Problem with modeling of gas combustion in room
 

Hi everyone,
I am begginer in DM. I am trying to create combustion of gas in room. But i have problem with creating the domain. Because I need to create room with burnner inside located on the center of the room (box) with fuel (gas). But i dont know how to create the walls were solid, the space inside was created as a flow and the burner inside was solid and fuel was flow too.

Thank you for the aswer

Kara