Rockets use different types of fuel. Diwali rockets use solid fuels like gunpowder variants, zinc-sulphur combinations, nitroglycerine, sugars, etc. Liquid fuel rockets are also common. Cryogenic designs use gases, liquefied and stored at very low temperatures. For example, a liquid oxygen-liquid hydrogen mix may be used. Hydrogen liquefies at minus 253 degrees Celsius and oxygen at below minus 183C. Semi-cryogenic engines use combinations of low-temperature liquefied gas, and kerosene at normal temperatures.
Cryogenics and semi-cryogenics offer desirable qualities by combining low weight and high impulse. But design is extremely demanding. The fuels must be stored separately at low temperatures and, once they ignite, 3,500C temperatures are generated in the combustion chamber. Catastrophic accidents can occur.