infrared industries FGA, Руководство оператора

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C O N C L U S I O N
Figure 10 Combustion Products Vs Lambda
Figure 10 shows the relationship between the air-fuel ratio and
the four exhaust gases monitored by the analyzer. It shows:
HC levels are lowest when the air-fuel ratio is ideal because most
of the fuel is consumed in combustion. Richer or leaner
mixtures or ignition problems cause the HC to increase because
of incomplete combustion.
1. CO levels are lowest when the air-fuel ratio is nearly
ideal because there is less oxygen and carbon left over
due to the more-complete combustion occurring at
ideal ratios. Richer than ideal mixtures cause CO to
increase; leaner has little affect.
2. CO
2
levels are highest when air-fuel ratios are close to
ideal, and decrease when the mixture becomes richer
or leaner.
3. CO levels are near zero when the air-fuel ratio is near
ideal because most of it is consumed in combustion. It remains low with richer mixtures, and increases
when the mixture leans out.
S T O I C H I O M E T R I C F U E L M I X T U R E S
As can be seen from Figure 11, the ideal (stoichiometric) 14.66:1 air-fuel ratio (Lambda 1.0), is near the point where
the emission levels drastically change. The stoichiometric air-fuel ratio, where the HC and CO levels are lowest, is as
close to perfect combustion as can be attained.
Figure 11 Carbureted Fuel Feedback System
Combustion temperatures and the air-fuel ratio requirements can change in engines under dynamic load. The only way
to ensure that the air-fuel ration remains stoichiometric under most operating conditions is to use a feedback system.
So modern engine computers monitor the O
2
content of the exhaust gas. The computer calculates the air-fuel ratio,
and commands the fuel delivery device, either fuel injector or carburetor, to deliver the amount of fuel required to
maintain the correct fuel-air ratio. A typical system is shown in Figure 11.