Fireballs are surprisingly difficult to make. This was my first attempt:
The result of the detonation is below:
Ry Jones and I tested a number of different substances to help with the ignition of the gasoline. Basically we needed something would ignite during the detonation and continue burning long enough for the gasoline to mix with the air in the proper ratio such that the gasoline will ignite and propagate. First we tried a Titanium "powder". It is more like a collection of flakes of various sizes. It varied roughly from -20 to 200 mesh. We put about a tablespoon of it in on top of a pint (about 1 pound) of explosive and put a gallon of gasoline on top it.
For scale, note the 30 gallon barrel off to the right of the picture to the upper right of the 'M' in 'PM'.
Next we tried some steel- wool instead of the titanium powder. The video shows it was a waste of the gasoline and steel-wool.
Next we tried small pieces of aluminum foil instead of the aluminum powder.
The video using aluminum powder is not particularly interesting either.
Notice the explosive by itself sometime generates a small flash, but the addition of the aluminum foil it makes a fairly large flash.
Next we duplicate the success with the titanium powder.
Ry and I again did some experiments. We used two pounds of explosives and put the titanium powder in various locations with the gasoline behind the explosives. Click on the pictures below for the video (you may need to install this codec).
Wanting to get a high resolution picture of a fireball I took my daughter Kim and her cousin Lacey out for some tests. Kim ran the rifle, the video camera was on a tripod, and I had the still camera. Lacey provided the additional sound effects.
The picture above was taken in daylight with some cloud cover. The light from the fire was so bright that it made the ground appear dark as the camera adjusted for the intensity. This used four gallons of gasoline (one gallon behind, one on each side and one on top) and four pounds of explosives. The shooter, daughter Kim, was about 100 feet away and was accompanied by her cousin Lacey (HOLY SHIT!) in the "giggle fit" after the fireball goes up.
Just as the fireball disappears out of sight you will hear some "happy sounds" from some other shooters. These guys came over as we were mixing up the next batch and said, "You're Joe, aren't you?". <heavy sigh> My reputation precedes me.
Here is what Kim and Lacey wrote about their experience.
We tried using diesel instead of gasoline but it didn't ignite. It has a lower ignition point but it doesn't vaporize nearly as easily. Liquids don't burn, vapors do. The second and third shots are using 'farm gas'. No road tax is paid on it so I can get it cheaper. I was concerned because we don't believe it has any ethanol in it but now we know it will work (at least some of the time) when the weather is warm. The temperature for today's test was about 60 F, plus the gas was in plastic containers sitting in the sun for many hours.
Click on the image to see the video:
Ry and I had an audience of six people not including the neighbors across the road who later told me (with huge grins on their faces) they saw it too. All seem pleased with the results.
May 4, 2003
See also the video and other pictures from this event.
We now have a recipe that almost always works. Occasionally we have unexplained failures to ignite. We are beginning to suspect that in cold weather we have better luck when we use gasoline that contains ethanol. In addition to the cold weather characteristics of gasoline with ethanol, it will ignite when the fuel concentration in the air is between 3.3 and 19%. Straight gasoline has a much narrower range of 1.2% to 7.6%. There is also data to indicate that we just need to use more titanium powder.
Email: Joe Huffman