The project described in this chapter, a sort of primitive fire lighter, is a wonderful example of physics in action. By quickly compressing air inside a cylinder, we can raise its temperature enough to start a small bit of fuel stuffed inside it on fire.

It sounds impossible, but with a few easy-to-find parts, we can make a device that produces fire from nothing but air!

A New Kind of Automobile Engine

Rudolf Diesel was one of the youngest students ever to enroll in the mechanical engineering program at the München Polytechnikum. During his studies at this prestigious German university, the precocious student met Professor Carl von Linde, who was famous for developing refrigeration and gas separation technologies. Rudolf assisted Carl in his lab and became one of his most trusted assistants.

In 1871, von Linde returned to the university after a lecture tour that took him to Malaysia. Because this was the late 19th century, the voyage had taken him months. Von Linde had seen and learned much during his excursion to Southeast Asia, and as a faculty member of the prestigious Technical University of Munich, he was obligated to deliver a presentation on the results and findings of his trip to students and faculty. Diesel attended the lecture and was quite eager to find out what his mentor had learned during his time away.

The talk was a lengthy one and during his lecture, the fatigued Herr Doktor felt the need for a nicotine hit. He paused and withdrew from his pocket a small wooden cylinder and plunger, which he called eine Feuerpumpe. The small device was a present from the people he had met on Penang Island in the Straits of Malacca. The indigenous people of the region used it to start fires. A person experienced in using die Feuerpumpe, or fire piston, could reliably provide hot glowing embers anytime they were needed, even under the humid conditions of the rain forest.

At the lectern, Linde slapped the plunger down and the tinder inside ignited. He plucked out a glowing ember and lit his cigarette with it. It was a neat gesture; to the audience, it looked like he had produced fire from nothing at all—they saw no match, no flint. The fire had magically appeared from the bottom of what they saw as an empty, hollowed-out tube.

The demonstration lit not just a cigarette, but an idea in Rudolf Diesel’s head. Diesel had been experimenting with the recently invented internal combustion engine and was growing frustrated with the spark-ignition cycle engine’s inherent low efficiency. When von Linde lit that cigarette, a question jumped into Diesel’s head: “Could the same thermodynamic process that ignited the tinder in the bottom of the fire piston also ignite fuel in an internal combustion engine?” If so, perhaps here was a way to significantly improve the efficiency of this type of engine. And as history proved, it was indeed.

Making a Fire Piston

You can start a fire by using chemical energy (a match), by using friction (rubbing sticks together), or by a phenomenon called pyrophoricity (which is the basis for flint and steel fire starters). But one of the most satisfying ways to start a fire is by quickly compressing air using a fire piston.

There are a lot of different names for the fire piston. It’s also called a fire syringe or a slam rod fire maker. But no matter what you call it, it is certainly a unique way of lighting your campfire! The following steps will explain how to make your own fire piston, the antecedent of the diesel engine. Take a look at Figure 1-1 to see what you’re shooting for.

Building the Fire Piston

Several steps in the building of the fire piston require careful attention to detail. Work carefully, especially when cutting the groove in the piston and fitting the O-ring into the groove.

1. Refer to Figure 1-1. Cut the groove for the O-ring about ¼ of an inch from the end of the rod.

   The depth of the groove should be just slightly less than the diameter of the O-ring. If the groove is deeper, the O-ring won’t seal against the tube properly. If the groove is too shallow, you won’t be able to insert the rod into the tube.

   The best way to cut the groove is with a lathe. But if you don’t have one, then what? Improvise! I used a table saw to cut the groove, and after a bit of trial and error, it worked fine.

   1. Raise the blade so the height of saw blade is protruding over the table an amount almost but not quite equal to the diameter of your O-ring.
   2. Carefully spin the rod as it contacts the blade to make an even slot (see Figure 1-2).

   

   You might not be successful on your initial tries. Never fear, the rod is long enough so you can cut off mistakes and try again.

   If you don’t have a table saw or lathe, then you can carefully file the groove using a flat file that is almost but not quite the same thickness as the O-ring. If you’re going to use a file, then select O-rings that are just a bit smaller in thickness than the thickness of the file.

