Passage III

The carburetors in gasoline engines have a constric­tion called a venturi, where gasoline and air are mixed (see Figure 1).

Because the diameter of the venturi is less than the diame­ter of the air inlet, air moves faster through the venturi than through the air inlet. As a result, the pressure in the venturi is less than atmospheric pressure, and gasoline is drawn into the venturi. Moreover, the faster air moves through the venturi, the lower the pressure in the venturi, and the greater the rate at which gasoline is drawn into the venturi.

The percent change in pressure (%△P) can be defined as:

The %△P of carburetors was determined under various conditions in the following experiments.

Experiment 1

A carburetor was mounted on an engine with an air volume capacity (the volume of air drawn into the engine during each piston stroke) of 0.55 liter (L). The %△P of the carburetor was found at various engine speeds. The results are given in Table 1.

Experiment 2

The engine used in Experiment 1 was fitted with car­buretors having the same air inlet diameter as in Experiment 1 but different venturi radii. The %△P for each carburetor was measured at an engine speed of 3,000 rpm (see Table 2).

Experiment 3

The carburetor used in Experiment 1 was fitted to engines having various air volume capacities. The %△P for each engine was measured at an engine speed of 3,000 rpm (see Table 3).