Can anyone, please, explain me what is the difference between Stage V vs Tier4F diesel engine? I searched OEM sites but no luck.
Why some engines are equipped with DOC while some are equipped with DOC+DPF?
DieselNet is a good source of info for these type questions.
Aftertreatment requirements vary based on where the engine is being applied, its rating, certification level and application.
A DOC (Diesel Oxidation Catalyst) is usually required to reduce CO emissions, a DPF (Diesel Particulate Filter) is used to reduce particulate emissions, in some cases only one is required, in others both.
Local, state and regional regulations may also apply.