid tank fill intervals are dependant upon usage, DEF tank size, and fuel tank size.
Applications/Duty Cycles with lower fuel consumption, lower average load factor, and vehicle space can potentially tie the urea fill interval to an engine maintenance interval.
Otherwise, other applications/duty cycles can tie the urea fill interval to a specified number of fuel fill intervals.

5. SCR Location
As shown in the Architecture section of this document, the SCR canister will be installed in series with and after the DPF.
Exhaust temperatures > 200 deg C into the SCR canister are important for two reasons:
Efficient chemical processing within the SCR
Prevent “polymerization” , or crystal growth of the DEF mixture around the injection nozzle
To minimize heat losses, the SCR should be mounted as close as possible to the DPF. However, there is a minimum required distance required between the urea injector and the front of the SCR. This distance is required for proper decomposition of the aqueous urea mixture. Refer to the Decomposition Piping section for more information.

6. SCR Sizing
The SCR’s being designed for Final / IV are expected to be similar to the DPF used at Interim /IIIB in terms of size, mass, orientations, and inlet/outlet configurations Like the DPF, the SCR will be sized to the engine. It is expected only one size SCR will be certified for each engine model.

7. Example Switchback Configuration
For length restricted applications, CES is developing a close coupled “switchback” DPF SCR packaging system like the one shown in the attached graphic.
The system in the graphic is a vertically stacked, horizontal orientation. The system could also be configured with the DPF and SCR side-by-side in the same horizontal plane.
SCR
FLOW
CPF

8. Dosing Module, Decomposition Piping
The urea injector is also called the Dosing Module (DM). It is installed between the DPF and SCR. Design details are not fixed at this time. It is expected the injector will be keyed, so the nozzle can only point downstream, and will be retained in the exhaust pipe by a threaded coupling. The injector needs to be located such that it can be removed and serviced if necessary.
The exhaust system pipe-work from 200mm upstream of the DM and all the way downstream to the SCR must be stainless steel grade 439, 321, 316 or 904. Aqueous urea is corrosive and in combination with heat, will aggressively attack mild steel components.
No brass, copper, mild steel, aluminium, 409SS, 304SS or zinc materials should be used in areas where aqueous urea is present
The length of piping between the DM and the SCR is known as the decomposition pipe. It allows the aqueous urea mixture injected to decompose into its base materials – ammonia + CO2 – prior to utilization of these compounds in the catalytic reduction of NOX
For proper decomposition to occur this pipe must be:
Minimum length of 700mm from nozzle to face of catalyst “brick”
Max degrees of bends TBD
Avoid sudden, step changes in pipe diameter downstream of the nozzle (prevents polymerization)

9. CES Supplied Decomposition Pipe

10. Total aftertreatment system utilizing CES supplied 486mm decomposition pipe
SCR +Pipe (~40 kg)
Urea Decomposition Pipe
DPF (~30kg)
Urea Dosing Nozzle
Total Length = ~2200mm

11. Urea Solution (DEF) Tank
The urea solution tank is an OEM supplied component.
It must be mounted in an easily accessible location for periodic addition of aqueous urea by the equipment operator
Tank specifications and design considerations:
Size (At least 25 % of fuel tank capacity)
Shape (depth and volume relationship to be linear)
Operating temperature constraints of urea [32F (0 deg C) min, 122F (50 deg C) max]
Materials (Stainless steel, magnesium aluminum alloy or medium-high density polyethylene)
A non-transparent tank is recommended
Venting at low pressure to and from atmosphere. Should not be susceptible to blockage
Relative location of tank and SCR supply module is important for system operation (see sketch)
Fill neck should be designed to prevent spillage
Tank contents, tank volume & full mark labeling required
Tank drain required
Tank heating for cold weather operation thermostatically controlled & located close to tank suction line
Tank expansion space (10 %)
Fluid level sensing required and must correspond to full and empty mark.
Minimum urea level will be approx. 5 liters
EPA requires an empty warning indication at a specified tank level
Suction line location not less than 5 mm from bottom of tank

