The steamers can run on anything burnable with enough caloric content, but they typically use coal because it has the most heat capacity. A hit and miss engine is exactly what the name says. If it's not under load, the engine will fire once and the flywheel will keep the system moving until a certain RPM is reached, at which time the engine fires again. If the engine is under load, it will typically fire just like a modern engine. It was a design kind of made to be fuel conserving, but it was also an evolutionary step to more modern, efficient engines.