Junkers Jumo 205

The Junkers Jumo 205 aircraft engine was the most famous of a series of aircraft diesel engines that were the first, and for more than half a century, the only successful aviation diesel powerplants. The Jumo 204 first entered service in 1932. Later engines of this type comprised the experimental Jumo 206 and Jumo 208, with the Jumo 207 produced in some quantity for the Junkers Ju 86P and -R high-altitude reconnaissance aircraft, and the 46-meter wingspan, six-engined Blohm & Voss BV 222 Wiking flying boat.[1] All three of these variants differed in stroke and bore and supercharging arrangements. In all, more than 900 of these engines were produced, in the 1930s and through most of World War II.

Jumo 205
Jumo 205 cutaway
Type Aircraft diesel engine
Manufacturer Junkers
First run 1930s
Major applications Junkers Ju 86
Blohm & Voss BV 138
Blohm & Voss BV 222
Developed from Junkers Jumo 204

Design and development
A similarly sectioned Junkers Jumo 207 aviation diesel engine

These engines all used a two-stroke cycle with 12 pistons sharing six cylinders, piston crown to piston crown in an opposed configuration. This unusual configuration required two crankshafts, one at the bottom of the cylinder block and the other at the top, geared together. The pistons moved towards each other during the operating cycle. Intake and exhaust manifolds were duplicated on both sides of the block. Two cam-operated injection pumps per cylinder were used, each feeding two nozzles, for four nozzles per cylinder in all.

As is typical of two-stroke designs, the Jumos used no valves, but rather fixed intake and exhaust port apertures cut into the cylinder liners during their manufacture, which were uncovered when the pistons reached a certain point in their strokes. Normally, such designs have poor volumetric efficiency because both ports open and close at the same time and are generally located across from each other in the cylinder. This leads to poor scavenging of the burnt charge, which is why valveless two-strokes generally produce smoke and are inefficient.

The Jumo solved this problem to a very large degree through clever arrangement of the ports. The intake port was located under the "lower" piston, while the exhaust port was under the "upper". The lower crankshaft ran 11° behind the upper, meaning that the exhaust ports opened, and even more importantly, closed first, allowing proper scavenging. This system made the two-stroke Jumos run as cleanly and almost as efficiently as four-stroke engines using valves, but with considerably less complexity.

Some downside exists to this system, as well. For one, since matching pistons were not closing at quite the same time, but one ran "ahead" of the other, the engine could not run as smoothly as a true opposed-style engine. In addition, the power from the two opposing crankshafts had to be geared together, adding weight and complexity, a problem the design shared with H-block engines.

In the Jumo, these problems were avoided to some degree by taking power primarily from the "upper" shaft, somewhat offset upwards on the engine's front end. All of the accessories, such as fuel pumps, injectors and the scavenging compressor, were run from the lower shaft, meaning over half of its power was already used up. What was left over was then geared to the upper shaft, which ran the engine's propeller. In all, about three-quarters of the power to the engine's propeller came from the upper crankshaft.

In theory, the flat layout of the engine could have allowed it to be installed inside the thick wings of larger aircraft, such as airliners and bombers. Details of the oil scavenging system suggest this was not possible and the engine had to be run "vertically", as it was on all designs using it.

Variants
Jumo 205
Jumo 206
An experimental version. Development halted in favour of the Jumo 208.
Jumo 207
High-altitude version with two inline centrifugal superchargers and a precooler. The 207 B-3 featured GM-1 nitrous oxide injection.
Jumo 208
with greater displacement, not produced
Jumo 218
A 12-cylinder version, the Jumo 218, was designed but never built.
Jumo 223
A single 24-cylinder four-crankshaft Jumo 223 was built and tested.
CLM Lille 6As
A license-built version from CLM Lille, delivering 650 hp (480 kW)[2][3](CLM was the predecessor to the Indenor engine maker, a sister company to Peugeot)
CLM Lille 6BrS
A developed version of the 6As used to power the Bernard 86[3]

Applications

The Jumo 205 powered early versions of the Junkers Ju 86 bomber, but was found too unresponsive for combat and liable to failure at maximum power, common for combat aircraft. Later versions of the design also used the engine for extreme high-altitude use, as with the Ju 86P and -R versions for high-altitude reconnaissance over the British Isles. In January 1940, the Luftwaffe tested the prototype Ju 86P with Jumo 207A-1 turbocharged diesel engines. It was far more successful as a power unit for airships, for which its characteristics were ideal, and for noncombat applications such as the Blohm & Voss Ha 139 airliner. Its more fuel-efficient operation lent itself for use on Germany's few maritime patrol flying-boat designs during World War II, such as the BV 138 and BV 222.

