User talk:John of Paris/Archive 1

Archive 1

Rewrite External combustion 11/03/07

Just a couple of points for Eric Norby: Re "It is then cooled or exchanged for cooler fluid (open or closed cycle"). Can't think off-hand of a case where an open cycle application needs to be cooled. Usually the issue is to prevent the steam from cooling throughout the cycle by avoiding wall effects etc. What often happens is heat recuperation at the end of the cycle, usually for feedwater heating etc. Feed can be heated in two ways: i) by waste combustion gases (economiser) and ii) by exhaust steam in many ways. The other point is that, at least in the case of steam what differentiates internal from external combustion is that a variety of radically different types of "heat exchanger"/"generator"/boiler can be married to an equally large variety of radically different types of "engine unit", "energy convertor", "expander" "mechanism" or what you will. Finally why, when discussing heat engine technology are we only allowed to envisage this question in terms of heat. Heat in itself never produced power; what produces power in any "heat engine" (EC, IC or even a Stirling) is surely the effect of heat on a fluid. In such a case pressure surely has to be an important consideration. Sorry to get back on my old hobby horse again!--John of Paris 17:21, 12 March 2007 (UTC)

---

John of Paris,

You are correct. Open cycle removes the necessity of "cooling" the fluid. That is true because the exchanged fluid is cool when entering and can cool the cold side. I suppose it is possible to evict the hot fluid from the cold side and pull cold fluid in the hot side, thus potentially needing a cooling system to cool one side just to eliminate damage to the mechanism, but that might likely be a result of poor engineering.

The sentence is vague and needs to be improved to the following. "It is then cooled (closed cycle) or exchanged for cool fluid (open cycle)". Sorry, I hashed it up when I was striving to be brief.

The heat exchanger, recuperator or economizer, in a steam plant are not necessarily just used just for open cycles, although I don't personally know that. I assume they can be used to heat either feed water, fuel or even oxidizer (air) to economize the plant. I don't know how much that is actually done. In a closed cycle, the feed-water can be used to cool the condenser.

This paragraph is in regard to the convertibility of moving a steam engine to any boiler system. Think about this. If you inject into the input of a steam engine liquid oxygen and hydrogen, slight modification of adding an input "burner", you could run steam engines off an internal combustion that generates "steam". Making any steam engine an internal combustion engine. Some rockets have used that process. Thus the terms are very general and not really used for or in engineering equations.

As far as the "heat" doing the work or not, think about the "fluid" as an integral part of the engine. The heat is the one consumable part, i.e., the input. Output is both work (motion) and waste heat. In addition, pressure doesn't produce work unless it is allowed to expand/escape. So the point is that no one part of the machine is sufficient to produce "work". However, heat applied to an open body of air produces motion/work without any other parts. They are called heat engines because you input heat, waste heat and get useful work/engine motion out of them.

Furthermore, one type of heat engine is the thermocouple. No gas. No pressure effects. Just electron flow/work as a reaction to heat. There is at least one liquid engine, some liquid to solid engines, and at least one solid to solid engine. Also Nitinol memory metal, as well as a whole host of other heat engines not using gases or fluids, such as a solar cell.

It all depends on how much you believe. If you believe definition must be true, you will never get past the semantics. If you see a clearer way of describing the situation, by all means, please type forth!

Just to add confusion to the issue someone should add that the external heat source could also be internal to the engine surrounded by the working fluid. An example is the case of the nuclear-cell fueled Stirling Engine where a small chunk of hot fission material is placed inside the hot section. Imagine being able to completely seal an engine and insulate everything hot, everything but the side that is supposed to be cold anyway. Excellent!

Wow! This soapbox I'm on is extremely high! ;) Eric Norby 15:49, 14 March 2007 (UTC)

---

Welcome onto the soapbox, Eric! Hope it doesn't collapse under the weight. As you no doubt have gathered by now I am not a mathematician, nor an engineer but am fascinated by systems and engineering philosophy. I think that where we differ fundamentally is in our evaluation of the mathematical approach compared with the semantic one. I don’t know if I believe “definition to be true” as you put it (not quite sure what you mean there), but what I do firmly believe is that there has to be a trade-off between the two, but with this proviso: if you don’t check your semantics now and then, mathematical theory will increasingly send you off on wild goose chases and ever further away from practical reality. No matter how “far out” we take our reasoning, we should constantly try to keep our feet on the ground; therefore definition of the parameters involved must be as accurate (and easily comprehended) as you can make it. I really don't view semantics as a limiting factor; on the contrary to me it's an essential discipline to acquire and enables you to approach your subject from as many facets as possible; in this way it should not engender a restricted, blinkered, reactionary view as you seem to suggest.

