Regan Brown
Diesel exhaust fluid (DEF) is an important additive for diesel engines that helps to reduce harmful nitrogen oxide emissions. DEF is composed of deionized water and urea, and it plays a crucial role in ensuring that diesel vehicles comply with federal emissions standards. While the primary focus of DEF is on reducing emissions, it also offers a modest improvement in fuel efficiency, typically boosting diesel vehicle efficiency by around 3% to 4%. The use of DEF is not just limited to cars, but also extends to engines in generators, farm equipment, boats, and other machines. In this context, it is worth noting that diesel fuel has a higher specific gravity than petrol, which is often mistakenly believed to float on top of diesel.
| Characteristics | Values |
|---|---|
| What is it? | Diesel Exhaust Fluid (DEF) is a liquid used to reduce air pollution created by a diesel engine. |
| Composition | DEF is composed of 32.5% urea and 67.5% deionized water. |
| Function | DEF is consumed in a selective catalytic reduction (SCR) system that lowers the concentration of nitrogen oxides (NOx) in diesel exhaust emissions. |
| Benefits | DEF can improve a diesel vehicle's fuel efficiency by around 3% to 4%. |
| Standards | The U.S. Environmental Protection Agency (EPA) has established standards for diesel fuel sulfur content and emissions, leading to the development of Ultra-Low-Sulfur Diesel (ULSD) fuel. |
| Vehicle Requirements | Diesel vehicles made since 2015 in South Korea and 2007 in the U.S. are required to use DEF and be fitted with SCR systems. |
| Freezing Point | DEF freezes at -11 °C (12 °F), requiring quick thawing methods for SCR systems to function at low temperatures. |
| Brands | Brands of SCR systems that use DEF include BlueHDI, BlueTec, and FLENDS. |
| Distribution | DEF distribution infrastructure has been a concern, with a shortage in South Korea impacting its economy. |
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What You'll Learn
Diesel exhaust fluid (DEF) freezes at −11 °C (12 °F)
Diesel exhaust fluid (DEF), also known as AUS 32 or AdBlue, is a liquid used to reduce air pollution from diesel engines. It is made with 32.5% urea and 67.5% deionized water. DEF is consumed in a selective catalytic reduction (SCR) process that lowers the concentration of nitrogen oxides (NOx) in diesel exhaust emissions.
DEF freezes at −11 °C (12 °F). This can be an issue for the SCR exhaust cleaning system, which requires DEF to function properly. To address this, various methods can be employed to thaw frozen DEF and enable full SCR operation. One approach is to utilise the engine's heat, such as by passing engine coolant through the DEF tank using a thermostatic coolant control valve. However, this method may take a significant amount of time, up to an hour or more, before the SCR system is fully operational. For example, the 2010 EPA emissions requirements mandate full DEF coolant flow within 70 minutes. In Europe, regulations specify that DEF from a frozen tank at −15 °C must become available within 20 minutes of starting the engine.
To expedite the thawing process, an alternative method is to integrate an electric heater directly into the DEF tank. This approach can significantly reduce the time required to melt the frozen DEF and ensure the SCR system's functionality at low temperatures.
The importance of ensuring DEF availability and functionality is underscored by its role in reducing harmful emissions from diesel engines. For example, in 2007, the United States Environmental Protection Agency (EPA) implemented requirements to significantly reduce exhaust emissions. This led to the development of aftertreatment systems, including the use of diesel particulate filters (DPF) and ultra-low-sulfur diesel (ULSD) fuel. Compliance with DEF distribution and infrastructure became a concern to meet these stricter emissions standards.
Additionally, DEF plays a crucial role in diesel engine operations at airports. However, its labelling and storage must be carefully managed to avoid accidental servicing of jet aircraft with DEF instead of fuel system icing inhibitor. This mix-up has been attributed to multiple in-flight engine failures and grounding incidents.
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DEF improves a diesel vehicle's fuel efficiency by 3-4%
Diesel Exhaust Fluid (DEF) is a mixture of 32.5% urea and 67.5% deionized water. It is used to reduce harmful emissions in diesel engines, specifically nitrogen oxide (NOx) emissions. DEF is stored in a separate tank in the vehicle and injected into the exhaust pipeline, where it breaks down nitrogen oxides into harmless nitrogen and water. This process is known as selective catalytic reduction (SCR).
The use of DEF improves a diesel vehicle's fuel efficiency by up to 5%. This is because DEF enables the engine to burn fuel more effectively. The elevated oxygen levels in DEF enhance the combustion process, resulting in reduced fuel consumption. Additionally, by reducing NOx emissions, DEF helps to optimise the vehicle's fuel efficiency and ensures the engine operates efficiently while emitting cleaner substances.
The consumption rate of DEF is typically around 2-3% relative to the amount of fuel burned. For every 50 gallons of diesel fuel consumed, approximately 1 gallon of DEF is used. Therefore, a diesel truck's DEF tank needs to be refilled once for every 3 to 4 times that the truck is refuelled with diesel fuel.
