9 Commissioning
KRONOS 20
43
9.3
Commissioning for OPEN LOOP (open control circuit)
In order to obtain a satisfactory control behaviour of the AFR system in an open control
circuit the set lambda values must not necessarily be equal to the actual measured values.
The same holds true for other values, such as calculated gas flow and pressure in relation
to the respective measured values. The control quality of the open loop system as a whole
is not prejudiced by these differences. Example: If there is no measuring device for lambda
measuring but a measuring device for the adjustment of NOx content in the exhaust gas is
available instead, the commissioning personnel does not need to know the actual lambda
value in order to carry out a satisfactory adjustment of the system.
Still in Open Loop too, it is advisable to carry out the correct adjustment of the AFR sys-
tem if the required devices are available. The clear structures of the respectively relevant
parameters allows an easy and understandable commissioning and fine-tuning and reduces
errors.
For a correct diagnosis, state monitoring and for the operation with a closed loop a com-
plete calibration is necessary. The actual measured values must correspond to the variables
and set values of the mixture control. For this calibration the following devices are re-
quired:
•
A universal lambda sensor or an oxygen analyzer for exhaust gas in connection with a
valid conversion table from O
2
% to lambda.
•
A gas flowmeter for the measurement of nm
3
/h (standardized measurement at 1013.25
mbar and 0° C). If gas quality and engine efficiency are known, the produced electric
power may be used instead to approximately determine gas flow. Qgas [nm3/h] =
(power [kW] x 3600)/(
η
set
x Hu[kJ/nm
3
]).
After the parameters have been determined and set, the engine may be started and load ap-
plied gradually. In order to avoid misfiring, ingnition failures and knocking and to adjust
the desired NO
x
value, continuous corrections of the set lambda value in dependence of
load and speed are necessary.
Adequate adjustment of the zero pressure regulator is particularly important during start-
up! Pressure offset should not normally be higher than + 2..3 mbar to ensure a safe engine
start. Experience shows that this is where errors frequently happen.
After engine warm-up the AFR control must be verified in open loop (5400
ClosedOrO-
penLoop=0
) and with different load-points according to the following procedure:
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