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For a piston engine, auto-ignition refers to a phenomenon that occurs when…

  • A

    There are hot combustion residuals or hot parts of the cylinder wall.

  • B

    Clean combustion chambers promote efficient combustion.

  • C

    The engine works with low compression ratios.

  • D

    The engine works under normal conditions.

Refer to figure.
Auto-ignition in a piston engine, a complex phenomenon, occurs when the temperature and pressure conditions within the cylinder reach a point where the air-fuel mixture ignites independently, without needing an external ignition source such as a spark plug.

Several factors can contribute to auto-ignition, including:

  • high compression ratios,
  • hot spots within the cylinder, and
  • the presence of hot carbon deposits or other contaminants.

When these conditions are present, the air-fuel mixture can ignite prematurely, leading to engine knocking, increased cylinder pressures, and potentially damaging engine components.

Engine designers carefully control factors such as compression ratio, ignition timing, and fuel quality to prevent auto-ignition.

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