AdBlue® tanks

Genesis and application of the SCR system

As environmental awareness and understanding of the negative impact of air pollutants on human health and ecosystems has grown, measures have been taken to reduce harmful emissions generated by motor vehicles.

All these efforts have been aimed at meeting increasingly stringent emission standards, set mainly by European regulators. These standards, such as the Euro standards, provide guidelines for the maximum permissible emission levels of various harmful substances. One of the key factors on which particular attention has been focused has become nitrogen oxides (NOx).

For example, the Euro 6 standards, introduced in 2014, set very strict NOx emission limits for new cars and vans sold in the European Union. For diesel cars, this requires the use of advanced emission control technologies, including SCR systems.

Originally developed mainly for heavy-duty vehicles, the SCR system quickly found its way into passenger cars as well. Its origins lie in the need to effectively reduce NOx emissions through selective catalytic reduction, a chemical process that converts harmful nitrogen oxides into environmentally inert substances such as nitrogen and water.

Thanks to the SCR system, cars can effectively reduce NOx emissions with minimal impact on engine performance and driving comfort. In this way, the SCR system has become an indispensable part of today's cars, vans and trucks, helping to achieve sustainability goals by reducing the negative impact of road transport on the environment and public health.

Construction and principle of operation of the SCR system

The SCR (Selective Catalytic Reduction) system consists of several key components that work together to effectively reduce oxides of nitrogen (NOx) in the engine exhaust. Here is a description of the design and main components of the SCR system:

1. AdBlue® fluid tank: A tank containing a urea solution, most commonly referred to as AdBlue® or DEF (Diesel Exhaust Fluid), which is injected into the exhaust gas stream to reduce NOx. This tank is usually located close to the fuel tank.
2. Dosing pump: A pump that delivers the AdBlue® solution from the tank to the injector in the correct amount depending on the engine operating conditions.
3. SCR system control unit: the electronic system responsible for controlling all components of the SCR system, including the dosing pump, injector, sensors. The controller also monitors various engine parameters and driving conditions to ensure optimum SCR system efficiency.
4. AdBlue® injector: The component responsible for the precise dosage of the AdBlue® into the exhaust gas stream in the exhaust system. The injector is located upstream of the SCR catalytic converter.
5. SCR catalytic converter: The main component of the SCR system, which contains a catalyst composed of chemically active substances such as vanadium oxide on a zeolite substrate. It is here that the chemical reaction for the selective catalytic reduction of NOx takes place with ammonia from the AdBlue® fluid.
6. NOx sensors: Sensors that monitor the level of oxides of nitrogen in the exhaust gas, located upstream and downstream of the SCR catalytic converter. Information from these sensors is used to control AdBlue® dosage and optimise SCR system operation.

Selective catalytic reduction (SCR) is a chemical process that reduces the pollutants produced by diesel engines. Specifically, SCR converts harmful nitrogen oxide (NOx) pollutants into nitrogen and water. The NOx reduction reaction occurs as the gases pass through the SCR catalyst chamber. Before entering the catalytic converter chamber, a reductant (AdBlue® fluid) is injected and mixed with the exhaust gas. The injected fluid acts as a catalyst to trigger the chemical reaction necessary to convert NOx into nitrogen and water. The fluid used in vehicles is called AdBlue® or DEF (Diesel Exhaust Fluid).

AdBlue® fluid (DEF)

AdBlue® fluid is an aqueous urea solution prepared from 32.5% urea and 67.5% deionised water. AdBlue® (DEF) is stored in a tank from where it is drawn during vehicle operation. Owners of cars with small tanks need to top it up every 5,000 kilometres or so, and those with the largest tanks even every 20,000 kilometres.

