The Development of the diesel engine

By Lynwood Bryant

Mr. Bryant, professor emeritus of the Massachusetts Institute of Technology, is a visiting research scholar at the Eleutherian Mills Historical Library. He wishes to acknowledge his indebtedness to the late Friedrich Sass, the late Eugen Diesel, the late Georg Strossner, and Kurt Schnauffer for their writing and especially for many helpful conversations about Diesel and his engine; to Irmgard Denkinger, another expert on Diesel, for her kindness and her guidance in the MAN Werkarchiv in Augsburg; and to A. R. Rogowski, Professor Emeritus of Mechanical Engineering at MIT, for ten years of patient explanation of the mysteries of engines.

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In 1912, when the diesel engine was about twenty years old, just coming of age after a prolonged infancy and a painful adolescence, it was the subject of a celebrated controversy, in which the inventor, Rudolf Diesel (1858-1913), and two distinguished professors of engineering discussed the very topic that concerns us in this symposium: the distinctions among invention, development, and innovation as parts of the total process of technological evolution. These three words are commonly used rather loosely, and I do not need to make very sharp distinctions among them because my main point is that in the real world the three processes to which these words refer are not sharply separated. But let me begin by saying that I am thinking of an invention as the appearance of an idea in someone’s mind, an eventing intellectual history; of development as the conversion of an idea into some kind of workable reality, such as an engine that runs; and of innovation as the introduction of the developed invention into the economy as a useful, salable product.

The 1912 controversy began when Diesel heard that Adolph Nägel of Dresden was planning a book on the history of the diesel engine. Diesel was naturally nervous about what Nägel would say, for he was a sensitive and proud man, and there had been some troublesome uncertainties and misunderstandings about the invention of his engine and the validity of his patent. So the inventor prepared his own account of the origin of his engine and presented it at a meeting of the German Society of Naval Architects in November 1912. In the discussion period following the paper, two professors launched an attack on Diesel that raised disturbing questions about his professional integrity. Their main point was that the engine that emerged from the development process was not the same as the engine that Diesel invented, and that credit for it should go to the practical engineers who developed it. Diesel, they said, was a promoter, a mere businessman, not an inventor.¹ This was the unkindest cut of all, for Diesel was an engineer with scientific pretensions. He thought of himself as the James Watt of the 20th century.

Four books grew out of this controversy, one by Diesel and three by his critics.² They were all published shortly before or shortly after Diesel’s mysterious death,³ and they all include theoretical discussion of the nature of invention and development, and argument about Diesel’s work. So the Diesel story is well documented in the sense that much has been written about it, but the literature is mostly polemical or promotional, so that there are still many uncertainties about what actually happened.

I propose to go over this story once more, and use it as a case study in the process of development. I shall try to indicate what different kinds of activity were going on at different times in the course of the early evolution of this engine, and then make some general remarks about the nature of development and how it is related to invention on the one hand and innovation on the other.

My main point is that these processes may be conceptually distinct, but when you look closely at what is going on, it is hard to say when one leaves off and another begins. It may be better to regard them not as chronological stages but as different kinds of forces operating in an evolutionary process, or different types of human interest and activity, all more or less involved in all stages of technological progress.

First Period: Invention, 1890 - 1893

The first period begins with the conception in Diesel’s mind, which occurred in 1890 or 1891, and ends with the first attempt at a real engine in 1893. In this period the engine is a concept, not a reality, and its history is intellectual history, the story of how a man got an idea and was guided by this idea.⁴

The system of ideas that constitutes the diesel engine includes a dozen important concepts and techniques, all of which appeared before 1890. But one key idea Diesel claimed as novel: the idea that combustion in an internal-combustion engine could be made to take place at constant temperature, that is, isothermally. As Diesel conceived it, such an engine (on a down stroke of the piston) would draw in a charge of plain air, and then (on an up stroke) compress it to a very high pressure and temperature. Then just as the piston started down again, fuel would be introduced gradually into the hot, expanding air in such a way that the tendency of the temperature to rise with combustion would be exactly counterbalanced by the tendency of the temperature to fall as the air expanded.

