Hi Abraham,
This depends on whether the company is purchased the diesel generator or this is under third party.
In most cases, diesel generator will be purchased by the company, so this will become their asset. When you create Asset for diesel generator, this will also include the alternator and engine.
SAP has given options, so you can maintain individual assets at Alternator & Engine. Since you can capture cost separately at Alternator & Engine.
Regards
Terence