infrared industries FGA, Руководство оператора

Страница: 28 / 58

27
When a fuel mixture is "lean", there is too much air and too little fuel in the air-fuel ratio. If a mixture is "rich", it has
too much fuel and too little air.
Because internal combustion engines are not 100% efficient, even with ideal fuel mixtures, other substances are formed
in the combustion chamber during combustion and are exhausted from the engine. The major by-products of "real-
world" combustion include:

Carbon Dioxide (CO
2
)

Carbon Monoxide (CO)

Oxides of Nitrogen (NO
X
)

Hydrocarbons (HC)

Oxygen (O
2
)
Because the carbon monoxide, oxides of nitrogen and hydrocarbon exhaust products are related to health and
environmental concerns, these emissions from automobiles are regulated by federal and state agencies.
O X I D E S O F N I T R O G E N ( O P T I O N A L )
Nitrogen makes up about 78% of the air in Earth's atmosphere, and oxygen about 21%. Therefore, about 78% of the
air in the combustion chamber is nitrogen. Nitrogen is inert and does not contribute to, or detract from, combustion.
Nitrogen and oxygen only combine with each other to form harmful oxides, including nitric oxide (NO) and nitrogen
dioxide (NO
2
), when both gaseous elements are heated above 1371°C [2500°F].
NOTE: Oxides of nitrogen (NOX) include all the nitrogen compounds formed in an engine's
combustion chamber, including nitric oxide (NO) and nitrogen dioxide (NO2). The (x)
subscript in place of numbers indicates that all nitrogen/oxygen compounds are included.
Under some engine conditions, the combustion chamber temperatures easily exceed 1371°C [2500°F], combining
oxygen and nitrogen to form NOx.
Figure 5: NOx vs. Lambda
Figure 5 shows the concentration of NO
X
in relation to the air-fuel
ratio. When based only on air-fuel ratio, combustion chamber
temperatures peak at air-fuel ratios of about 18:1 (Lambda 1.25),
allowing the formation of NO
X
. Since modern engines do not
normally run at 18:1 (Lambda 1.25), theoretically NO
X
emissions
should not be a problem. However, lean air-fuel ratios are not the
only cause of NO, emissions. Moderate to heavy engine loads also
cause combustion chamber temperatures to increase at ratios much
richer than 18:1 (Lambda 1.25).
NOx is not often monitored because; 1. NO
X
is normally only formed
when the engine is under load. Thus it would be ideal to measure NOx
while the vehicle is under load. 2. NO
X
does not indicate engine
performance or efficiency as does oxygen, hydrocarbons, carbon
monoxide and carbon dioxide. The formation of NO
X
does not affect
engine performance, but some devices used to prevent it from forming can affect performance and contribute to
higher levels of HC and CO if they are not functioning properly.