If this way of achieving isothermal combustion works, thought Diesel, then an approximation to the ideal engine embodying the Carnot cycle is possible. Such an engine would be much more efficient than any existing heat engine because it would operate through a wider range of temperature, and, with isothermal combustion, all the heat added would be converted to work on the piston. In a Carnot heat engine the heat to be converted into work has to be added at the highest temperature of the cycle and it has to be added without raising the temperature further. The practical difficulty in realizing this ideal in a combustion engine is that it is hard to see how combustion can take place without a rise in temperature. This was the essence of Diesel's invention: he conceived a way of burning fuel in an engine without raising the temperature.⁵

Diesel began by formulating the idea carefully and working out the details of a possible engine. He prepared a manuscript, with supporting calculations and illustrations, and sent it out for criticism to several experienced engineers and industrialists. One or two critics said encouraging things, but mostly they regarded the engine as impractical because of the extreme pressures and temperatures required. Diesel went back to the drawing board to prepare a more modest proposal for a more realistic engine, and with this revision as a supplement, sent the manuscript to Springer to be published.

Diesel had also formulated his ideas in the form of a patent application, which went through a similar process of negotiation and revision. The patent was issued and the book published early in 1893.⁶

Meanwhile Diesel had offered his engine, or his idea for an engine, to a number of machine-building firms (it was clearly much too large a project to be developed by a single man in a home workshop) and was rejected by all of them, but as a result of a second approach with more modest claims, the Maschinenfabrik Augsburg agreed to help Diesel develop his engine. This was a large firm led for almost fifty years by Heinrich Buz, an industrial statesman who plays a role in the Diesel story something like the role of Boulton in the Watt story.⁷ After the patent was issued, the firm of Krupp agreed to join the Maschinenfabrik Augsburg in this project, to share the expenses of development, and to pay Diesel a salary of 30,000 marks a year while he worked on the development.⁸ It was a good bargain for Diesel.

When Buz called for drawings, Diesel already had them prepared, for a two-cylinder, 50-horsepower engine. Buz proposed a more modest start, with a one-cylinder, 25-horsepower unit. There was no model, no preliminary work with components or processes. Diesel was so sure of himself that he moved at once to a full-size working engine. To him it was a scientific engine, built on sure thermodynamic principles.

I am labeling this first period “invention” because what is going on is primarily mental activity: thinking, calculation, argument, writing. But it is by no means a simple conception of an idea and nothing else. It includes an elaborate consideration of what is involved in realizing the idea, and a good deal of hard work in trying to sell the idea, to secure the endorsements of- scientists and the financial support of business men. I notice that the compromise between idea and reality, which we usually associate with development, is there trom the beginning and that the business negotiations and the balancing of economic interests, which we expect to be dominant in the later stages, have an important bearing on the early decisions to undertake development.

Second Period: Making the First Real Engine, 1893-97

The second period was a four-year struggle to get an engine that would run, a struggle that took place inside a large steam-engine factory in Augsburg. Diesel was in direct charge of the work himself, usually with one or two full-time mechanics assigned to the project.

Now what was Diesel doing during this period? We have a great deal of information about the technical work that was going on, for Diesel kept a meticulous journal in his own hand and wrote a book about it. He even kept thousands of indicator diagrams, so that you can still tell how the engine was doing on any given day, if you want to.⁹

In his own account Diesel divides the period into six series of experiments, each lasting a few weeks or a few months. At the end of each period of work Diesel would summarize his findings in the journal and prepare drawings for the changes he wanted to try next. While waiting for a modified or a new engine—it might be several weeks or months—Diesel did a good deal of thinking and writing, corresponding with experts, searching the literature for help with troublesome problems—perhaps in compressed air technology, lubrication, or ignition devices. He was also on the road a good deal, attending meetings, taking care of his patent affairs, keeping in touch with firms already signed up, such as Krupp and Sulzer, and trying to interest others In taking licenses to make and sell the engine when it was ready.

The first engine never ran at all under its own power, but it began to show Diesel what his problems were, and it sent him back to revise his theory. The first task was to get the high pressures necessary for the new process. The first experimental engine was designed for a pressure of 44 atmospheres, but at the beginning Diesel could reach only 18. With a good deal of work on mechanical details he was able to raise this to 33 atmospheres and to assure himself that compression ignition was possible, if not easy, at this pressure. The second engine, a completely new one, ran idle for a minute in 1894. In the next two years Diesel did a great deal of work on fuels, fuel injection, carburetion, and ignition, and finally settled on a kerosene for fuel and a compressed-air system for delivering it to the combustion chamber. It was 1897 before a prototype engine was running smoothly and Diesel was ready to announce the end of the period of development.¹⁰

Now let me list the technical problems that Diesel had to solve in order to transform his idea for an engine into a real engine. In order to make his engine work, Diesel had to: (1) compress air to a very high pressure and temperature, (2) choose the right fuel, (3) inject the fuel into the high-pressure air, (4) control the timing of the injection and the amount of fuel injected (in very small amounts, under very high pressure, in pulses), (5) mix the fuel with air in the very short time available, and (6) ignite the mixture. These problems may not sound very challenging, considering the experience engineers had already had with steam, hot-air, and gas engines by 1893, but they were all well beyond the state of the art at the time. Diesel certainly underrated their novelty and difficulty.