First a minor point: I never said that feedwater heaters and economisers were exclusive to open-cycle engines. The exhaust steam feedwater preheater recuperates residual heat from the steam whilst the economiser does so from combustion exhaust gases; this can happen whatever the cycle involved. What I was trying to say was that they are the only source of heat drop (cooling?) that I could think of beyond that which could be imputed directly to work. I am afraid I do not understand what you are talking about when you say things like, “exchanged fluid is cool when entering and can cool the cold side”; I can only see words there and can’t visualise their implications. In a steam engine, which for the moment remains the main topic of discussion in this article (and perhaps that should be remedied), as far as I can see the exchange is always in the same direction: from hot to cold, the heat being diffused into cooler bodies and reacting on them. At no point is the flow from “cool” to “hot”; (note that I am talking specifically about generated heat here, not about about the working fluid, once again two related aspects that are more conveniently considered separately). The engineer’s main task is to make sure that combustion of a given fuel is the most complete (and pollution-free) possible and that the heat generated is eked out as much as possible according to the work demanded. In this regard I fail to see how theoretical efficiency can be separated from fuel efficiency, as is often stated. The one must have repercussions on the other, otherwise I strongly suspect that some important parameter is not being taken into account on the theoretical side.

Your fifth paragraph only reinforces my view that pressure, created by the effect of heat on a fluid is what actually does the job. The whole point is that the gas under pressure, initially created by heat transfer to a fluid is encouraged “to expand and escape” in order to produce the work of which heat alone is incapable, so a gas is always the vehicle for transferring heat into work and surely as such pressure and fluid dynamics are equally worthy of being taken into account as heat — and of course they are interdependent. And as for your example of heat in free air, you are again dealing not with heat alone, but the effect of heat expanding a zone of free air causing it to rise and have potential to do work.

When you talk about thermocouple, nitinol or solar cells, I wonder if you are referring to components of engines or to self-contained prime movers capable of the complete process of transforming fuel combustion into work: i.e. driving machinery on land, sea or air? If so, then I for one would like more information.

As I said above I have problems when a whole process is considered only in terms of heat transfer as that only allows a restricted view of the process and encourages the concocting of ever more complicated and obscure jargon.

Most of what is discussed in this external combustion article for the moment concerns steam engines of various sorts. What is the process involved here? - A fuel is combusted in some way, changing its state as it does so. This gives off heat, boils water transforming it into its gaseous state called steam which tries to expand inside a container of constant volume, hence creating pressure. From this stage onwards, I do not say that heat is unimportant, but that it is only a relevant issue inasmuch as temperature has to be kept above boiling point in order to prevent premature condensation. You do this by means of thermal insulation, a high "temperature ladder" through superheating and eventually by reapplying heat at later stages in the trajectory where condensing threatens. In multi-stage and compound steam engines, there are more points for this to take place which is why there has sometimes been recourse to inter-stage re-heating or more usually re-superheating of the steam and this means that temperature is likely to be higher with more heat lost to atmosphere at the end of the process and why the provision of exhaust steam feedwater preheaters becomes doubly important. For steam locomotives the extreme importance of avoiding heat wastage through radiation from boiler; external piping and cylinder ends and conduction by way of the chassis was only fully understood by Livio Porta in the Forties and Fifties when it became too late in time to extensively apply “drastic insulation” as he recommended. All the above are means to an end, the end being maintaining pressure thoughout the steam's trajectory by maximising its expansive properties and consuming as little fuel as possible according to the work in hand. These principles were already well grasped by James Watt in the 18th Century and by the few 19th Century engineers not too involved in the daily grind of keeping the wheels turning to have found time for reflection; these last factors have tended to hold technology back along with contemporary limits of material resistance and of lubricant stability.

