Junkers Jumo 205
Encyclopedia
The Junkers Jumo 205 aircraft engine
was the most famous of a series of diesel engine
s that were the first, and for more than half a century, the only successful aircraft diesel engine
s. The Jumo 204
first entered service in 1932. Later engines in the series were styled Jumo 206, Jumo 207 and Jumo 208, and differed in stroke and bore and supercharging arrangements. In all more than 900 of these engines were produced.
with twelve pistons sharing six cylinders, piston-head to piston-head 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 ports instead of valves, 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 the pistons were not firing at the same time, but ran "ahead" of one another, the engine could not run as smoothly as a true opposed style engine. In addition, the power from the two opposing crankshafts has 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. 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 propellers. In all, about three-quarters of the power to the propellers came from the upper crankshaft.
In theory, the flat layout of the engine could have allowed it to be installed inside thick wings of larger aircraft, such as airliner
s and bomber
s. 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.
was built and tested.
The Jumo 204 and 205 were licensed to Napier & Son
, who built a small number as the Napier Culverin
just prior to the war. Late in the war, they mounted three Culverins in a triangle layout to produce the Napier Deltic
, which was for some time one of the most powerful and compact diesel engines in the world.
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. It was far more successful as a power unit for airship
s, for which its characteristics were ideal, and for non-combat applications such as the Blohm & Voss Ha 139 airliner.
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
was the most famous of a series of diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s that were the first, and for more than half a century, the only successful aircraft diesel engine
Aircraft diesel engine
The aircraft diesel engine or aero diesel has not been widely used as an aircraft engine. Diesel engines were used in airships and were tried in aircraft in the late 1920s and 1930s, but never "caught on" in a major fashion...
s. The Jumo 204
Junkers Jumo 204
-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
first entered service in 1932. Later engines in the series were styled Jumo 206, Jumo 207 and Jumo 208, and differed in stroke and bore and supercharging arrangements. In all more than 900 of these engines were produced.
Design and development
These engines all used a two-stroke cycleTwo-stroke cycle
A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft...
with twelve pistons sharing six cylinders, piston-head to piston-head 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 ports instead of valves, which were uncovered when the pistons reached a certain point in their stroke. Normally such designs have poor volumetric efficiency
Volumetric efficiency
Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More specifically, volumetric efficiency is a ratio of what quantity of fuel and air actually enters the cylinder during induction to the...
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 the pistons were not firing at the same time, but ran "ahead" of one another, the engine could not run as smoothly as a true opposed style engine. In addition, the power from the two opposing crankshafts has to be geared together, adding weight and complexity, a problem the design shared with H block
H engine
An H engine is an engine configuration in which the cylinders are aligned so that if viewed from the front, they appear to be in a vertical or horizontal letter H....
engines.
In the Jumo, these problems were avoided to some degree by taking power primarily from the "upper" shaft. 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 propellers. In all, about three-quarters of the power to the propellers came from the upper crankshaft.
In theory, the flat layout of the engine could have allowed it to be installed inside thick wings of larger aircraft, such as airliner
Airliner
An airliner is a large fixed-wing aircraft for transporting passengers and cargo. Such aircraft are operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an aircraft intended for carrying multiple passengers in commercial...
s and bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
s. 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
A twelve cylinder version, the Jumo 218, was designed but never built, while a single 24-cylinder 4-crankshaft Junkers Jumo 223Junkers Jumo 223
The Junkers Jumo 223 was an experimental 24-cylinder aircraft engine based on the Junkers Jumo 205. Like the Jumo 205, it was an opposed piston two-stroke diesel engine. It had four banks of six cylinders in a rhomboid configuration, with four crankshafts one at each vertex of the rhombus, and 48...
was built and tested.
The Jumo 204 and 205 were licensed to Napier & Son
Napier & Son
D. Napier & Son Limited was a British engine and pre-Great War automobile manufacturer and one of the most important aircraft engine manufacturers in the early to mid-20th century...
