# How to make the development and use of Steam Engines preferred over that of Combustion Engines?

Intro: I have gone some way to make airships more preferable over land-based transport in my beautiful conworld. E.g. making tunneling harder & making flying easier. Though there's plenty left to do...

For now I would like to address one of the bigger issues/themes of my creation: The usage of steam power in machinery and vehicles.

Setting: The world at its current state is a mix of Victorian Era society and Interwar Era technology.
Electricity is only slowly coming up so far and is mostly used as a novelty for e.g. telegraphing, heliographing, illuminating airships, treating materials, ...).
Normal households use fueled stoves and city lights are often gas-powered nowadays.

Goal: I am aiming to drive most of the machines that do actual work (e.g. drive/propel vehicles, produce electricity, move crankshafts, etc.) as well as things such as heating to be steam-based/powered.

As an explanation for the technological advance and widespread use in/of steam-technology in one of my nations/regions I am going to use the fact that there's hindrances preventing them from actually making good use out of combustion-technology.

Q: What are these hindrances that make the development and use of steam engines preferable over that of combustion engines?

My own ideas into that direction were mainly to make crude oil a very limited resource for the areas where this nation resides at, thus making it expensive and unappealing for using it as a common fuel. Instead I would've made wood, coal, peat and, of course, whale oil more readily available resources.
Thus, my thoughts go, the non-fluid fuels would still provide lots of energy when burned, but cannot be as easily used in an ICE.

Clarifications:
This question is looking for answers that leverage concepts and materials that actually exist.
This question is looking for answers that explain the whys and hows behind their proposed solutions. This question is not looking for more phlebotinum.
This question is not looking for lists of ideas without explanations.

• Are you looking for a hard-science answer? – Raisus Oct 7 '16 at 8:22
• @Raisus I am not averse to facts and numbers, but adding the hard-science tag would limit people - thus I did not include it – dot_Sp0T Oct 7 '16 at 8:26
• I think one of the Charlie Stross novels has a planet with nuclear powered steam engines as ubiquitous transport, due to abundant atomics but not much conventional fuel. – pjc50 Oct 7 '16 at 12:43
• No petroleum (or very little) is probably a sufficient condition. – RBarryYoung Oct 8 '16 at 18:59
• We still do prefer steam for many things like power plants. the efficiency is is comparable between the two. the biggest reason internal combustion won was becasue it was faster to start. a steam engine has to warm up. – John Dec 16 '16 at 19:44

## Thermodynamic Cycles

The thermodynamic cycles in major use today are Rankine (steam), Otto (gasoline engines), Diesel (obvious), and Brayton (gas turbines). There exist other cycles; I'm not as familiar with them and I won't cover them.

The major difference between the Rankine cycle and the others is that in Rankine, heat energy is produced outside of the working fluid, while in Otto, Diesel, and Brayton it is produced inside the working fluid. That is, in Otto and Diesel, liquid fuel is sprayed into a cylinder and combusted to move a piston, and in Brayton a liquid fuel is sprayed into a combustion chamber and combusted. Therefore, the Otto, Diesel and Brayton cycles all require a liquid fuel.

Rankine cycles are still used in power plants and other large scale applications, but fell out of use for mobile applications. Otto and Diesel cycles have the advantage of tiny working volume; all stages of the cycle take place in a piston that is only a liter or so at most. The Brayton cycle's advantage is that is not pressure sealed. A piston has to have thick walls to contain the explosion of inside it and direct that energy to the crankshaft. A Brayton cycle combustion chamber literally has a hole on both ends. No thick walls means much lighter. The Rankine cycle, on the other hand, has both thick walls and large fluid volume so there are limits to how small you can make it, and thermal efficiency drops sharply at small sizes.

## Remove Liquid Fuels

To make the Rankine cycle a better option for mobile applications, the solution is to make liquid fuel less accessible or unaccessible. If there are no petroleum deposits, then fossil fuel is going to come from coal and coal alone. Coal can be turned into a liquid but that would not likely occur to people as a good idea unless there was a pre-existing use for liquid petroleum.

The OP already touched on this so I'm concentrate on an alternative.

## Remove all Fossil Fuels

If you want to be more exotic, remove fossil fuels altogether. The geological conditions were never correct for fossil fuel development and no extensive oil or coal deposits ever formed. Remember, the Rankine cycle can use ANY external heat source. There are lots of whacky solutions like sunlight concentrated in a magnifying glass, magic crystals, electricity from a battery or rotary capacitor.

