Plus, what are some sources that emit blue fire?
The real question is “why is some fire yellow/orange”? Flame from a candle or a campfire is actually orange because of carbon particles (“soot” = “lampblack”) that gets heated to incandescence and glows with blackbody radiation. You really do want this in a candle flame, because it increases the light, but it also does generate soot that goes into the air and settles on things. You do NOT want such yellow flame in your gas burner on a stove, or from a Bunsen or Meeker burner in a laboratory, and if you get it you should adjust your fuel/air mixture, since you’re not having optimal heating, and are generating dirty soot.
I’ve been told that, in zero gravity, the flame is small and spherical and without the yellow part because convection doesn’t force it all upwards (no gravity = no convection).
You actually get a more useful bright output from a lantern that has a thorium mantle, which is more efficient at converting the heat output to visible light, and puts more of it into the visible range than a yelow candle flame.
One good source on the physics and chemistry of candles is Faraday’s “Chemical History of a Candle” lectures, which he used to give at Christmas:
http://www.fordham.edu/halsall/mod/1860Faraday-candle.html
I don’t know exactly why a blue flame is blue, but it’s the color you actually get from combustion of many common sources. You can also add chemical salts to fires to add colors like green or brighter yellow, but I’m sure that’s not what you’re asking about.
as mentioned and cited the more complete combustion will produce a blue flame or blue region in a flame, this can be seen with gases such as methane, butane and propane.
copper being burned will produce a blue and/or green flame, it is used as a flame colorant.
With gas space heaters, blue flame means the air vent to the burner is adjusted correctly.
yellow flame means you will probably die from carbon monoxide poisoning. Unless you notice the symptoms and get to a hospital.
I have a gas space heater in my bedroom. I have a carbon monoxide detector plugged into an outlet. It’ll alarm before I get sick.
all combustion produces carbon monoxide or carbon dioxide. without supplying combustion air under pressure you are likely getting considerable carbon monoxide. both carbon dioxide and carbon monoxide are not life supporting gases.
whenever you have combustion in a house for heating you should have ventilation for the combustion gases. if you have a portable unvented combustion heater then it is recommended to provide ventilation to that room, like leaving a window open a crack.