The Silent Otto

The Silent Otto

LYNWOOD BRYANT

The story of the gas engine that I am calling the Silent Otto—the first engine to operate on the four-stroke cycle, and the first to achieve compression of the charge within the working cylinder—has been told before.! But I should like to go over it again in order to consider a question that still seems significant to a historian interested in technology and culture: Why was this engine suddenly successful after seventy-five years of rather fumbling efforts to develop an internal-combustion engine?

Nicolaus August Otto (1832-91) built the first Silent Otto in 1876 in the Gasmotorenfabrik Deutz near Cologne (Fig. 1). In its original form the engine had one horizontal cylinder, drew in a charge of illuminating gas and air through a slide valve, compressed it within the cylinder with a compression ratio of about 24:1, and ignited it with a flame. The engine developed about three horsepower at a speed of 180 revolutions per minute, had a thermal efficiency of about 14 per cent (two or three times as good as a comparable steam engine), and weighed about a ton per horsepower.2 They called it “silent” not because you could not hear it when it was running—you certainly could —but because it ran much more smoothly and quietly than its immediate predecessor, the Otto and Langen, is a one-cylinder atmospheric gas MR. BryANT is associate professor of history at the Massachusetts Institute of Technology. engine that crashed and clanged like a rapid-fire pile driver and must have been a difficult engine to live with. So the great selling point of Otto's engine of 1876 was that it was quiet. In designing this engine Otto was aiming at the rapidly growing market for small stationary power plants; he needed an engine that was smaller and smoother and more flexible than the noisy and awkward Otto and Langen, and especially one that could be built for larger powers, for the atmospheric engine was limited to about three horsepower. In competition with the steam engine, the gas engine could offer superior efficiency, but it used an expensive fuel. For small pow- |

ers, though, where fuel economy was not a first consideration, it had |

the decisive advantage of easy operation and adaptability to intermit- |

tent use. A steam engine had a long warm-up period, and its fire had to |

be kept going whether the engine was working or not; it had a danger- |

ous boiler and required a full-time attendant, a license, and perhaps a |

separate structure to house the power plant and the fuel supply. The |

gas engine, on the other hand, could be started and stopped at will, it |

did not have to be fed when it was not working, and it could be safely |

installed right in a shop, with no license, no special operator, and no |

~~ fuel-storage problem if it used city gas. It was advantages like these |

that led Otto and other heroes of the development of the internal- |

combustion engine to dream of supplanting the steam engine. |

| The Silent Otto was a spectacular success. It was a sensation at the |

Paris Exposition of 1878, and within a few years it dominated the mar- |

ket for small stationary power plants. It proved to be a form of engine |

capable of development into many shapes and sizes, vertical and hori- |

zontal, large and small, with single and multiple cylinders, using gas |

or liquid fuel, and flame or hot-tube or electric ignition. Almost over- |

night the hot-air engine and the atmospheric gas engine were rendered |

obsolete, and the two-stroke engine was not a serious threat for some |

time. At the Paris Exposition of 1889, after the patents had been |

| broken in Germany and France, there were said to have been fifty types |

of engine operating on Otto’s principle. At the end of the century a |

four-cylinder engine of one-thousand horsepower was delivered,* and |

~~ there must have been one hundred thousand engines in service bearing |

~~ Otto’s name, not to mention the dozens of competing brands using the |

same principle, providing power for machine shops, breweries, printing |

presses, pumping installations, and electric-light plants.⁵

| In order to account for the sudden success of this engine let us |

| go back to the beginning of Otto’s work with engines, follow the

| course of his thought through the fifteen years of work that culminated |

| in the Silent Otto, and try to see what the breakthrough was that |

| led to an adequate solution to the problem that had been troubling

| workers on the internal-combustion engine for a generation: the prob- |

| lem of how to get a smooth flow of power out of an explosive fuel |

| burned in the working cylinder. |

| In the 1870's and the 1880’s it was not easy to say what made the

| Silent Otto silent. The question was argued in great length in courts |

| of law and in professional journals, and the most eminent experts dis- |

| agreed with each other and changed their minds. Otto thought that the

| key to his success was a special way he had of introducing fuel and air |

| into the cylinder that cushioned the shock of the explosion. The pre- |

| vailing—but not unanimous—opinion of the profession was that he was

| wrong, and even today engineers do not always agree on the desirabil- |

| ity of heterogeneous or stratified charges of the kind that Otto thought |

| he had in his engine.

| Otto was a traveling salesman without technical training in 1860 |

| when he read in the paper an enthusiastic account of a gas engine built |

| by a Frenchman named Etienne Lenoir (1822-1900). He arranged to |

| have a similar small engine built by a mechanic, started tinkering with |

| it in his spare time, and promptly ran up against the key problem that

| baffled everyone at that time: how to control an explosive fuel. |

| The Lenoir engine, which was very widely discussed in the popular |

| and the technical press in the period 1860-63, was a two-stroke, |

| double-acting affair that looked very much like a steam engine and |

| operated without compression. It sucked in a mixture of illuminating |

| gas and air, ignited it by an electric spark halfway through the stroke,

| and used the remaining half as the power stroke. On the way back the |

| piston was driven by a similar impulse on the other side. The publicity |

1. Recently, e.g. by Gustav Goldbeck in “Entwicklungsstufen des Verbrennungsmotors,” Motortechnische Zeitschrift, XXIII (1962), 76-80, and in several other articles; by Friedrich Sass in Geschichte des deutschen Verbrennungsmotorenbaues von 1860 bis 1918 (Berlin, 1962), pp. 19-74, 147-67; and by Arnold Langen in Nicolaus August Otto, der Schopfer des Verbrennungsmotors (Stuttgart, 1949). I rely heavily on Professor Sass for information about engines. I also acknowledge very helpful conversations with Dr. Goldbeck, archivist of Klockner-Humboldt-Deutz, and with Professors C. Fayette Taylor and Augustus R. Rogowski of the Massachusetts Institute of Technology.

1. Sass, p. 44; Paul Gille, “Beau de Rochas. Les trois mémoires de 1862 sur différentes conditions d’application de Iénergie,” Documents pour Pbistoire des tech- |

| niques, No. 2, p. 37; Conrad Matschoss, Geschichte der Gasmotorenfabrik Deutz |

| (Berlin, 1921), p. 55. |

184

3 Gustav Goldbeck, “Nicolas-Auguste Otto (1832-1881),” Documents pour Ibistoire des techniques, No. 1, p. 38. The year of Otto’s death is misprinted in this title. It should be 1891.

4 Sass, p. 319.

5 Matschoss, pp. 107-8.

6 For an early popular account see Alfred Darcel, “Un nouveau Moteur,”

L’Dlustration, XXXV (1860), 342-43. For a technical study see H. Tresca, “Procés-

Verbal des expériences faites sur les moteurs a gaz de M. Lenoir,” Annales du Con-

servatoire Impérial des Arts et Métiers, 1 (1861), 849-79. Articles by engineers

appearing in German journals that Otto could have seen are conveniently sum-

marized under the heading “Gaskraftmaschine” in Jabresbericht iiber die Fort-

schritte der mechanischen Technik und Technologie, 1 (1863), 111-31. “According

to Cosmos, and other French papers,” said the Scientific American (III [1860], 193),

“the age of steam is ended—Watt and Fulton will soon be forgotten. This is the way

they do such things in France.”