Going back to semantics, I would even question if it is correct to speak of “cycles” in many cases. A cycle by definition repeats itself over an indefinite period, going round and round or oscillating back and forth, so it is bound to be “closed”, - so is it not absurd to speak of “closed cycles”? “Closed” is surely a redundant term here. On the other hand, if the steam is released to atmosphere after performing work - well where is the cycle? And how is it an “open cycle”? By that token, is a piece of string an “open loop”? Is all this important, or just splitting hairs? Well I think it is important: it keeps your feet on the ground and stops from you going off into unproductive abstractions. --John of Paris 18:15, 18 March 2007 (UTC)

You're being too literal; and note that the wikipedia has to stick to the standard terminology. But it's still a cycle. The cycle goes via clouds, rivers etc. back into the engine :-). WolfKeeper 19:04, 23 March 2007 (UTC)

Surely the very process of semantics entails "being too literal". - And "everything" is part of a cycle when it comes down to it, that's the way things keep going. I was simply suggesting that as far as an engine is concerned, the action of heat upon it is perhaps more conveniently viewed as a component of "the greater cycle", i.e. as an open-ended process. That's not being literal, it's trying to define something i.e. to come to some sort of an agreement as to what we mean by a term. My point is I that perhaps now and again we should stand back and review what we are actually talking about and whether our ways of expressing a phenomenon are well-adapted. That said, I will always avoid putting non-standard terminology in Wickipedia - or any encyclopedia, which is why I have reserved my remarks for this talk page. Even so, I have long been unhappy the term external combustion itself as it often gives strange slants to dicussions, especially on steam technology with people only familiar with IC and I wonder just how long the term external combustion has actually been around. I seem to have only seen it for a few years, not so long, perhaps as Internal combustion which in my view is well adapted to describing the phenomenon of the "short " process that take place mainly inside a cylinder. I get the feeling however that external combustion may have been just coined as the converse of IC and as such is less well-adapted to representing the "long" chain of events that go to make up the steam process. In French neither term exists, they just speak of moteur à explosion, à vapeur , à air chaud... For a language so rigidly governed by an Académie where they like to "have a word for everything", this is intriguing, to say the least. I'd like to know what happens in German, Russian, or Japanese...--John of Paris 10:03, 24 March 2007 (UTC)

---

John,

The pressure and volume increase are the work. The pressure is the engine. The volume increase is the work. What makes the pressure? Heat. What makes the volume increase? Heat. Therefore anything with a substance in any state that has a delta V/ delta T, change in volume divided by change in temperature, is a heat engine. It will develop a pressure by being heated. The fact that motion of the pressure is converted to other mechanical motion is not really as important for the criteria of being an engine, although many erroneously thing of it that way. To be a heat engine something must move because of heat, be that by pressure or by voltage, or by ???

For a steam engine. The engine is the steam, the conversation of a low volume water to a high volume/pressure steam, is the conversion of heat to mechanical motion. The rest of the mechanism doesn't supply any more work to the situation.

Pressure and volume increasing are the engine working, and they are working because of heat addition. The turbine blades are just a windmill. The engines are not "pressure" engines, they are heat engines because it is the heat that causes the work. That work is then converted to different directions by the mechanical/electrical device.

The mechanical device just dictates the type of heat engine. Those engines can be organized in common terms several ways. By fuel, by materials, by configuration, turbine/reciprocating, by heat source, internal and external. And we can call them a multitude of different things. We can again sort them by name, or any other criteria.

I guess it depends on what you want to do here with the encyclopedia. Do you want to be a director? If so, we could "dictate" that the engines will be called 'internal combustion engines' and 'external heat source engines'. If you want to reflect what is the most used language such that people can adopt the most common usage and refrain from evolving our language to the point it means something else. Such as avoiding the adoption of, "Baad" meaning "good", and "good" meaning "well". We can attempt to get our historical reason for the term and the proper use and viewpoint of it.

IMHO, keeping the language somewhat static is the most important part of semantics. The best way to do that is to point out how some words are currently being used erroneously in a slang form but watch out for those usage's they are Bad example 1, BE 2, BE 3, etc... And to use the historical account of how a word was fist coined and how it came to be used as it most commonly is. Perhaps with a slight push towards the historical meaning.

