RogueRose
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Auto-ignition point of oils/fuels - what is needed to maintain combustion?
I was looking through some fuel stats that listed flashpoint and auto-ignition temps but I didn't see anything for oils such as vegetable oil.
After dealing with a stove-top fire of animal fats some time ago, I was kind of confused as to how the oil ignited as the oil had been in a boiling
pot of water which overflowed onto the heating element wher it caught fire. I don't know the temperature of the burner but I'm not sure how it could
have ignited oil that was ~ 212 (maybe slightly more). It was difficult to extinguish, used a powder fire extinguisher.
What I am curious about is how hot oil needs to be to have a self sustaining flame when pumped out of some restricted orifice (like needle valve or
some such thing). I'm curious how important the temp of the oil and surrounding air (forced air) is to start combustion or to maintain it.
Diesel fuel, as an example, has an auto-ignition temp of 410F, so am I correct in thinking that heating the fuel in something such as a SS or copper
tube to 410+, pumped through a restricted orifice spraying it into the air, it should ignite automatically?
Now if the 410 wasn't reached but it was heated moderately (say 200) and the same setup as previous paragraph, if a flame source is added at the
orifice to start combustion, should it continue until fuel is cut off?
If temp above the auto-ignition point are reached in a closed vessel, what happens? I've tried to find boiling points and see how they differ from
auto-ignition point and how they effect a fuel/oil that is to be burnt.
I'm trying to determine how dangerous some of the videos and "how-to's" I've seen on oil heaters that preheat the oils/fuel prior to burning.
Basically, if BP is reached under pressure, will auto-ignition happen if vented?
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hissingnoise
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Mood: Pulverulescent!
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| Quote: | | After dealing with a stove-top fire of animal fats some time ago, I was kind of confused as to how the oil ignited as the oil had been in a boiling
pot of water which overflowed onto the heating element wher it caught fire. |
The overflow contained some oil which ignited on contact with the element ─ this then, ignited the remaining oil, is my guess!
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aga
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'Burning' in this context is basically reacting the oil with oxygen.
Ignore 'flash points'.
Autoignition temperature is the temperature at which the energy barrier for this reaction is overcome (=activation energy).
The Oil + Oxygen reaction is Exothermic : it will release heat.
If Enough mass of oil is burning, then it will release enough heat to cause the next 'batch' of oil to also react, sustaining the burn.
Not enough, and the chain is broken (fire goes out).
You must have made a wood fire at some time that started to catch fire then went out : the energy released form the mass of burning material was not
enough to keep the reaction going.
A nozzle will cause Cooling in the oil as it is sprayed out. This will also heat up the nozzle, therefore the oil, so may cancel out.
Nozzle design is a specialised area of engineering.
It is a reaction : Oil + Oxygen. If you heat the oil above it's autoignition point, yet lower than it's boiling point with No oxygen present, there
can be no oxygen reaction, i.e. no burning.
Heat it past it's boiling point and you suddenly have a pressure problem with an Oil that wants Out and also to Burn real bad ...
Animal fat is not a single substance.
Likely there was a component of the fat with a low boiling temperature and the fumes from that caught fire, heating the remaining fat, releasing the
next lowest boiling material etc in a chain of reactions based on the rising heat.
Edit:
This kind of question should be in Beginnings RogueRose.
Chemistry in General is for discussion of actual referenced chemical procedures that others can copy/test.
[Edited on 25-12-2015 by aga]
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Bert
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Thread Moved
25-12-2015 at 21:16 |
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