The development of heat engines and machines gave humans greater speed and power, which fueled the Industrial Revolution and technological advances that allowed civilization to grow by leaps and bounds. This has led us to efficient energy sources and technological innovations, but we continue to consume fossil fuels and research to improve efficiency is still important.
We live in more machines than we realize. If you ask the average person to think of an object that they consider a machine, most people think of a car or a washing machine. In the movie The Three Stooges, Rancho, the main character, is asked by his professor to define a machine, and he replies that anything that saves human effort, even a nib or a zipper on his pants, is a machine.
Many tools and devices that we often overlook in our daily lives can also be classified as machines. As Rancho points out, even simple devices like handles, pulleys, screws, and electrical switches, as well as everyday nibs and zippers, use physical principles to reduce human effort. Together, these small devices form a larger machine, and we are able to harness their power and efficiency more effectively. I would argue that the things we consider machines are things that work and move with the power of an engine or motor, not human power. Machines such as washing machines and automobiles, which are powered by engines or motors, are considered to be machines because they take a lot of “human labor” out of the equation.
Before the 18th century, humans harnessed the power of human or animal muscles, so livestock were important as a means of transportation and production. Later, natural power sources such as water wheels and windmills were utilized. With the development of the coal-fired steam engine in the 1790s, this new prime mover increased the speed of travel and production beyond anything possible with primitive or natural power. Steam engines have since been replaced by internal combustion engines and electric motors, which are increasingly smaller and more controllable motors, depending on the application, and are used as sources of power in our daily lives.
The aforementioned steam and internal combustion engines are typical thermal engines. A thermal engine is a machine that converts thermal energy, which is the micro-movement of molecules, into kinetic energy, which is the macro-movement of objects. In other words, it’s a machine that burns fuel to make it hot and then uses the heat to move. All thermal engines receive heat energy from a high-temperature heat source and transfer some of it to the working fluid inside the engine. As the temperature of the working fluid rises from the heat energy, its pressure increases and its tendency to expand pushes against the mechanical parts of the engine, creating force and motion. To keep the engine moving, the remaining heat energy is dumped into the air at a lower temperature.
The development of machinery didn’t just make human labor easier, it changed human civilization as a whole. During the Industrial Revolution, the introduction of machines like the heat engine led to a dramatic increase in productivity, completely changing the economy and industrial structure. These modern production processes helped humanity rapidly urbanize and form large-scale economic systems. This chain of mechanical advancements laid the foundation for today’s abundance of life and many technological innovations.
Today, steam engines are used as heat engines to generate most of the electricity in power plants. Steam engines use the heat energy from burning fuel to boil water, the working fluid, to produce high-temperature, high-pressure water vapor, which is discharged into a turbine, where it pushes against the turbine’s blades and loses pressure, creating force and motion that allows the turbine’s shaft to rotate. The rotating shaft is wound with coils, and around the shaft are stationary magnets, which generate electricity by electromagnetic interaction. An electric motor is a surrogate for a heat engine in that it converts some of the work of a heat engine that produces work on one side into partial work on the other side.
Unlike steam engines, internal combustion engines burn fuel in the working fluid, that is, inside the heat engine, so they are smaller than steam engines, which have a combustion chamber separate from the working fluid, with a few exceptions. Also, steam engines need to be preheated until room-temperature water boils, whereas internal combustion engines do not need to be preheated and can be started immediately by providing a spark, such as an electric spark, to the working fluid mixed with fuel. Their small size and quick startup made internal combustion engines popular for transportation. They were also used in airplanes before the development of jet engines.
The heat engine allowed humans to consume fossil fuels, which are concentrated solar energy. About 4 liters of gasoline gives off the heat energy of about 90 tons of vegetable matter, which is the same amount of energy as all the wheat grains, rhizomes, etc. in a wheat field of about 160,000 square meters. This tremendous amount of energy made it possible for humans to harness faster and stronger power. John Smeaton, one of the pioneers of the steam engine, estimated that humans generate about 100 watts of energy when working long hours, meaning that a million slaves couldn’t get sugar from the West Indies or Brazil to Europe faster than a sailing ship. Even if a million people made candles, they wouldn’t provide enough light for a night game in the Colosseum. Heat engines fueled the Industrial Revolution, increased population and longevity, and are still the backbone of human civilization.
Since the commercialization of the steam engine in the 19th century, the overriding theme in heat engine development has been efficiency. The quest for greater kinetic energy while consuming less fuel continues to this day. Thermodynamics is a discipline that has been refined from the experience gained during the development of heat engines and provides criteria for the ideal heat engine with the highest efficiency.
In 1834, an engineer named Emile Clapeyron published a reorganized version of Sadi Carnot’s arguments in Force Motrice de la Chaleur. Carnot proved that an idealized cycle of four processes-isothermal expansion, adiabatic expansion, isothermal contraction, adiabatic contraction, and adiabatic contraction-was the most efficient, with the following efficiency (The unit of temperature is absolute temperature.)
Efficiency = 1 – (low heat source temperature / high heat source temperature)
Thus, unless the heat engine is operating at -273 degrees Celsius, or absolute zero, its efficiency will always be less than one, proving that perpetual motion is impossible. Carnot’s process of deriving this result was later used to establish entropy and the second law of thermodynamics.
These principles of thermodynamics and entropy were not merely academic discoveries, but an important realization of the limitations of the heat engines available to humans. This realization led to various attempts to increase the efficiency of heat engines, which has been extended to modern internal combustion engines, electric motors, and hybrid technologies, and continues to be the basis for various research and technological developments to this day.
There are many reasons why a real heat engine uses more fuel to produce the same amount of work than an idealized heat engine. These include heat escaping through the vessel, losses due to friction as the working fluid or engine moves, and interactions between the molecules of real gases as opposed to ideal gases. Many engineers are struggling to reduce this energy loss.
Humanity has harnessed thermal energy as a power source for the past 200 years, and our lives are more advanced than ever before. It is expected that we will continue to use fossil fuel-burning heat engines to sustain and advance human civilization for many years to come. Despite the development of alternative energy sources, the use of fossil fuels is here to stay. 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 is expected to remain at this rate through 2030. Research and development of heat engines, the foundation of human civilization, is still needed to ensure that we leave more of this supposedly finite source of concentrated solar energy to our descendants.
