Comparing color of light sources (in this case engines) is more accurate without interference of ambient light from other sources (in this case daylight) . I agree about camera settings .
I know what you want to say : AL-31 is blue , WS-10 and RD-93(33) are orange
But , it is not that simple . RD-93 has less power then AL-31 (and therefore lower temperature of exhaust ) .Yet , you can see at clip below that at full A/B (0:19-0:20) color of exhaust becomes almost white . As for WS-10 , it should have more power then AL-31 . Therefore I want to see what it could do at full throttle and I suspect they didn't go for that in your clip (J-10B had only light load so it was not necessary ) .
[video=youtube;ece0Xy6gvpU]http://www.youtube.com/watch?v=ece0Xy6gvpU[/video]
Well , color of EM radiation is primarily function of temperature . Of course , there are numerous other factors like scattering of light , interference etc ... But , higher the temperature of radiating body (in this case engine exhaust ) radiated EM waves move to shorter wavelengths (i.e. towards blue and violet) . Different chemical composition means that some substances simply burn at different temperatures .
Not exactly. You first have to look at the emission bands of the matter being discussed, which is related to that matter's composition. As energy input increases that matter emits higher energy radiation, but only at wavelengths specific to that matter's composition (these bands are determined by the energy states of the electrons absorbing and re-emitting EMR, and their orbitals). So yes, as temperature goes up you will get emissions at shorter wavelengths, but only at bands specific to the composition of the matter. The overall colour we see is a combination of those specific emissions. Depending on the composition of the matter, you could have a flame with emissions at shorter wavelengths but be at lower temperatures than a flame at longer wavelengths. For example, forest fires are orange, and ethanol burns blue, but forest fires are going to be far FAR hotter than ethanol flames.
The forest fire example brings up another point, which is that heat is ultimately determined by the amount of net energy being released by the net chemical reaction. Depending on the intermediate reactants within that reaction, you could have a flame that's very hot because the net amount of heat being released is high, but emit longer wavelengths, because the energy released by the intermediate reactants aren't enough to push their emissions to higher bands. In that sense, you can't simply use two flames of different colours and say for sure that the one emitting shorter wavelengths is hotter than the one emitting longer wavelengths. You're going to get more heat energy from something that emits more waves of infrared than fewer waves of a shorter wavelength.
This brings in ANOTHER factor, which is that visible light is a very narrow band of the EM spectrum, and far more radiation (and energy) is released at different bands. Based on the emission bands of a particular substance, it's entirely possible for it to burn at a longer wavelength in visible light but have an emission at the next energy state that is at a wavelength shorter than visible light, so that even when super hot what we see is a colour at a lower wavelength simply because we can't see the higher energy emissions!
Note, you don't need to be using fuel with different compositions to get reaction mass with different colours. This is a point I've been trying to hammer in for a while now, but the specific discussions of emissions gives another angle to explain it. If you stick the same fuel into two different engines, you'll probably end up getting two (sometimes only slightly) different colours because the two engines will just operate differently. Depending on how each operate they may create different proportions of different chemical products, as determined by things such as the fuel-air mix at different stages of compression, etc etc, which then means different composition of emissions, which then affect the colour.
The smart cookies reading the previous paragraph will realize that there's yet another potential factor that could determine the composition of the afterburner flame and therefore the composition of its emissions, which is the composition of the air reacting with the fuel. This is another added factor that must be accounted for, though usually a small one.
With regards to the attached video of the Mig-29, you'll notice that there is still an orange glow despite the white afterburner flame. The whiteness in the film may not be the actual colour of the flame, but the camera sensor/film being saturated by the amount of light it is capturing. This is particularly likely if the film is set at a high ISO, which increases sensitivity of the film/sensor to light. Personally, that's what I think is going on here, because I'm looking at pictures of the Mig-29 on afterburner and it's always a consistent orange colour.
Finally to put the nail in the coffin on the correlation between afterburner colour, temperature, and thrust, neither the F-35 nor F-22 have blue afterburner flames. Both are very clearly orange. In the F-22's case, the bypass ratio is also very low. Now it's possible that the F-22's afterburners are burning at a lower temperatures than an AL-31's while still generating a higher amount of thrust (at a higher instantaneous velocity), but the main point is that making a conjecture about the relationship between colour, temperature, and thrust, is an exercise in futility.
I hope my roundabout way of trying to explain why this discussion is silly was at least entertaining, if not educational.
EDIT: If you browse around for pictures of the F119's afterburners, you'll note the test pictures seem to indicate a blue flame, while pictures of the F-22 indicate an orange-purple flame. I'm not exactly sure exactly why this is, but my guesses are that the difference is either a result of the lighting (closed environment/night time) or a result of air density.