But I want to hard sell the technological development chain from radioisotopes to nuclear fission. Certainly this would be large scale departure from regular history, but let me make the case that it is practical.

## Without fossil fuels what else would you use?

The discovery chain that lead to radiation went from studies of fluorescence of chlorophyll in 1819, to fluorescence of uranium glass in 1852, to phosphorescence of certain metals, finally to radiation in 1896 and radioactive decay in 1910. This was all pure physics, no requirement for an industrial revolution to have happened. In that case, the potential for heat energy from radioisotopes, a heat energy that was no available any other way, may have outweighed the danger of losing a Curie or two along the way.

Specifically, there are two long lasting radioactive materials, Thorium-232 and Uranium-238. Both are relatively common and easily mined and each have a distinct decay chain. The key to utilizing them is to take a block of uranium or thorium, and separate out the elements that are in the middle of the decay chain, but still have a half-life of several years. This material can then be concentrated and stored as a power unit. A radioisotope sealed in a lead sleeve will simply generate heat energy at a predetermined rate over time; a hot rock, basically. Perfect for use in a steam engine.

Conceptually, each radioisotope will have a thermal generation rate per mass, and a half-life. It will keep generating heat at an exponentially decreasing rate dropping its output by half every half-life. There is a sweet spot for isotopes: U-238 has a half-life of 4 billion years but a heat output of 8 $\mu$W per kilogram. The next step down the decay chain is Th-234 with a half-life of 24 days and an output of 6 MW per kilogram. One generates marginally more heat than iron, the other will probably melt itself (and radiation poison you) before you are done manufacturing it. Neither are very useful. The sweet spot is half-lives of 1 to 10000 years.

From the Uranium decay chain, useful isotopes could be:

• Th-230 (called Ionium by early researchers), halflife 75000 years, power 0.6 $\frac{\text{W}}{\text{kg}}$
• Ra-226 (Radium) halflife 1600 years, power 168 $\frac{\text{W}}{\text{kg}}$.

From the Thorium chain:

• Ra-228 (Mesothorium), halflife 6 years, power 3.5 $\frac{\text{kW}}{\text{kg}}$
• Th-228 (Radiothorium), halflife 2 years, power 177 $\frac{\text{kW}}{\text{kg}}$

A good range of isotopes for different applications; a locomotive might use the more energy dense mesothorium that has to be relaced every few years, an electric generating station with lots of space the long lasting less dangerous Radium. The significant downside is that you cannot turn any of these off. Cars would be completely impractical since your car would melt in your driveway. But trains and ships that are moving most of the time, and power plants and factories that are working all the time would be just fine.

To finish up, let me give you a little context on the dangers of radiation from these materials. Most of the energy from these reactions (with the exception of Mesothorium) is caused by Alpha particles, which are not very dangerous. They don't penetrate into your body, so while they can cause skin cancer, its hard for them to cause radiation sickness. All told, the direct radiation effects of these materials are then surprisingly low. Using the rad-pro calculator, I got unshielded rem/hr for sitting on a 1 kg block of each material as Ionium: .7 mrem/hr; Radium: 0.2 rem/hr, Mesothorium: ~200 rem/hour Radiothorium: 149 rem/hour.

So Ionium is safe for your kids, Radium is safe by 19th century factory standards, and Mesothorium and Radiothorium, the most energy dense, will make you vomit within an hour and kill you if you spend 5 hours standing right next to it. On the other hand, shielded containers, lead gloves and aprons on workers, and limited exposure could cut that dose a lot and keep people reasonably well. If you can get down to 100 rem/year, there probably won't be too much radiation sickness. Keep in mind, in a coal-powered steampunk world, the smog would be doing just as much damage to the common citizen.

So there you have it. You can eliminate fossil fuels altogether, run your society on radio-isotopes or have them develop into nuclear fission.

