CenCon
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Appendix E – DJ/DG Fuel Curve Development
Clocking notes:
Correct values for Altitude.
Ensure inlet pressure is correct at each stage.
All clocked values should be within 5% of the calculated value.
Offset values are set by 0.1Vdc increments. If results at low fire are not exact, and either too little or
too much gas, use too much so as not to exceed maximum turn down.
Where possible, use a small meter to improve clocking times at lower firing rates
Whenever possible at each stage, allow a few minutes for the heat exchanger temperature to stabilize before
finalizing combustion values.
m
Ensure firing rates (and motor rpm, if used) increase as the combustion range increases
from low to high fire.
For example, do not have the clocked Near Low Fire rate less than the Low Fire value.
The pressure must be more than the Low Fire value.
1.
High Fire. Adjust inlet regulator to achieve correct clocking, while adjusting Pac-Man (DJ) or DG Air
Offset for clean burn.
2.
Near High Fire. Multiply High Fire clocking by Ratio (X 1.1), and re-clock. Adjust gas and/or air offset
values if required. Record new clocking value, manifold pressures, burn, and Air and Gas offsets.
3.
Low Fire. Multiply High Fire clocking by Ratio, and re-clock.
a.
Adjust bypass orifice and/or air offset if required on DJ. Record new values.
b.
Adjust gas and/or air offset values if required on DG. Record new values.
4.
Continue same process with Near Low Fire, Medium Fire 1, and Medium Fire 2.
5.
Set to High Fire and confirm correct inlet pressure.
6.
Set to Low Fire to confirm clean burn throughout range.
7.
Finished combustion setup. Save values.
8.
Shut down and restart heat to confirm good ignition.
9.
Allow heating to run on automatic for a few minutes.
Example #1: high fire clocking is 10 seconds
Example #2: high fire clocking is 30 seconds
Calculated
Name
% Fire
Ratio
Example #1
Example #2
High Fire
100
1.0
10
30
Near High Fire
90
1.1
11
33
Medium Fire 2
55
1.8
18
54
Medium Fire 1
25
4.0
40
120
Near Low Fire
10
10.0
100
300
Low Fire - DJ
6.67
15.0
150
450
Low Fire - DG
5
20.0
200
600