Example: Rather than "computer" meaning "man" or "electronic device" it could mean both. With a point that computer is short for electronic computer. Rather than calling it an electric torch, or flashlight, point out that torch is short for electric torch. As long as the reference here suggest a proper historical use of the word and a slang inappropriate current use, we will have better understanding and lack of change. Do you really want to call it earth-turn, or sunrise?

For the point of this discussion, the mechanical contrivance is considered the engine, because the engine is what shapes the cycle and the idea cycle the engine is closest to usually gives it the name. Modeling the engine more precisely will give the engine and cycle additional names. An example is: The Schmidt Cycle model of the Stirling Engine. Note: Nether the Stirling cycle nor the Schmidt Cycle have been fully realized in any engine.

Picture the trouble separating playing cards by different groups. Reds/blacks, or numbers/face, or odd/even or the four suits, etc... No single game uses all possible sorting schemes for the cards, nor does any one sorting scheme make sense in all games.

Sorting engines by internal or external is the same. It won't be correct in all situations. Identifying that viewpoint will show the appropriate way of using the strength of the sorted viewpoint, semantics or not. I encourage improvements to the definition such that people will have improved viewpoints with improved efficiency of using the encyclopedia. Eric Norby 15:47, 23 March 2007 (UTC)

You say that “keeping the language somewhat static is the most important part of semantics”, and believe it or not I agree with that, at least when dealing with a material science subject. So I wonder why you now seem to be bringing modern youth parlance into the debate where context, sociological factors and - and poetical expression - have more relevance to word meaning than just semantics. It’s in scientific research where we have to be very rigourous with our terms in order to avoid talking at crossed purposes. Don’t fall off this soapbox, it is very high! I have never seen work defined anywhere as “ pressure and volume increase”, nor an engine defined as “pressure” as you have just done. My understanding of work is closer to Wikipedia’s own definition of mechanical work: “In physics, mechanical work is the amount of energy transferred by a force. Like energy, it is a scalar quantity, with SI units of joules. Heat conduction is not considered to be a form of work, since there is no macroscopically measurable force, only microscopic forces occurring in atomic collisions;” The terminology there is fairly clear and I can just about hang on; but compare it with the hermetic Thermodynamics article, which seems to come closer to your proposition: “In thermodynamics work is defined as any quantity that flows across the boundary of a system during a change in its state and is completely convertible into the lifting of a weight in the surroundings. It is a path function”. Sorry, but that’s about as clear as mud to me; furthermore I think your own definitions are very reductive and force us to consider a rich multi-faceted problem from only one angle. I imagine that you will criticise my view as mechanistic and old-fashioned. Well aided by semantics I think we can take things much further than they have in the past and further than the purely mathematical approach has done because I believe that the former is easier to grasp. That means we can consult people of a wide range of experience once the “hermetic language barrier” has been broken down and they know what we’re taking about. This is not “dumbing down” but but recognising the richness of the field and that there is more than one answer to any problem.

This brings us to a fundamental problem with writing for an encyclopaedia such as Wickipedia whose aim is to communicate the present state of knowledge on a variety of topics from a neutral point of view (if such is possible); this of course implies referencing all the information you give and avoiding the imposing of imposing personal opinions, rules of the game that I have accepted from the start. No, I have never thought of being a "director" and you may have noticed that I have never edited your contribution (except for the suggested very minor one which started this discussion), nor do I intend to impose my personal opinions which I know go against the mainstream. However the issues I have raised have haunted me for many years and I could see no reason not to get it all off my chest on a talk page. However the problem I have found with Wickipedia is that, especially where technology and technological history are concerned it is overloaded with articles full of very conventional and often factually incorrect received ideas (schoolchild-cramming material and quiz-participant fodder), or at the other extreme more rigourous articles written in obscure and hermetic jargon, occasions for those in the know to flaunt their knowledge to their peers. My concern is precisely for those long-suffering schoolchildren and students who I know (often mindlessly) copy-paste these articles and frustratedly go round vandalising them. But on the occasions when they do actually read them and try to understand them, what intellectual nourishment will they actually find and of what likely use is it to be to them in their future life and career?