One set of problems, caused mostly by the need to achieve and contain very high pressures, was in the mechanical domain of pistons, cylinders, valves, pumps, compressors, and all the associated plumbing. Diesel had already had ten years of experience in this field (with refrigeration machinery) and the support of a large firm of engine builders with excellent resources and skills. He also had a well developed technology of steam, air, and hydraulic systems to draw on, as well as an internal-combustion engine technology that had been developing for twenty or thirty years (to which Diesel had not paid much attention). His achievements in this field were mostly refinements and extensions of existing technologies, and I will pass over them with the remark that everybody else seems to pass over them too—they do not have the dramatic or theoretical interest that attracts writers and readers. They ought not to be passed over, because this sort of activity, unglamorous and frustrating, is at the heart of the development process. I am sure that Diesel would have preferred not to bother with this type of problem himself. I think of him as the man in the white coat in the German laboratory who prefers to leave the routine work to the man in the gray coat. But Diesel put a great deal of time and effort into the mechanical details himself.

Another set of problems was in the area of fuels and combustion, and here Diesel was operating in the dark, with many unknowns and no guidance from theory. He did not even know what it was that he needed to know, which was the principles of combustion. At the beginning he probably assumed that almost any fuel would naturally flash into flame as soon as it entered the combustion chamber if only the air were hot enough. But he found it was not so easy. Fuels behaved in mysterious ways. When he could not get a kerosene to ignite, for example, he turned to gasoline, which common sense says ought to be easier to burn. But it turned out that kerosene burned better than gasoline, no one knew why. Work in this area was wholly empirical, with the simplest cut-and-try methods. It was also experimentally difficult because success depended on so many variables interrelated in sensitive ways, and because the combustion event of interest was an extremely brief one. In a slow one-cylinder engine (say, 120 revolutions per minute) the pulses of combustion would come at one-second intervals. Each pulse might last one-fiftieth of a second, and Diesel had promised a gradual, controlled burning in this interval.

The key problem in getting a diesel engine to run, we now know, is to get a good mixture of fuel and air inside the cylinder in the very short time available. A gasoline engine has combustion in very brief pulses too, usually much briefer than a diesel, but it mixes fuel and air at leisure outside the cylinder and draws in a charge already mixed.

In a diesel the mixture cannot be prepared in advance. The fuel has to be driven into the combustion chamber at the time of maximum compression, and somehow get pulverized or atomized so that each particle of fuel can find a particle of oxygen to combine with in a small fraction of a second. Successful combustion depends on the size and location of the jets of fuel and the force behind them, the shape of the spray and the degree of atomization, and the shape of the combustion chamber. Different sizes of cylinder, different speeds, and different types of fuel all require different tactics of injection. After seventy years of development there are still plenty of uncertainties in this area, and in the first decade getting an engine to run smoothly was mostly a matter of accidentally hitting on the right combination of fuel, injection mechanism, and shape of combustion chamber, and sticking to the right formula with fingers crossed. The engine might falter with the slightest change, or with no apparent change at all.

In these first four years, Diesel tried nearly everything to get reliable ignition: different fuels; different ways of mixing fuel (“external” and “internal” carburetors); and different kinds of artificial ignition (spark, flame, and hot-tube).11 For fuel injection he began by trying to drive the fuel into the combustion chamber by some sort of plunger or pump, but after a year or more of work he concluded that this kind of injection (called solid injection) was impossible, and turned to a compressed-air technique. Eventually this turned out to be a good solution: the blast of air not only carried the fuel into the cylinder, but it also helped atomize the fuel and mix it violently with the air inside. But it was expensive: it required extra pumps and cylinders of air which added weight and plumbing complexity to the engine, and absorbed a good deal of its power. Air injection made the diesel a large and expensive engine, unable to compete in the market for small powers.

