In this blog post, we will look at the historical significance of how the development of heat engines and machines have replaced human labor and increased the speed and efficiency of civilization.
We live in more machines than we think. When asked to think of an object that is a machine, most people think of a car or a washing machine. Rancho, the main character in the movie “The Three Stooges,” answers the professor’s question about the definition of a machine by saying that it is something that relieves human labor, and even a pen tip or a zipper on a pair of pants is a type of machine.
Many tools and devices that we easily overlook in our daily lives can also be classified as machines. As Rancho said, not only the nibs and zippers we use in our daily lives, but even simple devices such as handles, pulleys, screws, and electrical switches use physical principles to reduce human effort. These small devices come together to form larger machines, and we can use their power and efficiency more effectively. I guess what ordinary people think of as machines are things that work and move with the power of an engine or motor, not human power. It seems that machines like washing machines and cars that run with the power of an engine or motor save us a lot of “human effort.”
Before the 18th century, humans used the strength of human or animal muscles, and livestock were important as a means of transportation and as a means of production. Later, they also used natural power sources such as watermills and windmills. With the development of the coal-fired steam engine in the 1790s, this new driving force brought about an increase in travel speed and production that was incomparable to that of using primitive or natural power. The steam engine was later replaced by internal combustion engines and electric motors, which are smaller and easier to control, and are used as a source of power in our lives.
The aforementioned steam engine and internal combustion engine are typical heat engines. A heat engine is a machine that converts thermal energy, which is a microscopic movement at the molecular level, into kinetic energy, which is a macroscopic movement of an object. Simply put, it is a machine that burns fuel to generate heat, which in turn powers the machine. All heat engines receive thermal energy from a high-temperature heat source and transfer some of it to the working fluid inside the heat engine. The working fluid, which has received heat energy and increased in temperature, pushes the mechanical parts of the heat engine as it increases in pressure and tries to expand, thereby creating force and motion. The remaining heat energy is released into the air at a lower temperature to keep the engine moving.
The development of machines has not only reduced the labor of humans, but has also brought about major changes to human civilization as a whole. During the Industrial Revolution, the introduction of machines such as steam engines brought about a dramatic increase in productivity, completely changing the economy and industrial structure. The modern production processes that were created in this way contributed to the rapid urbanization and formation of large-scale economic systems. This chain reaction of machine development has become the foundation of today’s affluent lifestyles and various technological innovations.
Recently, steam engines are used as thermal engines that generate most of the electricity in power plants. The steam engine generates high-temperature, high-pressure steam by boiling water, the working fluid, using the thermal energy produced by burning fuel. When the steam is discharged into a turbine, the steam pushes the turbine blades, and the loss of pressure creates the force and movement that allow the turbine’s shaft to rotate. The rotating shaft is wound with a coil, and there are stationary magnets around the shaft, which produce electricity through electromagnetic interaction. And an electric motor can be said to be a proxy for a heat engine in that it partially converts some of the work produced by one side of the heat engine to work on the other side.
Unlike a steam engine, an internal combustion engine burns fuel inside the working fluid, i.e. the heat engine, and so, with a few exceptions, it is smaller than a steam engine with a combustion chamber separated from the working fluid. In addition, while a steam engine requires preheating until water at room temperature boils, an internal combustion engine can be operated immediately by providing only a source of ignition, such as an electric spark, to the working fluid mixed with fuel, without the need for preheating. The internal combustion engine was in the spotlight as a means of transportation due to its small size and quick start-up. It was also used in airplanes before the development of jet engines.
The heat engine has enabled mankind to consume fossil fuels, which are concentrated solar energy. About four liters of gasoline produce about 90 tons of thermal energy from plant matter, which is the same amount of energy as that produced by the rhizomes of wheat in a wheat field of about 160,000 square meters. This enormous amount of energy allowed humans to harness more power, faster. John Smeaton, one of the pioneers of the steam engine, estimated that humans generate about 100 watts of energy when working long hours. In other words, even if 1 million slaves were mobilized, it would not be possible to transport sugar produced in the West Indies or Brazil to Europe faster than a sailing ship. Even if a million people made candles, they wouldn’t even produce enough light to hold a night game at the Colosseum. The heat engine caused the Industrial Revolution, led to an increase in population and an extension of life expectancy, and is still the foundation of human civilization.
Since the commercialization of the steam engine in the 19th century, the most important topic in the development of heat engines has been “efficiency.” Efforts to generate large kinetic energy with less fuel consumption are still ongoing. Thermodynamics is a discipline established from the experience gained in the development of heat engines and presents the criteria for the most efficient ideal heat engine.
In 1834, a technician named Emile Clapeyron published a book titled “Force Motrice de la Chaleur” (The Power of Heat), which reorganized Sadi Carnot’s arguments. Carnot proved that an engine that repeats the ideal four-process cycle of isothermal expansion, adiabatic expansion, isothermal contraction, and adiabatic contraction is the most efficient, and its efficiency is as follows. (The unit of temperature is absolute temperature.)
Efficiency = 1 – (Low heat source temperature / High heat source temperature)
Therefore, if a heat engine is not operating at -273 degrees Celsius, or absolute zero, its efficiency is always less than one, proving that infinite power is impossible. Carnot’s process of deriving this was later used to establish the entropy and the second law of thermodynamics.
As such, the principles of thermodynamics and entropy have not only been academic discoveries, but have also been an important opportunity to realize the limits of heat engines that humans can use. This realization has led to various attempts to increase the efficiency of heat engines, which has expanded to modern internal combustion engines, electric motors, and hybrid technology, and is still the basis for various research and technology development.
There are many reasons why real-life engines use more fuel to produce the same amount of work than ideal engines. For example, heat escaping through the engine’s container, losses due to friction caused by the working fluid or engine movement, and interactions between real gas molecules, unlike ideal gases. Many engineers are struggling to reduce these energy losses.
Over the past 200 years, humanity has enjoyed an incomparably improved quality of life by using thermal energy as a force. It is expected that human civilization will continue to be maintained and developed for a long time using thermal engines that burn fossil fuels. Although the development of alternative energy is active, the use of fossil fuels is expected to continue in the future. According to the International Energy Agency (IEA), consumption of oil, coal, and natural gas accounted for about 81% of total energy consumption in 2006, and this ratio is expected to remain the same and consumption to increase by 2030. Research and development of the heat engine, the foundation of human civilization, is still required to leave fossil fuels, concentrated solar energy that is presumed to be finite, to our future generations.
