Over the course of human existence, the most significant catalyst for growth has been our
ability to draw energy from our world. Taming fire gave birth to the modern human and drawing
power from the wind allowed early explorers to travel the world, but today we are going
to explore the history and science behind one of humanities greatest inventions, the
steam engine. The evolution of the steam engine completely
revolutionized our society. It opened new avenues for trade and caused mass migrations
of rural populations into the newly industrialized cities.
But what I find most fascinating, was the lessons its evolution taught us about science
and engineering. This is one of the first practical steam engines, and it was used to
pump water. The engine was incredibly inefficient. This machine was not going to start any industrial
revolution, but it found a niche in coal mining, where it’s fuel was cheap and readily available.
To investigate why this engine was so inefficient let’s first talk about how it works. The
engine takes the energy stored in the coal and converts it to heat. That heat is then
used to form steam, which expands into a piston cylinder. Causing the pressure to increase
and forcing the piston to rise against atmospheric pressure. No mechanical work occurs on this
stroke, because this chain can only transmit force in tension.
The power stroke occurs when cold water is sprayed into the cylinder. This lowers the
temperature, causing the pressure to drop. Atmospheric pressure now pushes the piston
back down. We want to be able to quantify how much work
is being done per cycle of this engine. To do that, we plot the pressure and volume inside
the piston cylinder for one cycle, like this. The area inside is the work done, but this
is the idealized PV diagram. In practice there is a lot more energy being wasted.
We lose a big chunk here because the steam is prevented from expanding to it’s full
volume. A lot of energy is lost to the environment
too. This is clearly visible with thermal imaging.
The effect is made worse by cooling the entire cylinder with cold water. So an immediate
improvement is to make a separate condenser. Here the steam can be cooled without cooling
the entire cylinder. There are a lot more inefficiencies involved
that reduce the total work done. Many of them are unavoidable, but we can improve the situation
by upgrading the piston cylinder. The manufacturing techniques needed to bore
accurate and strong piston cylinders were not available in the early days of the steam
engine. That changed when John Wilkinson invented this machine. This boring machine allowed
for precise machining or solid iron cylinders. Which reduced steam leakage and made the piston
cylinder stronger, thus allowing the max pressure to rise.
We are starting to see a steam engine capable of sparking the industrial revolution, but
this reciprocating motion isn’t much use for most applications. Especially with this
flexible chain connecting them. What we need is rotational motion, which requires a very
different set-up. To convert this linear motion to rotational
motion, we need a crankshaft and connection rod. We have turned this piston cylinder on
its side, so atmospheric pressure can no longer force the piston back down, so we need to
use steam on the return stroke. This requires a control valve to control when
the steam enters and leaves each side of the cylinder. The valve is controlled by a cam.
The steam engine is now working on both strokes of the engine,
improving its efficiency and power, but piston engines like this do not produce constant
torque. They will pulsate in speed and torque, during a single cycle, like this.
This can cause vibrations and jerky movement.We can reduce this with the use of a flywheel. Which stores rotational energy with inertia
and evens the torque out. It’s essentially a mechanical battery.
David robert demonstrates this beautifully with a V8 solenoid engine of his own creation.
Here you can see the engine will continue to rotate without additional power
, but the engine comes to a dead stop without a flywheel attached.
The development of steam engines taught us a lot about thermal and mechanical efficiencies
and you may think that steam engines have become obsolete, but nearly all of our large
power stations still use steam technology to convert heat energy, whether that be from
coal, nuclear or solar, to mechanical energy. The technology has simply evolved into an
even more efficient form, with steam turbines. Thanks for watching, I have one last device I want to
include in the development of steam engines, which is one
of the most iconic inventions of the industrial revolution, the centrifugal governor. I
am already hearing the angry screams in the comment section about me using the word centrifugal.
So I am going to talk about this device in a completely separate video to discuss the
difference between centripetal and centrifugal force. If you would like to see that don’t
forget to subscribe.
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