I have searched the internet and this forum and can't totally understand how the scr actually works. My first question is is def being injected into the scr constantly when the engine is running? Second, what is in the scr? Is it built like a muffler or a dpf or something else? Third, Does the scr get hot when the dpf is not regenerating? Last, can the scr be cleaned like a dpf or it that not necessary? I went to the Cummins store and asked all these questions. No one seems to comprehend how this stuff really works. I walked out a little more confused than I started. Any help understanding this would be greatly appreciated. Obviously this stuff is here to stay and I am going to have to live with it. I hope to understand it enough to learn how to avoid down time. Thanks for reading.
Is the scr constantly active?
Discussion in 'Trucks [ Eighteen Wheelers ]' started by circle h, Sep 20, 2021.
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DEF is not being Dosed or injected all the time.
SCR stands for Selective Catalyst Reduction - Do some Google searches and you can find plenty of reading to do. Basically DEF is injected and atomized ahead of the catalyst to covert NOX- (oxides of Nitrogen) to less harmless- Carbon Dioxide-(CO2) and Water. The exhaust temperatures or SCR temp must be above 500 degrees F for sufficient NOX conversion to occur.
A catalyst does not require normal cleaning or routine service as it is not a filter but a flow thru catalyst- Similar to an automotive catalytic converter. The only reason cleaning wound be needed is if it were contaminated with heavy amounts of oil or coolant discharge from the engine that caused the unit to become restricted or plugged.
Maintenance to the system would include- keeping the fill cap in place and fill the system with good clean DEF- Change and DEF filters as per Manufacturer recommendation. Think of the SCR-DEF a completely separate system from the DPF. They serve two completely different purposes to the treatment of the Diesel Engine exhaust.BoxCarKidd, spsauerland, AModelCat and 4 others Thank this. -
Goodysnap Thanks this.
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circle h Thanks this.
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Now DOC will have soot build that is cleaned or washed during a DPF maint. Oil and coolant buildup- otherwise known as face plugging is common with Oil and coolant consuming engines.circle h, spsauerland, AModelCat and 2 others Thank this. -
circle h, spsauerland and pushbroom Thank this.
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circle h, spsauerland, Flint1 and 1 other person Thank this.
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Mine for example only had 600k and the can was full to near bursting and had to be cleaned.circle h Thanks this. -
The SCR does not trap or collect soot. Neither does the DOC.
It is the DPF that contains the soot and particulates from the engine which is converted into ash. Once the ash load reached a certain level, then a cleaning or replacement is needed.pushbroom, circle h and spsauerland Thank this.
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