Doosan 12/154, Operation & Maintenance Manual

Page: 57 / 108

OPERATING INSTRUCTIONS 53
12/154
If the machine has been switched off because of a machine
malfunction, then identify and correct the fault before attempting to re-
start.
If the machine has been switched off for reasons of safety, then
ensure that the machine can be operated safely before re-starting.
Refer to the PRIOR TO STARTING and STARTING THE UNIT
instructions earlier in this section before re-starting the machine.
MONITORING DURING OPERATION
Should any of the safety shut–down conditions occur, the unit will
stop.
Refer to the wedge diagnostic display codes table for a listing of
shutdown conditions.
AFTERTREATMENT DEVICES
The Aftertreatment Architecture for the QSB6.7 T4F engine used in
this compressor is based on three key subsystems:
1. Diesel Oxidation Catalyst (DOC)
2. Selective Catalytic Reduction (SCR)
3. Diesel Exhaust Fluid (DEF) Dosing System
Diesel Oxidation Catalyst (DOC)
Modern catalytic converters consist of a monolith honeycomb
substrate coated with platinum group metal catalyst, packaged in a
stainless steel container. The honeycomb structure with many small
parallel channels presents a high catalytic contact area to exhaust
gasses. As the hot gases contact the catalyst, several exhaust
pollutants are converted into harmless substances: carbon dioxide and
water.
The diesel oxidation catalyst is designed to oxidize carbon
monoxide, gas phase hydrocarbons, and the SOF fraction of diesel
particulate matter to CO
2
and H
2
O.
Selective Catalytic Reduction (SCR)
The purpose of the SCR system is to reduce levels of NOx (oxides
of nitrogen emitted from engines) that are harmful to our health and the
environment. SCR is the aftertreatment technology that treats exhaust
gas downstream of the engine. Small quantities of diesel exhaust fluid
(DEF) are injected into the exhaust upstream of a catalyst, where it
vaporizes and decomposes to form ammonia and carbon dioxide. The
ammonia (NH
3
) is the desired product which in conjunction to the SCR
catalyst, converts the NOx to harmless nitrogen (N
2
) and water (H
2
O).
Diesel Exhaust Fluid (DEF)
DEF is the reactant necessary for the functionality of the SCR
system. It is a carefully blended aqueous urea solution of 32.5% high
purity urea and 67.5% deionized water.
A 32.5% solution of DEF will begin to crystallize and freeze at 12
deg F (-11 deg C). At 32.5%, both the urea and water will freeze at the
same rate, ensuring that as it thaws, the fluid does not become diluted,
or over concentrated. The freezing and unthawing of DEF will not
cause degradation of the product.
During cold weather engine operation the engine coolant will be
used to heat up and thaw the DEF fluid, there is a delay built in to the
engine software to ensure engine operation even with frozen DEF fluid
during warmup.
OPERATION OF THE AFTERTREATMENT DEVICES
1. DEF tank fluid level gauge
2. Aftertreatment system warning lights
3. Aftertreatment regeneration switch
Aftertreatment System Lights
DEF System Status
1. High Exhaust Temperature
2. Regeneration in process
3. DEF fluid level warning
4. Regeneration Inhibited
CAUTION: To ensure an adequate flow of oil to the compressor at
low temperature, never allow the discharge pressure to fall below 3,5
bar.