jcb EcoMAX - Page 49

JCB EcoMAX Engine Installation Manual
© JCB Power Systems Ltd. 320/A9164-1 Page 49 of 64
correct operating temperature. At start up, the sensor is operated with a low heating power to
protect it from damage which could be caused by contact with condensed water droplets.
Once the risk of exposure to condensed water can be ruled out, the element is fully heated
and prepared for operation. Temperatures in the sensor probe can reach up to 800 °C.
Communication between the dosing control unit and other and other control units is through
CAN bus.
Dosing Module (DEF Injector)
The dosing module injects DEF under a specified pressure into the exhaust flow through the
mixer, upstream of the SCR catalyst. The injected DEF decomposes inside the exhaust pipe
into ammonia (NH
3
) and carbon dioxide (CO
2
). The NH
3
produced is the active component in
the catalytic reduction of NOx emissions inside the SCR catalyst. The engine generated NOx
reacts with the NH
3
to form nitrogen (N
2
) and water (H
2
O).
Mixer
A mixing component is installed in the exhaust pipe. This homogenises the distribution of
DEF in the exhaust stream upstream of the SCR catalyst and allows the decomposition of
DEF to ammonia whilst reducing the formation of urea deposits.
SCR Catalyst
The SCR catalyst reduces engine emitted nitrogen oxides (NOx) using ammonia (NH
3
) as
the reductant on its catalytic surface. To achieve high NOx conversion efficiency, a catalyst
temperature of more than 250°C is essential. There are several SCR sizes and
configurations (see the aftertreatment Technical Data Sheet for specifications).
DEF Tank & Solenoid Valve
The DEF tank stores the DEF supply. To guarantee DEF availability at low temperatures, the
tank is heated. This is implemented by a coolant heated heat exchanger in the tank. To
prevent the tank overheating, the cooling water inlet is regulated by a solenoid valve which is
operated ‘closed’ when the in-tank temperature has reached the calibrated threshold.
DEF Lines
DEF lines transport the solution around the system. In low ambient environments, these are
heated to prevent freezing and allow defrosting. The dosing control unit does the heating
control by using the engine control unit’s ambient temperature sensor signal.
Sensing Techniques
The SCR system is monitored by the following sensors:
2 NOx sensors (control of DEF injection quantity and monitoring)
Temperature sensor upstream of the SCR catalyst
Temperature sensor (DEF tank) (control of heating strategy)
Level sensor (DEF tank)
Quality sensor (DEF tank)