Diesel’s activity during this period could be classified as either invention or development. Looking back later, Diesel regarded it as invention. An invention, he said, is not a pure idea, but rather the product of a struggle between Idea and Nature. The product is always a compromise between the Ideal and the Attainable, and working out the details of this compromise is a part of the process of invention.¹² To me this work looks more like what I would call development: the messy job of constructing something new and trying to make it work, adjusting something and trying again, changing dimensions, working out the details of piston ring or valve or gasket, coping with unexpected difficulties, retreating from one approach and trying a new one, giving up for a while and groping for guidance from books and journals and people—that sort of thing.

At the same time, every day, Diesel was deeply involved in theoretical work, for the first experience with a real engine had revealed new phenomena that had to be accounted for, and forced a revision of his original theory. The real engine had to be rationalized. An invention as described in a patent may be the embodiment of a permanent, fixed idea, but in real life ideas may not stay fixed. In this case, at least, the development modified the invention.

Diesel found that to get a practical engine he had to use much more fuel than his theory of isothermal combustion called for, and with more fuel the temperature had to go up. So he wrote a justification for using a constant-presssure instead of a constant-temperature process and tried to reconcile it with his patent. He also discovered at once that the engine had to be cooled, and the cooling required an explanation, because the patent and the book had said that cooling would not be necessary because no heat would be wasted: all the added heat would be turned into work on the piston. So in addition to keeping a running account of his work in the-journal, Diesel wrote 150 pages of theoretical discussion intended for publication in the next edition of his book, which never appeared, and a curious rationalization of cooling as a requirement of thermodynamic law.¹³

For this theoretical work that accompanied the development Diesel had two incentives. One was the normal human need to explain puzzling phenomena and to publish the explanation. This need Diesel felt rather more keenly than most men, I think: he seemed to have a neurotic need to rationalize what he was doing. The other incentive was to protect his economic interests. The plan was to exploit the engine primarily through the sale of patent rights. Before development began, the book had been attacked in public as describing an unworkable process.¹⁴ The success of the whole enterprise seemed to depend on the validity of the patent. One of Diesels sponsors, Krupp, was already uneasy about it, and other prospective licensees had expressed misgivings.¹⁵ So Diesel felt a strong pressure to reconcile the real engine as it was developing with the original theory as expressed in the patent. The theoretical work was an essential part of the exploitation of the engine.

This early development experience also revealed certain economic characteristics of the new type of heat engine that influenced the marketing plans being developed in this period. High thermal efficiency—that is, fuel economy—was supposed to give the diesel its chief competitive advantage over steam, but its versatility was also an important selling point. Diesel thought of it as a universal heat engine, adaptable to any fuel, solid, liquid, or gas, and practical in any size, so that it could drive anything from a sewing machine to a battleship. But the extreme sensitiveness to fuel revealed in the development limited the range of applicability of the diesel, and the need for air Injection made it uneconomical in small sizes. Diesel remained optimistic on these points all his life: in papers and speeches and in some experimental work he continued his plans to exploit different fuels—and to develop different sizes and applications of his engine. But for the prudent businessman the process of development revealed characteristics of the engine that limited its economic role. It has remained an oil engine to this day, and it was twenty-five years before the development of direct injection made the small diesel practical.

Third Period: Premature Innovation, 1897-1902

By early 1897 Diesel felt that the main problems were solved and it was time to turn over the final details of development to lesser talents. In the spring of 1897 a prototype engine was running smoothly on the Augsburg test stand where it was inspected by engineers and businessmen from many countries. Its performance was measured and evaluated by the eminent professor Moritz Schroter, the results were published, and the triumph was announced with appropriate ceremony in June 1897 at the annual meeting of the Society of German Engineers. The engine was formally introduced as fully developed, ready to be sold.¹⁶

In 1897 Diesel devoted himself chiefly to promotion. The policy was to market the engine by selling patent rights to established machine manufacturing firms in all industrial countries. The German market was divided among three firms, and licenses were negotiated for a dozen foreign countries, usually with the leading engine makers of the country,” except in America, where the brewer Adolphus Busch acquired the rights for a million marks cash and organized a new firm to exploit the Diesel patents.¹⁸ Diesel did most of the negotiating himself. The arrangement usually provided for a royalty,with a large advance payment in cash. Augsburg supplied drawings and technical advice, and the licensees agreed to exchange information on technical improvements (so development was expected to continue into the innovation period). The licensees began at once to build prototype engines. Four of them managed to get engines running, more or less, at an exhibition of machinery in Munich in 1898.¹⁹ The first diesel in the United States, a German import with a German engineer in attendance ran in public for a month in May-June 1898 at an exhibition of electrical machinery in Madison Square Garden, New York.²⁰

