Here in the early decades of the twenty-first century, steam turbines can still be found (though they are almost never seen) but steam piston engines are archaic relics. Nearly every moving machine that we see—cars, trucks, lawnmowers, the aircraft in the sky and the boats in the water—derives its power directly from the combustion of a fuel (such as gasoline) inside of a cylinder: internal combustion, unlike the external combustion that produces steam from fuel burned outside the boiler.

The internal-combustion engine requires its own chapter in the story of the age of steam, for two reasons. The more obvious is the role the former played in the demise of the latter. The internal-combustion engine could be accused with some fairness of the crime of slaying the steam engine. The other, less obvious, reason is internal combustion developed in reaction to, and under the shadow of, steam. Through the nineteenth century, internal-combustion remained an upstart, seeking a place for itself in a world where steam had become the default choice for anyone in need of mechanical power.[1]

Early Internal Combustion: A Motive Without Means

The story of the internal combustion engine is an enormously complex one ranging over a century and more; it branches, then converges then branches again as engineers repurposed and remixed design ideas to solve new problems and fill new niches.[2] One could certainly trace it back at least as far as Huygens’ seventeenth-century gunpowder engine; the modern internal combustion engine could be seen as the revenge of the gunpowder engine, much in the same way that the modern water turbine was the revenge of the horizontal water wheel. To tell the complete story in any detail would require another volume at least as large as this one, so I will provide only a montage of the most significant moments and trends as they relate to our larger story.

A thorough history of the internal combustion engine (which I will shorten from now on to “combustion engine” to spare the reader from either an eight-syllable mouthful or the infelicitous initialism “ICE”) would include a laundry list of inventors and inventions, dating back into the eighteenth century or even beyond, almost all of whom have faded into obscurity along with their machines. This is a pattern that should by now be familiar: the steam engine, the steam boat, the locomotive; in every case, a decades-long history can be found of inventors striving after the same vision without quite producing anything that they could convince others of using.

In the case of the combustion engine, the probable motive for most of these early inventors was simplicity and ease of use: the steam engine was a large, complicated machine of many parts that required careful tending. The boiler, in particular, had an unnerving propensity to explode at high pressures. To be able to dispense with the firebox and boiler, and simply burn fuel inside the working cylinder, presented a very attractive prospect.[3] Moreover, boilers were not just large and potentially dangerous, they also had a kind of momentum. You couldn’t simply switch a steam engine on and begin using it, you had to build up a head of steam first, and as long as you maintained that head of steam, you were burning fuel. So, steam engines demanded continuous use: that worked out fine for factory owners who wanted to keep their expensive capital running day and night, but small craftsmen and workshops that needed power on an ad hoc basis were less happy with the age of steam.

By the early nineteenth century, another reason for looking elsewhere than steam for a source of power had appeared: the advent of gas lighting. Gas, quite evidently, burned easily, and by mid-century could be drawn at will from city gas systems in every major urban center of Europe and the United States. What if you could dispense not only with firebox and boiler, but also with the coal storage house, and the transport costs for hauling the stuff to your place of business, and the labor costs for stoking the engine?

Volta’s electric pistol, developed in the 1770s, and exhibited all over Europe, may have served a similar role in the early development of combustion engines that the vacuum pump did for the steam engine: a dramatic demonstration that inspired new inventive ideas. The pistol used a spark across two electrodes to detonate a charge of hydrogen gas in a stoppered glass vessel, shooting the stopper across the room. An imaginative mind might have realized that the if vessel could be rapidly refilled with gas and the spark repeated, one would have a machine that generates a continuous series of mechanical impulses, much like a steam engine. Issac de Rivas, a Swiss inventor who dreamed of replacing horses with self-propelled vehicles, used exactly Volta’s spark mechanism to drive the motor of his gas-powered carriage.[4]   

The concept and the advantages were clear enough; making internal combustion work was another matter. It required mastering a variety of new techniques: properly mixing fuel and air before or while adding them to the combustion chamber, igniting the mixture inside the chamber, and, most difficult of all, timing the ignition to the cycle of the engine so that each explosion would occur at exactly the right point in the motion of the piston. Unlike a steam engine, which would still function to some extent even with leaky valves, poor timing, and other deficiencies, an ill-tuned combustion engine was useless. The existing body of engineering experience provided no guide in these matters, and so everyone was groping in the dark—quite literally, in the sense that would-be inventors could not witness the combustion, hidden within the cylinder, that they were striving to control.[5]

