Internal combustion engine smoke appears blue due to specific molecular phenomena
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The evidence indicates that the blue appearance of internal combustion engine smoke is attributable to physical scattering phenomena, such as Rayleigh or Tyndall scattering by particulate matter that favors short-wavelength blue light.
Tyndall effect | Definition & Facts | Britannica
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# Tyndall effect
physics
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Also known as: Tyndall phenomenon, Tyndall scattering
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Tyndall effect, scattering of a beam of light by a medium containing small suspended particles—e.g., smoke or dust in a room, which makes visible a light beam entering a window. As in Rayleigh scattering, short-wavelength blue light is scattered more strongly than long-wavelength red light. However, Rayleigh scattering occurs from particles much smaller than the wavelength of light, while the Tyndall effect occurs from particles roughly the same size as the wavelength of light. The effect is named for the 19th-century British physicist John Tyndall, who first studied it extensively.
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# Why does internal combustion engine smoke appear blue? Could there be "blue molecules" in it?
Tags: everyday-chemistry, combustion
- Score: 10
- Views: 1333
- Answers: 3
- Answered: yes
- Asked by: uhoh (6122 rep)
- Asked: 2017-03-28
- Edited: 2019-03-16
- Site: chemistry
## Question
Four-stroke and two-stroke gasoline engines as well as diesel engines can all emit dense clouds of blue-tinged smoke under various transient loads or incorrectly tuned conditions.
Raleigh scattering - in this case probably from particulates of a limited range in size - strongly favors short wavelengths, so there is a possible physical explanation.
But I would like to know if there are any chemistry effects that could lead to or contribute to the slightly blue color sometimes seen in engine smoke under these conditions.
Could there be large "blue molecules" in the smoke? I don't think so; usually gases are transparent, though there are a few notable exceptions like molecular iodine and chlorine, but I'm not sure.
above: Iodine gas, from here
above: Chlorine gas, from here
below: snapshot sitting on a bicycle, looking at adjacent scooter while holding breath and waiting for the light to chang
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