853730 Mercury COVER

Illustration 1 g06073295
(1) Diesel Exhaust Fluid (DEF) injector
(2) Selective Catalytic Reduction (SCR) system
(3) SCR mixing tube
(4) Diesel Oxidation Catalyst (DOC)
(5) Diesel Particulate Filter (DPF)
(6) Exhaust intake connection
(7) Exhaust outlet connectionClean Emissions Module Basics
A flexible exhaust pipe connects the engine to the Clean Emissions Module (CEM). The Clean Emissions Module (CEM) contains the Diesel Particulate Filter (DPF) and the Selective Catalytic Reduction (SCR) cannisters. The CEM contains several mechanical and electrical components that reduce various exhaust emissions emitted from the engine. The CEM uses an ECM for aftertreatment controls but must communicate (send and receive) with the engine ECM. Exhaust gases entering the CEM flow through the DOC first, then the DPF, both located inside the DPF cannister. From there, the exhaust flows into the SCR mixing tube before entering the SCR canister.
Illustration 2 g06073282
(1) DPF
(2) DOC
(3) DPF canisterThe first filter media that exhaust gas is exposed to, the DOC, is a flow through style filter. The DOC is contained in the inlet section of the DPF cannister. The DOC filter contains platinum and palladium. The minerals aid in oxidizing hydrocarbons, carbon monoxide, and soluble organic fractions as the exhaust gas flows through the filter. The inlet section of the DPF cannister contains a temperature sensor, a pressure tap for the DPF inlet pressure sensor, and a DPF delta pressure sensor. All three of these components are before the DOC. The purposes of these components are:DPF inlet temperature sensor The DPF inlet temperature sensor measures the temperature entering the DPF cannister assembly. This temperature is used to help control opening and closing of the turbocharger compressor bypass valve to maintain a desired DPF inlet temperature during regeneration.DPF Delta Pressure sensor The delta pressure sensor is used to measure soot collected in the DPF. The delta pressure sensor is measuring the pressure drop across the DPF. Since the delta pressure sensor is measuring flow resistance across the DPF, the sensor will also detect ash loading.DPF Inlet Pressure sensor Used to measure the backpressure being generated by the DPF.
Illustration 3 g03876544
Cross section of the DPF
Once the exhaust gas flows through the DOC, the exhaust gas enters the DPF. The DPF is a catalyzed ceramic filter. The DPF uses a wall flow design. This design is a porous wall structure which allows clean exhaust gas to flow through, but does not allow particulate matter (soot) to pass. The trapped soot is cleaned from the DPF through a catalytic reaction by heating the filter through a process called Regeneration.
Illustration 4 g06073288
(1) SCR Inlet Temperature Sensor
(2) SCR
(3) SCR Mixing Tube
(4) AMOXAfter the exhaust gas flows through the DPF, the gas enters the SCR mixing tube where Diesel Exhaust Fluid (DEF) is injected. DEF contains deionized water and urea. The exhaust gas and DEF mix and enter the SCR cannister. The SCR is a cordierite catalyst substrate which is coated with a copper zeolite wash coat. A portion of the substrate (at the outlet end) is coated with an extra washcoat making it a selective ammonia oxidation (AMOX) catalyst. Once temperatures are hot enough, the water in DEF evaporates and the urea in DEF is converted to ammonia. Once converted, the ammonia is absorbed by the catalyst. As exhaust flows through the catalyst, the NOX within the exhaust reacts with the ammonia and the catalyst, reducing NOX by turning it into nitrogen and water. During certain engine operating conditions, too much ammonia will be stored and may pass through the catalyst. The AMOX is responsible for removing excess ammonia that was not converted from the exhaust. At the inlet of the SCR cannister is the SCR inlet temperate sensor. This sensor is used to make sure that the temperature is hot enough in the catalyst for DEF dosing to occur and react with the catalyst.Turbocharger Compressor Bypass Valve
Illustration 5 g03749874
(1) Turbocharger compressor outlet
(2) Turbocharger compressor bypass valve
(3) Turbocharger compressor inletThe Turbocharger Compressor Bypass Valve is located between the compressor inlet and outlet. It is used to route compressor outlet air back through the inlet to increase exhaust temperatures when needed to regenerate the aftertreatment system. Regeneration includes converting soot in the DPF into gas, removing sulfur from the SCR, and removing crystals that form inside the DEF injector. This is considered a low temperature regeneration system and works more efficiently at higher speeds and loads. At lower speeds and loads system may not achieve high enough temperatures for regeneration.The soot load on most Tier IV Final products is burned passively. This is due to the addition of the SCR. The SCR cleans up NOx, which allows the engine to produce more NOx. The engine now produces less soot since the higher NOx output allows soot to burn off at lower temperatures. For this reason, active regeneration may not be required to burn soot. Regenerations will still be desired to remove sulfur and deposits from the SCR and remove crystals that form in the DEF injector.To regenerate the DPF at the right time, theAftertreatment ECM must know what the soot and sulfate levels are. The sulfate levels are calculated in software and available to view as a percentage in Cat® Electronic Technician (ET). The soot input is a function of:
Delta pressure measurement across the DPF
Calculated model based on developed engine out soot measurementsThe information gathered from these two inputs is converted into a percentage of soot output. Soot level can be viewed through Cat ET.Regeneration Triggers
There are four methods for triggering a regeneration:Soot - The DPF will collect soot produced by the engine. An automatic regeneration will become active to reduce soot level. Details on how soot level is used to trigger regenerations are explained in "Regeneration Action Strategies" section.Crystal Removal - It is necessary to run a regeneration to remove crystals that form inside the injector during a hot shutdown and/or during extended operation at low ambient temperatures.HC Evap - It is necessary to run a regeneration to evaporate Hydrocarbons that can accumulate in the DPF when operating at cold exhaust temperature. Running HC Evap regenerations protects the DPF against