I don't have much experience with different types of gas, but this looks like a natural gas burner to me. And correct me if I'm wrong, but running propane through a natural gas burner will cause it to burn less completely
The pictures aren't from the right perspective for me to tell if you have a natural gas or a propane burner. The air orifices shown in the pictures are the same size for natural gas and propane. Take a picture down the burner tip so I can see the size of the gas orifice relative to the burner tip.
Running propane through an NG burner will be tremendously inefficient and produce prodigious amounts of soot, carbon monoxide, and possibly unburned propane. Let's say you use 40 cfh of propane (100,000 BTU/hr per Morticai), the NG burner will only draw in enough air to burn 40 cfh of natural gas (~39,000 BTU/hr).