A reel doing the rounds on Instagram poses a question that comes up in every aviation comment section sooner or later: why do Russian jets burn blue, not orange like American ones?

Look at the photograph above. That is an American F/A-18F Super Hornet in full afterburner on a carrier deck at night, and its exhaust is unmistakably blue. Further down there is a Su-27 y un MiG-29, both Soviet designs, both in afterburner, both glowing orange.

The premise is wrong. Nationality is not a combustion variable. But the question is a good one, because the real answer involves two different kinds of light, a camera setting, and a genuine difference between individual engines that the internet has flattened into a flag.

Two Different Kinds of Light

A flame produces light in two quite separate ways, and almost the whole question comes down to which one dominates.

The blue comes from short-lived molecular fragments — chiefly the radicals CH and C2 — created in the middle of the combustion reaction. As they drop out of an excited state they emit light, most of it below roughly 565 nanometres, in the blue and green. It is light produced by the chemistry itself.

The orange is something else entirely. When fuel burns with too little oxygen locally, it forms soot: microscopic carbon particles. Those particles are heated by the flame and glow, exactly as the element of an electric heater glows. That is thermal radiation, and at flame temperatures it sits firmly in the yellow and orange.

So the colour tells you mostly about soot. A flame with little or no soot shows its blue. A flame with plenty of soot is dominated by the far brighter orange glow, which swamps the blue even when the blue is still being produced underneath.

Colour Is Not a Thermometer

Which disposes of the second half of the myth, the one that usually rides along with the first: that blue afterburners are hotter, and that Russian engines are therefore somehow more powerful.

The blue is not a temperature effect at all. It is emission from specific molecules, and it appears whenever combustion is clean enough for it not to be drowned out. Hot soot, on the other hand, glows orange at precisely the temperatures an afterburner runs at. An orange plume and a blue plume can be at comparable temperatures; they simply have different amounts of soot in them. As one recent explainer put it, flame colour alone cannot provide a meaningful comparison of fighter-engine temperature or performance.

So Why Do Russian Jets Look Blue Online?

Because of which pictures get taken and shared. The dramatic blue-plume photographs that circulate are overwhelmingly shot at dusk, at night, or into a dark test cell. The blue chemiluminescence is faint; in daylight it is simply not bright enough to register against the sky, while a sooty orange core is. Pilots and ground crew who have looked at the same engines from both sides of the day make the point repeatedly: the blue shows at night, the orange dominates by day.

Then comes the camera. Digital sensors and phone processing handle the extremes of an afterburner plume badly, and white balance, exposure and post-processing can push a mixed flame towards blue or towards orange. A photograph is a poor instrument for flame colour, and a compressed, filtered reel is worse.

Finally, there is a real effect hiding inside the myth. Individual engines, and individual versions of the same engine, do burn with different amounts of soot. The Tupolev Tu-22M3 bomber, whose Kuznetsov NK-25 engines produce a strikingly deep blue plume, is the favourite example. The Aviationist attributed that to the fuel being burnt almost completely before it leaves the nozzle, which is a claim about that engine design, not about Russian engineering in general. Plenty of Soviet-designed fighters, as the photographs on this page show, burn orange.

The American Engine That Burns Blue

The cleanest demonstration that nationality has nothing to do with it comes from an American engine on a British base. In 2020 The Aviationist published footage from the Propulsion Test Cell at RAF Lakenheath, where USAF maintainers run the Pratt & Whitney F100 engines of the F-15E Strike Eagle on a test stand. In full afterburner the plume is vividly blue, stacked with shock diamonds.

The same engine family also turns up as an anecdote in the pilot forums: some who flew or maintained different versions of the F100 describe older variants as burning yellower and later ones bluer. That is plausible, since combustor and afterburner design changed between versions, but it is anecdotal, and it again points to the engine, not the flag.

What the Shock Diamonds Are

The bright, evenly spaced rings in many of these plumes are shock diamonds, sometimes called Mach diamonds. At low altitude the exhaust leaves the nozzle at a pressure that does not match the surrounding air, and it adjusts through a repeating pattern of shock and expansion waves. At each strong shock, the Mach disk, the gas is compressed and heated again, and any unburnt fuel still in the stream can ignite. That is why the diamonds glow, and why they are most vivid close to the ground, where the pressure mismatch is greatest.

Where You Actually See the Blue

If you want to see a blue afterburner with your own eyes, the recipe is simple and has nothing to do with where the jet was built: find a clean-burning engine, wait for darkness, and stand where you can see the plume against a dark background. Carrier night operations are the classic example, and the blue cones of a Super Hornet going to full power on the catapult are exactly what the reel says American jets do not produce.

In daylight the same engine will mostly show a paler, yellow-orange core, sometimes with faint blue edges, because that is all the eye and the camera can pick out against a bright sky.

What the Colour Does and Does Not Tell You

Blue tells you the flame is clean at that point: little soot, combustion close to complete. Orange tells you there is soot being heated in the flame. Neither tells you the engine is hotter, more powerful or more advanced, and neither tells you the nationality of the aircraft. As a Greek Reporter explainer on the same question concluded, there is no consistent national pattern.

The honest one-line answer to the reel is therefore: some jets burn blue and some burn orange because of soot, light and cameras, and you will find both on both sides of the old Iron Curtain.

Sources: NASA Glenn Research Center (flame colour and chemiluminescence); Wikipedia, “Flame” (CH and C2 radical emission, soot incandescence); The Aviationist (F100 engine test at RAF Lakenheath, 2020; Tu-22M3 NK-25 afterburner, 2019); PPRuNe pilot and engineer discussion; Greek Reporter; US Navy; Wikimedia Commons.