Fox: Hey Guys! Today we’ll be looking into how, when certain mixtures are burnt together, produce so little heat that you can’t even boil water with much, much less burn own skin!
The Glitch: Basically, what fox is trying to imply is that, Cold flames!
Noob-Kun: What? Cold flames? The legendary flames of hell with extreme freezing and burning abilities? How can that be possible in the mortal realm? What is humanity coming to? AAAAAHH!
Fox: No, Noob-Kun, not in the least. What we actually call cold flames, are just a form of fire that provide less than 400*C of heat. They don’t have any form of freezing abilities, or anything of that sort. But they are still useful in conducting a lot of experiments. A lot of people don’t know about these flames, therefore, as researchers, it’s our job to do this.
The Glitch: Like how it happens in all JRPGs, Cold flame is just such an awesome weapon to have. Sigh
Fox: Okay, Okay, guys! Lets stop wasting time, and get serious.
We’ll first start with defining what combustion is:
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds (especially hydrocarbons) in the gas, liquid or solid phase. Wiki
Essentially, combustion is when a material, rapidly oxidizes (combines with oxygen) to give out heat and/or light. While, it must give out heat, it may or may not give out light (of the visible range).
This is clear in the case of cold flames, as most of the materials which produce these flames, arn’t visible at all, or would appear in a translucent blue shade. These materials, are quite volatile (reactive), and so when heated easily combine back into thier orignal state.
Glitch: You can consider them as hermit crabs. They’d just walk small distances before hiding back in thier shells. These reactions are behave like them, as they don’t easily combine with oxygen. Thus, making the reaction slow, and long process. Essentially, they can burn for long, long time.
Fox: While, it’s true that we know these flames for their significantly low temperatures, we still don’t have the data on how low a temperature can the start burning. One of the reasons for this is, that these flames produce radiations of the UV range (which is not visible to us) when the actually start burning.
Noob-Kun: So, how do we know what is the coldest cold flame known to us till now?
Fox: To find the coldest cold flame, we use CFT (Cold Flame Temperature), which is the temperature of the flame when it is barely visible to the naake eye. However, this method can only tell us the the coldest cold flame, not the temperaature at which it burns or anything of that sort. It’s also not a very accurate method to find the coldest flame, as it uses naked eyes and our judgment as the instrument.
According to wiki, one of the lowest CFTs (156 °C) was reported for a C2H5OC2H5 + O2 + N2 mixture at 300 mmHg (40 kPa).
Glitch: It depends a lot on the fuel. The coolest flames are usually the result of a water-alcohol mixture, since the water evaporates with the alcohol to cool the flame. For example, a 50:50 mixture of isopropyl alcohol and water will burn on a rag without charring the rag. Other partially-oxidized hydrocarbons are also able to burn in this manner, like acetone or MEK for example.
Fox: Yes, mixtures incidentally have lower CFT that that of pure substances, especially so for water spirit mixtures, however, their principle of working is different from that of cold flames. Spirits are highly volatile materials, so they easily become vapours, before they even start burning. Thus, if you put these mixtures in water, they’ll still burn on it’s surface.
Spirit, in themselves, cannot be considered as cold flames, as, while they can easily ignite (an essential propert of CF), they produce much more heat energy than cold flames, and generally tend to have temperatures higher than 400*C.
But, in water-spirit mixtures, water evaporates by taking in the excess heat energy, thus lowering the heat produced by spirits into the range of cold flames.
Noob-kun: What are these cold flames used for?
Glitch: Cold flames have not much application known till now, except that the result in an undesirable phenomenon called engine knocking(see this link).
By the laws of the world, there are [currently] no flames that are actually “cold”, and could freeze something. Thus, we need more research to make the famous superpower actually possible.
Fox: Possibly certain endothermic reactions could cause so. Who knows……