Just a PS on your last paragraph: my concern is not so much whether the terms are "correct" or not, but whether they are appropriate to the phenomena they purport to represent. In that context I believe that Internal Combustion is a meaningful term, whereas I know from experience that External combustion is not so and confuses the uninitiated (which does not mean stupid).--John of Paris 12:14, 25 March 2007 (UTC)

As a matter of interest, I just looked up Internal combustion in Apple's Webster dictionary widget and got: "noun, an engine that generates motive power by the burning of gasoline, oil or any other fuel with air inside the engine, the hot gases produced being used to drive a piston or do other work as they expand"; for External combustion I got: "could not be found". Same thing in my Oxford Handy Dictionary, 1986 edition. This confirms my idea that the latter term was coined much more recently and is not yet in common usage (And I for one would prefer it never to be).--John of Paris 13:04, 25 March 2007 (UTC)

---

John,

Just a quick blurb. A gun is a heat engine. By that same token, a stick of dynamite is also a heat engine. However, for the stick of dynamite what is the "mechanism"? Air? More precisely heated gas of the combustion of the nitroglycerin and cellulose, along with the air heated around it as it "expands" outwards making a loud noise/"pressure" differential.

I never thought of a gun being a heat engine until they were described as such in a book called "The Evolution Of The Heat Engine" by Ivo Kolin, Moriya Press ISBN 0-9652455-2-7 (Written and hand drawn beautifully in small sections. Easy for most to read. it has both technical and comfortable descriptions. (Even my botanist/geneticist PHD dad was excited reading parts of it.)

Since reading that book, I've noticed that most things are heat engines in various disguises, however, not all function on the specific process of heating a fluid to develop pressure. Some work on salt and rinse, to contract a collagen. Even a wind mill or water mill, because the heat for those two is greatly removed from the location the engine resides.

I do not know how that viewpoint renders my thoughts regimented, it seems rather to expand them to what else might be an engine/heat engine.

Please, let me get back in a few days!

Always busy, Eric Norby 17:29, 27 March 2007 (UTC)

Well I'm busy this week too and off next weekend. See you next week, if you've got the time--John of Paris 19:25, 27 March 2007 (UTC)

Continued discussionExternal combustion 04/14/2007

John, Let me briefly organize, We are talking Semantics Definitions Cycle Open, Closed Heat Engine Internal Combustion Engin External Combustion Engine Work Modern Youth Parlance

Let me add, Explanations Viewpoints

Definitions should be static, this is mostly a semantic process. Explanations are used to describe those definitions from various viewpoints such that people will understand how the definitions work. Often that requires new explanations from the viewpoint of modern youth and parlance. There is also the process of learning more about the word, or the name, or even what the name is given to. Once we learn more about such an item, we can then perhaps provide an improved explanation. None of that changes the definition, however, the definition may need a minor rewrite to reflect then new information, while keeping the historical content of how that word was first chosen.

Work is defined as force times direction traveled in the direction of the force. Pressure times volume-increase equaling work/energy, is a rewrite of the same definition. It changes nothing. It is a derivation, a new viewpoint. Pressure is force per area, P. Volume change is just area times direction increase VC. P x VC = Work P = F/A VC = A x DL

F/A x A x DL = Work

The "A's" cancel we get, F x DL = Work

Force times distance moved = work, often expressed in Joules.

There is nothing new about that. It is just multiplying the equation by A/A, top and bottom by A, or One.

My previous letter should have added light on the definition of "heat engine". However, let me just say that pressure is not enough for a heat engine to work. It must have differential pressure. The way a heat engine gets differential pressure is by heating some of the air, or cooling some of it or both. However, many heat engines do not work on pressure differential, they ignore that and go straight to pumping electrons. Thermocouples, solar cells and Fuel cells seem to be the most popular types.

I doubt you will get much challenge to a thermocouple or fuel cell, being a heat engine, as both require "heat" and one also requires combustion. Solar cells being the exception, one must remember that heat absorption is accomplished by photon absorption and direct motion interaction, which also may involve a photon interchange, I don't know. So a solar cell absorbs, photons, just as a heat engine absorbs heat.

Again that is a viewpoint difference, and improvement, not a change in the definition of heat engine. It is a change as we look at new devices that produce a conversion of heat/light energy to another form. It is an attempt to open peoples minds to the idea that they can do work from heat and light, using very similar and way different methods. We do not need to be stuck with piston in cylinder engine configurations if we think Heat Engine.

