92
To check the combustion quality, the CO
2
content or
the O
2
content of the flue gas is measured. The pre-
vailing air ratio is determined using the actual values.
The correlation between CO
2
or O
2
content and air
ratio
λ
is shown in the following table.
Air ratio
λ–
CO
2
/O
2
content
Air ratio
λ
O
2
content (%)
CO
2
content (%) for nat-
ural gas E
CO
2
content (%) for natu-
ral gas LL
1.20
3.8
9.6
9.2
1.24
4.4
9.2
9.1
1.27
4.9
9.0
8.9
1.30
5.3
8.7
8.6
1.34
5.7
8.5
8.4
1.37
6.1
8.3
8.2
1.40
6.5
8.1
8.0
1.44
6.9
7.8
7.7
1.48
7.3
7.6
7.5
To achieve optimum combustion control, the system
regularly carries out an automatic self-calibration; also
after power failures (shutdown). For this, the combus-
tion is briefly regulated to maximum ionisation current
(corresponding to air ratio
λ
=1). Self-calibration takes
place shortly after the burner start and lasts for about
5 s. During calibration, higher than normal CO emis-
sions may occur briefly.
Function description
Electronic combustion control unit
(cont.)
5839829
Functions
