This is a great project. The hybrid motor uses a solid fuel and a gaseous or liquid oxidizer. Here the fuel is a clear acrylic tube that lets you see inside the chamber. Note how bright it is: the flame that comes out of a motor is often bright, but inside there must be far more radiation.
The spike nozzle, aerospike, uses atmospheric pressure and can help maintain high efficiency. Bell nozzles can only be built for a certain fairly small pressure range (altitude) and then they lose efficiency outside of it.