Diesel himself was badly overworked during this critical period, on the verge of a nervous breakdown, trying to do everything at once. He wanted the Maschinenfabrik Augsburg to move at once into the manufacture of diesel engines in quantity, but Buz was not willing to shift his plant over to the new engine fast enough to suit Diesel. Therefore Diesel formed two new companies, with the cooperation of Buz and Augsburg bankers: one to manage his contracts and patent rights and coordinate the activities of the licensees, and one to manufacture and sell engines in a part of the German market.²¹

All these enterprises failed. No licensee was able to build an engine that would run reliably in the hands of a customer, not even with blueprints from Augsburg and borrowed Augsburg mechanics.

Diesel’s own manufacturing firm took back every engine it made and went bankrupt. The diesel got a bad name that set back development by several years and made innovation difficult. Diesel had stopped keeping the development journal himself in early 1897, when he became preoccupied with the business and the public-relations side of the enterprise, so that it is not easy to say exactly what he contributed to the continuing development. But he was clearly more concerned with distant and visionary projects than with the incremental improvement of the existing engine. He was always talking about new applications—to automobiles, locomotives, ships, and later even aircraft—and planning new types of engines burning new fuel—powdered coal, blast-furnace gas, even peanut oil.

In 1898 and 1899 he found time for some experimental work himself. He actually built and operated a monstrous three-cylinder compound diesel of the type described in the patent as the preferred form for the ideal Carnot engine. It proved to be less efficient than the simpler compromise engine and was scrapped. He also attempted a coalburning engine, and worked on a gas-burning type of special interest to Krupp.²²

This work came at the lowest ebb of the diesels reputation. Buz finally cut it short at the end of 1899 and began the long task of developing the 1897 engine into a reliable oil engine, and the longer task of rebuilding the diesel reputation. Diesel had his nervous breakdown and made no more important contributions to hardware development.

Meanwhile, main-line development continued in Augsburg. A two-cylinder 60-horsepower engine (a large step forward in power) was built and sold to a match factory in Kempten, which was managed by Buz’s brother. This was the first realistic trial: the engine replaced a steam engine supplying power to a factory. Two experienced mechanics went along, to tend the engine during the day and to maintain and overhaul it at night. From this experience the engineers learned what kind of cooling and lubrication was necessary, and how to control the engine under a fluctuating load. Fuel injection remained the key problem. The system they were using formed a spray by forcing the oil through a mesh of brass wire. It worked well enough if they took it apart and cleaned it every night. After about a year of this experience, they dismantled the engine and shipped it back to Augsburg for a complete redesign and rebuilding.²³ The rebuilt engine might be called the first successful diesel.

One of Diesel’s uncharitable critics at the 1912 meeting, Alois Riedler, a distinguished professor and an experienced machine designer himself, said some interesting things in the discussion period about engine development, and development in general. He divided the process of developing the diesel (or anything else) into three stages. First, he said, is the development of a machine that works, an engine that runs (that is, gangbar). The second stage is the development of an engine that is useful (brauchbar), that can carry a load, reliably, for a reasonable time. This is a quite different thing from the gangbar engine, he said, and it may be a greater and more costly achievement.

But this is not the end of development; a third stage, the most important of all, is necessary to make the engine markifihig, that is, ready to be sold, able to take its place and hold its own in the existing economic system. Diesels 1897 engine, said Riedler, with the advantage of hindsight, was barely gangbar.²⁴

In any case, the judgment that the 1897 engine was fully developed, ready to be sold, was a disastrous mistake. Such an error of judgment might be expected from an.overoptimistic inventor, but in this case the hard-headed businessman, the practical mechanic, the professor of engineering, and many of the expert observers agreed. It is extraordinary that so many good people could be so wrong. The lesson, I suppose, is that development takes longer than anyone expects. It needs to continue well into the innovation phase. The inventor tends to underestimate the need for development, and the developer is ready to pronounce his work finished too soon. For some kinds of products, at least, a realistic trial in the hands of the ultimate user is a necessary part of development, necessary to reveal problems that cannot be anticipated in the laboratory. The mechanical and economic performance of a complex and sensitive system like a diesel engine cannot be safely predicted from laboratory simulation or theoretical analysis, but only from prolonged experience on the job.