• Otto, Diesel and Brayton cycle engines can all operate using gaseous fuels, including using a pyrolyzer to convert wood into fuel gas and feeding the gas into the engine (sometimes done in WWII to avoid rationing). While not very energy dense at all, wood gas fuel still can get the job done. Coal gas is even more energy dense as a possible substitute fuel. – Thucydides Oct 7 '16 at 15:42
• @Thucydides While what you say is true, I argue that if there were no liquid hydrocarbons as a technological intermediary, Otto, Diesel, and Brayton engines would never get past the technical curiosity stage. For the purposes of my answer, gases are not commonly employed in such engines, so I feel comfortable leaving them out of the discussion. – kingledion Oct 7 '16 at 15:51
• Diesel patented a method for running one of his engines on powdered coal ... We had oil so it never became commercial. – nigel222 Oct 11 '16 at 20:36
• I think you are missing the obvious alternative to fossil fuel: alcohols. – Diego Sánchez Nov 11 '16 at 11:10
• @nigel222 it'd be useful if you could link to that – dot_Sp0T Dec 21 '17 at 21:08

To start answering this question we need to look at why and when steam engines were replaced by internal combustion.

When most people think of a steam engine they think of this:

In this case the Flying Scotsman.

But for the sake of this question we need to be thinking of this:

The Keen Steamliner #2

Wait a minute! That looks like an ordinary car! Well yes, it might as well be, it's just steam powered. It's a very late example and it's an oil burner. The simple fact that the external combustion aspect of steam engines can burn any fuel of your choice makes any arguments about energy density of fuel invalid. You can heat the boiler with just about anything. This is the first of your steam advantages, hang on to it.

Heat the boiler? Yes, this is a problem. It's one of the two killers of the steam engine for domestic use, depending on the size of the boiler it can take considerable time to get the water hot enough for the vehicle to run. It's a killer for the morning commute. The other was the fact that while steam cars were competitive you still needed to stop regularly to top up the water as they were open cycle. Closing the cycle is possible but significantly increases the weight you need to carry.

The other great advantage to steam power is that you get full torque from a standing start. None of that revving the engine rubbish, it's full torque all the way. This kept steam power competitive until after WWII for industrial use.

Late steam wagon

Steam was finally killed off by war surplus vehicles and the introduction of the first emissions regulations in around 1950.

However, this in practice is actually the answer to your question. You asked for interwar technology, and in the interwar period, steam wagons were still very much in use (at least in the UK), as were steam trains until 1968.

Let's go past the war and consider a modern steam powered vehicle. It burns oil or petrol, it has a closed steam cycle so you don't need to top up the water. It's user friendly, maybe a little less inefficient than IC but practice there's no difference on the outside. As soon as you take the "punk" out of steampunk and take it to the real consumer you end up with much the same sleek product that we get today.

In practice if you want to maintain external combustion as opposed to internal combustion you're better off with the Stirling engine. This is again a closed cycle engine but capable of hitting the 50% maximum theoretical efficiency, it has a much faster startup cycle as it's heating air not water, and it's capable of running on anything that can generate a thermal gradient. Small demonstration engines have been built that will run on 0.5K difference.

Let's group Steam and Stirling under one heading of external combustion, and petrol and diesel under internal combustion and consider what could force you to stay on external combustion.

The key to this is going to be fuel availability.

The external combustion engine can burn just about anything to run. Whether wood, coal, oil, or gas, or even a Fresnel lens, add a bit of that "punk" back in and all you need to do is generate enough heat and the engine runs, you need to make a few modifications to change between liquid solid or gas fuels, but ultimately it doesn't matter to the engine.

The internal combustion engines can only run on the designated fuel. If the fuel is limited or contaminated you're looking at a couple of tons of dead metal.

• Some ICEs are more versatile than others. Spark-ignition ones are fuel picky, that is certain, but compression-ignition ones (diesels and gas turbines) can be adapted to a variety of fuels. – Shalvenay Oct 8 '16 at 19:24
• ISTR a Sterling engine is very poor at operating across a wide range of power outputs. No throttle-ability. So until electric tech advances to today's levels, it's useless for automotive applications. I'm hoping to see a Sterling hybrid car sometime soon. – nigel222 Oct 11 '16 at 20:43
• @nigel222 yes, that can be inferred from a basic understanding of how it operates. You could run a generator off it for a hybrid engine but you could also use a continuously variable transmission for a direct drive – Separatrix Oct 11 '16 at 20:52

## Hindrances

In steam engines, the water is boiled in a container, producing steam. The steam then expands and travels through a set of tubes, eventually arriving at the piston, which is situated elsewhere.

