DEF Injector
Illustration 28 g03708843
Typical example
(1) Electrical connector
(2) DEF outlet connection
(3) DEF inlet connection
The DEF injector is mounted to the Clean Emissions
Module (CEM). The DEF injector is a valve that
injects DEF as a fine spray into the exhaust gases as
an atomized mist before the Selective Catalytic
Reduction (SCR). The spray pattern being conical for
good mixing with the exhaust is critical.
The tip of the injector, located in the exhaust flow, is
cooled by the DEF that flows through an internal
passage from the DEF heated lines.
Nitrogen Oxide (NOx) Sensors
There are two NOx sensors supplied with the engine.
One NOx sensor is installed in the Clean Emissions
Module (CEM). The other NOx sensor is installed in
the exhaust pipe of the application.
The engine produces NOx as the engine operates.
The engine out NOx sensor measures the amount
and communicates that value to the Diesel Exhaust
Fluid Control Unit (DCU). The tailpipe out NOx
sensor monitors the NOx level out of the catalyst and
communicates that value to the DCU. Engine out and
tail pipe out NOx sensor values will determine the
flow rate of the Diesel Exhaust Fluid (DEF) to meet
the desired tail pipe out target.
Illustration 29 g03403971
Typical example
(1) Sensing unit
(2) Cable (black for engine out, gray for CEM out)
(3) Sensor electronic control unit
(4) Electrical connector
The NOx sensor contains a sensing element, a
harness, and an electronic control unit. The sensing
element is composed of two chambers and a heater.
The first chamber measures the amount of oxygen
and the second chamber measure the amount of
NOx and NH
3
. Using electrochemistry, a ceramic
material attracts ions at approximately 800° C
(1472° F) and an electrode on the chamber wall
measures the electrical charge in voltage or current.
The voltage or current signal is then received by the
NOx sensors electronic control unit and interpreted
into a NOx concentration. The heater is used to
maintain the sensing element temperature, as
sensing element is sensitive to moisture. If the
sensor detects moisture while at 800° C (1472° F),
the moisture could quickly cool the element which
would cause the element to crack. At engine start-up
there is always some moisture within the exhaust
pipes. The sensors will not operate until the exhaust
temperature around the sensors is greater than
100° C (212° F) for approximately two and a half
minutes.
DEF System Heated Lines
The DEF flows in the heated lines from the DEF tank
to the pump in the Dosing Control Unit (DCU). The
DEF then travels through another heated line from
the DCU to the DEF injector. The heated lines are
heated by an electrical resistance.
34 UENR4490-01
Engine Operation
This document has been printed from SPI2. NOT FOR RESALE
To Next Page
Loading...
