Following Denis Papin’s 17th century experiments in atmospheric and pressure steam engines, steam power continued to evolve, with a need for efficiency driving innovation. The invention of the train, in particular, resulted in the second step of steam power development via high pressure.
In parallel to their use in mines and factories, steam engines started being considered for transportation purposes or traction. One famous example is the ‘Fardier à vapeur’, often considered to be the very first automotive vehicle, which was propelled by a Newcomen type 2-cylinder engine (1769). The vehicle was created to carry military materials instead of using heavy horse-pulled carriages. It ran well, but because of a lack of brake effort and engine power, it was finally put on hold. The prototype is still visible at the Museum des Arts et Métiers in Paris.
The lack of power from early steam engines was the biggest challenge for vehicles; the only way to adapt the steam engine was to increase its power density which – even after the improvements brought by James Watt – was still not sufficient.
The key to adapting steam engines for transportation was to switch from an atmospheric engine to a high-pressure engine. In such engines, instead of vacuuming the cylinder and using the atmospheric pressure, high pressure steam (at a pressure equal to several times the atmospheric pressure) is introduced directly into the cylinder to push on the piston (generally at double effect). As a result, power density and efficiency strongly increased.
One of the main issues slowing down this technological step forwards came from the fact that James Watt patented the ‘high pressure’ cycle without believing in it, fearing explosions, which prevented other inventors and engineers from taking on the challenge.
Once the patent fell into public domain in 1800, however, Richard Trevithick – a British engineer – started elaborating and patenting a high-pressure compact steam engine. It was capable of powering a road car (1801), but also his (and the world) first locomotive: the Pen-y-Darren. Several safety measures were also invented at this time to prevent risk of boiler explosion. First trials at an average speed of ~4km/h on iron tracks showed the attractiveness of Trevithick’s invention, and the train was born.
Richard Trevithick and Andrew Vivian's high-pressure engine, 1802
Further improvements and second steam locomotive generation
After Trevithick, the steam engine benefitted from many improvements. The first steam boilers were very rudimentary; the heat exchange between fire and water was limited and a large amount of energy was lost. An innovative idea was to increase the surface of exchange between fire exhaust gases and the water to be heated and vaporized, by adding a multi-tubular exchanger inside the boiler.
The first to put this idea into operation on ships and locomotives was French engineer Marc Seguin, a man also known for his invention of the wire-cable suspension bridge. Seguin patented the multi-tubular boiler between 1827 and 1828, and built two locomotives of his own design for the Lyon-Saint-Etienne Railway (Marc Seguin Locomotive), after buying and examining Stephenson’s locomotive.
It’s worth noticing that Seguin’s locomotive was also equipped with two mechanically driven blowers as a way to increase the power of the fire – recognize the link with turbochargers? For a given size and weight, the multi-tubular blower enabled a locomotive to multiply its speed by four for a given load, making it far more effective.
Robert Stephenson – in permanent close contact with Seguin – also designed his next locomotive, the very famous Rocket, around the multi-tubular boiler solution. Stephenson went one step further, however, by adding the steam extractor. This was a nozzle which drove the expanded steam from the cylinder toward the chimney, a genius solution that enabled the recovery of steam energy as a means of providing draft through the fire – another taste of things to come with turbocharging.
The combination of multi-tube boiler and steam blast are often cited as the principal reasons for the high performance of Rocket in 1829, and with speeds of 40 km/h, horses were left far behind.
Stephenson's locomotive rail-way carriage, 1829
Steam and thermodynamics
After these first developments and improvements, steam power brought Europe deeper into the first industrial revolution. More and more coal was burnt to supply different machines operating in mines, factories, ships and trains, emitting increasing amounts of smoke and dust; for the first time pollution became a real issue, and the consumption and efficiency of steam machinery became a key question for society.
To solve the problem, engineers and physicists began thinking about improving steam machines using a more systematic and scientific approach. A new physics domain relating mechanical work and heat was born: Thermodynamics.
One of the key principles of thermodynamic theory can be seen in work published in 1824, ‘Reflections on the Motive Power of Fire’ by Sadi Carnot, a French mechanical engineer, military scientist and physicist.
Carnot was the first to establish the fundamental physical limit when converting heat into work. After ruling that a thermal machine can only provide work if there are two heat sources with two different temperatures, he wrote that the higher the maximum temperature of the working fluid, the higher the base efficiency. Once this point was admitted, Carnot gave an ideal cycle for the best efficiency for a given couple of temperatures: the Carnot Cycle.
As James Prescott Joule was for the first law of Thermodynamics (conservation of energies, whatever their kind), Carnot can be considered as precursor of the second Law of Thermodynamics (all energies do not have the same ‘value’).
The exact way that engineers understood and used work from Carnot is not completely clear and linear. For example, it’s known that Carnot was in contact with Marc Seguin and Sir William Robert Grove, the respective inventors of multi-tubular boiler and fuel-cell, and they corresponded about the correlation of physical forces, but we don’t know how much influence Carnot had on these big inventors and their inventions.
Along with such improvements, compounding or multiple steam expansion, steam superheaters, the Giffard injector (the use of steam to fill the boiler in water) and the very valuable contributions from Kyösti Kylälä and André Chapelon can be considered as the most important elements for taking steam locomotives on a journey that would see them go from racing horses to racing the first high speed trains within 100 years.
In fact, the famous English Pacific 231 steam locomotive LNER Class A4 4468 Mallard reached 203 km/h in 1938 – just an incredible 7 km/h less than the operational 210 km/h seen on the first Japanese Shinkansen bullet train in 1964.
After 1850, work from Carnot, and thermodynamic outcomes in general, became more and more clearly considered by engineers and machine builders, leading to steam turbines taking over from piston steam engines on stationary installations. In 1860, we saw a definitive switch from External Combustion Engines (ECE) to Internal Combustion Engines (ICE), while on rails, steam power would continue to evolve for more than 100 years.
Today, ultra-modern ships and stationary plants are still powered by steam turbines, with the technology continuing to improve, showing how breakthrough technology can develop without necessarily replacing alternative options. Alongside, we saw the creation of the first petrol and Diesel internal combustion engines. But that’s a story for another day…