Charcoal from a burned out fire works well in the pistons as well. A little harder to get the ember. If you want to send the top launching like a rocket put a few drops of gas or lighter fluid on yer cloth
Kind of OT but have you ever wondered how primitive people invented what is really very advanced tool like the fire piston? It is a huge advancement over flint and iron or fire bows. LOL and probably easier to light on some days than my zippos. The entire concept of sealed compression = combustion just does not seem like something a very primitive culture would stumble across.
It did originate in South East Asia sometime before 1500BC. An amazing tech advancement given the overall technology of the time.