What function does an automatic engaging mechanism in a starter system serve?

The automatic engaging mechanism in a starter system is crucial for initiating the engine's start-up sequence. When the pilot switches on the starter, the mechanism engages the starter motor with the engine. This engagement is essential because it allows the starter motor to spin the engine's flywheel or starter ring gear, which ultimately rotates the engine to initiate the combustion process.

Once the engine reaches a certain speed or starts running, the mechanism will then automatically disengage the starter motor to prevent damage from running the starter motor when it is no longer needed. This automatic functionality not only ensures a smoother start-up process but also protects the starter motor from excessive wear and potential failure due to continuous operation after the engine has started.

In contrast, the other options relate to different components and functions within the engine system. Regulations of voltage and control of fuel injection have separate roles that do not involve the engagement of the starter motor during the critical moment of starting the engine.