New page: 15 July 2008 Updated 8 Nov 2019 Better engine cross-section added

Left: The Dolgorouki Engine. According to Nature, this machine was exhibited at the Exposition Internationale d'Electricité, in both the Russian and the German sections; in the latter it was on the stand of the Siemens & Halske company, where it was running a direct-current dynamo. The example on display (shown here) was destined for the Lichterfelde tramway, in Berlin, the world's first electrical tramway. The engine had two pairs of semi-cylindrical rotors, synchronised by gearing which appears to have resided in the middle part of the casing. It was noted that it had no dead-centre points. There is a centrifugal governor in the steanm inlet pipe at top left. The lever on the front also controls motor speed; the technical French is a little hard to decode but it is now clear that it was a throttle, not a cut-off control. The cut-off was fixed. The position of the steam exhaust is not clear, but it appears to have been the blanked-off flange just behind the inlet pipe. Image & info from the French journal Nature 1882/1, p155

Pictures of real rotary engines that are still in existence are unfortunately very rare. I am therefore very glad to report that I have just discovered a Dolgorouki Engine in the Vienna Technological Museum.

Left: Dolgorouki Engine at Vienna. This engine is not the one in the drawing above. It is approximately half the size, and the engine-dynamo combination was put together by Siemens & Halske in 1883 to power the first ever electrical passenger train in 1879. The dynamo output was 20 Amps. There is a flywheel, and quite a substantial one. Obviously constant torque was not one of the Dolgorouki's best features. According to the description in front of the baseplate, the engine gave 5 to 6 horsepower at 900 to 1000 rpm, which is a much faster speed than any reciprocating engine would run at, and much better suited for direct coupling to a generator. The engine casing is about 14 inches long. Author's photo July 2008

Left: Dolgorouki Engine at Vienna A close-up of the left-hand end of the engine Author's photo July 2008

Left: Dolgorouki Engine at Vienna Photo of the label in front of the displayed engine. Author's photo July 2008

Left: Dolgorouki Engine at Vienna. A close-up of the engine cross-section, which gives some clue to the internal construction. It appears to be very similar to the Behrens engine of 1886, having two C-shaped rotors turning around fixed centres. The Behrens engine has the advantage that it avoids the usual rotary engine error of line-contacts between rotor and casing that make sealing virtually impossible, and it looks like the Dolgorouki also used one of the more promising engine geometries. Image courtesy of Bernd F.

Left: Dolgorouki Engine at Vienna. This appears to be original drawing of the engine-dynamo combination. Note the absence of dotted lines. Taken from The Electric Motor and Its Applications by T. C. Martin And Joseph Wetzler, Third Edition. Figure 48. Apparently the drawing was first done for Electrical World, a journal published in New York.

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THE BERLIN PATENT

Left: Diagram of the engine from the German patent: 1879 Dolgorouky took out patents for his engine in France, Italy, Britain, Germany, Belgium, and Austro-Hungary. This must have been expensive, but presumably for a Russian prince money was plentiful; it certainly shows he had faith in his invention. It is surprising he did not take out a USA patent. This diagram shows many minor differences from the Vienna engine, but the basic principle of two C-shaped rotors is clear. The two rotors are synchronised by spur gearing at each end of the engine. The small lever is the steam throttle, and the large lever R controls the steam admission cutoff. From German patent DE6870.

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THE INVENTOR: PRINCE ALEXIS DOLGOROUKY

Left: Reference to Belgian Dolgorouki Engine patent From the British The Commissioners of Patents Journal, 1879 Volume 2, July to December. They might have given us the patent number. Here the name is spelled A S Dolgorouky.

Left: Reference to Belgian Dolgorouki Engine patent Here we learn that inventor was, as I suspected, Prince Alexis Sergueevitch Dolgorouky, a Russian nobleman, based in St Petersburg. I am not all sure the middle name is spelled correctly there. From the British The Commissioners of Patents Journal, 1879 Volume 2, July to December.

Left: Prince Alexis Dolgorouky: 1846-1915 This is now a rare case where we know quite a bit about the inventor of a rotary engine. See here. Dolgorouky married the English socialite Frances "Fanny" Fleetwood Wilson. (1850 - 1919) Dolgorouky was awarded a number of patents in different countries, including German patent DE6870 (C) 'Improvements in Rotary Machinery) dated 1879-08-22. He is stated as being based in St Petersburg. There is more information here. He is buried at Hitcham. Unfortunately none of these links make any reference to engine design or even an interest in technical subjects.