Fourth Period: Continuing Incremental Development, 1902-1908

My last period is a time of incremental progress in technical development and of steady, slow growth in numbers of engines in use.

Call it both development and innovation, running parallel. The period begins with one more or less reliable engine offered for sale by the Augsburg firm, and ends in 1908 when the basic patent runs out and the Augsburg plant drops steam to devote itself to the manufacture of diesels. By this time a thousand engines are in service, averaging perhaps 50 horsepower, mostly replacing steam engines in small stationary power plants.²⁵ The licensees that had dropped the diesel around 1900 picked it up again, one by one, and by 1908 a dozen or more firms in half a dozen countries were contributing to the development, providing a considerable diversity in form and variety of detail: good raw material for the forces of natural selection to work with.

The mechanical development of the engine in this period is the kind of continuous refinement of design that I normally associate with the word “development”: improvements in detail that make for reliability and economy, slow growth in power and speed of individual units, weight reduction, and simplification of design to reduce cost of manufacture. This type of development is controlled throughout by strong economic pressures, especially strong for the diesel because it was competing with the mature and reliable steam technology. It was not a wholly new thing like an airplane or computer. It did exactly the same job as the steam engine it replaced, and its initial cost was higher. It had nothing to offer a buyer except an uncertain fuel economy, and in some applications a certain amount of convenience.

Nevertheless the diesel gradually won itself a modest place in the stationary power market in the intermediate range of say 20-100 horsepower, largely on the promise of fuel economy. It was by no means the universal rational heat engine that Diesel had in mind in 1890, but it was clearly a viable species of engine in 1908.

Later Development

The Diesel story has many more chapters, in which I think I can see more or less the same pattern of the interacting forces that I am calling invention, development, and innovation. The most interesting chapters cover the development of special forms for special purposes, such as power for ships, heavy road vehicles, and locomotives. The general lesson that I see in these chapters is that each of these special applications requires what really amounts to a new species of engine, and each species has to go through its own independent evolutionary process. Diesel himself assumed that once the basic problems were solved, a change of application or a change of scale was a rather simple matter. He was wrong. The period of development for each of these species was surprisingly long—say twenty years—but once it was fully developed, it took over the field surprisingly fast: ships in the 1920s, trucks in the 1930s, and locomotives in the 1950s.

* * *

So I conclude that the three kinds of human behavior that we label invention, development, and innovation are going on more or less all the time in the process of technological evolution. The emergence of new ideas, which we label “invention,” clearly takes place throughout the process. The refinement of design that comes with experience in the real world, which we label “development,” is endless. The effort to fit a new technique into the existing economic and social structure, which we label “innovation,” is a guiding force from the beginning. In considering the creative process, we naturally think of the idea as coming before its object; we conceive of a machine as the realization of a preexisting idea. Our institutions, our language, and our patent law reenforce this impression. Our language seems to require that a machine be conceived, constructed, and operated, in that order. But in real life the idle curiosity, the tendency to play with ideas and to try new ways of doing things just for fun, which we regard as the special virtue of the inventor, is also a virtue for the developer and the innovator. The experience of development is in fact a great generator of new ideas, and it can modify the idea being developed, as it did for Diesel.

The experience of innovation, the effort to find an economic role for a new machine, can reveal problems unsuspected in the laboratory, and redefine the task of the developer. The economic considerations, which are the special field of the innovator, are usually of great interest to the inventor. Economic questions may be suppressed for the moment while a developer devotes himself to the urgent task of getting the thing to run regardless of cost, but they cannot be put off for long. I suggest that the model of some sort of dialectical interaction among these three types of forces may be a more realistic description of what is going on in technological evolution than the conception of chronological stages.

