The Adblue or Selective Catalyst Reduction (SCR) system is a solution for the exhaust gas aftertreatment used to reduce the NOx within the exhaust gas emissions.
For this purpose a specified amount of (Adblue) or Diesel Exhaust Fluid (DEF) is injected into the gas inlets of the Diesel Particulate Filter (DPF) and the SCR catalytic converter. The injected DEF into the exhaust system is converted to ammonia (NH3) and carbon dioxide (CO2). The resulting ammonia (NH3) is used within a special catalyst in the exhaust stream. The resulting reaction converts the unwanted NOx into harmless nitrogen (N2) and water (H2O) vapor.
The SCR system is equipped with LNT catalytic converter and DPF assembly is located in the downpipe from the turbocharger. An additional SCR catalytic converter is located in the exhaust center section.
The DEF is a pure, odorless, colorless, synthetically manufactured, aqueous solution. The DEF is used for the aftertreatment of exhaust gases in the DPF and the SCR catalytic converter.
The SCR catalytic converter can be contaminated by low quantities of metals and thus the quality of the DEF is held to closely controlled standards. The DEF cannot be substituted or diluted with any other fluid.
The diesel exhaust fluid is not categorized as a dangerous substance, because
· The DEF is non-flammable
· The DEF is non-toxic
· There is no danger in the event of spills.
The DEF can be stored on board vehicles, despite the limitation that it crystallizes at temperatures below -11°C (12°F).
In Europe, DEF is also known as AdBlue®, the fluid is specified by ISO22241.
The DEF tank is blow moulded from High Density Polyethylene (HDPE). The DEF tank unit contains the DEF module. The DEF tank includes a 12% unusable volume to protect the internal components because of fluid expansion under freezing conditions.
If the ambient temperature falls below -11°C (12°F), the DEF will freeze in the DEF tank and this will provide difficulty with the refill procedure. In order to thaw the DEF in the DEF tank, place the vehicle in a warm place for 2 hours before refilling the DEF.
The DEF level sensor is an ultrasonic device, which sends the DEF level value to the Powertrain Control Module (PCM) through Pulse Width Modulated (PWM) signals. The ultrasonic cone angle is 10° and the readings are most accurate when the vehicle is stationary and on level ground.
The heater element is a Positive Temperature Coefficient (PTC) type heater, which provides safe operation to the system. Increased heater element temperature results in decreased current drawn from the DEF heater control module, which actuates the power supply of the heater element. Under normal operation the maximum current is 6A.
The DEF injection pump is an assembly of 2 solenoid pumps, located in the DEF tank module. The pressure pump provides 6.5 bar (94.3 psi) operating pressure. The 6.5 bar (94.3 psi) pressure is required to maintain the complete DEF atomization in the exhaust gas. The purge pump purges the DEF from the DEF line at engine shutdown to prevent freezing in the DEF injector at low temperatures. The PCM controls the ground connection of the pumps individually.
The DEF line provides hydraulic connection between the DEF injection pump and the DEF injector. The DEF line is manufactured from a plastic material, which is specifically designed for use with DEF. A copper based resistor wire is installed within the DEF line with an electrical connector. The resistor wire enables electrical heating of the DEF at low-ambient temperatures.
A pre DPF DEF injector is located on the top of the DPF. The DEF is injected vertically to the exhaust gas flow direction. The mixer plate and the high exhaust gas speed provide the DEF is mixed well and distributed evenly within the exhaust gas. The DEF injector consists of an injector and a liquid cooled housing. The liquid cooled housing connects to the engine cooling system to protects the injector from overheating.
The DEF injectors works at high pressures to obtain the complete atomization of the injected DEF. This provides the SCR catalytic converter is working to its optimum performance. The PCM controls the DEF injector with PWM signals.
The DEF heater control module has hardwired connections to the DEF tank module and the DEF line heater element. If the ambient air temperature is below -7°C (19.4°F) the PCM switches on the DEF heater control module through the private CAN bus.
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20 янв 2018
