One of man’s most fundamental needs is for fire – for both cooking and heat. With modern furnaces and electric cook-stoves, we no longer appreciate how important these things are – until we are without. In the true ProvideYourOwn spirit, I am always looking at how to use things at hand to meet these needs.
In that vein, I have been curious how various fuels compare regarding volatility and ignition points. It is a useful thing to know if you want to understand, or possibly discover, new ways of making cooking or heating stoves or starting fires. We can expand our thinking by asking some of the following questions:
- What kinds of fuel can I use for a camping/backpacking stove?
- If I have to cook my food in a pinch, what sort of materials are available?
- How can I make my own waste motor oil burning stove?
- How can I use alternative fuels for my needs?
- What can I use for fire starting besides newspaper?
and make better use of the materials we have on hand, design new types of cooking and heating stoves that better suit our needs, and make better fire-starters.
To do any of these things, we need to know the flammable characteristics of the materials we have available. Before we look at numbers, we need to understand what each of the parameters pertaining to flammability mean. There are three:
This is the temperature at which a fuel will spontaneously ignite into flame. There are different ways to measure this temperature, and they all basically heat the substance in a vessel without actually introducing a flame. When the substance begins combustion on its own is the auto-ignition temperature.
This is the temperature at which a fuel will begin to turn into a gas. A fuel must be gaseous in order for combustion to occur. Since many of our fuel sources are liquid or solid, they must first be turned into gas. This temperature is therefore critical in determining how to ignite the fuel and to make a stove from it.
This temperature is similar to the auto-ignition point in that is a measure of what temperature a fuel will burst into flame. The difference is that the fire point is the temperature when a fuel will ignite when exposed to a flame or source of ignition.
Comparing Temperature Points
None of these temperature points by themselves tell us what we need to know. By examining the three together, we can piece together the whole story of how a fuel will react and perform. The auto-ignition and fire point temperatures tell us about how hot a fuel needs to be in order to burn. The fire point is always lower than the auto-ignition point and is general related to it. The flash point while not directly related to actual combustion temperatures, actually gives us the most insight into ignition and burning characteristics. Because the flash point is not a combustion related temperature, it can be radically different from the other two temperatures.
Of the three, flash point is probably the most critical temperature for the applications we most likely will use. Let’s look more closely at it.
Referring to the combustion table below, note that the flash point is much lower than either ignition point. It also various widely. One of the best ways to think of the flash is the ease with which a fuel will catch fire. There is even a classification of various flash points as regards to volatility:
Consulting our chart, we can see why gasoline is so dangerous. At virtually any normal temperature it is constantly vaporizing, ready to ignite. Alcohols, with a flash point of only 55 degrees F, will also ignite at most temperatures when exposed to flame. This characteristic makes it useful for camping stoves and requires no wick.
Hazzard Temp (degF)
Very low >200
When the flash point increases above any normal room temperature, we begin to need a wick in order to burn it. The wick is an ingenious device which provides a heat source just above the fuel which will then vaporize it for burning while drawing up the liquid fuel for a continual supply. It will even liquefy some solid fuels, such as wax, with which we are familiar.
Petroleum-based fuel oils such as diesel and kerosene are examples of fuels that burn easily with a wick. Even higher temperature petroleum-based fuels such as paraffin and petroleum jelly (Vaseline) will burn readily with a wick. When we climb over 500 degrees F, we begin to have problems with burning fuels such as wood, paper, and vegetable oils. Wicks don’t work and their substantial flash points require a hot fire to maintain the vaporization needed for combustion.
In some experiments I verified that, while vegetable oil does not burn with a wick, motor oil burns easily. This information can be used to devise a stove to burn what otherwise goes to waste or becomes pollution. What was formally a disposal problem, now becomes an asset.
Used vegetable oil can also be made to work by mixing with another fuel to decrease its flash point.I did some experiments in order to determine at what point vegetable oil can be made to burn with a wick and it only needed a slight addition of kerosene. Therefore, the flash point seems to need to be just slightly less than 600 degrees for a wick based combustion.
ConclusionKnowing the various properties of fuels gives us the information we need in order to devise novel stoves and make use of materials we have at hand. Fire starters can be made with petroleum jelly (candles too), and any type of alcohol will burn readily without wicks. Lighter petroleum fuels require wicks, while heavier oils also burn using wicks, they can be more difficult. Some of this knowledge is common, but some is not as well-known. Also, even the common knowledge was without understanding. Now you know why.
Please share in the comments any experiences you have with novel stoves or unique uses for fuels.
Temperature points for various fuels
Fuel Auto-Ignition Flash Point Fire Point -temps degC degF degF degF Fuel Oil No.1 210 410 100 - 162 Gun Cotton 221 430 Peat 227 440 Paraffin Wax 245 473 390 Diesel Fuel #2 246 475 125 Fuel Oil No.2 256 494 126-204 Fuel Oil No.4 262 505 142-240 Gasoline 280 536 -45 Petroleum Jelly 290 554 360 Kerosene 295 563 >100 Charcoal 349 660 Ethyl Alcohol 365 689 55 Motor Oil 365 690 420-485 435 Methyl Alcohol 385 725 52 Isopropyl Alcohol-70% 399 750 65 Semi anthracite coal 400 752 Petroleum 400 752 Butane 420 788 Canola Oil 424 795 600 379 Pine Wood - dry 427 800 572 Paper 450 842 451 Bituminous coal* 454 850 Propane 470 878 -156 Oak Wood - dry 482 900 572 Hydrogen 500 932 Lignite* 526 979 Semi bituminous coal* 527 980 Coal-tar oil 580 1076 Methane (Natural Gas) 580 1076 Anthracite* 600 1112 Carbon monoxide 609 1128 Coke 700 1292 * glow point
- Google Books – Industrial fire protection engineering