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Typical example (1) Aftertreatment Regeneration Device (ARD) (2) Diesel Oxidation Catalyst (DOC) (3) Diesel Particulate Filter (DPF) | |
The CEM for the engine consists of the following components.
- Aftertreatment Regeneration Device (ARD)
- Diesel Oxidation Catalyst (DOC)
- Diesel Particulate Filter (DPF)
The Diesel Oxidation Catalyst (DOC) oxidizes the carbon monoxide and the hydrocarbons that are not burnt in the exhaust gas into carbon dioxide and water. This is a through flow device that will continue to operate during all normal engine operating conditions.
The wall flow Diesel Particulate Filter (DPF) collects all solid particulate matter in the exhaust gas.
The Aftertreatment Regeneration Device (ARD) increases the exhaust gas temperature to a sufficient level. The soot that is collected in the DPF is oxidized.
If applicable, a flexible exhaust pipe can connect the engine to the Clean Emissions Module (CEM). Refer to Disassembly and Assembly for the correct procedure to install the flexible exhaust pipe.
The solid particulate matter that is collected by the DPF consists of soot (carbon) from incomplete combustion of the fuel and inorganic ash from the combustion of any oil in the cylinder.
The rate of accumulation of ash is slow. The filter is designed to contain all the ash that is produced until the defined service interval. Refer to Operation and Maintenance Manual for more information.
The soot that is collected must be removed at regular intervals by a process of regeneration.
The wall flow DPF continuously regenerates at modest temperatures, using passive regeneration to continually control soot loading.
Active regeneration occurs when the engine does not create enough heat in order to regenerate the DPF.
Air is supplied to the ARD through pressurized air from the turbocharger and air pump. Fuel is supplied from the leakoff line to the ARD.
Fuel is injected onto a wire gauze by the first injector. The fuel is ignited by the glow plug. The ARD is air cooled.
The combustion of the fuel generates heat. Once the temperature recorded by the inlet temperature sensor has reached
The DOC oxidizes the soot into carbon dioxide, which then passes through the filter and into the atmosphere.
The ARD may automatically switch ON and OFF. The ARD may be manually controlled by the operator. The ARD is controlled by the sensor for the soot level. The sensor for the level of soot will ensure that the level of soot in the filter is kept within limits. This is referred to as a regeneration of the filter.
In order to regenerate the DPF at the right time, the engine ECM must know how much soot is in the DPF. Measurement of soot is accomplished through the following means:
- Delta pressure measurement across the DPF
- Calculated model based on developed engine out soot measurements
The soot level may be displayed as a graphical bar, or as an actual percentage. Soot level can also be viewed through the electronic service tool.
The frequency of regeneration will depend on the operating conditions of the engine. The frequency of regeneration will depend on the ambient conditions of the operation of the engine. Regeneration will be most frequent if the application operates with a high transient content or the atmospheric temperature or the altitude is high.
The soot level percentage that is generated by the engine ECM is used in determining:
- When to activate the DPF lamp
- When to activate the DPF and flashing warning lamp (for high soot load events)
- When to activate the forced engine shutdown strategy
DPF Lamp - The DPF lamp will be illuminated at a 80 percent soot level on engines.
DPF and Flashing Warning Lamp - The action lamp will be illuminated at a 100 percent soot level for engines. The DPF lamp will remain on with the action lamp.
Limited speed strategy - The limited speed strategy will be activated after the soot level has reached 100 percent. At this time, the engine will automatically drop to the programmed speed of 1800 rpm with 50 percent engine load. The only method to unlock the limited speed is to perform a regeneration.
Forced engine shutdown strategy - The forced engine shutdown strategy will be activated when the soot level reaches 140 percent soot level. The engine will operate between 800 and 1800 rpm. After 30 seconds, the engine will automatically shut down. The engine can be restarted but will only operate for 30 seconds before shutting down again.
Force Switch Regeneration - Regeneration initiated by the force switch is allowed at all times.
Passive Regeneration - Passive regeneration is allowed at all times.
Active Regeneration - Active regeneration will be allowed once soot level is greater than 60 percent.
Regeneration Types and Operating Criteria
There are two types of regeneration. These regenerations are referred to as passive regeneration and active regeneration.
Passive Regeneration
Passive regeneration occurs when the engine is operating and the exhaust temperatures reach sufficient levels.
Active Regeneration
Active regeneration occurs when the soot load in the DPF reaches 60 percent. The ARD must be used to create the heat necessary to regenerate the DPF.
The ARD may perform an active regeneration while the engine is at any operating condition.
Active regenerations consume more fuel and take a shorter time to complete compared to passive regenerations. This longer time is due to maintaining lower desired DPF inlet temperatures to avoid damaging the DPF from extreme changes in temperature.
Active regeneration has one distinct operating region. The operating region is determined by the soot level. The region is between 60 and 140 percent soot level. The parameters listed below outline the operating criteria that are monitored to activate and sustain active regeneration.
Note: All of the parameters listed below are independently developed for each application. All applications may not meet the exact criteria outlined below.
Regeneration switch - The disable regeneration switch is not enabled.
Engine Coolant Temperature - The engine coolant temperature should be above
Engine Load Factor - The engine load factor should be between 0 percent and 80 percent.
DPF Outlet Temperature - The DPF outlet temperature should be above
Manual regeneration is accomplished by pressing the force regeneration switch. Refer to the Operation and Maintenance Manual for correct location of switch.
Fuel System for the Clean Emissions Module
The fuel is sent directly to the ARD from the leakoff line for the engine fuel injectors.
When an active regeneration begins, fuel to the ARD fuel injectors is controlled by the ECM. The ECM controls the amount of fuel based on the standard regeneration control strategy. As the active regeneration progresses, different levels of fuel are required by the ARD.
Excess fuel for the ARD is then returned to the fuel tank.
Air System for the Clean Emissions Module
Exhaust air flows from the turbine housing to the ARD. The exhaust air then flows through the DOC and the DPF.
An air pump supplies the pressurized air to the ARD. There is a reed valve to stop exhaust gas going back through the system when the air pump is not active.
The air supplied to the ARD is proportional to the engine speed as the air pump is driven from the crankshaft.
The combustion air is used with the supplied fuel and the glow plug to ignite the fuel in the wire gauze.
All electronic devices on the CEM are controlled by the engine ECM. The ECM sends signals in order to complete the following functions: sending fuel pressure to the ARD, the ignition and the actuation of the glow plug.
Differential Pressure Sensor ( DPF) - This sensor measures the difference in pressure of the gases as the gases pass through the DPF.
Inlet Temperature Sensor - This sensor determines the temperature of the air that is entering the DOC and the DPF.
Outlet Temperature Sensor - This sensor determines the temperature of the air that is exiting the DPF.
Temperature Sensor - This sensor measures the temperature within the ARD.
The orifice for the fuel creates a high amount of atomization of the fuel for ignition and operation.