If these are burn marks or the stain has impregnated the tile's surface, then they will be difficult to remove. It would be best to start with the least aggressive stain removal method before moving on to more potent chemicals. Start by trying dishwasher liquid in warm water and a scrubbing brush. You could try micro-abrasion, and these eraser pads would be excellent for that. Make sure to do a test section in an inconspicuous location to make sure they don't scratch your tile.