What happens during the intake stroke of a four-stroke internal combustion engine?
A. The piston moves downward, creating a partial vacuum that draws in air and fuel.
B. The piston moves downward as a result of the air/fuel mixture doing work on it.
C. The piston moves upward, compressing the air/fuel mixture and raising its temperature.
D. The piston moves upward, doing work on the air/fuel mixture to push it out of the cylinder.
A. The piston moves downward, creating a partial vacuum that draws in air and fuel.
https://en.wikipedia.org/wiki/Four-stroke_engine
A. The correct answer is A. During the intake stroke of a four-stroke internal combustion engine, the piston moves downward, creating a partial vacuum that draws in air and fuel.
To understand what happens during the intake stroke of a four-stroke internal combustion engine and determine the correct answer, we need to know the basic operation of the engine.
A four-stroke internal combustion engine operates on the principle of converting the potential energy stored in fuel into mechanical work. It achieves this through a sequence of four strokes: intake, compression, power (or combustion), and exhaust.
During the intake stroke, the engine draws in the air-fuel mixture needed for combustion. To do this, let's go through the answer choices one by one:
A. The piston moves downward, creating a partial vacuum that draws in air and fuel.
This answer accurately describes what happens during the intake stroke. As the piston moves downward, it creates a partial vacuum or low-pressure area in the cylinder. This drop in pressure allows air and fuel to enter the combustion chamber through the intake valve.
B. The piston moves downward as a result of the air/fuel mixture doing work on it.
Although the downward movement of the piston is a result of the air/fuel mixture's presence, it is not the primary effect of the intake stroke. The piston's main purpose during the intake stroke is to create the low-pressure area, as described in choice A.
C. The piston moves upward, compressing the air/fuel mixture and raising its temperature.
The upward movement of the piston is associated with the compression stroke, which follows the intake stroke. During the compression stroke, the piston moves upward, compressing the air-fuel mixture and raising its temperature. So, this choice does not describe the intake stroke.
D. The piston moves upward, doing work on the air/fuel mixture to push it out of the cylinder.
The upward movement of the piston during the power stroke is when the previously ignited air-fuel mixture is pushed out of the cylinder. This does not occur during the intake stroke.
Based on the explanations provided, the correct answer is A. The piston moves downward, creating a partial vacuum that draws in air and fuel.