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| Illustration 1 | g03536143 |
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(1) CEM
(2) Air compressor (3) Dosing control cabinet (4) DEF main tank (5) Engine | |
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| Illustration 2 | g03410867 |
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(1) CEM
(2) Dosing control cabinet (3) DEF main tank (4) Compressed air supply (5) Air to air aftercooler (6) Air cleaner (7) Turbocharger compressor (8) Turbocharger turbine (9) Diesel Oxidation Catalyst (DOC) (10) Mixing tube (11) Selective Catalyst Reduction (SCR) (12) Exhaust out | |
Note: A tool is available to measure the DEF concentration. The tool is the 360-0774 Refractometer.
Selective Catalyst Reduction (SCR) refers to a method of treating engine exhaust in order to reduce the undesired oxides of nitrogen compounds NOx. SCR uses a catalyst which promotes a desired chemical reactions over other possible chemical reactions. The catalyst remains unchanged. Ammonia (NH3) is mixed into the exhaust, and reacts with the NOx in the presence of the catalyst to form harmless compounds (water and nitrogen). In this system, urea ((NH2)2CO) is injected into the exhaust, which quickly decomposes into ammonia under the heated conditions. Urea is used because urea is inexpensive, and does not need the special handling that ammonia requires.
DEF is aqueous urea (urea salt dissolved in water).
A 32.5 percent (by weight) solution of DEF is required for the system.
A 32.5 percent concentration has the lowest freezing point possible,
A 32.5 percent concentration of urea keeps a constant concentration through freezing and thawing.
DEF must be stored below
Note: The customer is responsible for providing primary filtering of the DEF from the site tank to the main tank. The system requires a 40 micron primary filter.
Use only DEF that meets quality properties per ISO 22241-1. Using DEF that does not meet ISO 22241-1 can result in clogging of the injection nozzle.
Refer to Operation and Maintenance Manual, "Maintenance Section" in order to obtain locations for DEF suppliers.
DEF is a non-toxic source of ammonia. A 32.5 percent concentration is slightly alkaline, having a pH of 9.5, similar to baking soda or soap.
DEF is corrosive. Do not store DEF in a tank or use supply lines that are made of the following materials: aluminum, brass and steel. Use only corrosion resistant materials such as PVC or stainless steel. Any O-rings must be Ethylene Propylene Diene Monomer (EPDM).
Clean Emissions Module (CEM) for Progress Rail
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| Illustration 3 | g03536316 |
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Internal view of the CEM for the 3500 engine (1) Treated exhaust leaving the CEM (2) SCRs (3) Mixing tube (4) DOC | |
The aftertreatment system for the exhaust combines the following technologies:
- Selective Catalyst Reduction (SCR)
- Diesel Oxidation Catalyst (DOC)
The SCR reduces NOx.
The DOC reduces the following:
- Carbon monoxide
- Hydrocarbons
- Soluble organic fraction
The DOC and SCR are packaged together in a module. The module is called the Clean Emissions Module (CEM).
Exhaust gas enters into the CEM through the inlet housing and passes through the DOC.
The exhaust gas then enters the mixing tube, where the DEF is injected into the exhaust stream.
The DEF decomposes into ammonia and carbon dioxide.
The mixture of exhaust and ammonia travels through the SCR.
The ammonia reacts with the NOx in the exhaust stream at the SCR catalyst to produce water vapor and nitrogen.
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| Illustration 4 | g03539539 |
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Dosing control cabinet (1) Dosing control cabinet (2) SCR system ECM (3) DEF pump (4) DEF manifold | |
The dosing control cabinet controls the following:
- Rate of DEF flow to the injector
- Compressed air
Compressed air is used for the following:
- Assist in the atomizing of the liquid DEF during injection into the exhaust stream
- Shield the liquid DEF in the injector from the exhaust heat until spraying, so that no crystallization occurs which could plug the injection nozzle.
- Purge the DEF line to the injector during shutdown in order to prevent crystallization of DEF resulting in a plug.
Compressed Air Supply to Dosing Cabinet
The air provided to the dosing cabinet needs to be dry and clean. An oil-less air compressor is required.
Oil can foul the catalyst and prevent the necessary chemical reactions from occurring. Sediment in the airline can plug the injection system.
| Aftertreatment Air Supply Specification | |
| Air Quality | Class 5 |
| Oil content – maximum | 25 mg/m3 |
| Particle size – maximum | 40 micron |
| Particle density – maximum | 10 mg/m3 |
| Relative air humidity – maximum | 10% |
| Air flow capacity – minimum | 9 SCFM / 255 L/min |
| Air pressure – minimum | 60 psi / 414 kPag |
| Air pressure – maximum | 150psi / 1034 kPag |
The SCR system will use up to 255 L/min (9 SCFM) at 414 kPag (60 psi). The system contains an air regulator with a maximum rating of 1034 kPa (150 psi) inlet pressure.
To avoid clogging the air system with oil and/or sediment from piping, use a coalescing filter/separator that is 90 percent effective rated for 1034 kPa (150 psi) and 849.5 L/min (30 CFM).
Air lines must be sized and routed so pressure loss across the line is no greater than 1.0 psi with air delivery at 50 psi and 5 CFM.
The purpose of the dosing control system is to meter DEF into the exhaust stream.
The dosing control cabinet houses an Electronic Control Module (ECM) that provides the basic logic.
The desired rate of DEF injection is determined via a closed loop system, utilizing NOx sensors for feedback. The sensors measures the level of nitrogen oxide in the exhaust gas exiting the SCR.
If the NOx sensor indicates high NOx in the exhaust outlet, the closed loop system will request an increase of the DEF flow rate.
DEF flow rate is increased by increasing the duty cycle of the command signal to the dosing pump.