   Of course, it will take a fair amount of time to file away enough plastic to fit the O-ring, but with patience, it can be done. No matter what tool you use, work carefully because the depth and width of the groove must be quite accurate in order to seal the piston inside the cylinder.

2. Using the cyanoacrylate- or methylene chloride-based adhesive, glue the short rod into an open end of the tube as shown in Figure 1-3.

   

   It is very important that the glue makes the end air tight. Rotate the plug in the tube to distribute the glue.

3. Use a die and handle to cut a ½-inch-13 thread on the other end of the rod (see Figure 1-4).
4. Screw the ball knob onto the thread.
5. Insert the rod in the polycarbonate or acrylic tube and check the sliding fit.

   

6. Use a sanding belt, sandpaper, steel wool, and polish to make a close but free-sliding fit between the rod and the tube (see Figure 1-5).

   

7. Cut the rod to a length of about 9½ inches. Optimally, there should be about ¹/₈ of an inch of space separating the end of the rod from the plug when the piston is fully inserted into the cylinder.
8. Install the O-ring into the slot you made in the rod in step 1. Depending on the width of the cut you made and the shape of the O-rings you procured, either one or two O-rings will fit in the slot (see Figure 1-6).

   

9. Drill a ¼-inch hole (the divot), about ¹/₈-inch deep in the middle of one end of rod as shown in Figure 1-7.

   The components of your fire piston are now complete (see Figure 1-8).

   

   

Using the Fire Piston

Now that you’ve assembled the parts of your fire piston, it’s time to test it out.

1. First you need to test for air leaks. To do so, smear petroleum jelly on the O-ring and carefully insert the rod into the tube, working the O-ring past the edge of the tube.

   If you’ve done everything correctly, the piston will smoothly and easily pop back up, nearly to the top, when you release the knob after pressing down. If you press on the piston and it just stays in the tube, this means it won’t work. If this happens you can troubleshoot with the following steps:

   1. Check for leaks in the plug by spraying the end with soapy water and looking for bubbles when you compress the piston.
   2. Improve the sliding fit by adjusting the depth of the O-ring groove and repolishing the surface of the piston.
2. Once you’ve got your piston moving smoothly, it’s time to load it. Place a pinch of material that catches fire very easily in the divot you drilled in the end of the rod.

   The best material for this is called charcloth. I describe how to make charcloth later in this chapter.

3. Smear more petroleum jelly on the O-ring.
4. Carefully insert the rod into the piston, working the O-ring carefully past the edge of the tube.
5. Place the plug end of the fire piston on a hard surface.
6. Quickly and firmly press down on the knob. You’ll see a bright flash in the bottom of the fire piston (Figure 1-9).

   

7. Carefully remove the piston from the tube and blow on the glowing charcloth in the divot. You can now use the smoldering ember to start a larger fire.

How Fire Pistons Work

Unlike typical gasoline engines, the eponymous and now ubiquitous diesel engine has no spark plug or carburetor. Instead, the diesel engine works by compressing fuel under very high pressures. When the fuel/air mixture in the cylinder compresses, it also gets very hot. In fact, the mixture quickly exceeds the flash temperature of the fuel and ignites. The compressed gas expands violently upon ignition and pushes the compressing piston away with enough force to easily turn a drive train. Figure 1-10 explains this process in more detail using a fire piston as an example.

Making Charcloth

What is charcloth? Basically, it’s cotton cloth that’s been roasted to blackness at high temperature but in the absence of air. The wonderful thing about charcloth is that it is very easy to ignite with just a small spark. Charcloth doesn’t really burst into flame easily, but it doesn’t take much for it to catch fire and smolder, making it just right for starting something else on fire, like tinder or even a cigar.

To make charcloth, follow these steps:

1. Begin by taking an airtight metal container such as a candy tin and punching a small hole in the top (see Figure 1-11).

   

2. Next, place some 100% cotton cloths in the tin and replace the top (see Figure 1-12).

   

3. Go outside and place the container on a handful of hot charcoal briquettes (see Figure 1-13).

   Almost immediately the cloth inside will start to roast and white smoke will pour out of the hole. After several minutes, the smoke volume will decrease or stop, signaling that the charcloth is done.

4. Remove the tin and let it cool. Once the container has cooled, you can remove the top and take out the charcloth.