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Page 3-11
Outer Envelope
Inner Cone Pushes
Through Outer Cone
Outer Cone
Flame Lifts
Off Burner
Figure 3-15
The outer cone surrounds the inner cone. The outer cone is the hottest part of the flame. Secondary
air is drawn into the flame at this point and accelerates combustion. As the by-products from the
inner cone move into the outer cone, they are burned and transformed into harmless water vapor
(H
2
O) and Carbon Dioxide (CO
2
). If there is not enough secondary air, or if it is poorly ventilated
and stagnant, this process cannot occur completely, and some of the harmful by-products from the
inner cone will skip into the outer envelope.
The outer envelope surrounds the outer cone. The combustion process has been completed by
the time the chemicals reach this point. The glow of the envelope is the result of the hot Carbon
Dioxide and Water Vapor exiting the outer cone.
Too Much Primary Air
As the primary air is increased, the gas/air mixture burns at a faster speed (like fanning a flame).
The additional primary air results in a greater volume of air/gas flow through the burner ports.
With increased delivery pressure and a faster burning flame, the result is a flame that blows straight
out of the burner and burns with a sound similar to a blow torch. The flames lift off the burners and
the cone structure of the flame is disrupted. (see Figure 3-15).
Proper Flame Characteristics:
• Blue Color
• Flame Seated On Burner Port
• Well Defined Shape
Outer Envelope
Outer Cone
Inner Cone
Unburned Air/Gas
Figure 3-14
FLAME CHARACTERISTICS
A Properly Burning Flame
A properly burning flame has an inner cone, an outer cone, and an outer envelope. These three
parts should be definable and distinguishable, although the outer envelope may not be easy to see.
(see Figure 3-14).
The inner cone is the point where the air/gas mixture ignites and the combustion process begins.
High levels of Carbon Monoxide and Aldehydes are produced in this cone.