Definition
The narrowed section inside a carburetor where intake air is forced to speed up as it passes through. This acceleration causes a drop in pressure and temperature, which draws fuel into the airstream and mixes it with the incoming air before it reaches the engine cylinders.
Plain English
A pinched, narrow passage inside the carburetor that speeds up the air flowing through it. Faster air means lower pressure and cooler temperature at that spot, and that combination is what pulls fuel into the air so the engine has a fuel-air mixture to burn.
Context Anchor
Seen in carburetor icing and induction icing discussions, especially when explaining why ice can form inside the engine air intake system.
Derivation
Named after Giovanni Venturi, an 18th-century Italian physicist who studied how fluids behave when forced through a narrowed passage. He showed that fluid speeds up and pressure drops in the narrow section -- the principle the carburetor relies on to draw in fuel.
Why Pilots Care
Ice can form inside the venturi because the pressure drop and fuel evaporation cool the air; this restricts airflow and fuel flow, leading to power loss or engine failure.
Analogy
It is like partly covering the end of a garden hose with your thumb: the water speeds up through the smaller opening. In a carburetor venturi, air speeds up through the smaller opening, and that change helps pull fuel into the airflow.
Grounding Statement
Picture moist air being squeezed through a narrow throat inside the carburetor, cooling quickly enough that ice can start building on the metal surfaces.
Intuition Check
Do not think of the carburetor venturi as just an empty tube. The important point is that its narrowed shape makes air speed up, pressure drop, and temperature fall.
Example Sentence 1
Air rushing through the carburetor venturi can drop in temperature by as much as 30 to 40 degrees Fahrenheit, which is why carb ice can form even on a warm day.
Example Sentence 2
Applying carburetor heat warms the venturi area and melts any ice that has formed on the throttle plate or venturi walls.