PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
(4) Volatility. The term volatility refers to how fast a liquid
vaporizes. Alcohol, for instance, vaporizes more easily than water. Some
liquids vaporize easily at room temperature. A highly volatile liquid is
one that is considered to evaporate easily.
c. Venturi Effect (figure 10). A venturi effect is used by the
carburetor to mix gasoline with air. The basic carburetor has an hourglass
shaped tube called a throat. The most constricted part of the throat is
called the venturi. A tube called a discharge nozzle is positioned in the
venturi. The discharge nozzle is connected to a reservoir of gasoline,
called the float bowl. The negative pressure that exists in the combustion
chamber, because of the downward intake stroke of the piston, causes
atmospheric pressure to create an airflow through the carburetor throat.
This airflow must increase temporarily in speed as it passes through the
venturi, due to its decreased size.
The increased speed of the airflow will also result in a corresponding
decrease in pressure within the venturi and at the end of the discharge
nozzle. When this occurs, atmospheric pressure will push gasoline through
the discharge nozzle and into the carburetor throat, where it will mix with
the intake airflow.
FIGURE 10. VENTURI EFFECT.