There are a few topics here about using a pulsejet as the flameholder for ramjet, but it occurs to me that you don't need the PJ to be the flame
holder, you can use the PJ as the
flame. The air in a ramjet doesn't need to
burn, it just needs to be made
hot by the time it goes out the back. You can do it with a heating element and the thing PJs do better than anything is get super hot. Imagine a valved PJ with an aerodynamic shell around it running through the middle of a ramjet body. This simplifies things a lot since you don't have to worry about most of the fiddly bits involved in ramjets.
IIRC the X-jet was supposed to have a full-length shroud. Maybe this is why? You could even add full-length fins to the PJ to maximize the amount of heat dumped into the ram air.
Now I understand there are issues with PJ intakes at such high speed but this issue seems a bit more solvable than getting them to work together in other ways.
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