I have played with quite a few ignition circuits and from experience not clamping down gate voltage is the surest way to destroy a mosfet or igbt. Gate to source with a zener very close to drive voltage prevents negative gate voltage as well as positive spike.

Is this in addition or as a replacement of the usual pull-down resistor on the gate? In this case it would be using an N-channel MOSFET with the source connected to ground via the induction coil.

 

I wish the TS good luck with the project. But from the big companies doing the research on this detonation jet engine after light off they don't use a spark, but a type of tube to delay from the last ignition to the next one.

Thanks! We're still running at pretty low frequencies (maximum of around 2Hz), so using a longer tube to sustain detonation isn't practical quite yet... We've so far have had good luck starting the cycle with a relatively low intensity spark (automotive magnitude), which causes deflagration which then transitions to detonation with the aid of a Shchelkin spiral. We're aiming to eventually move to experimenting with continuously-rotating-detonation-engines (CRDEs) but they're a different kettle of fish to PDREs so we're trying to learn as much as possible here first. It all takes time and is a challenge to balance with my undergrad work with only two or three people working on it, but thanks All for the advice!

 

which causes deflagration which then transitions to detonation with the aid of a Shchelkin spiral.

That is what I meant by a special tube, couldn't remember the name. Have you thought of having a separate small ignition chamber to cause the detonation? Some diesel engines used that back in the day, a very small ignition chamber in the head to get the main cylinder running.

Using a regular spark plug, how do you keep the insulator nose from shattering? Bad detonation/pinging in a car engine can cause that to happen, this was before electronic control of engines.

 

That is what I meant by a special tube, couldn't remember the name. Have you thought of having a separate small ignition chamber to cause the detonation? Some diesel engines used that back in the day, a very small ignition chamber in the head to get the main cylinder running.

Using a regular spark plug, how do you keep the insulator nose from shattering? Bad detonation/pinging in a car engine can cause that to happen, this was before electronic control of engines.

I can't think of the name of the tube you mean, but I don't think it's a Shchelkin spiral, they tend to be in essence a coarse solid spiral like a compression spring. We have looked at running a pre-detonator tube, i.e. a small diameter tube which takes less fuel/ox volume to fill and contains the deflagration to detonation transition into the main engine but still have plenty of research to be doing with the current configuration.
We haven't had a problem with the spark plug insulation yet, I suppose because it only sees deflagration, the detonation never occours directly at the spark plug. Also the chamber pressures are faily close to atmospheric, the beauty of a PDRE is the combustion takes place at the flame/shock front so combustion is virtually isochoric and much more efficient than deflagration-based engines., and ridiculous pressures aren't meanigfully seen by the combustion vessel.

 

I can't think of the name of the tube you mean, but I don't think it's a Shchelkin spiral, they tend to be in essence a coarse solid spiral like a compression spring.

I guess I was just assuming the the Shchelkin spiral was tubular, and transferred the energy though it.