I veered off my usual topics on a few posts lately, taking some time to explain the historical reasons for global warming being attributed to the Industrial Revolution. Specifically, we looked at the thermodynamic concept of heat engines. See How Global Warming Started. The following post about An Ice Powered Heat Engine further reinforced the concept by broadening exactly what constitutes a heat engine. This post continues the trend by looking at a little-known heat engine nicknamed the “Flame Eater.”
The Flame Eater is a form of vacuum engine that utilizes atmospheric pressure (along with a heat source) to do useful mechanical work. Vacuum engines date back to the early 1700s. They worked in a manner similar to the Newcomen steam engine [great animation at that link]. There is no recorded “first” inventor, since the basic principles of heat engines were being widely investigated and shared. The Flame Eater is shown running in the video.
This is what it looks like at rest:
The essential components of the heat engine are indicated. Heat input is provided by the flame on the alcohol burner, which when burning isopropyl can reach temperatures of 1000 °C (1832 °F). Heat output is provided by the cooling fins on the brass cylinder. The difference between heat input and output is converted to rotational kinetic energy in the heavy flywheel.
The next photo shows the piston (barely protruding from the cylinder), and the crankshaft linkage that converts the back-and-forth motion of the piston to the rotational motion of the flywheel:
Operation can be explained easily, since this is a 2-cycle engine. We start with the intake stroke. Hot air in the cylinder has cooled from the previous cycle, so has also reduced its pressure. As the valve pops open the piston begins its outward motion. This draws the flame into the interior of the engine, ingesting a small parcel of very hot air, after which the valve closes. When the air already in the cylinder is heated, it expands and exerts a force on the piston adding rotational energy to the flywheel. Here’s what the intake stroke looks like:
Note the blur of the spinning flywheel spokes and the flame being pulled into the cylinder. The piston is not yet visible at the end of the cylinder, so the intake stroke is still in progress. The valve is just about to close.
The exhaust stroke follows immediately. You can see the valve is now closed and the piston is visible at the end of its intake stroke. At this time the hot air in the cylinder is losing heat through the cooling fins, which reduces its pressure and helps the piston move back inward. This isn’t an “exhaust stroke” in the sense of an internal combustion engine, but it nonetheless returns the system to a point where heat can again be input.
The flywheel provides rotational inertia to keep the system moving against inevitable losses to friction. In fact, this engine will not self-start and requires a manual spin of the flywheel to begin operating. Also, the cylinder needs to warm up for 5 minutes or so before it will support both cycles efficiently. Still, it’s a great example of an ingenious design that found some practical applications in the 1700s.
Modern internal combustion engines like you have in your vehicle are far more advanced than the Flame Eater, but are nonetheless brethren heat engines. With the development of variable cams, fuel injection, and electronic spark timing, the internal combustion engine is pretty much as good as it will ever get … it’s what they call a “mature technology.” It’s a masterpiece of engineering. Still, I feel it’s instructive to look back at the Flame Eater as the humble progenitor of modern heat engines.
Next Week in Sky Lights ⇒ Rocket Powered Cars