I see what you are driving at. You see "internal combustion engine" as a specific and easily defined machine. Any engine that burns an oxidizer fuel mix inside the working cylinder is an internal combustion engine.

You would like to limit the terms to that and heat engine. If we do that, what term do we use to define all heat engines be they internal or not? And if they are not internal combustion what term do we use to separate them? Is it beneficial to even have a separation?

I see "external combustion" to be a term that is difficult to define, unless you compare it with internal combustion. All heat engines that don't burn a fuel air mixture, are external combustion engines regardless of actual heat source. However, my comparison added a negative into the opening paragraph that someone disliked. It seemed to be clearer to me.

Would you like to redefine the terms as "internal combustion" and "external heat" engines? If so then, what should we do about the old term "external combustion"?

I find that similar to your complaint about "cycle". Any cycle requires a process of repeating. Open cycles are those cycles that bring new things into the cycle and repeat a process to the new things. Closed cycles repeat the process on the same old things.

Would it help to say "Open to the atmosphere cycle" and "closed to the atmosphere cycle"? "Sealed cycle" and "breathing cycle"?

In which case what do we do about the shorthand old method of calling one "open" and the other "closed" cycles?

I hope this helps, I realize what you are saying and hope we can come up with a solution to what to define these terms, what viewpoints need appropriate explanations, and what historical information we need to provide, so many people can understand that the definition is just a beginning and there is a large world of discovery that the terms open up.

I'm going to go off-line for a while and don't know when I'll be able to get back with you. Work around the farm, is taking precedence now that the weather is getting better. Eric Norby 16:47, 14 April 2007 (UTC)

And so you should! I hope the weather is as you would wish. In the meantime I have jotted down a few comments as they came to me over the last few weeks.

It was a good idea to sort out the themes. As you will see, I agree with you on a number of points. All the same I think we are still ranging rather wide and would like to concentrate the debate on the two closely-related themes, that is to say the definition of Work and the appropriateness of the term External combustion which IMO is ill-adapted to define the steam process.

Concerning Work, your definition is much wider-ranging than mine. Let me take your points one by one...

1) “Work is defined as force times direction travelled in the direction of the force.” (I take it you mean “distance travelled”).

To me Work in this sense is the conventional yardstick used to quantify the force needed to overcome given gravitational and/or frictional resistance (in the past this was measured in foot-pounds) - or else to produce an acceleration in space (how do you measure that?). This limited definition is still quite enough to handle.

2) “Pressure times volume-increase equalling work/energy, is a rewrite of the same definition. It changes nothing. It is a derivation, a new viewpoint.”

No, you are not describing the same thing; there is no Work involved here, as defined in (1).

3)“Pressure P is force per area. (e.g. pounds per square inch).”

Standard accepted definition - no problem

4) “Volume change VC is just area times direction increase.” (e.g. Length times Breadth times Height with increase or decrease of one dimension or more - no problem).

Again there is no Work done here as defined in (1), (e.g. it could not be expressed in foot-pounds).

Pressure or vacuum derives from the tendency of a fluid to change volume being restrained by imprisoning the said fluid within a fixed volume.

5) "P x VC = Work"

Mixed criteria - Volume is a parameter as is Area and Force, pressure is a derivative of force per area as defined in (3)

Again no Work here as defined in (1).

6) "P = F/A"

7) "VC = A x DL" (What is DL?)

8) "F/A x A x DL = Work"

9) "The "A's" cancel we get, F x DL = Work"

(6) - (9) are all abstract extrapolations that I am unable to visualise.

“Force times distance moved (against gravity or friction or acceleration of a body in space as defined in (1)) = work, often expressed in Joules.

There is nothing new about that. It is just multiplying the equation by A/A, top and bottom by A, or One.”

Abstract extrapolation again. You are trying to convince me that there can be multiple definitions of Work. I say that it is only useful to have one. When I talk about to multiple viewpoints, that does not mean redefining parameters, but re-examination of a given phenomenon, from different viewpoints - but using accepted parameters. That’s quite a different kettle of fish. As you see I am in agreement with your definitions of pressure and volume - no problem, and almost in agreement with your first definition of Work. However when you talk about “new viewpoints” you are in reality redefining Work and I can’t accept that as it just shifts the goal-posts and makes it impossible to fully describe an engine of any sort from any viewpoint. As you yourself say, and I agree, "Definitions should be static".