Thermodynamics and Internal Combustion

The rise of thermodynamic science at mid-century and its gradual percolation through the engineering community intensified interest in internal combustion as it exposed the weaknesses of steam. The expansive elasticity of steam, which had been thought a key to the success of the steam engine in its guise as a pressure engine, became a liability when it was considered as a heat engine. As Carnot had observed, to maximize the power of the engine required making the working fluid as hot as possible (and then cooling it as far as possible), but transforming water into steam at high temperatures created immense pressures, beyond the capacity of even iron and steel to contain.

Thermodynamics made it possible to measure steam engines against the efficiency of an ideal heat engine, and it came up severely wanting. To some degree, this led engineers who had incompletely absorbed the lessons of Carnot and Rankine on a wild goose chase. Believing that a large amount of heat was “wasted” to evaporate the water, they diverted themselves into dead ends building engines that operated on other fluids without so much latent heat, such as ether, alcohol, carbon disulphide, and ammonia. As engine historian Lynwood Bryant sympathized, “to a man in a commonsense world of pressures and volume,” such substitutions appeared sensible because “with a given expenditure of heat he can reach higher pressures with ammonia than with steam.” It required a mind more thoroughly steeped in the new abstractions of energy to grasp that the latent heat was not truly wasted, as energy could not be destroyed; all of that energy still existed in the hot steam, which made it a more energy dense working fluid than most of its would-be competitors.[6]

What, then, of the air engine, whose advantages Rankine had touted back in the 1850s? Ordinary atmospheric air did not build up to the same immense pressures when heated as steam, so why not simply substitute air for steam as the working fluid of an external combustion engine? Some inventors tried this too, but the approach failed, for two reasons: first, the poor conductivity of air meant that huge conduction surfaces were required to transfer heat from the fuel source to the air, which made air engines larger, heavier, and more expensive to build than an equivalent steam engine. Second, extremely high temperatures still could not be reached because of the mechanical limits of the iron that had to conduct the heat from the fuel to the air. When pushed beyond about 1,300 degrees Fahrenheit, the iron would weaken and become unusable.[7]

Air could be used in another way, however, as the perspicacious Carnot had observed back in 1824 (emphasis mine):

Vapors of water can be formed only through the intervention of a boiler, while atmospheric air could be heated directly by combustion carried on within its own mass. Considerable loss could thus be prevented, not only in the quantity of heat, but also in its temperature. This advantage belongs exclusively to atmospheric air. Other gases do not possess it.[8]

That is to say, the fact that air contains oxygen means that it can be mixed directly with fuel and then burned inside the engine, without any intervening loss of heat. This was the thermodynamic promise that drove an intensified search for a workable combustion engine in the second half of the nineteenth century. Combustion can generate temperatures of 2,700 degrees Fahrenheit inside the cylinder, allowing for a greater drop in temperature and this greater efficiency, and these hot gases are created exactly where they are needed; there’s no need to transport them through conduits and valves that inevitably lose heat to the environment. In this circumstance, the poor conductivity of air becomes an advantage: relatively little of this heat is conducted into the surrounding metal, and that metal, not needed to transmit heat to another part of the engine, can be kept cool enough to prevent mechanical failure.[9]

German Engineering

Infused with new purpose by the science of thermodynamics, and bolstered by the ever-improving precision of machine tools, the combustion engine finally made the leap from experiment to industry in the 1860s. It began as a classic “disruptive innovation,” as described by Clayton Christensen, beginning with small, inexpensive engines, at the bottom of the market. It could not yet compete with large-scale industrial steam power in textile or flour mills; instead it found customers in small workshops and industries with modest power needs. The combustion engine’s closest competitor were derivatives of the 1807 Maudslay table engine, a small steam engine of as little as 1.5 horsepower that could sit (as the name suggests) on a table.[10] A combustion engine could start and stop more quickly without continuing to burn fuel, draw fuel straight from the town gas line, and be built even smaller, delivering one half or one third of a horsepower.

