there’s more than enough info on his site to try and recreate some of his experiments, but perhaps you should start here instead: How to Design, Build and Test Small Liquid-Fuel Rocket Engines.

We are fascinated by the hybrid rocket engine which [Ben Krasnow] built and ... That is not the case with this design. The acrylic is actually burning, but if the flow of oxygen is cut off it ...

In the ’60s, rocket engine design and manufacturing company Rocketdyne had tried to make the J-2T Aerospike, a toroidal aerospike concept intended as an improvement over the Rocketdyne J-2 ...