Reference

1. Diesel's paper appeared under the title “Die Entstehung des Dieselmotors” in Jahrbuch der Schiffbautechnischen Gesellschaft 14 (1913): 267-355, with a transcript of the following discussion on pp. 355-67. Marine engineers were especially interested in diesel power at this time. The major powers had recently adopted it for submarines, and the first motor ship had crossed the Atlantic in 1911.
2. The four books were: Rudolf Diesel, Die Entstehung des Dieselmotors (Berlin, 1913), which is the 1912 paper, slightly revised, without the following discussion; P. Meyer, Beutrage zur Geschichte des Dieselmotors (Berlin, 1913); J. Luders, Der Dieselmythus: Quellenmdssige Geschichte der Entstehung des heutigen Oelmotors (Berlin, 1913); and A. Riedler, Dieselmotoren: Beitrige zur Kenntnis der Hochdruckmotoren (Berlin, 1914). The inventor's son, Eugen Diesel, wrote two books and many articles about his father, which tend to be a little colorful and obscure, but they are fundamentally sound, I think, and the best source for biographical information. They also include technical information about the development of the engine. The standard biography is Diesel: der Mensch, das Werk, das Schicksal (Stuttgart, 1937). This book was reissued a number of times, at least once with sensitive passages slightly revised. Another important biographical work of Eugen Diesel’s is Jahrhundertwende: Gesehen im Schicksal meines Vaters (Stuttgart, 1949).
3. Diesel disappeared from a channel steamer in the night of September 29-30, 1913. His body was recovered ten days later by a pilot boat at the mouth of the Scheldt River and returned to the sea, but unmistakably identified by articles taken from the body. Lurid rumors appeared at once and persist to this day, for example the legend that Diesel was executed by the German secret service because he was about to betray submarine secrets to the British. All known facts are consistent with the conclusion that he was a suicide. He was in financial trouble, and deeply disturbed by these attacks on his integrity.
4. The best summary of this piece of intellectual history is in Friedrich Sass, Geschichte des deutschen Verbrennungsmotorenbaues von 1860 bis 1918 (Berlin, 1962). The last third of this monumental work is an excellent history of the diesel engine. It rests on several years of research by Kurt Schnauffer, which is recorded in many volumes of typescript now in the library of the Deutsches Museum in Munich. Schnauffer’s own account of the invention is “Die Erfindung Rudolf Diesels,” Zeitschrift des Vereines deutscher Ingenieure 100 (1958): 308-20 (hereafter cited as ZV DI). All the books cited in note 2 discuss the invention. Paul Meyer, the most objective and temperate of these contemporary critics of Diesel’s work, wrote his book in 1913 on the basis of some experience with Diesel—he worked with him for a while beginning in 1898—but without access to Diesel's papers. Thirty years later, during the Second World War, he went through the Diesel papers and wrote a new history of the invention of the diesel. This work was sponsored by the Verein deutscher Ingenieure (VDI) but never published. It remains a manuscript entitled “Die Geschichte des Dieselmotors” in the Diesel papers in the Deutsches Museum. Meyer later published two important articles based on this work:“Aus der Enstehungsgeschichte des Dieselmotors,” Schweizerische Bauzeitung 66 (1948): 485-87; and “War der Dieselmotor jemals durch Patente geschiitzt?” Schweizerische Bauzeitung 67 (1949): 309-10.
5. My article “Rudolf Diesel and His Rational Engine,” Scientific American 221 (August 1969): 108-18, tries to explain the Carnot cycle and its relation to the diesel engine. The famous Carnot cycle was first described in Sadi Carnot, Réflexions sur la puissance motrice du feu (Paris, 1824).
6. The German patent is number 67,207, dated February 28, 1892. (Another patent, number 82,168, dated November 30, 1893, is for a modified process and was applied for after the experimental work began.) The book is Theorie und Konstruktion eines rationellen Wirmemotors zum Ersatz der Dampfmaschinen und der heute bekannten Verbrennungsmotoren (Berlin, 1893). An English translation by Bryan Donkin (London, 1894) omits some material on applications of the engine that appears in the German original. The idea of achieving this kind of isothermal combustion in an engine appears in Otto Kohler, Theorie der Gasmotoren (Leipzig, 1887), and the engine that Kohler hypothesizes is similar in a number of interesting ways to the engine that Diesel describes in his book and his patent. This prior publication of Diesels key idea was a disturbing threat to the validity of the patent. Diesel said that Kéhler’s book was unknown to him at the time. But Kohler’s idea was picked up and published in F. Grashof, Theorie der Kraftmaschinen (Hamburg and Leipzig, 1890). This is the third volume of Grashof’s Theoretische Maschinenlehre. It is hard to see how Diesel could have overlooked this book by a distinguished authority in his field.
