Over the last couple of months, I've been testing direct spark ignition of my NOP engine. It works, but it can be flakey, and usually makes a rather disconcerting "pop" at ignition. I also tried RC glow plugs, but with standard currents and voltages, they don't provide enough power (i.e. heat to the coil). I think that with PWM you could control or set the power level to get the right wire temperature but that's a rabbit hole I didn't want to go down right now.
So, I finally decided to build a torch igniter. I've been testing various plumbing configurations, spark plugs, and orifice sizes and I think I've arrived at something that works fairly well. It accepts liquids for both oxidizer and fuel, which is nice. I'm not sure if other's torch igniters run on on gaseous oxidizer or not.
The next step is to weld it onto the motor.