Is diesel example of fuel?
Yes. Diesel is a fuel oil, similar to kerosene and jet fuel both.
If the van has a diesel engine, then you MUST use diesel fuel. Unleaded gasoline will destroy a diesel engine. Diesel fuel is also used as a lubricant in a diesel engine. The use of any other fuel except diesel will result in serious damage. If you have put unleaded in your diesel, do not start or drive this vehicle until you drain the tank and change all the fuel filters.