Most of the early developments in combustion engine technology took place in continental Europe. A promising effort by a pair of Tuscans, Eugenio Barsanti and Felice Matteucci, was cut short by the death of one of the principals. The honor of the first (modestly) successful commercial combustion engine went instead Jean Joseph Étienne Lenoir, born in Luxembourg (later part of Belgium) but working in Paris. His 1860 gas engine was the most conservative design possible, borrowing the form of a double-acting steam engine, but with burning gas to push the piston and a water jacket to keep the cylinder cool. It ran poorly under load with a great deal of loud banging, its electric ignition system required constant attention, and it did not achieve the gains in fuel efficiency that Lenoir expected (and, indeed, had promised). Nonetheless, the small size of the engine and the availability of on-tap fuel were enough to attract some customers. Lenoir sold five hundred engines, or so, almost all of three horsepower or less.[11]

Shortly thereafter, Nicolaus Otto, a traveling tea salesman from the Duchy of Nassau in Western Germany, learned about, and became obsessed with improving upon, Lenoir’s engine. For several decades to come, the most famous names in internal combustion would all be German ones: Otto, Diesel, Maybach, Benz, Daimler. One can trace the reasons that the steam engine first appeared in Britain with some confidence to a handful of geographic and economic factors. The German affinity for internal combustion is harder to explain. One factor may have been the later take-off of industrial growth in Germany, based less on textiles and more on chemicals, mining, and metallurgy. Small-scale craftsmen, inheritors to the ancient traditions of the guilds, running workshops with a handful of employees, remained a major economic presence in German manufacturing throughout the nineteenth century.[12] Such businesses constituted exactly the market to which combustion engines were most suited.

This explanation is not entirely satisfactory, however. Britain, and other countries, still had small workshops and tradesmen aplenty who could benefit from a compact, convenient engine.[13] But the combustion engine also had an ideological dimension in Germany, and this may be where the key lies. Struggles over the protection of the traditional rights of tradesmen remained vigorous in mid-century German states, and many traditionalists perceived capital-intensive business interests as a novel and predatory force. The conservatives in several states, after crushing the liberal revolutions of 1848-1849, introduced industrial regulations to resurrect the traditional rights of craftsmen.[14]

In this context, the combustion engine carried special meaning as a weapon of the weak; a means for the little guy to fight back against big business. This is particularly evident in the writings of Franz Reuleaux, an academic mechanical engineer from Prussia. In 1875, he wrote a treatise on kinematics which includes, under the heading “The Meaning of the Machine for Society,” an extensive treatise that expounds on the evils of industrial society in terms redolent of Marx, but proposes to cure those ills with a return to traditional values, not through a proletarian revolution.

Reuleaux laments the dominance of centralized capital, before which the small craftsman lies prostrate, replaced by the grim and alienating monotony of factory work. This is not, he argues, because the productive machinery itself is so expensive, but because “[o]nly capital is able to build an operate the powerful steam engines around which is grouped the remainder of the establishment.” His solution lies in new prime movers like the combustion engine:

To combat most of the evil, engineers must provide cheap, small engines, or in other words, small engines with low running costs. If we give a power supply to the small master as cheaply as the great powerful steam-engines can be obtained by capital, and we thus support this important class of society, we shall strengthen it where it happily still exists and we shall re-create it where it has disappeared.

…Air and gas engines… can be used almost everywhere and are being steadily perfected. These little engines are the true prime movers of the people [Volk]; They can be obtained at reasonable prices and are very inexpensive to operate.[15]

Breaking the bonds tying the workman to capital would allow the former to seize the means of production and restore the traditional moral order of craft work: a hierarchical but harmonious household of family, apprentices, and assistants guided by the hand of the tradesman.[16]

Tellingly, the English translation of this same section, provided by a British academic engineer, Alex Kenedy, is a bowdlerization rather than a true translation. Kennedy provides only four anodyne pages on the machine and society rather than seventeen, stripped of all the ideological fire of the original. He evidently did not feel that this plea for a conservative industrial democracy held any interest for his British readers.[17]