Steam engines were used to power vehicles in the past, steam trains being an obvious example. However, with the advent of Diesel engines, steam engines fell out of use. This was because the energy losses in steam engines are comparatively much greater. A significant amount of heat is lost on the way from the boiler to the piston. Steam engines are also quite bulky, giving them low power-to-weight ratios.

Now that I've talked about the hindrances to Steam Engines, let me propose a solution that could match your ideas

## Solution

A Stirling engine is a heat engine that operates by cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, such that there is a net conversion of heat energy to mechanical work. More specifically, the Stirling engine is a closed-cycle regenerative heat engine with a permanently gaseous working fluid.

Closed-cycle, in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and regenerative describes the use of a specific type of internal heat exchanger and thermal store, known as the re-generator. The inclusion of a re-generator differentiates the Stirling engine from other closed cycle hot air engines.

Stirling engines have a high efficiency compared to steam engines, being able to reach 50% efficiency. They are also capable of quiet operation and can use almost any heat source. The heat energy source is generated external to the Stirling engine rather than by internal combustion as with the Otto cycle or Diesel cycle engines. However, it has a low power-to-weight ratio.

Since such an engine has a low PtW ratio, you'll want to adjust this. With modern materials such as Aluminium, we could easily adjust the weight of a Sterling Engine to have a much higher PtW ratio.

## Alternate Solutions

Other solutions could include the following:

${\displaystyle \eta ={\frac {work\ done}{heat\ absorbed}}={\frac {Q1-Q2}{Q1}}}$

where, Q1 is the heat absorbed and Q1−Q2 is the work done.

Please note that the term work done relates to the power delivered at the clutch or at the driveshaft.

This means the friction and other losses are subtracted from the work done by thermodynamic expansion. Thus an engine not delivering any work to the outside environment has zero efficiency.

Change this or make engines that use Internal Combustion fuels (Brent Crude / Petroleum / etc.) less efficient and you'll find that people will make Steam and other External Combustion engines more prevalent

• +1 for mentioning the Stirling cycle engine. While there are still many issues in complexity and power to weight ratios, at least you eliminate the danger of the boiler and live steam. I suspect if high strength materials had been invented earlier, Stirling engines would have had a much more prominent place in the 19th century world. – Thucydides Oct 7 '16 at 15:38
• Another +1 for the Stirling cycle - you don't need to keep topping up with water, and they can be built to run on a wide range of heat sources - I used to have a little Stirling engine that would run on the heat of your hand (or bright sunlight). Not enough power to run anything else at that size and heat difference :) but a great demonstration of how it worked. – JerryTheC Oct 8 '16 at 15:14

(Nitpicking) Steam engines were much faster developed in reality and are still popular way to go in power plants (especially nuclear ones).

To answer the question i would look into where the differences lie.

1. combustion engines are more efficient because basically they not only harvest the thermal energy but also kinetic energy from the explosion. But this requires more understanding about how combustion works. Over the thumb steam engines reach around 30% energy efficiency while combustion gets close to 50% (still poor to the >95% for electrical ones... - but there you have an example of a less efficient technology overtaking a poorer one).
2. combustion engines are smaller - not only since they are more efficient, but steam engines also require a regeneration system to turn steam back into water for the next cycle.

So for your world you could

1. set it at a time before combustion was understood well enough
2. efficiency is not an issue (it was in our world not really till the world wars)
3. cheap(er) sources of energy that can not be combusted. Think nuclear or more simple coal. A real world example are steam engines powered not only nuclear but also solar radiation is commonly used.

1. having more powerful materials so all engines can be smaller
2. having higher energy densities in fuel
3. have a simple source for clean water so it wouldn't need to be regenerated
4. all things that lower performance requirements on the machines - like lower gravity, smaller people, lighter materials, etc.

OTOH if you aim for a modern world you might need to reason away synthetic fuel. Even plain alcohol would work for a combustion.

Having written all this there is still a large part of the society. Causes may be

• all powerful companies could block the development of combustion
• a religion might forbid combustion
• a society that is averse to innovation

As you have noticed english is not my first language. So I may have used a few words wrongly. But I would like to adress the critiques. tl;dr — just longer explanations, same conclusions. If you find spelling or grammar mistakes feel free to correct.

