[Re-edit. My original wording didn’t make sense.]
While I too believe it’s an alternator, if it were a generator, I didn’t think they solved the problem for how to get a generator to produce sufficient output current at low rpm’s.
I think a real DC generator would have to be considerably larger in physical size to an alternator in order to be able to produce the large amount of current used in todays cars. I think one of the reasons alternators are used today is because they are more efficient in producing the power.