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Difficulty: EasyEngine Principles and Internal Components

During the exhaust stroke of a four-stroke internal combustion cycle, how do the piston and valves operate to clear burned gases from the cylinder?

  1. A
    The piston moves downward toward bottom dead center while the exhaust valve remains open
  2. The piston moves upward toward top dead center while the exhaust valve is openAnswer
  3. C
    The piston moves upward toward top dead center while both intake and exhaust valves remain closed
  4. D
    The piston moves downward toward bottom dead center while drawing in a rich fuel mixture

Answer

The piston moves upward toward top dead center while the exhaust valve is open.
In the fourth stroke of the four-stroke cycle (the exhaust stroke), the exhaust valve opens and the piston rises from bottom dead center (BDC) to top dead center (TDC). This upward sweep forces the burned exhaust gases out of the cylinder through the open exhaust valve.

Step-by-Step Solution

1
Identify the primary function of the exhaust stroke in a four-stroke engine
The goal is to expel spent combustion gases out of the cylinder into the exhaust manifold.
Each stroke in a four-stroke cycle performs a distinct phase: intake, compression, power, and exhaust.
2
Determine the required piston motion and valve state for expelling gases
The exhaust valve opens while the intake valve remains closed, and the crankshaft pushes the piston upward from bottom dead center (BDC) to top dead center (TDC) to sweep out the exhaust gases.
Upward piston movement reduces cylinder volume, physically pushing the burned gases out through the open exhaust port.

Key Concept

Four-stroke engine cycle phases and exhaust stroke mechanics
Estimated Time:45s
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Topics

Engine Principles and Internal Components

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