The aftertreatment ECM controls the duty cycle of the command signal to the dosing pump.
A communication adapter plug is provided on the side of the dosing control cabinet for easy connection.
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| Illustration 5 | g02432876 |
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(1) Nozzle
(2) Injector | |
The injector (1) is a structural member and holds the nozzle assembly (2) in the central axis of the mixing tube. The nozzle delivers the mixture of DEF and air.
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| Illustration 6 | g02433079 |
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(1) Nozzle
(3) Air (4) DEF (5) Fluid cap (6) Air cap | |
The DEF and air are mixed between the fluid cap (5) and a multi port air nozzle cap (6). The mixed fluid is forced through the multi port air nozzle cap into the exhaust stream. The compressed air causes the DEF to atomize (separate into tiny particles).
A main tank supplies the DEF pump. The main tank is equipped with a level sensor and a temperature sensor.
Note: The system requires a 40 micron primary filter.
If ambient temperature falls below
DEF must be provided from the main tank to the dosing cabinet between 2 psi and 5 psi head pressure.
DEF flow will vary with engine operating conditions, specifically with load. The DEF flow requirement is calculated as a percentage of fuel flow. Worst case, DEF flow will be 6 percent of fuel flow.
The NOx sensor communicates to the SCR system ECM over the CAN data link. The sensor has built-in diagnostics to indicate sensor failure modes.
The SCR system ECM controls the power supply to the NOx sensors. The NOx sensors are not powered until the SCR system ECM detects engine speed.
The NOx sensors are precalibrated. No calibration is required for the NOx sensors.
The SCR inlet NOx sensor is monitored to control the DEF dosing rate based on engine out emissions levels.
The SCR outlet 1 NOx sensor is monitored to control the DEF dosing rate based on catalyst out emissions. The SCR system ECM monitors the sensor to calculate the necessary DEF flow rate to meet emission targets.
The SCR outlet 2 NOx sensor is monitored to control the DEF dosing rate based on catalyst out emissions. The SCR system ECM monitors the sensor to calculate the necessary DEF flow rate to meet emission targets.
SCR Inlet 1 Temperature and SCR Inlet 2 Temperature
The SCR inlet temperature sensors are monitored for dosing control and system protection.
The temperature indicates the capability of the SCR system ECM to calculate the DEF dosing rates. The temperature is monitored to indicate temperatures that are too low or too high.
SCR Outlet 1 Temperature and SCR Outlet 2 Temperature
The SCR inlet temperature sensors are used by the SCR dosing system ECM to check that the Inlet Temperature Sensors have not failed in range.
The SCR Outlet Temperature sensor is used as a redundant sensor. If the SCR inlet temperature sensor fails the SCR dosing system ECM will use the SCR Outlet temperature sensor for dosing control and protection.
Exhaust Gas Differential Pressure
Exhaust Gas 1 Differential Pressure
The SCR system ECM monitors the sensor for system protection. The pressure is monitored to indicate pressures that are too low or too high.
The pressure is measured between the engine exhaust intake for the CEM and the treated exhaust leaving the CEM.
Exhaust Gas 2 Differential Pressure
The SCR system ECM monitors the sensor for system protection. The pressure is monitored to indicate pressures that are too low or too high.
The pressure is measured between the engine exhaust intake for the CEM and the treated exhaust leaving the CEM.
Sensors (Dosing Control Cabinet)
The SCR system ECM monitors the sensor for system protection. Pressures that are too low or too high indicate a failure in the dosing system.
The SCR system ECM monitors the sensor for system protection. Pressures that are too low or too high indicate a failure in either the dosing system or the air supply to the dosing cabinet.
The control cabinet temperature sensor is monitored by the SCR system ECM. The cabinet temperature is used to control the DEF heated lines and the DEF dosing pump heater.
The DEF Manifold Temperature sensor is monitored by the SCR system ECM. The manifold temperature is used to control the manifold heater. High or low temperature indicates failures in the manifold heating system.
The main tank temperature sensor is monitored by the SCR system ECM. The main tank temperature is used to control the tank heater. High or low temperature indicates failures in the tank heating system.
The sensor is used to warn when the DEF tank level is less than desired. The DEF level sensor is monitored by the SCR system ECM.
This type of sensor was used on early production units.
An ultrasonic sensor is a non-contacting sensor that uses sound waves to detect the level.
This type of sensor was used on later production units.
A reed switch sensor detects the level of a float that rides on the sensors cylindrical body.
These valves are electrically actuated and control air pressure.
- Air assist valve
- DEF return valve
- DEF tank fill valve
The air assist valve (solenoid) is controlled by the SCR system ECM. This valve is used to control the flow of air into the DEF manifold.
The DEF return valve (solenoid) is controlled by the SCR system ECM. The solenoid valve is used to control the flow of air to the DEF return valve (pneumatic). The controlled air pressure actuates the pneumatic valve.
The DEF tank fill valve (solenoid) is controlled by the SCR system ECM. The solenoid valve is used to control the flow of air to the DEF tank fill valve (pneumatic). The controlled air pressure actuates the pneumatic valve.
These valves are actuated with air pressure and are used to control the flow of the DEF.
- DEF return valve
- DEF tank fill valve
The DEF return valve (pneumatic) is used to control the flow of air or DEF back into the main tank. When the valve is closed, DEF from the pump will flow towards the nozzle. When the valve is open, DEF from the pump will return to the main tank. The valve is also opened to allow purge air to flow back through the DEF line and into the main tank.
The DEF tank fill valve (pneumatic) is used to control DEF flow into the main tank. When the valve is open, DEF will flow into the main tank. When the valve is closed, DEF will not flow into the main tank.