De Dion's "Le Mono"

A most significant development in internal combustion engine design.

De Dion at Don Robertson's.
De Dion at Don Robertson's
In 1876, Dr Nicolas Otto demonstrated the first practical* internal combustion engine, It utilised the four stroke principle, but, unknown to Dr Otto, this had been described (but never tried) by French engineer Alphonse Beau de Rochas in an obscure 1862 German publication.

In 1884, De Rochas's prior publication came to light and in anticipation of Otto's patent being invalidated (which occurred in 1886), many designers took up the development challenge.

After Otto, Gottlieb Daimler's hot tube ignition "grandfather clock" design of 1884 and Karl Benz's arguably more advanced (spark ignition) patent motorenwagen engine from 1885-86 are regarded as the next significant steps in the development of the four stroke internal combustion engine (which is still the world's dominant portable power source 125 years later).

But the design that really led to this dominance is unheralded and almost forgotten now. It came in 1893; just after Daimler and Benz's early offerings

Marquis Albert De Dion.
Marquis Albert De Dion
It's designer was the Count (later Marquis) Albert De Dion, a French nobleman complete with Chateau and an illustrious history dating back to the 13th century. Born in 1856, De Dion was everything the 'egalaterie' disliked; rich, connected, a gambler and a playboy,. As a young man he was involved in society scandals, fought at least 3 duels, and his father took a court order preventing his access to family wealth (except his 'allowance' of course, which must still have been more than adequate). The bourgeoisie eventually forgave all this and later in life he became France's most popular politician. In a stellar public career, he went on to start the FIA (Federation Internationale de L'Automobile), Guides Michelin, the Aeroclub de France, did more than anyone else to fix France's previously terrible roads, developed the largest circulation newspaper in France, and founded the Tour de France.

But what the bourgeoisie (and the world) have yet to acknowledge is his towering engineering talent. By any rational measure, Albert de Dion was one of the world's greatest engineers; up with my personal heroes; Watt, Whitworth, George and Robert Stephenson, Marc and Isembard Brunnel, Daimler, Benz, Diesel, Henry Leyland (Cadillac), Ford, and Kelly Johnstone (SR 71 Blackbird). During his lifetime De Dion was granted 394 patents, including; for steam engines and boilers (1883), for the rotary and radial engine (1889) and more than 300 that pretty much defined the motor car.

From 1882 he had teamed up with George Bouton and Charles Trepardoux to produce and race highly successful steam cars, but seeing Daimler's and Benz's new engines at the 1889 Paris Exposition convinced him that the future of the automobile was with the internal combustion engine. Trepardoux disagreed and split over this while Bouton was at first a reluctant convert, so Albert began developing IC engine ideas on his own account.

He hit the jackpot in 1893 with the "Le Mono" prototype; a 137cc, 4 stroke, air cooled, single, producing 0.5hp at 1800rpm. With an "F head" side valve layout and twin disc flywheels (as used earlier by Daimler), it was to become the most studied and copied engine, ever.

De Dion, Bob Lynn, June '06.
De Dion, Bob Lynn, June '06.
But initially it had a problem. 'Designed' to run at 900rpm -usefully faster than Daimler's 600rpm 'high speed' engine- when first fired up there were bad vibrations. The solution was discovered when it revved out to a previously unheard of 2000rpm and above. Not only did the vibrations disappear (when gas and inertial forces cancelled each other), but the specific power (output/size) leapt to three or four times that of previous engines.

Was this genius or luck? That Le Mono's valve system and ignition enabled such high speeds, and that it's design was robust enough to survive to 3000rpm wasn't just luck. The breaker points ignition system, invented for this engine became the standard, it's "F " head side valve layout endured well into the 1950's and all IC engines now run at Le Mono speeds and above.

Larger and water cooled versions were quickly developed, and by 1900, De Dion-Bouton had become the world's largest maker of automobiles and by far the largest supplier of engines to other manufacturers.

Le Mono became the pattern for most motorcycle engines. Even more than 100 years later, many motorcycles still show obvious De Dion ancestry.

And Le Mono was also the starting point for rotary and radial aircraft engines (which, along with the gear oil pump, synchromesh gear box, epicyclic automatic transmission and his eponymous suspension were also De Dion inventions). Samuel Langley, (aircraft pioneer and director of the Smithsonian) took a Le Mono to the USA in 1900 for 'study' (that is, so that they could copy it). During testing it astounded local engineers by running happily at 4000rpm.

De Dion, 1908 12 hp, engine, Aug 2004.
De Dion, 1908 12 hp, engine, Aug 2004.
In homage, I acquired one of these engines- as per the accompanying photo's. As a bonus- or an unnecessary appendage- depending on your point of view, it came with a car attached- a 1908 De Dion-Bouton "Type de Cours". This car used the final and most powerful development of Le Mono by De Dion-Bouton. It develops 16hp at 3000rpm from 1.25 litres, is flexible, reliable, and economical- and provides a top speed of 80kmhr; not so bad for a single cylinder car that's now more than 100 years old (brakes weren't a priority then though)!

The legacy of Le Mono is incalculable. There are very few spark ignition engines today that don't owe at least something to features first pioneered in this design.

So why has Albert De Dion not yet been accorded the fame he so obviously deserves.?

Peter Lynn, Ashburton NZ, May 2010

*Italians Mateucci and Barsanti made the first known functional IC engine in 1856, Ettiene Lenoir and others (including Dr Otto) all made, and sold 'atmospheric' (that is, non-compressing) IC engines prior to 1876, but the IC revolution truly began with the Otto and Langen four stroke compressing engine of that year.

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