Hybrid rocket engine with acrylic and gaseous oxygen

I built a small rocket engine for demonstration purposes. The engine is built from a 2" diameter acrylic rod through which I drilled a 0.5" hole. The oxygen at 80 psi or less is passed through the hole and then is forced through a convergent-divergent nozzle at the tail end. The nozzle's throat is about 0.25" and expands to 0.625". I lit the engine by inserting a burning cotton swab (with wooden stick) while a small amount of oxygen was flowing. The acrylic catches fire very easily in a pure oxygen environment. The engine can be throttled and shut off completely, which is a major benefit to hybrid engine designs. Solid-fuel rockets cannot be throttled or shut off, which makes them difficult to control.

Lighting a BBQ with liquid oxygen

http://www.youtube.com/watch?v=1bjvj5FjUPE
After watching the famous liquid oxygen BBQ lighting video on the internet, I knew it was time for me to try it myself. In this video, I am pouring 1.5 liters of liquid oxygen on a bunch of smoldering charcoal briquettes. The oxygen rapidly turns to gas and accelerates the rate of combustion at the surface of the briquettes. Some of the charcoal fractures and shoots off tiny pieces that burn with a bright light.

I made the liquid oxygen by passing gaseous oxygen through a copper tube that was submerged in liquid nitrogen. The liquid nitrogen is colder than the boiling point of oxygen, so it causes the oxygen to condense and be ejected as a liquid from the other end of the tube. Liquid nitrogen can be bought at welding supply stores, however I made a batch myself with a cryocooler.
http://benkrasnow.blogspot.com/2008/08/diy-liquid-nitrogen-generator.html