DEF also offers other benefits, such as enhanced engine performance, increased fuel savings, and improved engine longevity. It is especially useful for heavy-duty vehicles, which often carry large loads and travel long distances. By using DEF, these vehicles can reduce fuel consumption and ensure compliance with stricter emissions regulations.
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DEF is made with 32.5% urea and 67.5% deionized water
Diesel Exhaust Fluid (DEF) is a solution used to reduce air pollution created by diesel engines. It is composed of 32.5% urea and 67.5% deionized water. This mixture is critical to the proper functioning of the DEF system. The urea used is of high purity and is non-toxic and safe to handle. The water used is also of high purity, achieved through deionization, which removes cations and anions.
The urea in DEF is a compound of nitrogen that turns into ammonia when heated. When DEF is injected into the hot exhaust gas stream of a diesel engine, the water evaporates and the urea decomposes to form ammonia and isocyanic acid. This mixture then reacts with nitrogen oxides (NOx) in the diesel exhaust, converting them into harmless nitrogen, water, and small amounts of carbon dioxide.
The specific concentration of 32.5% urea in DEF is essential for maintaining the effectiveness of the DEF system in reducing NOx emissions. If the urea concentration is too low, the NOx conversion efficiency is reduced. If the urea concentration is too high, it can lead to the formation of urea crystal deposits in the exhaust system over time.
DEF is consumed in a selective catalytic reduction (SCR) process, which is used by diesel engines to reduce harmful nitrogen oxide emissions. Several brands of diesel vehicles use SCR systems, including Peugeot, Citroën, and Daimler AG. DEF is also known as AUS 32 and is sometimes marketed as AdBlue.
The quality of DEF can be influenced by factors such as the grade of urea used, the purity of the water, and the concentration of the solution. It is important to store DEF properly to maintain its effectiveness. It should be stored in a cool, dry, and well-ventilated area, out of direct sunlight, and used within 12 months of production.
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DEF is sold under the trademarked name AdBlue
Diesel Exhaust Fluid (DEF) is a liquid used to reduce the amount of air pollution created by a diesel engine. It is a mixture of urea and deionized water, with a 32.5% and 67.5% composition, respectively. DEF is consumed in a selective catalytic reduction (SCR) that lowers the concentration of nitrogen oxides (NOx) in the diesel exhaust emissions from a diesel engine.
DEF is also sold under the trademarked name AdBlue, which is a registered trademark of the German Association of the Automotive Industry. AdBlue is a high-purity synthetic urea mixed with de-ionized water, and it is not blue but transparent. It is injected into the exhaust gas upstream of the converter, where it mixes with the heated exhaust gases and breaks down into carbon dioxide and ammonia. The NOx in the SCR catalyst then reacts with the ammonia and breaks down into safe nitrogen gas and water vapour.
AdBlue is widely available and can be purchased at gas stations, auto parts stores, and big-box stores. It is also available in bulk, which is a better option for owners of diesel fleet vehicles and gas stations. AdBlue is not a fuel or a fuel additive, but it is transported, stored, and dispensed like fuel. It requires its own separate, dedicated, clearly marked tanks in vehicles and for bulk storage.
AdBlue is not to be mixed with diesel fuel, as it is injected outside the engine after diesel combustion. It is the driver's responsibility to ensure the AdBlue tank is kept topped up and to pay any associated costs.
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Petrol will not float on diesel fuel; it will mix
Mixing gasoline and diesel is not advisable and can cause serious issues in engines and fuel systems. Diesel fuel is heavier than gasoline because it is made up of large molecules. It has a higher flashpoint and auto-ignition temperature.
Petrol typically has a specific gravity of 730 grams per litre, while diesel typically has a specific gravity of 840 grams per litre. This means that diesel is heavier and will sink to the bottom of a petrol tank. However, in reality, petrol and diesel do not remain separated, and the petrol will mix with the diesel. This is because the diesel in a tank is usually warmer than the petrol being pumped in, and the action of pumping stirs the tank, causing the petrol and diesel to mix.
While petrol and diesel can mix, this does not mean that it is safe to do so. Mixing petrol and diesel can cause engine damage and reduce the octane rating of the fuel, causing premature ignition and potential damage to pistons and rods. It can also damage the fuel pump and diesel injectors.
In the past, small amounts of petrol were sometimes added to diesel fuel in cold weather to prevent the diesel from solidifying. However, this practice is no longer recommended, as modern diesel engines have become more sensitive to petrol contamination. If petrol is accidentally added to a diesel tank, it is important to drain the tank and not to drive the vehicle to avoid potential engine damage.
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Frequently asked questions
Diesel exhaust fluid (DEF) is a liquid used to reduce the amount of air pollution created by a diesel engine. It is made with 32.5% urea and 67.5% deionized water.
DEF is consumed in a selective catalytic reduction (SCR) system, which lowers the concentration of nitrogen oxides (NOx) in the diesel exhaust emissions from a diesel engine.
DEF can improve a diesel vehicle's fuel efficiency by around 3% to 4%. Keeping your DEF topped up can help you save money on gas and reduce your carbon footprint.
Without enough DEF, your diesel vehicle may not start. Most modern diesel vehicles will issue warnings when their DEF reservoirs run low, and some will limit the vehicle's speed.
