Understanding Basic Combustion

Useful Information on Combustion Efficient Fuel Use

A 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:

Ch5 + 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

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