Otto’s Engines

Whatever the true reasons for Germany’s outsize contributions to internal combustion, they began with Otto. Brimming with ideas and entrepreneurial energy, he threw himself into the work of improving Lenoir’s engine. However, as a clerk and salesman with no formal technical education, he made little effective progress. He needed the guidance of someone with a strong engineering background and good business sense. He found it in Eugen Langen, who had studied at a polytechnic institute in Karlsruhe, and worked his way up to a partnership in his father’s sugar refining business while running a side hustle making equipment for gas producers. Restless for a new venture, in 1864 he somehow came across Otto’s work and decided that it had promise (the exact circumstances of how the men met are unknown, though both worked in Cologne).[18]

Even with the addition of Langen’s talents and money, and the further advice of Reuleaux (an old school chum of Langen’s) it took a further three years Otto and Langen’s partnership to produce a commercially useful engine, which debuted publicly at the 1867 Paris Exhibition. With the help of Reuleaux, who served on the judging board, it won the grand prize by dint of its efficiency: it used half the gas to do the same work as competing engines. This first Otto and Langen machine was an atmospheric engine, a direct descendant of the Newcomen engine, and indeed Huygens’ gunpowder engine. The cylinder was set vertically, and the explosion of the burning gas drove the piston up freely (that is, without any connection to the drive mechanism). The power stroke came as the piston descended, pushed down by the weight of the atmosphere into the cylinder just evacuated by the explosion. The complexities—the attributes that made it a viable prime mover, and not just a demonstration piece like Huygens’ machine—came in the timing of regular ignitions, the valve controls, and the intricate design of the clutch that engaged on the down stroke to turn the drive shaft.[19]

In 1872, flush with orders for the Otto and Langen and with new capital from Langen’s brothers and other interested businessmen, the company reorganized as Gasmotoren-Fabrik Deutz (after the Cologne suburb where their new headquarters was located). Langen hired Gottlieb Daimler to get the factory running efficiently and Daimler brought with him the young Wilhelm Maybach, hired as a design engineer.[20]

With this new company, new team, additional advice and encouragement from Reuleaux, and four more years of work, Otto produced in 1876 the machine that immortalized his name: the so-called “Silent Otto.” Though not tremendously more efficient than its atmospheric predecessor, a Silent Otto weighed 1/3 as much and had a cylinder volume 1/15 the size for the same horsepower. This made it possible to scale to larger sizes: because of the large cylinder required to draw power from the atmosphere, the Otto and Langen could not practically grow much over one or two horsepower. Between their own factory and British and American licensees, Deutz sold tens of thousands of engines of this type by 1890.[21]

As usual, practice outran theory: Otto had made a great advance, but without a clear idea as to why. He believed that he had created a stratified charge which, by gradually increasing the mix of fuel in the air over the length of the cylinder, cushioned the blow of the explosion, allowing the engine to run much more smoothly and quietly than the clanging Otto and Langen. However, this was not an accurate model of what was actually happened during an explosion in the cylinder. The real key to the success of the Silent Otto lay in its four-stroke cycle, in which the first stroke draws the fuel-air mixture into the cylinder, the second stroke compresses it, the third delivers power as the mixture explodes, and the fourth pushes the exhaust gases out of the cylinder. Compressing the gas inside the cylinder before ignition made for a far more powerful and efficient explosion, and it was much easier to achieve this with a four-stroke cycle than with fewer.[22]

The four-stroke cycle went completely against the grain of what most of Otto’s contemporaries (including Daimler) were trying to do: they hoped to recapitulate the history of the Watt engine by turning a single-acting atmospheric engine into a double-acting engine that derives power from every stroke. But a combustion engine is not a steam engine: explosive combustion is very powerful and very fast, and at hundreds of cycles per minute one power stroke out of every four is sufficient to drive many kinds of machinery.[23]

Otto’s engines provided power to many small workshops and tradesman, but did not turn the tide away from capital and towards industrial democracy, as Reuleaux had hoped. His assertion that the economics of large-scale factory work rested only on the need to share a large prime mover was simply wrong; an error born of wishful thinking, perhaps.

An industrial democracy of mechanized craft households did not replace factory work, but many businesses found a use for a more compact, user-friendly engine: from bakeries and printers to sawmills and soda water makers.[24] Combustion engines also moved up the market as engines with tens of horsepower engines became possible, horning in on more and more of the steam engine’s traditional territory.