I am far from an engineer and am the most amateur of science followers and I have a question about the development of steam power.
I was in the navy and had to stand engine room watches and learn about marine steam engines (complete with condensers and other stuff) and I was recently watching a series called “Genius”, one episode of which covered James Watt and his refinement of steam engine design. This was (the use of pistons), in my mind, bloody complex. ISTM that the most intuitive thing would have been the use of turbines (as an offshoot of windmills for example).
How on earth did people first come up with pistons and the associated condensers etc?
It’s bloody fascinating but I don’t understand it.
A steam turbine is more complex to build than a recip. Curtis developed his engine in 1884 and Parsons developed his in 1894. The blades on a turbine have to be cast and machined to close tolerances. Then there is the problem of sealing the shaft while it turns. And then a turbine needs either reduction gears or a generator. That is fine machining.
Watt modified the atmospheric engine by 1761. Using condensers.
Well the summary of Watt’s improvements in his first working engine is
uses the positive pressure from boiling steam. Watt was working at university and knew how much pressure that could produce… A lot more than the one atmosphere of the condensor !!!
he knew that the more metal in a cylinder, the more coal it would take to warm it up from one temperature… and his high pressure cylinder would have a lot more metal than a 1 ATM cylinder.
He knew how to distill water with a boiler and a condensing section , so he realised the Newcomen machine needed a seperate condensor, which made sense, as it didn’t have to be a high pressure container then, it was just a 1 ATM pressure, so a cheap thing off to the side
So thats what his first engine was… a positive pressure piston with seperate condensor.
A somewhat seperate invention was the regulator, to keep the pressure in the cylinder at the right pressure to drive the engine at constant velocity. it was a very stable regulator, while anything that just rigged up, like a weight on a stick, was very unstable and liable to vibrate itself to failure… the rotating regulator was ultra smooth, which mean reliable regulation.
His second great progress in engine design was the dual action… so that it would push up as well as push down… no more relying on gravity to do the reset… No more massive counter weight. faster start up, constant speeds, regulator didn’t wear itself out in a day.
He had been working with gears for the regulator, and his gear man, boulton, argued that the up down action used to pump water, was ok, but why bother pumping water to turn a water wheel, why not just convert the up down movement to rotation with gears ? But the cranks used to to turn human arm or leg movement to rotation, eg a wool spinner, wasn’t strong enough for steam power. So under Watt, Boulton produced the sun and planet gear to be used as a crank shaft. The rod connected to the planet gear , and the planet gear rotated around the central sun gear and made it rotate too. The sun and planet gear was perhaps fast to wear out, but well perhaps it lasted a week between services. Not particularly expensive… perhaps highly dangerous to use, prone to breaking and killing people, but it worked.
These inventions came about as fast as the materials and manufacturing capability allowed them to. The early atmospheric engines were built from materials and with methods that could barely cope with the stresses they were placed under, and as above, Watt was limited by the strength, wear resistance, and engineering tolerances that could be achieved. These engines were manufactured with very basic tools, and the materials available were very limited. A significant part of the art was being able to turn theory into practice. In addition, the theory was being developed as time went on as well. An understanding of the thermodynamics of gases was a key enabler.
A steam turbine would have been essentially science fiction in terms of the ability of the technology of the time to be able to make.
In fact the steam turbine was invented long before the steam piston engine. The classic example is https://en.wikipedia.org/wiki/Aeolipile which was a sort of turbine. There were many other proposals of the same sort in the 18th century.
The problem is that to be even slightly efficient, this sort of turbine needs to go round at enormous speed, much faster than any available reduction gears could cope with. Meanwhile, the big steam piston engines driving mills would turn at maybe 100 rpm, which was much better suited to driving machinery.
The high speed of an efficient turbine was still a problem for some applications, and many technical issues had to be solved before successful reduction gearing was developed so that a turbine could drive a ship’s propellor efficiently.
Also, as noted above, turbines require very accurate machining and the ability to make turbine blades of complex shape.
Would it also be fair to say that a steam turbine needs hotter, higher pressure steam to operate at a usable efficiency? I can’t find an exact figure for the steam pressure of Watt engines, but it can’t have been much more than 10 psi, considering the high-pressure engines that represented the next breakthrough were in the 40 - 50 psi range.
To your materials science point, it’s worth noting that Watt’s most difficult challenge was finding a way to manufacture a piston that fit tightly enough to not let too much steam escape, while still having freedom of movement. No iron worker at that time was capable of turning out perfectly circular pistons or cylinders. (IIRC he eventually settled on an as-close-as-possible iron disk with a layer of carefully trimmed leather sealing it on the top.)