The Development of the Steam Engine
Question (To the fifth grade science class) “Who invented the steam engine?”
Answer (All together now) “James Watt invented the steam engine.”
Indeed James Watt was an important player in the development of the steam engine. In fact, he held many patents and spent much time defending those patents in Her Majesty’s Court. Obtaining patents is a part of the invention process. The patent and invention processes are legal processes - not a technological process. The question that we should ask he is who developed steam engine? The answer to that question undoubtedly involves many people, however we are going to look at the contributions of the important few people who labored to perfect their ideas – notably Thomas Savery, Robert Newcomen, and James Watt. Before we look into the specifics, however, there are a few general thoughts that need be considered.
First all the development of the steam engine is undoubtedly the most important technological step in a history of mankind. The steam engine allowed mechanical power to be created to a degree vastly greater than that of the traditional means of man, beast, wind, and water power. Even today power produced by a steam engines and the their successors, the steam turbines, dominate the electrical generation process. Major power plants use steam power, although there is growing involvement on a part of gas turbines in ‘combined cycle plants’ which promise greater thermal efficiency. Even the nuclear power plants rely on the use of steam turbines to actually turn the electrical generators.
Now it is useful to be specific in use of language when dealing with the principles behind the development of the steam engine. First of all, the term, engine, is a contraction of the phrase heat engine. The heat engine is the device which enables the conversion of heat to mechanical power. This is the subject of thermodynamics, a discipline that was developed to help explain how engines operate and the limitations that exist relative to the amount of power made available by a given device. Heat is energy that flows as a result of a temperature difference. The temperature difference of which we speak in the difference between the temperature of the products of combustion of the fuel-air mixture and the temperature of the sink to which the energy is eventually delivered, perhaps the atmosphere or a body of water. The First Law of Thermodynamics tells us that energy is conserved – that is, the heat released by the burning of fuel is converted to the sum of the mechanical energy produced by the engine plus the internal energy of the medium which is heated to drive the engine. In this case, the medium is steam, or more precise precisely, water – water in its liquid form or its the vapor form (steam). The Second Law of Thermodynamics allows one to derive the amount of the heat energy which can actually be converted to mechanical energy in a given device – it is a fact that only a portion of the heat can be so converted. (Sadi Carnot, a French engineer, explored this issue.) The ratio of the amount of mechanical energy produced to the heat available in the fuel is the thermal efficiency of the system. At the time of which we speak, the 1800s, the efficiency of this conversion process was probably less than 5 percent. Today, with sophisticated engine cycles and highly efficient components, that efficiency can reach approximately 60 percent.
In a combined cycle plant the exhaust of the high temperature gas turbine generates steam for the steam turbine.
This combined cycle plant generates 360 Megawatts of electrical power.
A further notes on vocabulary should be noted. An engine develops power from fuel. A motor converts one form of mechanical energy to another. For example, the device which converts electrical energy to mechanical shaft power is a motor. That hunk of iron under hood of your car he is an engine, not a motor. Somewhere along the line Detroit advertisers began to the call that hunk of metal a motor; one of the major oil companies wished you “Happy Motoring” NASCAR drivers believe they have motors under the hoods of their race cars. They do not. Those are engines.
Finally, if you go back in the literature, you will find treatises on steam that date back as far as Hero of Alexandria, who lived in the second century B.C. These musings had little to do with the actual development of the steam engine, but are referenced here for completeness.
Three of many of Hero-sketches
Now to get back to the story of the development of the steam engine. It all started with the observation that when water is heated and boiled in a closed vessel, the pressure in the vessel rises. In my day as Boy Scout, soda cans had a screw top. It was the ritual when sitting around a camp fire, that after finishing your soda, you put a little water in the can, screwed the cap on tight, and tossed the can into the campfire. If things went right, the can would eventually blow apart due to the high pressue of the steam produced by the boiling water. Back in the days of steam engine development, people realized that if the bottom of the vessel were made into a moving piston, mechanical work could be performed by such a moving piston.
We need some Boy Scouts with soda cans.