First a short excursion in physics. When it comes to convert energy from one form into another. For most conversions it is theoretically possible to achieve 100% conversion rate. Say electricity to motion, motion to heat, potential energy to kinetic energy. Only thermal energy is an outsider - due to thermodynamics you can at most get the efficiency of the carnot cycle, and this efficiency basically on the temperatures and pressures you are working at. So what does this practically mean - if you could build a heat engine where at the low temperature end would be 0K it would reach also 100% efficiency (theoretically). Obviously practically this is not really feasible not only due to the cooling requirement but also would would have to deal with solid water in your engine. But cooling this side a little can provide some extra efficiency. A more promising increase is to increase temperature and pressure on the high side. There one is limited by the materials available. During my education 10 years ago that in typical commerical possible scenarios one could expect 30-40% conversion rate, if one could build an engine larger and use experimental materials higher rates may be possible - but was considered not a good alternative. I had a look at the link provided in the comments - but personally I am always a bit wary about the numbers claimed in a prospect, I did a search myself and was unable to find other companies claiming similar performances. The numbers were certainly theoretically possible but without knowing how large, heavy and costly such an engine would be I find it impossible to judge if it would suit for a vehicle.

Now to technique. I misused the words for combustion. Wikipedia differentiates between internal and external combustion engines. For this discussion the important differentiation is in external combustion engines (which I called steam engines) the burning of fuel takes place outside the work cylinder. This means all chemical energy is first turned into heat and then transfered to the work cylinder. Therefore the efficiency is totaly defined by the conversion from heat into mechanical work. In difference in internal combustion engines it is possible to directly harvest some explosive (=mechanical) energy from the combustion. This always gives the internal combustion engine a little edge as this conversion is at a much better rate than the conversion from heat.

During my education I learnt that car engines had about 40% conversion rate - and nowadays car companies broadly show numbers around 50% for their engines. Again more is possible if the machines are built larger and from better materials at some cost.

I also would like to slightly correct about the "work medium". As stated before in the internal combustion engine the gas that also propels the cylinder is the same that is used in combustion. In external combustion engines you have different media - one from the combustion, and a second (e.g. steam) that goes to the cylinder. This means on one side external combustion engines need to be more complex since they need to transport around two media and therefore usually larger and heavier. But in some context this is beneficial - consider if you would have very corrosive or dirty combustion, than the additional circuit would prevent the work cylinder from getting dirty and corroded. I mentioned that you usually would have some extra machinery to regenerate the steam into water. But I forgot to mention there is another way - one could just bring along enough water so the loss of steam can be replaced. But again this means dragging along a lot of extra mass.

• And how would you rephrase the question? – dot_Sp0T Oct 7 '16 at 8:35
• Keep in mind directly comparing combustion engine efficiency to electric engine efficiency is misleading, because electricity is often generated as the result of a steam turbine in a powerplant somewhere. – enderland Oct 7 '16 at 12:21
• 50% for a combustion engine requires an extraordinary good setup. Further, the earliest combustion engines were far away from even the 30% you name for steam engines. Without the cheap oil available when combustion engines took off, the development of better combustion engines up to the point when their efficiency exceeded that of stream engines perhaps never took place. – Holger Oct 7 '16 at 12:44
• @enderland: well, either you compare the engines alone, or you compare the entire supply chain, which implies that you would have to consider how much energy oil drilling and refining costs and how much transportation costs. Unlike electricity, the fuel does not flow through a wire. Dishonest is to demand, that only the electricity generation cost should be considered… – Holger Oct 7 '16 at 13:18
• "Over the thumb steam engines reach around 30% energy efficiency while combustion gets close to 50% (still poor to the >95% for electrical ones... - but there you have an example of a less efficient technology overtaking a poorer one)." What? This is terrible grammar and also wrong. Electric motors are ~%95 efficient but they require a source of electricity which is NEVER %95 efficient. Your estimate for combustion efficiency is way high and steam is way low. brighthubengineering.com/power-plants/… – Sam Oct 7 '16 at 15:40

The reason why 99% (my personal estimate) of our real world vehicles are powered by internal combustion engines has to do with energy density and the cost of that energy. 1 gallon of gas contains 114,000 BTUs of energy. Using wood pellets (probably the most efficient wood fuel source but I do not have facts to guarantee this presumption), you get about 8,000 BTUs per pound. So 14 pounds of wood pellets gets you roughly the same amount of energy as 6 pounds of gasoline. If you tweak your forests a bit so they produce slightly more energy when burned (not too much or you'll have odd incongruities like kitchen stoves that melt or torches that have to be quite long so people faces don't burn.) This page was interesting to me because different species of trees produce very different thermal outputs.