, who built a small number as the Napier Culverin
Napier Culverin
-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.-External links:*...
just prior to the war. Late in the war, they mounted three Culverins in a triangle layout to produce the Napier Deltic
Napier Deltic
The Napier Deltic engine is a British opposed-piston valveless, two-stroke diesel engine used in marine and locomotive applications, designed and produced by Napier & Son...
, which was for some time one of the most powerful and compact diesel engines in the world.
Applications
The Jumo 205 powered early versions of the Junkers Ju 86Junkers Ju 86
The Junkers Ju 86 was a German monoplane bomber and civilian airliner designed in the early 1930s, and employed by both sides during World War II. The civilian model Ju 86B could carry 10 passengers. Two were delivered to Swissair and five to Luft Hansa...
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. It was far more successful as a power unit for airship
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...
s, for which its characteristics were ideal, and for non-combat applications such as the Blohm & Voss Ha 139 airliner.
Applications list
- Blohm & Voss BV 138
- Blohm & Voss Ha 139
- Blohm & Voss BV 222
- Dornier Do 18Dornier Do 18The Dornier Do 18 was a development of the Do 16 flying boat. It was developed for the Luftwaffe, but Lufthansa got 5 aircraft and used these for tests between the Azores and the North American continent in 1936 and on their mail route over the South Atlantic from 1937 to 1939.27–29 March 1938 a...
- Dornier Do 26Dornier Do 26The Dornier Do 26 was an all-metal gull winged flying boat produced before and during World War II by Dornier Flugzeugwerke of Germany.It was operated by a crew of four and was intended to carry a payload of 500 kg or four passengers on the Lisbon to New York route.-Design and development:The...
- Junkers Ju 86Junkers Ju 86The Junkers Ju 86 was a German monoplane bomber and civilian airliner designed in the early 1930s, and employed by both sides during World War II. The civilian model Ju 86B could carry 10 passengers. Two were delivered to Swissair and five to Luft Hansa...
Specifications (Jumo 205 A)
Other notable opposed piston engines
- Commer TS3Commer TS3The Commer TS3 was a diesel engine fitted in Commer trucks built by the Rootes Group in the 1950s and 1960s. It was largely the product of Tilling-Stevens, but was developed by Rootes Group when they bought out Tilling-Stevens...
"The Commer Knocker" commercial vehicle engine. - Leyland Motors L60 tankTankA tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
engine, used in the Chieftain tankChieftain tankThe FV 4201 Chieftain was the main battle tank of the United Kingdom during the 1960s and 1970s. It was one of the most advanced tanks of its era, and at the time of its introduction in 1966 had the most powerful main gun and heaviest armour of any tank in the world...
. Similar in layout to the Junkers Jumo 205 and NapierNapier & SonD. Napier & Son Limited was a British engine and pre-Great War automobile manufacturer and one of the most important aircraft engine manufacturers in the early to mid-20th century...
Culverin. - Rolls-RoyceRolls-Royce plcRolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...
K60 engine, smaller and improved version of the L60 used in the FV430 series armoured fighting vehicles and Swedish tank Strv 103. - Napier DelticNapier DelticThe Napier Deltic engine is a British opposed-piston valveless, two-stroke diesel engine used in marine and locomotive applications, designed and produced by Napier & Son...
. - Soviet engine 5TDF used on tank T-64T-64The T-64 is a Soviet main battle tank, introduced in the early 1960s. It was used solely by the Soviet Army in its front-line divisions and was a more advanced counterpart to the T-62...
. - Soviet engine 6TD used on tanks T-80UD, T-84T-84The T-84 is a Ukrainian main battle tank, a development of the Soviet T-80 main battle tank. It was first built in 1994 and entered service in the Ukrainian Armed Forces in 1999. The T-84 is based on the diesel-engined T-80 version, the T-80UD...
and Al-Khalid. - Fairbanks Morse 38 8 1/8
