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Useful Information on Combustion Efficient Fuel Use
Definition: Combustion is the rapid oxidation of a fuel resulting
in the release of usable heat and the production of a visible
flame
The Combustion Equation:
Natural Gas With Air:
CH4 + 2O2 + 8N2 ----------->
CO2 + 2H2O + 8N2 + 1000 BTU Heat
Examples of Combustion
Perfect Combustion Provides:
The hottest flame
Minimum exhaust volume
Perfect Combustion
Characteristics:
- All fuel combusted
- Blue near burner tile
- Forms a yellow conical flame shape
- Produces the highest flame temperature
- Provides the minimum exhaust volume
Lean Combustion
Characteristics:
- Flue products oxidizing (Free O2)
- Pale blue color
- Forms a more conical flame
- All fuel combusted
- Flame temperature drops (Heating
excess air)
Incomplete Combustion
Characteristics:
- Air starved or fuel rich
- Carbon Monoxide and H2
formed
- Reducing atmosphere
- Flame color is predominantly yellow
color
- The flame is less defined
- Flame temperature drops
Optimum Energy Utilization Occurs When Perfect Combustion Ratios
Are Maintained. When A Furnace Tune-Up Is Done Right The Technician
will have taken time to:
- Verify proper mix and directed air/fuel
supply
- Confirm that you have stable combustion
- Check to make sure that the system
is venting all the by-products of the exhaust flue gases
A Definition of Combustion Terms
Excess Air Definition:
Air remaining after the fuel has been combusted
-or-
Air supplied in addition to the quantity needed for stoichiometric
combustion
Primary & Secondary Air:
- Primary Air -- Air mixed with the fuel
prior to ignition
- Secondary Air -- Air supplied to the flame
after it is ignited
Secondary Air Effects --
- Imprecise air/fuel ratio control
- Exhaust volume increases
- Fuel rate rises
- Less available heat
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