And why bring in thermocouples, fuel cells or solar cells? Do these qualify as “engines”? To me they are heat sources or converters you can eventually apply to different sorts of engines.

And now for"External combustion". I can only repeat what I said about it in my last letter: It is definitely not an “old term” as you put it and I am not even sure that it is an accepted term in the English language; you only have to look in any dictionary ancient or modern and you will find Internal combustion alright, but External combustion..? That is simply to say that my criticising the use of “external combustion” does not go against generally accepted wisdom. “Separate combustion”, a term that I myself often use when trying to put over the specific nature of the steam process to a layman has proved to be better adapted than “external combustion which has proved an endless cause of misunderstanding.

As for “open cycle”, once again if we limit our discussion to the steam-generation process nothing is repeated, it’s a chain of simultaneous events, i.e. combustion, heat transfer and exhaust; on the other hand, I will grant you that what happens to the steam once produced can be seen as an open or closed cycle according to your own latest definition which I accept. We are therefore dealing with two symbiotic but separate events (heat process and a pressure process) to which different criteria can apply.

Now for thermodynamics - and I know I am charging a big windmill there - but as I have no reputation as an engineer or scientist to defend, it’s no skin off my nose. That said I had better not attack it head-on.

Before we start I have to say that one point you make that I do agree with is that what counts is pressure differential, not pressure per se - which makes "atmospheric engine" a bit of a misnomer too and it seems wrong to say, as they did in the 18th century that "the weight of the atmosphere pushes down of the piston"; - "pressure differential displaces the piston towards the rarified volume" would perhaps be more correct.

Yesterday I had a look through the archived volumes of the WP Steam engine article to see how the opening definition evolves. One comment already to be found in the first version, caught my eye in passing and I think it is relevant to our debate: "One source of inefficiency is that the condenser causes losses by being somewhat hotter than the outside world. Thus any closed-cycle engine will always be somewhat less efficient than any open-cycle engine, because of condenser losses." Now this statement looks impressive and authoritative at first but does not stand close scrutiny for the simple reason that any steam engineer will tell you that his biggest struggle comes from the fact that water in its vaporised state, far from carrying heat, is always doing it's damnedest to lose heat and turn back into water again. This is a particularly serious problem with compounds where the pressure range is wide. The solution is to keep steam/water temperature within a relatively narrow range and never to let it drop too low (isothermal) - the last thing you need to do is to let it pass between the extremes of a "hot source" and a "cold sink" — and this in the interests of efficiency - thermal included. In fact this maintaining of water temperature above a certain level cannot decrease thermal efficiency; it has just the opposite effect, simply because cold water entering the boiler absorbs more heat in order to come up to temperature and convert into steam. At the end of the process at least three heat transfer methods are at the engineer’s disposal to recuperate heat remaining in the gases and the steam:

i) hot well (insulated container of warm condensate);

ii) economiser (recuperates residual heat of combustion gases in order to to warm the feed-water)

iii) exhaust steam feed-water heater (recuperates heat remaining in exhaust steam).

The very last thing we can say about any of these economy devices is that they are a “source of inefficiency”, so is it valid to count them as ineffectual “cold sinks” in a heat cycle? No, their efficacy is proven by long use and the only way I can see to get out of the conunfrum is to admit that not one but two separate energy processes are taking place : one in which heat is generated by burning fuel, then transmitted to a working fluid, the rest going to atmosphere and waste; the other is the working fluid itself acting in either an open or closed circuit - once again two separate but symbiotic processes. The decision as to whether any of the above devices is worth employing is not a thermodynamic consideration (they always bring thermodynamic advantage) but an economic one as to whether the extra equipment is worth its capital investment and maintenance costs and whether these are counterbalanced by the savings. In this context, understanding thermodynamics is primordial, but it is not the whole story: in a steam engine, it is clear that where the working fluid is concerned, we are dealing with a separate process; although undeniably dependent on the heat source where the essential role is less that of “carrying heat” (what the French refer to as le fluide caloporteur ) than one of obtaining the widest possible range of expansion and never allowing the steam to cool enough to condense whilst it’s supposed to be producing work. This is done by restricting the lower temperature limits of the working fluid and is the reason why the warmer the boiler feed water by whatever method(s) chosen, including condensation the less heat energy will be expended in turning it back into steam at working pressure. Unlike the combustion/heat transfer process, the steam process can be either open-ended (exhaust to atmosphere), or cyclical (condensing engine). Of course steam temperature is a still an important consideration, but its significance changes and what counts at least as much in mastering the steam process is the effect of fluid dynamics and pressure, the important thing being to maintain at a relatively isothermal state with the minimum of temperature drop.

