[teoman]

400 deg C is 752 deg F. What they are using.

I would heat some fuel in an injector and see for yourself how it performs. If it acts like a flamethrower you can maybe fill a clear container with exhaust or argon or nitrogen and observe what the transonic guys are doing. Then you can try it in the air. Your injectors will not work for long but i guesstimate it will be long enough for you to see. Then you can have a look at cooling the same vapor. Maybe attaching the injector to a copper pipe (that is heat controlled or just running through boiling water) to see if you can get vapor out or if you get condensation of your sludge once the fuel cools down.