12. DEF Tank & Dosing Unit Main Fuel Tank Urea Supply Module
Urea Solution (DEF) Tank

13. Urea Solution (DEF) Tank
(internal view)
Level (Magnetic Float)
&
Temperature Sensor

14. DEF Supply Module & Pressure Line
The supply module is a regulated component and must be supplied by the OEM.
Operation of the Supply module (SM) will be controlled by the engine ECM
SM heating will be electric. Requirements (TBD)
Solid mounting the SM to the chassis is acceptable
Permitted mounting positions will +/- 45 deg in two directions. Reference point will be filter centerline
SM should be located in an area that provides protection from damage or splash.
Pressure Line from Supply Module to Dosing Module. OEM supplied
Line must be flexible to allow relative movement between SM and the DM.
It is recommended that the internal diameter of the line be 2.0mm, maximum 3.0 mm
The recommended line length should be 2.0 m, maximum 5.0 m.( longer option to be confirmed)
Relative height between pressure line inlet and outlet should be +/- 1.0 m
Pressure line maximum pressure loss 100 mbar
Maximum number of bends 10
Minimum diameter of bends 150 mm
For cold weather operation, line heating and insulation will be required to prevent urea freezing. Minimum temp required is 32F (0 deg C)
Recommended line heating power input – minimum 12 W/m, Max 120 Watts
Assembly must meet class A cleanliness requirement of Cummins Standard 16599

15. DEF Freeze Protection
Freeze protection must be designed into the OEM’s system. It is not clear yet if it will be mandatory for all regional markets.
Engine Manufacturers Association (EMA) is currently working to understand DEF freeze prevention statements issued by EU and EPA.
Example of EU statement dated July 15, 2007

16. Connection to Engine Cooling System
Based on EPA 2010 MR Engine design that is underway, it is expected that two SCR components must be connected into the engine cooling system.
Heating of DEF tank (Aqueous Urea can freeze if cold soaked below -11C/11F)
Cooling of the DEF dosing module
OEM installed Water Valve Required for Controlling Tank Heating
Dosing Module Coolant Connections are 3/8” SAE J2044 Quick Connections
Using electric heating elements to provide freeze protection for the tank and lines is possible in extreme environments. See the following page for a basic schematic.
Supply Module
Suction Line
Throttle Line
Urea Tank
Tank Heater Valve
Doser Control Unit
Dosing Module
Pressure Line
Coolant Supply from Engine
Coolant Return to Engine
Tank Sensor
Dosing Module Cooling Water Line
Urea Tank Heating Water Line

17. Electric Heating

18. DEF Temperature Degradation
Diesel Exhaust Fluid decomposes when exposed to elevated temperatures for an extended period of time. Therefore precautions must be taken to avoid prolonged exposure to elevated temperatures
< 90F (32C) = OK
90F (32C) < 125F (52C) = ~ 21 days life
125F (52C) < 135F (57C) = ~ 3-5 days life
> 150F (66C) < 8 hours life

19. SCR Harnessing
The OEM will have to provide a harness between the engine ECM harness and the SCR’s
1. Outlet Pipe NOx Sensor
2. Thermister Junction Box

20. Operator Notification of DEF Level
Engine Manufacturers Association (EMA) is currently working with EMA members and EPA on a proposal for how to notify DEF level to on-highway truck drivers (see following slide).
Current EPA guidance on a driver warning system:
Consists of visual and possibly audible alarms
Should escalate in intensity as urea level approaches empty
Consists of a unique light or message
Low levels will likely be tied to a negative effect, such as an engine power derate to “induce” the driver to fill the DEF to acceptable operating levels
This need will require the addition of another, dedicated lamp to warn of low DEF levels

21. EMA Driver Notification Proposal
Urea (DEF) Threshold
Notification*
Inducement
w/o Level Indicator
w/ Level Indicator
Lamp or Message
>2:1 range
[>1000 mi for LD]
>0.3:1 range
None
<2:1 range
[<500 – 1000 mi for LD]
<0.3:1 range
DEF lamp solid
Warning message
<0.1:1 range
[<250 – 500 mi and
<50 – 250 mi for LD]
DEF lamp flashing
<Threshold above, based on urea qty, time delay, etc.
[TBD for LD]
Amber warning lamp solid
Inducement message
TBD, needs further discussion E F E F
Increasing message duration and/or frequency E F E F
*Use of chimes with notification is optional and OEM specific