All of us who have been to a railroad museum or have taken a ride behind a steam locomotive, have an idea that the original steam engines involved boilers which produced high pressure steam that, with a great hissing sound, when admitted to a cylinder pressed down on a piston and caused the piston to move. In fact, that is just the opposite of how the original engines operated. The problem was that means of manufacturing cylinders that did not rupture or leak even at very modest pressures did not exist. In fact, the highest pressure at which the early engines operated was precisely zero. How then did those early engines operate?
Back to the campfire. If you did not screw the cap back on tightly, when you tossed the can in the fire, the water would boil and the steam would leak out of the container. As the fire cooled, the steam in the can would begin to condense, lowering the pressure in the can. The atmosphere would push down on the cap, sealing the contents. Then, eventually there would be a ‘crumping sound’ as the atmospheric pressure collapsed the can - the steam inside had condensed ‘leaving a vacuum’. Indeed, the early steam engines were based on the creating a low pressure on one side of a piston by condensing steam that had occupied the volume on the low pressure side of the pistoned chamber. The engines were known as ‘atmospheric engines’ or ‘atmospheric fire engines.’ (Fire engines in the sense of fire being the source of energy – not fire engines used to put out house fires.)
The individual given most credit for developing an atmospheric engine which used the low pressure produced by condensing steam to produce mechanical work was Thomas Savery. The Savery engine was used for removing water from mines. The Savery engine did not use a piston – it merely connected the chamber in which the ‘vacuum’ was produced to the undesired water by means of pipes and valve gear. As the steam in the cylinder (reservoir) condensed, water was drawn up the pipe to the fill the reservoir. Then the water was expelled from the resevoir by displacing the water with steam at a slight pressure above atmospheric pressure.
The next major contributions were made by Thomas Newcomen. Newcomen was the first to bring together all the vital elements of steam engine in one successful package - the cylinder, piston and separate boiler. Savery had filed a patent in 1698 for "an engine to raise water by the impellant force of fire." To avoid infringing Savery's patent, Newcomen was forced to go into partnership with him. But Newcomen's design was far superior and it possessed all the basic features of machines being built more than a century later.
A boiler was connected to a cylinder, in which a piston was lifted by the pressure of steam. At the top of the stroke, cold water was sprayed into the cylinder. This condensed the steam, causing a vacuum, and atmospheric pressure acting on the top of the open cylinder forced the piston down again, completing the cycle. It was this downward stroke, rather than the upward, steam-induced one, that was the power stroke, so the device became known as an atmospheric engine.
Newcomen's engine had more than a few drawbacks, notable among which was its inefficiency. It was expensive to run because the cold-water spray, besides condensing the steam, also cooled the cylinder which was heated again at the next cycle. Constant heating and cooling meant the boiler required more fuel, but this was not a problem where the engine was designed to be used - in coal mines. The first Newcomen engine went into operation at a coal mine at Dudley Castle in Staffordshire in 1712. It was the first of many which helped power the early part of the Industrial Revolution.
The Newcomen Engine.
No picture of Thomas Newcomen is known to exist.
The most important improvements to the atmospheric steam engine were made by a James Watt. Watt was trained in the sciences and brought an engineering approach to the subject. His most important contribution was that of the use of a separate condenser. The prior designs of Savery and Newcomen had used injection of water in directly into the cylinder to condense the steam and produce the vacuum needed to move the piston. The cyclical cooling and reheating of the cylinder due to the water injection caused the cycle to be inefficient. By employing a separate condenser that inefficiency was removed and the cost of operation of the new engines was considerably reduced. From a science and engineering point of view, Watt understood what was called the 'expansive power' or 'elasticity' of steam which, when incorporated in his designs, further reduced the cost of operation. Watt also was a businessman this; he teamed with a financier and manufacturer by the name of Matthew Boulton to form the famous and Boulton and Watt Manufactury of Solo, near Birmingham. This factory manufactured and the erected over 500 steam engines during the period from 1774 to 1800. There are many other inventions credited to Watt and the patents that he received would allow Boulton and Watt to accumulate a great deal of wealth due to their successful activities.
Further information on the development of steam power in the early years may be gleaned by reading more of the classic publications. A selection of these classics is available here.
Rev. January 2011