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Understanding DPF, SCR & AdBlue(DEF)

Understanding DPF, SCR & AdBlue(DEF)

Samarth Bhardwaj's photo
Samarth Bhardwaj
·Oct 1, 2021·

3 min read

Today I am going to discuss two bad boys named NOx and DPM (Diesel particulate matter) that are coming out of your tailpipe and drawing so much of the attention from various agencies around the world from diesel engines. Two culprits are mentioned below

  • NOx (Nitrogen Oxides) is formed in the combustion chamber. These gases are formed when fuel is burnt at a higher temperature, the higher the temperature, the more gas is produced.
  • DPM (Diesel Particulate Matter) or Soot is basically partially burnt fuel. Soot is released into the air as either extremely small particles or liquid droplets. So, unfortunately, these kinds of harmful particles are formed under opposite conditions. We can’t get rid of one without creating a large amount of another one. Since higher efficiency and higher temperature combustion created NOx and cooler and less efficient combustion creates more soot.

Let's now have a look at what measures are taken to regulate the amount of these harmful particles before they get out of the vehicle tailpipe.

DPF(Diesel Particulate Filter)

image.png image.png

Is a particulate filter as the name goes, and is used to reduce the pollution caused by soot in the diesel exhaust. Diesel engines have a smoking problem as we all know and to prevent this, the DPF concept was introduced many years ago and that would be essential for Euro 5 (BS6 in India) and later. It kinda looks like a muffler and is about the same size and shape but it is a very fine filter that filters up to 1 micron.

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DPF is to trap the particulates created by all diesel engines preventing them from entering the atmosphere these particulates are extremely harmful to the respiratory system the particulates are trapped by microscopic channels which are within the diesel particulate filter the particulates or soot that attach to the walls of the channels within the DPF are burned off regularly in a process called regeneration(the regeneration prevents the diesel particulate filter from blocking up).

SCR(Selective Catalytic Reduction)

image.png DPF needs some very high temp to bring that soot level down to permissible limits but high temperature creates NOx. In 2010 EPA(Environmental Protection Agency) came up with SCR in order to lower NOx levels.

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SCR is an advanced active emissions control technology system that injects a liquid-reductant agent through a special catalyst into the exhaust stream of a diesel engine. The reductant source is usually automotive-grade urea, otherwise known asDiesel Exhaust Fluid (DEF) aka AdBlue. DEF is a mixture of pure urea and water it reacts with NOx to convert the pollutants into nitrogen, water, and tiny amounts of CO2, natural components of the air we breathe.

keep a check on your DEF level indicator if you don't want to be stranded as when it is on a very low level your vehicle goes into low power mode but if it runs out entirely, then the vehicle will not start at all.

So...

this is it for now. Hope you all liked it and found it useful. This is my first blog with limited knowledge, will try to improve further as this is the first time I wrote something. Comment down if you liked it or not or what you found lacking😀