Also, you mentioned that tunneling is harder so it could be assumed that drilling is harder too. Cost is a factor in our real world decision to use gasoline over wood. Deforestation is a reality. How many forests would we have left if we burned wood for cars too? The scarcity of wood would drive the price of a house through the roof (badump ching!). If the oil in your world is located in shale or tar sands, the cost for extracting it would be even higher (presuming they haven't invented fracking yet). Genetically engineer a tree that gives ~10,000 BTU per pound when pelletized and grows like bamboo, and you'd have a viable competitor to gasoline even in the real world.

You could also go the Tyranny of Small Decisions route and throw in some other minor things that make gasoline less attractive. Maybe the king was burned by naphtha as a child and hinders research into refining by refusing to grant land rights. Or maybe your world's JP Morgan owns an interest in an ammonia plant and refuses to invest in oil technologies so no one else invests because they follow the "smart money". Or maybe a religious sect in your world refuses to use gasoline because it comes from the ground and is therefore a product of Hell.

Ultimately, the "Why" behind everything is money. If you only changed the amount of time between the invention of the steam engine and the invention of the internal combustion engine, you could easily pass off a reliance on steam power as path dependence.

• Coal is around 10,000 BTU/lb – Separatrix Oct 7 '16 at 14:58
• That's darkly funny. It takes millions of years to turn wood into coal and we only gain 2,000 BTUs from the process. – Tim Oct 7 '16 at 15:00
• @Tim Actually, it is a net loss. Despite the higher energy density of coal, some amount of wood turns into a much smaller amount of coal. – Hohmannfan Oct 7 '16 at 15:04

Religious beliefs can explain just about anything. Perhaps the idea of using oil (the product of decomposed plants and animals) is abhorrent.

If it's alternate earth, make oil & gas very expensive or unavailable in your world. If barrel costs hundred times more I'm pretty sure the cars would be quite different, or if they can't be economical we would be stuck with riding public transport.

P.S

Oh and whales would probably be extinct.

• Oil and gas already cost hundred times than at the beginning of the combustion engine based cars. The history plays an important role… – Holger Oct 7 '16 at 12:48
• Also, no alcohol – RIanGillis Oct 7 '16 at 16:31
• And make coal really cheap - lots of shallow coal seams. – Patricia Shanahan Oct 8 '16 at 22:05

All it takes is one horrific accident in the early days of a technology (e.g., Hindenberg) to put people off from the technology. If there's enough luck to not have that accident before people realize it's likely to happen sooner or later and take steps to prevent it (like switching to helium), the technology can take off. If not, not.

So there was bad luck, and a horrible gasoline accident made people realize that every gas tank holds the explosive power of a neighborhood-leveling bomb (true), and steam takes over the marketplace. The reason why we don't have huge gasoline explosions routinely today is only because we figured out how to prevent them.

• It's an interesting mention, but I feel obliged to point out nonetheless that the Hindenburg has been loaded with hydrogen because the only country producing enough helium to fill the ship did suddenly change their minds and decided not to sell the helium they assured to be selling before the Zeppelin Reederei started building this enormous airship :) – dot_Sp0T Oct 8 '16 at 8:12
• Cool. I sure didn't know that. (Truth is, I always wondered why Hydrogen seemed like a good idea.) But today, when any industrialized country can produce enough helium, airships might be in common use if they hadn't been nipped in the bud. History is full of products that died on the vine because there was a terrible accident when the product was new(-ish). Gasoline certainly could have been one of them, especially since there were always multiple alternatives. (True, I did completely avoid the issue of diesel; diesel fuel is really hard to make explode, even if you want to.) – Jeffiekins Oct 9 '16 at 4:32

# Heat the road, Jack Steam.

Let's say the Stirling engine was invented in a region where parts of the ground are quite hot by natural means, e.g. near a Volcano, or the Granite that hinders your tunnelling is radioactive above average. In that case it seems likely our Mr. Stirling and his mentor Cugnot could make a convincing case for everyone in that region to use Stirling-Cugnot-Automobiles what with no need to fuel them thanks to their getting heated by the ground heat.

