Junkers Jumo 205
|Jumo 205 cutaway|
|Type||Aircraft Diesel engine|
|Major applications||Junkers Ju 86
Blohm & Voss BV 138
Blohm & Voss BV 222
|Developed from||Junkers Jumo 204|
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-altiude reconnaissance aircraft, and the 46-meter wingspan, six-engined Blohm & Voss Bv 222 Wiking flying boat. 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.
Design and development
These engines all used a two-stroke cycle with twelve pistons sharing six cylinders, piston crown to piston crown in an opposed piston 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. There were two cam-operated injection pumps per cylinder, each feeding two nozzles, for 4 nozzles per cylinder in all.
As is typical of two-stroke designs, the Jumos used fixed intake and exhaust port apertures cut into the cylinder liners instead of valves during their manufacture, which were uncovered when the pistons reached a certain point in their stroke. 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 valve-less 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 eleven degrees 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.
There is some downside 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.[dubious ]
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.
- CLM Lille 6As
- A license-built version from CLM Lille, delivering 650 hp (480 kW).
- CLM Lille 6BrS
- A developed version of the 6As used to power the Bernard 86.
- Jumo 218
- A twelve-cylinder version, the Jumo 218, was designed but never built.
- Jumo 223
- A single 24-cylinder 4-crankshaft Jumo 223 was built and tested.
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 the version Jumo 207A1 turbocharged diesel engines. It was far more successful as a power unit for airships, for which its characteristics were ideal, and for non-combat 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.
- Blohm & Voss BV 138
- Blohm & Voss Ha 139
- Blohm & Voss BV 222
- Dornier Do 18
- Dornier Do 24 (V1 and V2 prototypes)
- Dornier Do 26
- Junkers Ju 86
Specifications (Jumo 205D)
Data from 
- Type: Six-cylinder 12-piston liquid-cooled opposed piston inline two-stroke diesel engine
- Bore: 105 mm (4.13 in)
- Stroke: 160 mm (6.3 in)
- Displacement: 16.63 L (1,015 in³)
- Length: 1,934 mm (76.5 in)
- Width: 547 mm (21.54 in)
- Height: 1,325 mm (52.17 in)
- Dry weight: 595 kg (1,312 lb)
- Supercharger: Spülgebläse
- Fuel system: Fuel injection
- Fuel type: Diesel
- Oil system: Forced with one pressure and two scavenge pumps
- Cooling system: Liquid-cooled
- Power output: 880 PS (868 hp, 647 kW) at 2,800 rpm
- Specific power: 39.0 kW/L (0.86 hp/in³)
- Compression ratio: 17:1
- Power-to-weight ratio: 1.09 kW/kg (0.66 hp/lb)
Other notable opposed piston engines
- Commer TS3 "The Commer Knocker" commercial vehicle engine.
- Leyland L60 tank engine, used in the Chieftain tank. Similar in layout to the Junkers Jumo 205 and Napier Culverin.
- Rolls-Royce K60 engine, used in the FV430 series of armoured fighting vehicles and Swedish tank Strv 103.
- Napier Deltic.
- Soviet engine 5TDF used on tank T-64.
- Soviet engine 6TD used on tanks T-80UD, T-84 and Al-Khalid.
- Fairbanks Morse 38 8 1/8
- Charomskiy ACh-30 and Charomskiy M-40: Two Soviet aircraft Diesel engine designs, only ever built in small numbers.
- List of aircraft engines
- "Smithsonian National Air & Space Museum - Junkers Jumo 207 D-V2 In-line 6 Diesel Engine". airandspace.si.edu. Smithsonian Institution. Retrieved December 29, 2017.
- "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.
- "Charqacteristiques et Description du Moteur Type Lille 6Brs de 600CV" (in French). Retrieved 6 November 2017.
- Jane's 1989, p. 294.
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