A few gratuitous words on the matter of electrical generation.

Both of the devices ("generators" & "alternators") found in automobiles that provide electrical energy are energy conversion devices; mechanical energy is converted to electrical by the device. That process of conversion we commonly refer to as "generating".

Within the current carrying windings of both devices the current alternates in polarity from positive to negative. Hence, internally, both are alternating current (AC) generators, aka "alternators".

To produce an output of direct current (DC) that is usable in the automobile, the internal AC must be rectified to DC. It is the method of rectification that differentiates a "generator" from an "alternator". [Internally both are generators, and both are alternators.]

In the device which we call a "generator" the magnetic fields are stationary and the current carrying windings rotate. The AC in the rotating windings is rectified to DC by the interrupted contacts of the brushes on the segments of the commutator. A segment of positive sign is always presented at one brush, and a segment of negative sign at the other brush. In 180 degrees of rotation, a segment changes sign from + to -, and then back to + in the next 180.

In the device referred to as an "alternator", the magnetic field rotates, and the current carrying windings are stationary. The AC generated in the windings is rectified to DC by diodes which allow current of + sign to pass, but block current of - sign.