Talk:External combustion engine

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[edit] Scope of what this definition should contain

I rewrote the introductory paragraph. It seems to me that we should also add a history section to this definition.

The introductory paragraph needs to spell out the difference between the internal and external combustion engine. The main difference, as I see it, is that an internal combustion engine burns the working fluid, "Internal combustion". Hence, it must cycle the fuel oxidizer mix to have a new charge to burn. The external combustion engine doesn't burn the internal working fluid. The EC engine can burn the external working fluid but the heat can come from anywhere and thus is not a "combustion" engine at all. The IC engine's internal working fluid heats to a high temperature very rapidly, where the conduction of heat for an EC engine requires more time and surface area.

Both the internal and external engines work by the internal fluid expanding from heat. Both run a large variety of cycles. So the difference mainly appears to be whether the fluid inside is burnt or not. If it is an inert fluid it will not burn. It doesn't need to be inert to not burn.

The history should mention some of the first EC engines built and theorized, specifically the steam/vacuum and steam engines and those experiments of Guericke and Denis Papin, Savery, Newcomen, James Watt, and Ericsson.

We could also mention the difference between an IC engine, EC engine and a theoretical engine.

One more thing: Many EC engines have been built and run with no heat exchanger, what so ever, they work by directly heating the outside of the engine mechanism/cylinder itself, and cooling it or the opposite side. A heat exchanger can be built into the mechanism or be a completely separate entity. Either way, a heat exchanger is an addition to the basic operating mechanism and should not be considered as a secondary function of that structure.

If anyone has some improvement to the above viewpoint, or main article, please mention them so we can get the best description possible for the main page.

Thanks Eric Norby 17:10, 27 March 2007 (UTC)

[edit] Nuclear fission; non-related?

In the article it mentions steam turbines, which I assume are widely regarded as external combustion engines, also often run on the heat provided by nuclear fission. Nuclear fission, then, must be a form of combustion - which it isn't. Can somebody explain this?

Not qualified to discuss nuclear fission. However I think that as much as anything, your point is a semantic one and as such I have to say that I have long had problems with the whole term External Combustion - not just combustion. I think that the root of the problem is historical. In the early days of coal or wood firing, this was used to heat a boiler to provide steam pressure and that and/or condensation of it did the work. This immediately brings up another problem I have with the term heat engine, IMO heat in itself never drove an engine. What drives the engine is the effect of heat on a gas or liquid; if the expanded fluid is constrained in a restricted space such as a boiler or a cylinder, pressure is created which can be made to act upon a moveable piston or rotor. If we restrict the term "heat engine" to disinguish its working principle from that of a "gravity engine" (water turbine) or an "eolian" engine (windmill), for instance, where the effect of heat is far less direct (sun on the atmosphere), then the situation is clearer. Consequently if you look on nuclear fission as a component of a heat engine or more specifically of a steam engine, its role is no different from that of, say, coal burning in a firebox, which answers your objection. It is when we develop the heat engine idea further that we run into problems. The term heat engine goes back to the very early days of industrial steam. Late 18th Century scientists were fascinated by heat: was it a substance (caloric, phlogiston) or a phenomenon (kinetic theory)? Today the latter theory has prevailed, but a man like Sadi Carnot who laid the foundations of thermodynamics saw heat in terms of the substance, "caloric". (By the way, the Carnot heat engine article is much improved lately). In the mid-19th Century the internal combustion engine comes along with the invention of gas (coal-gas, not gasoline) engines and what is the process there? The same as before only faster: compression or an electric spark or a glowing coil ignites a volatile gas or air/liquid mixture creating a rapid pressure increase which moves the piston. As this all takes place inside the power cylinder and eliminates the requirement for a separate boiler, the process is called internal combustion. The point is that before the invention of internal combustion, there was no need for an opposite term and one wonders when external combustion was coined. I suspect it was relatively recently and what seems likely is that it was coined simply as the opposite of internal combustion. Today when most heat engines you see working every day are of the internal combustion type, that is the term of reference. Being a defensor of of steam technology, I can tell you that the level of ignorance regarding steam, even on the part of many engineers is unbelievable. One of Ted Pritchard's [http//www.pritchardpower.com] quips is something like "we never show the cylinders what we are burning", which aptly sums up the situation. External combustion may be semanically correct and just about applicable to a Stirling cycle engine, but regarding steam engines it represents absolutedly nothing and just adds to the general confusion. I have suggested that we should speak rather of separate combustion. It is interesting in this context to quote the opening sentence in the Wikipedia article: "An external combustion engine is a heat engine which burns fuel to heat a separate working fluid". The difference is that I visualise it in terms of the heat source being separate from power delivery. Of course I am on a personal hobby-horse here (POV) and as such my suggestion has no place an encyclopedia - or Wikipedia. No problem with that, but it does mean that when writing for Wikipedia or any encyclopedia we sometimes have to compromise and accept things we don't completely agree with or cope with inadequate terminology that nevertheless allows clarification of some essential point. I haven't answered your question but perhaps I have shown that it is part of a wider, fundamental one that nobody seems willing or able to tackle - the weight of history! The proof is that nobody has taken me up here on this yet, even though my point of view is very controversial. --John of Paris 11:58, 25 November 2006 (UTC) --John of Paris 09:22, 18 December 2006 (UTC)

[edit] Rewrite 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)

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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)

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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)

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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).

PPS Eric, I'm really enjoying this debate, but it is getting a bit lengthy so I have copied it onto to my talk page and suggest we go over there now--John of Paris 12:09, 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 13:03, 25 March 2007 (UTC)

John,

I will mention two things that seem to apply here, then we can discuss the rest over at your talk.

One is in reference to your confusion about pressure and expansion being work when compared to work being force and motion.

Pressure is force per area. Volume increase (Expansion) is delta volume, volume is length cubed

Assuming pressure doesn't change when volume changes for simplicity, the following is a units formulation.

P = F/L^2 dV = V2 - V1 = dL^3 = L^3

W = F x L P x dV = L^3 x F/L^2 = F x L = W

In English, Pressure multiplied by Volume Change ; is force per square length times multiplied by the change of length cubed, or just length cubed, which equals work

Pressure is force, change of volume (Expansion) is motion

So Pressure times Change of Volume is, force times motion or work as defined.

It is quote often used to express the "work per time" (Power) of a pump by the pressure times the change of volume per time, flow rate per time, or (work per time) Or (Joules per second) (Watts) (Horsepower).

and

I see your goal is to recognize that external combustion engines were invented first cover a wide range, and the internal combustion engines were invented later and hence the term internal combustion was invented to identify the difference. Since the "IC" engine term was invented first for the separation the EC engine term should not be used as it is a meaningless term.

Sir George Caley Built an internal combustion engine running on coal in 1807. Before that guns were perhaps the first internal combustion engine, unless you want to mention the natives that used bamboo diesel cycle to light tinder for starting fires, origin date unknown to me. I will have to modify my scope post as well to remove the invention date of the IC verses the EC engine and type of cycles possible.

I don't think either category is really important in engineering practice, and neither limits people to a viewpoint. It is just a beginners view of the difference in the card deck. Would it make you happy if we included in the opening paragraph that "combustion" is not part of the important process of heat engines, except for an internal combustion engine?

The basic difference is burning the internal working fluid subjects the internal moving parts to the corrosive nature of the fluid, where having an inert gas as the internal fluid doesn't. Burning the fluid make all the fluid heat very rapidly to the "high temperature" where moving heat into the internal fluid by conduction requires more time and surface area.

See you at your talk. Give me a few days.

Thanks, Eric Norby 17:10, 27 March 2007 (UTC)