What Causes Diesel Exhaust Fluid to Crystallise?

May 1, 2024

Diesel Exhaust Fluid (DEF) plays a crucial role in modern diesel engines equipped with Selective Catalytic Reduction (SCR) systems, helping to reduce harmful nitrogen oxide (NOx) emissions. However, one common issue that users may encounter is DEF crystallisation. Understanding the causes of DEF crystallisation is essential for maintaining the efficiency and reliability of diesel engines.

What is DEF?

DEF is a non-toxic, colourless, and odourless solution composed of 32.5% urea and 67.5% deionised water. It is injected into the exhaust stream of diesel engines equipped with SCR systems, where it reacts with NOx to form harmless nitrogen and water vapor, thereby reducing emissions.

Causes of DEF Crystallisation

Several factors can contribute to DEF crystallisation, leading to the formation of solids within the solution. Understanding these causes is crucial for preventing crystallisation and ensuring the proper functioning of diesel engines. Some common causes include:

  1. Exposure to Extreme Temperatures – One of the primary causes of DEF crystallisation is exposure to extreme temperatures. DEF is susceptible to freezing at temperatures below 12°F (-11°C). When DEF freezes, the water in the solution forms ice crystals, which can separate from the urea and result in crystallisation. Similarly, exposure to high temperatures can cause DEF to evaporate, leaving behind urea crystals.
  2. Contamination – Contamination of DEF with foreign substances can also lead to crystallisation. Common contaminants include dust, dirt, metal particles, and other impurities that can enter the DEF storage tank during handling or storage. These contaminants can act as nucleation sites, were urea molecules cluster and form crystals.
  3. Evaporation – DEF is hygroscopic, meaning it readily absorbs moisture from the surrounding environment. If the DEF storage container is left open or improperly sealed, water vapor from the air can enter the solution, altering its concentration and promoting crystallisation. Additionally, prolonged exposure to sunlight can accelerate evaporation and crystallisation.
  4. Chemical Reactions – Certain chemical reactions can also contribute to DEF crystallisation. Exposure to incompatible materials, such as certain metals or plastics, can catalyse reactions that degrade the urea molecules and promote crystallisation. Similarly, exposure to acidic or alkaline substances can alter the pH of the DEF solution, leading to crystallisation.
What Causes Diesel Exhaust Fluid to Crystallise? »

Preventing DEF Crystallisation

To prevent DEF crystallisation and ensure the proper functioning of diesel engines, several preventive measures can be taken:

  1. Proper Storage – Store DEF in a clean, dry, and temperature-controlled environment to prevent exposure to extreme temperatures and contaminants.
  2. Sealed Containers – Use sealed containers to store DEF and minimise exposure to air and moisture.
  3. Regular Inspection – Inspect DEF storage tanks and dispensing equipment regularly for signs of contamination or damage.
  4. Proper Handling – Handle DEF carefully to avoid spills and contamination during storage, handling, and dispensing.
  5. Quality Assurance – Use high-quality DEF from reputable suppliers to minimise the risk of contamination and chemical reactions.

DEF crystallisation can adversely affect the performance and efficiency of diesel engines equipped with SCR systems. By understanding the causes of DEF crystallisation and implementing preventive measures, users can ensure the proper storage, handling, and usage of DEF, thereby maintaining the reliability and effectiveness of diesel engines while minimising emissions and environmental impact.

When to Seek Professional Help

Banlaws DEFMate offers a reliable solution to common DEF problems, seeking professional help is crucial to minimise downtime and ensure optimal system performance. Our team of experts is equipped to address complex issues, conduct thorough troubleshooting, and provide timely repairs and maintenance. Don’t let DEF-related challenges disrupt your operations—contact us today for expert assistance and keep your equipment running smoothly.

For more information about DEFMate, please refer to the Product Flyer and Technical Product Data Sheet available on our  Downloads page. If you have any further questions or would like to discuss how DEFMate can benefit your operations, please don’t hesitate to contact a Banlaw specialist. We’re here to help optimise your fluid transfer processes and minimise downtime.