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Why do diesel engines require exhaust fluid?

Diesel engines require exhaust fluid, a urea-based solution commonly known as diesel exhaust fluid (DEF), to comply with stringent emissions regulations, mainly nitrogen oxides (NOx). NOx emissions significantly contribute to air pollution and are associated with respiratory problems and environmental damage.


Here's how the system generally works:


  1. Emission Control Standards: Governments worldwide have established strict emission standards to limit vehicle pollutants, including diesel engines. NOx is a primary target for reduction due to its harmful effects on air quality.

  2. Selective Catalytic Reduction (SCR) System: Diesel engines use Selective Catalytic Reduction (SCR) technology to reduce NOx emissions. This system injects DEF into the exhaust stream upstream of a catalytic converter.

  3. Chemical Reaction: When DEF is introduced into the hot exhaust gases, it undergoes a chemical reaction. The main component of DEF is urea (a nitrogen compound), and when it reacts with the NOx in the exhaust, it forms harmless nitrogen and water vapor.

  4. Emission Compliance: Using DEF and the SCR system, diesel engines can significantly reduce NOx emissions, bringing them within the acceptable limits set by regulatory authorities.

  5. AdBlue: DEF is often marketed as AdBlue in some regions. Vehicle owners must ensure that the DEF/AdBlue tank is regularly filled to maintain the proper functioning of the SCR system and comply with emission standards.

The addition of DEF helps diesel engines meet stringent emissions regulations without sacrificing fuel efficiency or performance. It's an effective way to balance the power and efficiency advantages of diesel engines with the need to minimize their environmental impact.

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