The purpose of this test is to build a pre-heater which causes cleaner and deterministic ignition of the Hybrid rocket motor.
Small thin center tube which opens first
The center orifice, which normally doubles as the fill tube, is replaced with a small, thin walled, plugged Nylon tube. This center orifice hopefully opens first and combustion gets started before Nitrous begins flowing from the larger outer orifices. The radial flow created by the segmented pre-heater should help.
The segmented pre-heater, with gaps between the segments, will light quickly compared to a monolithic pre-heater.
The pre-heater contains 4 tapered holes which align with the outer injector orifices. The 4 holes permit free flow of Nitrous and prevent unexpected pressure gradients in front of the injector during early stages of ignition.
The results look good. The motor came up to pressure quickly and cleanly.
The motor burned hotter than previous motors. The brass fittings actually melted and the O-rings were slightly "cooked."
A loud pop was heard at the end of the burn (0:36 sec in video). Im not sure what caused the pop. If it happens again with more energy I will investigate.
A small amount of soot blew-back into the injector. The amount of soot is insignificant. Unless the back side of the injector is completely black Im inclined not to worry.