Consider the flame inside a rocket engine's pre-burner, where the pressure is truly immense (400~600 bar) but the temperature is quite mild (<1500 K), and the flame is of the premixed type. Under these conditions, the mean free path of the reacting gas molecules is very small. If one was to be able to somehow take a look at this flame, what would he see? Would the spectral characteristic of specific lines of chemiluminescence be irrelevant and the flame would look almost like a blackbody of similar temperature? The molecules would collide and redistribute the energy so often that an exited molecule seldom has the chance to radiate this energy away.