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difference between dpf and def


dave110

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Hope I never have to deal with this stuff but I like to learn. With a DPF the engine basically over-fuels to burn hot and burn out the DPF, correct me if I'm wrong. What does DEF do? Does it burn also or is it just a cleaner that is pumped through? If so what happens to it when it's done cleaning? Probably a dumb question to you guys but I don't have these systems so I need educated. Dad has an 09 and burned the second tail pipe off already, and it re-gened, melted the plastic on the P.B. cable and locked the wheel up because it would not release. He was nose front to a building with a trailer on when he found it..... what a mess. Thanks for the education in advance.

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I will take a shot at a real simple discription of the questions you have asked. 

 

DPF (diesel particulate filter) is designed to take the particulate out of the air that is created when diesel is burned in the combustion chamber.  The filter collects the particulate matter and the the cleaning of the filter (regeneration) when it gets full (loaded) to a specific prescribed level is the addition of extra diesel into the exhaust stream to physically burn the collected particulate matter out of the filter.  This creates very high temp in the filter to burn this particulate.  It takes extra fuel and is one of the causes of lower mpg that is a function of vehicles equipped with DPF emission type system.

 

Diesel engines are usually setup run with an lean air-to-fuel ratio in an attempt to get full combustion of soot and to prevent the exhaust of unburnt fuel. This is done by supplying excess of oxygen to the combustion process but then this creates NOx (nitric oxides), which are viewed as harmful emmissions.  Selective catalytic reduction is used to reduce the amount of NOx

 

DEF (diesel exhaust fluid) is a urea based solution that is injected into the diesel exhaust system SCR  (selective catalytic reduction) in order to lower the NOx discharge from the exhaust system.

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There is still a DPF with the use of DEF and the DEF is consumed.

 

Like John said the DPF traps the particulates(carbon) that come out of the engine in the exhaust stream, then once it collect so much it will run a regen injecting extra fuel into the exhaust to get the temps up in the 1100°F range to clean the DPF out.

 

The DEF is part of the SCR system, it is injected into the exhaust stream in a decomposition chamber that is right before the SCR catalyst, when the DEF is injected into the decomposition chamber is reacts and turns to ammonia, then in the SCR catalyst the ammonia and NOx react and form water vapor and nitrogen.

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