James Watt had grasped most of this by 1770 and when you look at the main issues preoccupying more recent steam engineers such as Chapelon or Porta, you can see that these have not changed that much - so why all the complication these days? I think that it derives from two main mental impasses whose origins are historical:

i) from the 17th Century, mathematicians and physicists had an all-consuming fascination with fire which for them was a total mystery; they first considered it as one of the Four Elements, next they saw heat as a substance dormant or latent in all matter which could be “roused” in various ways but by the time that the kinetic nature of heat had become generally accepted, the “substance” paradigm was already in place and worked reasonably well for most circumstances (it is strange to think that notions such as “quantity of heat” are still current). As such a sort of self-perpetuating mindset has developed from which we have never fully recovered; with the advance of time the situation has become, not clearer but more and more difficult to unravel;

ii) this concerns more recent history - As internal combustion engines have replaced steam for small and medium to large scale appliances, notably for transport, our main point of reference has nowadays become the internal combustion engine. The main difference between this and steam plant is one of “ length” of chain reaction: in the internal combustion engine the event is almost instantaneous, but I would argue that there is still a chain reaction occurring in two distinct phases: combustion of the inflammable vapour, leading to ultra-rapid expansion of the gas (we are told not to call it an “explosion” - why not? Such is the very definition of an explosion). In the steam engine similar phases occur: combustion, and a pressure phase caused by a working fluid reacting to heat transfer; the distinctive feature is that here each phase occurs separately and “each in its own time”. For instance in a gas-producer system, solid fuel combustion can be slowed and take place at low cherry-red temperature (about 700°C) being slowly consumed avoiding clinker; this produces a second-stage gas that can burn at a much higher temperature giving very high heat-transfer rate. The advantage in transferring this heat to water creating a steam phase is that the steam can be stored for a while permitting energy conservation, the ultimate expression of which is the “fireless” locomotive. Such is to an extent impossible with internal combustion, apart from the momentum imparted to the flywheel.

One aspect these two prime movers, IC and steam, have in common and where both have the advantage over the other big contender, the Stirling engine, is the possibility of rapid speed variation, steam supply being throttled at some stage, whilst with IC the throttling depends on regulating the fuel supply (Diesel cycle) or the intake of the air/fuel mixture (Otto cycle). Both steam and IC technologies have become reliable over time. and all aspects have been mastered in practice.

IC development appears to me to be reaching its limits. About 50 years ago this seemed to have happened with steam, but there are many signs that its long-term future would now seem more promising - on condition of a top-to-bottom rethink of the whole process along with intensive reassessment of historical data.--John of Paris 17:45, 10 May 2007 (UTC)

Just a thought on the IC process, explosions and the like. We are still talking about the EFFECT of heat on a gas. And what is happening? Rapid temperature change gives rise to rapid pressure change and vice versa. The heat generated in a diesel engine or a fire piston comes from a rapid pressure hike; that ignites the fuel creating a still greater pressure hike: that's what does the work whatever the final temperature. In contrast, a steam engine, reciprocating or turbine, does not care whether it receives hot steam or compressed air at room temperature. In the boiler/steam generator, the effect of the heat applied is to continuously convert the water into steam; the more water you convert in a confined space, the higher the pressure that results and that's what does the work. Loss of pressure due to work will bring down steam temperature and condense it turning it back into water. this is why you need either to start the steam cycle at very high temperature or to resuperheat it at an intermediate stage enabling it to continue to work at lower pressure. Temperature and pressure are therefore complementary, but temperature is always the "slave" to pressure.--John of Paris 10:37, 13 July 2007 (UTC)

Archive 1