infrared industries FGA, Руководство оператора

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Chapter 3 –
Exhaust Gas/Emission
C O M B U S T I O N F U N D A M E N T A L S
To understand and interpret the information provided
by the analyzer, it is helpful to have an understanding of
what the analyzed combustion byproducts are, how and
where they are formed in a gasoline engine, and the
relationship between them at different air-fuel ratios.
In a gasoline-powered, internal combustion engine,
normal combustion is the spark-ignition of a
compressed mixture of hydrocarbon fuels and air,
taking place in the combustion chamber. This action
produces the pressure that forces the piston downward.
Figure 4 shows the compressed air-fuel mixture being
ignited by the spark plug.
The fuel induction system of a gasoline engine forms
air-fuel mixtures by vaporizing gasoline (a hydrocarbon),
and mixing it with air in a given proportion (always
more air than gasoline vapor).
Figure 4 The Combustion Process
There is 14 times as much air as fuel (by weight), needed to vaporize the fuel into a state for ignition and to supply
enough oxygen to the fuel so it can burn in the combustion reaction.
G A S F U N D A M E N T A L S
L A M B D A
The ideal air-fuel ratio for perfect combustion in a gasoline engine is 14.66:1, or 14.66 pounds of air to each pound of
vaporized gasoline. This is known as a stoichiometric ratio or stoichiometric fuel mixture.
NOTE: Lambda (

) is Air Fuel Ratio/14.66. This parameter is easier to use because it is 1.0
when the combustion is optimal. Lambda is less than one for “rich” combustion and greater
than one for “lean” combustion. We will use Lambda in our discussion of combustion.
Under perfect conditions the combustion of a stoichiometric air-gasoline mixture would result in carbon dioxide (CO
2
),
water vapor (H
2
O) and nitrogen (N
2
), which are all harmless combustion byproducts. Therefore if we measured the
exhaust of a gasoline engine and found only CO
2
, H
2
O, and N
2
we could assume that the engine was operating at an
optimal level. This also implies that if you measure the products of complete combustion (CO
2
, H
2
O, and N
2
) and the
products of incomplete combustion (CO and O2) that the Air Fuel Ratio or Lambda could be calculated from these
measurements. This, in fact, is the case and the FGA 4000 series product offers an option to calculate Lambda from
the gas concentrations measured. The equation used by the system to calculate Lambda is discussed in detail in
Appendix C.
NOTE: Air-fuel ratios are expressed by weight, not volume. An air-fuel ratio of 12:1 (Lambda .8)
is 12 pounds of air mixed with one pound of fuel.