Can the Diesel engine afford to have a large compression ratio? Why?

Yes

Explanation:

Diesel engine:

All diesel engine woks on diesel cycle. diesel cycle consists of four process in which one is constant pressure heat addition, one is constant volume heat rejection and other two are adiabatic processes.

Actually in diesel engine first air compresses to high pressure and after that fuel inject in this compress air to burn the air fuel mixture. Generally the compression ratio of air is around 10 to 15. To produces high power it become necessary to put high compression ratio. That is why size of diesel engine is more.