7. The Maschinenfabrik Augsburg merged with the Maschinenbaugesellschaft Nürnberg in 1898. The firm, which took the name Maschinenfabrik Augsburg-Nürnberg (MAN) in 1908, has a well-managed museum and library at its headquarters in Augsburg, with much interesting Diesel material.
8. The role of the Krupp firm in the development of the diesel can be followed in the correspondence in the Diesel papers in the Deutsches Museum, and it is described in a mimeographed publication by Wilhelm Worsoe, Die Mitarbeit der Werke Fried. Krupp an der Entstehung des Dieselmotors in den Jahren 1893-97 und an der Anfangsentwicklung 1897-99, Erweiterte Ausgabe von 1933 (Kiel, 1940).
9. Diesel was a self-conscious inventor who saw himself as a historical figure and kept careful records. Some of these he destroyed before he left Munich on the trip that ended in his death, but the journal covering development between 1893 and 1897, with supplementary notes and memoranda and a great many indicator cards, he gave to the Deutsches Museum. An indicator card is a pressure-volume diagram, a curve that shows how pressure changes with changing volume as the piston moves inside the cylinder of a heat engine. The area enclosed by the curve measures the work done inside the engine.
10. Sass, pp. 431-81, gives a good summary of the development. Diesel, Entstehung, gives more details. Most popular accounts of diesel development are legendary. The most widely repeated legend is that the engine exploded and nearly killed the inventor. What actually happened was that the indicator broke under the high pressure (80 atmospheres) of the first firing of the engine.
11. Compression ignition, now usually thought of as the defining characteristic of the diesel, was not essential to the process as Diesel viewed it (see Diesel, Entstehung, pp. 3-4). It was foreseen by Carnot in 1824, and attempted by a number of inventors before Diesel.
12. Entstehung, pp. 1, 151.
13. The manuscript intended as a supplement to the 1893 book, entitled “Nachtrage zur Brochüre: Theorie und Construction . . .,” is in the Diesel papers in the Deutches Museum. Diesel also applied for a supplementary patent (see n. 6 above). The rationalization of cooling is repeated in Diesel's 1897 paper cited in note 16.
14. Speech of Otto Kohler at a meeting of the VDI in Cologne, April 10, 1893, reported in ZVDI 37 (1893): 1103-9.
15. Diesel-Krupp correspondence in Diesel papers, Deutsches Museum.
16. Rudolf Diesel, “Diesels rationelle Warmemotor,” ZVDI 31 (1897): 785-821; and M. Schroter, “Diesels rationelle Warmemotor,” ZVDI 31 (1897): 845-52. Diesel's paper was widely noted in the technical press. In England a “summarized translation” by Bryan Donkin appeared in the Engineer 84 (1897): 364-66, and in the United States a full translation was published in Progressive Age (December 1 and 15, 1897, and January 1 and 15, 1898).
17. Sass, pp. 481-82.
18. The best account of the diesel in America is Eugen Diesel and Georg Strossner, Kampf um eine Maschine (Berlin, 1950). See also Richard H. Lytle, “The Introduction of Diesel Power in the United States 1897-1912,” Business History Review 42 (1968): 115-48.
19. Sass, p. 488.
20. Diesel and Strossner, p. 53; Sass, p. 490.
21. Sass, pp. 484-86, 492-93.
22. Rudolf Diesel reports on development during this period in “Mitteilungen über den Dieselschen Wärmemotor,” ZVDI 43 (1899): 36-42, 128-30. A translation appeared in Progressive Age (May 1 and 15, 1899). Imanuel Lauster, who was in charge of diesel development for MAN, covers this period in pp. 8-18 of a manuscript “Die Entwicklung des Dieselmotors” in the library of the VDI in Düsseldorf.
23. Sass, pp. 505-11; Lauster, pp. 10-12.
24. I am paraphrasing Riedler’s analysis of the process of development offered in the discussion period following Diesel's 1912 lecture in Jahrbuch der Schiffbautechnischen Gesellschaft 14 (1912): 356-57 (see also Riedler [n. 2 above], pp. 4-5; and Meyer, Beitrige zur Geschichte des Dieselmotors, pp. 3, 16-19). Meyer was present at the 1912 lecture but did not participate in the open attack on Diesel.
25. This is a conservative guess. An MAN promotional booklet in volume 15 of a collection of pamphlets entitled “Gas Engines” in the Detroit Public Library lists all MAN engines delivered and ordered to March 1909. The total is 1,298 engines amounting to 104,952 horsepower.