Post #1889530

Spectrometry seems closest to what you're asking for (studying composition through light frequencies), it can be done to a fire but you don't usually resort to fire for testing substances unless it was already going to burn. For stuff like fuels you wouldn't really do that except for calibration purposes (calculating what the mixture and temperature is and how to adjust it) and even that is so rare I haven't heard of it in use (but some searches show dyes are in use for this although not through burning).