0328542 JOHNSON ORIFICE PLUG, (NO.47D)

Illustration 1 g03275157
Caterpillar (standard) Tier 4 open genset system configuration for the C175 engine
(1) CEM
(2) Dosing control cabinet
(3) Diesel Exhaust Fluid (DEF) buffer tank
Illustration 2 g02665059
Caterpillar (standard) Tier 4 open genset system configuration for the 3500 engine
(1) CEM
(2) Dosing control cabinet
(3) Diesel Exhaust Fluid (DEF) buffer tank System Block Diagram
Illustration 3 g02430859
(1) CEM
(2) Dosing control cabinet
(3) DEF customer supply 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) Ammonia Oxidation (AMOx) Catalyst
(13) Exhaust out Diesel Exhaust Fluid (DEF)
Note: A tool is available to measure the DEF concentration. The tool is the 431-7087 Tool Gp (Refractometer). Refer to Testing and Adjusting, "Diesel Exhaust Fluid Quality - Test" for the correct procedure.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, −11 °C (11 °F), for this solution.A 32.5 percent concentration of urea keeps a constant concentration through freezing and thawing.DEF must be stored below 50 °C (122 °F) to delay decomposition.Note: The customer is responsible for providing primary filtering of the DEF from the site tank to the buffer 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 C175 Engines
Illustration 4 g03274338
Internal view of the CEM for the C175 engine
(1) Engine exhaust to the CEM
(2) DOCs
(3) Treated exhaust leaving the CEM
(4) Ammonia Oxidation (AMOx) Catalyst
(5) DEF injector
(6) SCRs
(7) Mixing tube Clean Emissions Module (CEM) for 3500 Engines
Illustration 5 g02693696
Internal view of the CEM for the 3500 engine
(1) Engine exhaust to the CEM
(2) Treated exhaust leaving the CEM
(3) DOCs
(4) DEF injector
(5) Ammonia Oxidation (AMOx) Catalyst
(6) SCRs
(7) Mixing tube CEM Operation
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 fractionThe 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. Any residual ammonia in the exhaust gas is decomposed in the Ammonia Oxidation (AMOx) Catalyst before exiting the CEM.Dosing Control Cabinet
Illustration 6 g02626381
Dosing control cabinet
(1) Dosing control cabinet
(2) SCR system ECM
(3) DEF pump
(4) DEF manifold
(5) DEF buffer tank The dosing control cabinet controls the following:
Rate of DEF flow to the injector
Compressed airCompressed 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
Air can be supplied by using shop air already available at the site or by installing a Cat-approved air compressor arrangement. In either case, 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.Note: An optional air compressor system is available from Caterpillar that is designed specifically for use with the aftertreatment system.