AdBlue® fluid characteristics:

• Clear and odourless liquid classified as non-toxic and safe for transport and storage
• Recommended shelf life is 12 months
• Freezing point: -11 °C
• Hydrolysis occurs from +30 °C
• Crystallisation during drying can cause corrosion, so spills should be cleaned up with water
• Has a corrosive effect on iron, copper, bronze and some aluminium alloys

AdBlue® freezes at -11°C, so the AdBlue® hose and pump can freeze in cold areas. AdBlue® level and temperature sensors are also fitted in the tank to ensure that AdBlue® is operating at the correct temperature at all times, so it can be used safely. In order for the SCR exhaust gas aftertreatment system to operate at low temperatures, a sufficient amount of frozen DEF must be restored to a liquid state in the shortest possible time, ideally in the order of minutes.

In Europe, Regulation (EC) No 692/2008 specifies in Annex XVI, point 10, that DEF from a frozen tank with a core temperature of -15°C (5°F) must be available within 20 minutes of starting the engine. Therefore, most tanks are equipped with electric AdBlue® heaters.

Design and principle of operation of the AdBlue® tank

PSA/Stellantis brand vehicles with HDi/BlueHDi engines use tanks that incorporate several major components of the SCR system. These include:

1. AdBlue® tank with volume measuring system
2. Heating elements
3. Electronic controller to manage system operation
4. Dosing pump
5. Pressure accumulator
6. Solenoid valve
7. Pressure and temperature sensors

The system starts dosing AdBlue® into the exhaust system as soon as the temperature of the exhaust gas reaches a sufficiently high value (usually about 175^oC). A pump is then activated, which pressurises the AdBlue® into the injector, which doses it directly into the exhaust system upstream of the SCR catalytic converter. There is usually a mixer upstream of the catalytic converter, which helps to properly mix the sprayed agent with the exhaust gas to ensure an effective chemical reaction.

Remanufacturing process of the AdBlue® tank

The technology for the remanufacturing of AdBlue® tanks is our in-house development, which was created through the work of the research and development team together with the technology department. The remanufacturing process is divided into stages, with successive steps such as: technical condition assessment, tank cleaning, disassembly of components, component diagnostics, component replacement, assembly and final functional testing and quality control of the AdBlue® tank after the remanufacturing process. The high standards of our AdBlue® tank remanufacturing process, confirmed by TUV ISO 9001 certification, provide a guarantee of failure-free operation of the component for a period of 24 months.

The remanufacturing process consists of the following steps:

1. Preliminary verification
2. Tank cleaning
3. Verification after cleaning
4. Disassembly of components
5. Verification of tank components
6. Replacement of damaged and critical tank parts (mechanical parts, electronics, seals, etc.).
7. Assembly of components, completion of the tank
8. Final diagnostic test
9. Evaluation of functional test results
10. Final quality control.

Causes and types of damage to AdBlue® tanks

The most common damages to AdBlue® tanks are:

1. Leaks: Leaks of AdBlue® fluid can be caused by mechanical damage to the tank, leaks in hose connections or damaged seals.
2. Crystallisation: crystallisation of AdBlue® fluid can occur in the tank, especially when it is exposed to extremely low temperatures, which can lead to blockage of lines or nozzles in the injection system. The phenomenon may be encouraged by the use of AdBlue® fluid of inadequate quality.
3. Use of other liquid (fuel, water): If a liquid other than AdBlue® is used, such as fuel or water, leakage can occur, which can lead to damage to the tank components and the entire AdBlue® injection system. 
4. Electronic/electrical faults: Electronic faults in the SCR control system can lead to malfunction of the fluid level, temperature, pressure sensors or other electronic components, which can affect the efficiency and performance of the AdBlue® injection system.

The most common symptoms of failure are:

1. Message displayed on the instrument cluster - "UREA (or AdBlue) Emissions control fault: Starting prevented in xxxx km".
2. At the same time, the UREA light is on or blinking, the engine fault light and SERVICE light are on.
3. The ECU records error P20E800 (P20E8) - "AdBlue pressure - pressure too low".