DUBAI — Under the steaming midday sun, a vessel with a large, lime-green circle emblazoned on its side docks near the site of the United Nations climate conference (COP28) here.The colorful ship is the FFI Green Pioneer, the product of an 18-month engineering project by Australian metal, energy and green-tech company Fortescue to convert ship engines to run on a mix of green ammonia and diesel. Green ammonia is produced in a process that emits no carbon dioxide, typically powered by renewable energy.