Which of the following devices is not used to start a gas turbine?

The correct response indicates that small gas engines are not typically used to start a gas turbine. Gas turbines are usually started using methods that create the necessary initial conditions for combustion and turbine rotation.

Pneumatic starters utilize compressed air to rotate the turbine's shaft to a speed sufficient for ignition, making them a common starting mechanism in gas turbines. Electric motors can also serve this purpose, providing the necessary torque to initiate turbine operation. Steam turbine expanders can utilize steam to drive the turbine up to operational speeds as well, although this is less common than the other methods.

In contrast, small gas engines are primarily designed to operate independently and do not provide a practical solution for the starting process of gas turbines, which require specific starting methods to achieve the required RPM and temperature for efficient operation. This delineation helps clarify why small gas engines aren't associated with gas turbine startups.