5-1
Fundamentals
This chapter contains essential information required to understand
and interpret analyzed combustion by-products and information
provided by the analyzer. Included is a description of how and
where combustion by-products form in an engine and common
methods used to help reducing their formation.
Combustion and Air-Fuel Ratios
In a gasoline-powered internal combustion engine, normal
combustion is burning a compressed mixture of hydrocarbon fuel
and air in the combustion chamber. This action causes the
compressed fuel mixture to expand, producing the pressure
required to move the pistons downward.
Figure 5-1
shows the air-
fuel mixture inside a cylinder being ignited by the spark plug.
The fuel induction system of a gasoline engine mixes vaporized
gasoline, a hydrocarbon, with air in a given proportion. There must
be more air than fuel to keep the vaporized fuel in suspension and
to supply oxygen for combustion.
✓
Air-fuel ratios are measured by weight, not volume. An
air-fuel ratio of 12:1 is 12 pounds of air mixed with one
pound of fuel.
Figure 5-1
: Combustion Process
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