How to Use Math to Build the Perfect Bonfire

To make a decent campfire, you should stack your wood structure just as high as it is broad, like a pyramid. This strategy was initially discussed in a 2015 publication published in Scientific Reports. 
If you don’t have a fire pit, start your fire on dirt or near a fire blanket.

While fire may be one of the oldest human technologies, creating a bonfire—and keeping it safe—isn’t always a simple undertaking. After gathering dry wood or twigs from around your campground, you must decide how to arrange them for the best burn. Is placing them in a stack, like a log home, the appropriate call? Or maybe just throw them all in and see what happens?

In principle, there are infinite ways you might organise your fuel source, but according to Adrian Bejan, a professor of mechanical engineering at Duke University, there’s only one sure-fire way: your fuel should be piled equally as high as it is broad, like a pyramid. It’s no accident, Bejan believes, that a pyre and a pyramid are so linguistically similar

Even though this ideal answer has been lying in plain sight for millennia, Bejan first wrote down the mathematical formula for it in a 2015 study in the journal Scientific Reports. “I was able to sort it out as a homework issue for my students,” Bejan explains. “It takes around two hours one evening.”

Why Fire Is Like Swiss Cheese

The solution, he believes, comes with knowing what type of science determines how flames burn. This is an incredibly intricate subject, yet ultimately boils down to two key contenders: thermodynamics and fluid dynamics.

“Thermodynamics is the study of power, [in this instance] power from fire,” Bejan tells Popular Mechanics. “Which then is utilised to move things [like air].” This air movement supports the combustion process, and subsequently, the produced heat is convected away by the airflow itself.

You may think of a fire sort of like a slice of Swiss cheese. In between separate bits of fuel (whether you’re using coal, wood, or another source), there are plenty of holes or spaces that air may pass through. If your fire is packed too thickly, air can’t flow through to cause combustion; if your fuel is packed too loosely, then the air can’t obtain enough power to move swiftly. The technical word for this sort of hole-filled form is “porous medium,” Bejan adds.

However, Bejan believes that conical-shaped flames aren’t the only efficient form. As long as this width-to-height ratio is maintained, he argues there’s no actual limit to the form of the fire. Too flat or too tall, and the fire won’t be able to sustain its heat for very long, or even get properly started.

Tips From A Firefighter

Understanding the mathematical concepts underpinning the building of a fire is just the beginning, says Daniel Jimenez, a research engineer at the Missoula Fire Sciences Laboratory. Knowing the arithmetic at work to keep a fire safe—and properly extinguish it—is essential not only for firemen but also for nature lovers.

As part of his profession, Jimenez helps arrange an online course to educate firefighters about the mathematics underlying the blazes they combat.

“Most of the math in our course is really simple geometry,” Jimenez tells Popular Mechanics. “But it does get a lot more sophisticated when you start thinking about quantities and pressures and [water] distribution systems.”

While some firefighters come to the field after college and have a prior understanding of physics and math, it’s also typical for others to join firemen right out of high school, Jimenez adds. This online course contributes to the creation of a common ground of science-and math-based knowledge in order to keep firefighters safe and smart on the job.

Jimenez also builds mathematical modelling tools to assist firefighters keep track of growing flames. Landscape and wind models may be included in this app and in computer-based software, which may replace traditional pocket-size guides. This lets firefighters not only limit blazes but also undertake safe, planned burns that may help avoid uncontrolled blazes later in the season.

As for how to keep your mathematically perfect campfire safe, Jimenez believes the solution is very straightforward: containment. A great technique to guarantee your fire won’t mistakenly extend beyond its base is to make sure its fuel supply is discontinuous, Jimenez explains, meaning there isn’t stray fuel surrounding the fire.

A metal fire pit is one simple method to accomplish this, or you may set your fire on dirt or near a fire blanket. And before you leave your fire, be sure to shut down the thermodynamics at work with a nice dousing of water.

“If I had any suggestion for anyone with a campfire, it would be to drown them,” Jimenez adds. “You can’t throw too much water on a campfire.”

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