Final answer:
In a four-stroke gasoline engine, there is one power stroke every four strokes of the piston, which corresponds to every two revolutions (720° rotation) of the crankshaft.
Step-by-step explanation:
Understanding the Four-Stroke Internal Combustion Engine
The question revolves around the functionality of a four-stroke internal combustion engine and its cycle of operation. In a four-stroke gasoline engine, also known as an Otto cycle engine, the crankshaft completes two revolutions for each power stroke. This equates to 720° of rotation. The four distinct strokes in the cycle are the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. Here's a brief explanation of each:
- Intake Stroke: Air is mixed with fuel as the piston moves downwards, creating a vacuum that draws in the air-fuel mixture.
- Compression Stroke: The air-fuel mixture is compressed as the piston moves back up in the cylinder with all valves closed. Work is done on the gas during this nearly adiabatic process.
- Power Stroke: The air-fuel mixture is ignited, leading to a significant increase in pressure which pushes the piston down, delivering power to the crankshaft.
- Exhaust Stroke: The exhaust valve opens and the piston moves back up, expelling the burnt gases and preparing the cylinder for a new cycle.
Addressing the student's question, yes, in a four-stroke engine, there is one power stroke for every four strokes of the piston, resulting in one power stroke for every two revolutions (720° rotation) of the crankshaft. It's important to note that despite the pistons moving up and down twice, the engine is designed in a way that only the third stroke (the power stroke) delivers the force to propel the engine.