Diesel Exhaust Fluid (DEF) is precisely formulated to contain 67.5 percent deionized water.
This vital fluid, commonly used in modern diesel vehicles, is not primarily a component of the diesel fuel itself, but rather an additive injected into the exhaust stream to reduce harmful emissions. Its composition is crucial for the efficient operation of Selective Catalytic Reduction (SCR) systems, which help meet stringent emission standards.
What is Diesel Exhaust Fluid (DEF)?
Diesel Exhaust Fluid (DEF) is a non-toxic solution that plays a crucial role in reducing nitrogen oxide (NOx) emissions from diesel engines. It is a key element in the SCR technology designed to make diesel engines cleaner. DEF is stored in a dedicated tank on the vehicle and is automatically injected into the exhaust gas before it reaches the catalytic converter.
The Composition of DEF
DEF is a standardized solution, ensuring consistent performance across different vehicles and systems. Its exact composition is critical for its function.
- Urea (32.5%): This is the active ingredient in DEF. When heated in the exhaust, urea converts into ammonia, which then reacts with harmful NOx gases in the SCR catalyst, transforming them into harmless nitrogen gas and water vapor. Interestingly, urea holds a significant place in chemistry as the first organic compound ever synthesized from inorganic chemicals.
- Deionized Water (67.5%): The majority of DEF is deionized water. This specific type of water is used to ensure purity, preventing contaminants from damaging the SCR system. It acts as the carrier for the urea and facilitates its controlled injection into the exhaust.
Here's a quick breakdown of DEF's components:
| Component | Percentage | Role |
|---|---|---|
| Urea | 32.5% | Active ingredient; converts to ammonia to neutralize NOx emissions. |
| Deionized Water | 67.5% | Solvent for urea; ensures purity and controlled injection into exhaust. |
The Role of Water in DEF and Exhaust
The deionized water in DEF serves several critical purposes:
- Solvent: It dissolves the urea, creating a stable, homogeneous solution that can be accurately dosed into the exhaust system.
- Purity: Using deionized water prevents the introduction of impurities that could clog injectors, contaminate catalysts, or cause damage to the sensitive SCR system.
- Carrier: It helps in the even distribution of urea into the hot exhaust gases, where the urea then undergoes hydrolysis to form ammonia.
While the water in DEF becomes part of the exhaust gases, it's important to differentiate it from the water vapor that is naturally produced as a byproduct of the diesel combustion process itself. The water from DEF is deliberately introduced to facilitate emissions reduction.
For more detailed information on DEF and SCR systems, you can refer to resources like the Environmental Protection Agency (EPA).
