Combustion is a chemical reaction. When a source
of ignition is present, the process of combining
fuel and oxygen results in the release of heat.
Fuels are made up of varying amounts of
hydrogen and carbon. When hydrogen (H) and
carbon (C) are combined with the oxygen (O) in
the air, the by-products are carbon dioxide (CO2),
water vapor (H2O), and heat. Three things must
be present in order for combustion to take place:
fuel, oxygen, and heat. These three ingredients
frequently are referred to as the “fire triangle”
(see Figure 2-1). Remove any one of these three
components and the fire will go out.

Once the mixture of fuel and oxygen is ignited,
the chemical reaction of combustion supplies
sufficient heat of its own for the process to
continue. The chemical change that takes place
in the complete combustion process can be
expressed in the form of a balanced chemical
equation. For methane, the equation is written
as follows:

If an insufficient amount of oxygen is mixed
with the fuel or if the temperature is cooled by
flame impingement on the cooler surfaces of
the heat exchanger, incomplete combustion can
occur. Incomplete combustion results in the
formation of carbon monoxide (CO) and soot.
The two sides of the chemical equation cannot
be balanced. For example:

Excerpt from “Gas and Oil Heating, PREPARING FOR THE NATE EXAM”

Available at the Refrigeration Service Engineers Society online store: RSES.ORG


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