CA-7
I know that O
2
, CO, CO
2
, temperature and
smoke can tell me a lot about combustion.
How do they all relate to efficiency?
Theoretically, peak fuel efficiency is achieved by “per-
fect” combustion, also called the Stoichiometric Mix
(see charts #2 and #3).
If it were possible to have perfect combustion, CO
2
would be maximized and O
2
would be at, or close to,
zero in the flue gas stream. Because perfect combustion
is not practically possible, most combustion equipment
is set up to have a small percentage of excess O
2
pre-
sent. The lower the temperature for a given O
2
or CO
2
reading, the higher is your combustion efficiency. This is
because less heat is lost up the stack.
In a Stoichiometric Mix, all the fuel and oxygen (O
2
)
present combines to generate only heat, water and car-
bon dioxide (CO
2
).
Smoke is the usual indicator of incomplete combustion
in oil burners. In addition to indicating poor combus-
tion, smoke can deposit soot on your heat exchangers
which will further reduce fuel efficiency; and smoke
coming out of the stack can be cause for air quality vio-
lation.
To give you a graphic illustration of how dramatically
smoke and soot can effect fuel combustion efficiency,
we have included chart #4. We have also included a
common fuel characteristics chart (chart #5) for several
of the common fuels used in combustion equipment.
CA-8
Is measuring draft important?
Draft measurement is important because draft controls
how rapidly the gases (O
2
, CO, CO
2
- and even fuel)
pass through the furnace and boiler.
3
Chart 2
T HE O R E TI C A L A I R C U RV E / F UE L O I L
Chart 3
T H E OR E TI C A L A I R C U R V E / N AT U R AL G A S
Chart 4
E F F E CT O F SO O T O N F U E L C O N S U M PT I O N
Chart 5
CO M M O N F U E L C H AR A CT E R I S T I C S
(Complete Combustion)
Higher
Heating
Carbon
Hydrogen
Ultimate
Moisture
Value
NATURAL GAS
21,830 BTU/lb.
69.4%
22.5%
11.7%
-
KEROSENE
19,942 BTU/lb.
86.5%
13.2%
15.12%
-
137,000 BTU/gal.
PROPANE
21,573 BTU/lb.
81.6%
18.4%
13.8%
-
FUEL OIL NO.2
18,993 BTU/lb.
87.3%
12.5%
15.7%
-
137,080 BTU/gal.
FUEL OIL NO.6
18,126 BTU/lb.
88.5%
9.3%
16.7%
-
153,120 BTU/gal.
ANTHRACITE COAL
12,680 BTU/lb.
80.6%
2.4%
19.9%
-
BITUMINOUS COAL 14,030 BTU/lb.
80.1%
5.0%
18.5%
-
B A G A S S E
8,200 BTU/lb.
45.0%
6.4%
20.3%
50.0%
WOOD
8,800 BTU/lb.
50.0%
6.5%
20.0%
10.0%
(10%moisture)
