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Difficulty: MediumEngine Principles and Internal Components

In a standard four-stroke spark-ignition engine, mechanical actions inside the cylinder occur in a precise sequence to complete one operating cycle. Arrange the following cylinder events in the correct chronological order, starting from the induction of the fresh charge.

  1. 1The intake valve opens as the piston travels downward from top dead center to draw the air-fuel mixture into the cylinder.
  2. 2Both valves seal tightly while the piston travels upward toward top dead center, squeezing the air-fuel mixture into the combustion chamber.
  3. 3The spark plug fires near top dead center, igniting the compressed mixture and driving the piston downward to deliver mechanical work.
  4. 4The exhaust valve opens as the piston moves upward from bottom dead center, pushing the spent combustion gases out of the cylinder.

Answer

The correct sequence of events is: 1) The intake valve opens as the piston moves downward to draw in the air-fuel mixture; 2) Both valves seal while the piston moves upward to compress the mixture; 3) The spark plug ignites the mixture, driving the piston downward to produce power; 4) The exhaust valve opens as the piston moves upward to expel the burned exhaust gases.
A four-stroke engine operates strictly in the sequence of intake (piston moves down, intake valve open), compression (piston moves up, both valves closed), power (combustion forces piston down, both valves closed), and exhaust (piston moves up, exhaust valve open). Arranging the cylinder events from intake through exhaust accurately reflects the mechanical cycle.

Step-by-Step Solution

1
Identify the first stroke of the internal combustion operating cycle.
The intake stroke begins at top dead center with the intake valve open and the piston traveling downward, drawing in the air-fuel charge.
An engine must bring a combustible charge into the cylinder before any compression or combustion can take place.
2
Determine the mechanical event following cylinder charging.
The compression stroke follows as both valves close and the piston moves upward toward top dead center, compressing the mixture into a smaller volume.
Compressing the air-fuel mixture increases thermal efficiency and combustion speed prior to ignition.
3
Identify the working phase resulting from mixture ignition.
The power stroke occurs when the spark plug ignites the compressed charge, creating high-pressure expanding gases that push the piston downward.
This is the only stroke in the four-stroke cycle that produces positive mechanical work to rotate the crankshaft.
4
Determine the concluding event of the four-stroke cycle.
The exhaust stroke concludes the cycle as the exhaust valve opens and the rising piston expels the spent combustion byproducts.
Residual burned gases must be cleared from the cylinder volume before a fresh intake stroke can begin.

Key Concept

The operational sequence and mechanical events of the four-stroke internal combustion engine cycle (intake, compression, power, exhaust).
Estimated Time:1m 0s
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Topics

Engine Principles and Internal Components

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