5-2
Fundamentals
The ideal air-fuel ratio for perfect combustion in a gasoline engine
is 14.66:1, commonly referred to as 14.7:1. This is the
stoichiometric ratio or stoichiometric fuel mixture. Under perfect
conditions, the combustion of a stoichiometric air and fuel mixture
results in carbon dioxide (CO
2
), water (H
2
O) and nitrogen (O
2
), all
of which are harmless.
A lean fuel mixture has too much air or too little fuel. A rich fuel
mixture has too much fuel or too little air.
Combustion Emissions
Internal combustion engines are not 100% efficient, even with
ideal fuel mixtures. For this reason, other substances form in the
combustion chamber during combustion and exhaust from the
engine. Major by-products of “real-world” combustion include:
•
Oxides of nitrogen (NO
x
)
•
Hydrocarbons (HC)
•
Carbon monoxide (CO)
•
Oxygen (O
2
)
Because exhaust gases relate to health and environmental
concerns, federal and state agencies regulate automobile
emissions.
Figure 5-2
: Ideal Combustion By-Products
To Next Page
Loading...