Applications list

Specifications (Jumo 205E)

Data from Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944[4]

General characteristics

  • Type: six-cylinder air-cooled inverted inline
  • Bore: 105 mm (4.13 in)
  • Stroke: 160 mm (6.30 in) x2
  • Displacement: 16.62 l (1,014.21 cu in)
  • Length: 2,051 mm (80.7 in)
  • Width: 600 mm (23.6 in)
  • Height: 1,325 mm (52.2 in)
  • Dry weight: 570 kg (1,257 lb) dry, unequipped

Components

  • Supercharger: engine driven supercharger at 8.85:1
  • Fuel system: direct injection through four nozzles per cylinder
  • Fuel type: Diesel fuel
  • Oil system: dry sump, pressure feed with scavenge
  • Cooling system: liquid-cooled

Performance

  • Power output:
  • 700 PS (690 hp; 515 kW) at 2,500 rpm (5 minutes) at sea level
  • 630 PS (621 hp; 463 kW) at 2,420 rpm (30 minutes) at sea level
  • 560 PS (552 hp; 412 kW) at 2,250 rpm (max. continuous) at sea level
  • 500 PS (493 hp; 368 kW) at 2,000 rpm (cruise) at sea level
  • Specific power: 42.1 PS/l (0.68 hp/cu in; 30.96 kW/l)
  • Compression ratio: 17:1
  • Specific fuel consumption: 0.170 kg/PS/h (0.380 lb/hp/h; 0.231 kg/kW/h) at max continuous
  • Oil consumption: 0.006–0.008 kg/PS/h (0.013–0.018 lb/hp/h; 0.008–0.011 kg/kW/h)
  • Power-to-weight ratio: 1.228 PS/kg (0.549 hp/lb; 0.903 kW/kg)
  • B.M.E.P.: 7.6 atm (7.7 bar; 112 psi)
  • Reduction gear: 0.633:1

Other notable opposed-piston engines

See also

References
  1. "Smithsonian National Air & Space Museum - Junkers Jumo 207 D-V2 In-line 6 Diesel Engine". airandspace.si.edu. Smithsonian Institution. 2016-03-20. Retrieved December 29, 2017.
  2. "POWER at the SALON j Detailed Review of the British and Continental Engines at the Show : A Remarkable Variety of Types". Flight. 26 November 1936. p. 577. Retrieved 14 March 2015.
  3. "Charqacteristiques et Description du Moteur Type Lille 6Brs de 600CV" (in French). Retrieved 6 November 2017.
  4. Schneider, Helmut (Dipl.Ing.) (1944). Flugzeug-Typenbuch. Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944 (in German) (Facsimile reprint 1986 ed.). Leipzig: Herm. Beyer Verlag. p. 396. ISBN 381120484X.

Further reading
  • Bingham, Victor (1998). Major Piston Aero Engines of World War II. Shrewsbury, UK: Airlife Publishing. ISBN 1-84037-012-2.
  • Gunston, Bill (2006). World Encyclopedia of Aero Engines: From the Pioneers to the Present Day (5th ed.). Stroud, UK: Sutton. ISBN 0-7509-4479-X.
  • Kay, Antony (2004). Junkers Aircraft & Engines 1913–1945. London: Putnam Aeronautical Books. ISBN 0-85177-985-9.
  • Katz, Hans (Dr.Ing) (1940). Der Flugmotor. Bauteile und Baumuster. Luftfahrt Lehrbücherei Band 7. Berlin: de Gruyter.
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