Many many years ago when I was still in school we went through classes to learn how to weld. Both Heliarc and Oxy-acetylene welding. I recall that if you put to much acetylene into the torch you got a nice black plume of smoke. I'm guessing that an acetylene source in the plane (small tank) with an electronic shut off valve, nozzle and a pizio electric ignitor or glow plug might give you the black you are looking for. Lighting the acetylene in the rapid air flow might be a challenge so a form of flame holder would be required. That system certainly avoids the messy oil and dye issues.