Since it's a regional phenomenon, air travel was still preferred, but thanks to this different start the Stirling engine became the established standard. Thus, cities started heating their sewerage and thereby the roads in order to let their inhabitants also use the boilerless cars - establishing teleheating as another standard en passant. This probably also increased urbanization, although the ever-improving Steam technology ultimately allowed the introduction of Steam coaches for rural areas without road-heating.

• Could you elaborate on how these vehicles would have, as you call it, no need to fuel them? – dot_Sp0T Oct 11 '16 at 8:23
• What I mean is in those regions with the hot ground, that heat would be enough to power a Stirling engine (though probably a larger heat sink would be necessary since the surrounding air would also be warmer), i.e. the ground heat is the "fuel". – Zommuter Oct 11 '16 at 8:59
• I don't see how that heat could be used to drive a moving vehicle. How do you harvest the heat? How much heat needs to be provided from down below and wouldn't the heat quickly dissipate via the air? – dot_Sp0T Oct 11 '16 at 9:09
• Dissipation would indeed be the reason why the first models would be not too efficient or require the expansion cylinder (assuming an Alpha-style engine) to be close to the ground or even dragged along. Later iterations would probably simply use good heat conductors in the wheels. Concerning the how much, I haven't done the maths (yet), but let's say the special region has an active natural nuclear fission reactor underground (which the inhabitants have not understood yet but someday will), that could yield about 100 kW. – Zommuter Oct 11 '16 at 9:18
• ...not much, but probably enough to give the engine the boost it needs before cities start to actively the roads. Probably some heat recycling above vehicle level would be introduced for efficiency... – Zommuter Oct 11 '16 at 9:19

What are these hindrances that make the development and use of steam engines preferable over that of combustion engines?

Interesting question. The answer is straightforward. External combustion engines can be fueled by damned near anything that can be burned in a controlled manner. There also is concentrated solar thermal energy.

Now, external combustion includes such cycles as the Stirling - and someone mentioned it. However, getting good performance in a Stirling is very difficult and consequently very expensive. A surprisingly simple piston steam engine system can be literally just as compact and powerful as a modern gasoline engine. The peak efficiency is NOT nearly so high. However, the efficiency of this very simple system can be 20% net.

As to your question, the hindrances to using steam include the ready availability of inexpensive fuels that can be easily adapted for use in internal combustion engines. Interestingly, wood fuel is easily adapted for use in internal combustion systems using gasification. However, a fully developed steam engine system would show superior performance with wood fuel.

There also is solar thermal that I mentioned previously. By far the most inexpensive way to store solar energy for electricity generation has been demonstrated to be storing pressurized saturated water in steel piping with soil used as a thermal mass and with the entire system contained in a highly insulated enclosure. Steam is taken from the system and used to drive a highly efficient compounded piston engine.

With respect to biomass fuel, consider grass as a fuel source. Pelletized grass burned surprisingly well.

In summary, a society that cannot for whatever reason maintain the complex capital structure required to sustain a high level of technological advancement would do well to optimize relatively simple technology like piston steam engines using fuel sources that are readily available including solar thermal, biomass of all kinds, and solid fossil fuels such as coal… or otherwise too costly to process for use in the ICE.

• Your answer might be good, but your formatting makes it very hard to read. Please consider editing your answer to make use of paragraphs & subtitles. Also consider linking/quoting where you make claims such as xyz has proven to be superior to vw – dot_Sp0T Jul 3 '17 at 12:18

A variant of the no liquid fuels idea could be that there are liquid fuels but all known deposits of them have dangerous/toxic impurities that are too costly to remove for mass production use. For example, maybe plants in the Red Queen battle had to have strong venoms to prevent them from being overgrazed and those venoms survived and developed higher concentrations as the plants were broken down over time into oil, so that smoke from burning it without purification spreads a potent nerve gas to anyone in the vicinity.

I also take issue with those who say that "steam power" in the colloquial sense as a defining characteristic of Victorian technology, really is about the steam. In my experience one reaches more sensible conclusions if one assumes that the word "steam power" is really code for coal power, as historically, petroleum was not available until decades after the steam age and was used to power mobile steam engines only briefly.