Robust Submarine Diesel Engines: Some Important Considerations

Mainly from an Anonymous Comment of 10/6/17 10:16 AM

Submarine experts (including submarine Vice-Adm (retired) Kobayashi [1] and Tadashi Sano, Ex-Director Submarine Design, KHI [2] ) see the following as important for submarine diesel engines.

1.  Submarine diesels must be robust enough to tolerate rapid starts and stops without warm-up periods [3] and without undue wear or breakdown. Rapid stop starting minimises:

-  diesel operating (indiscretion) time during snorting (recharging batteries - see history), and

-  improves the submarines high engine stress [4] manoeuvring performance in action (eg. after

   torpedos and/or Harpoon missiles are fired and then an Oyashio or Soryu accelerates into a deep

   dive)

Diesel engines are exposed to high heat differences as some engine parts heat up much more quickly than other parts. High dispersal of oils and lubrication are required.

2.  Another requirement are diesel engines compact enough to provide enough space:

-  for several types of maintenance during long missions, and

-  room for engines to use rubber/elastic rafts to minimise through hull vibrations/noise.

3.  A third requirement are diesels powerful and robust enough to quickly generate high pressures within the hull:

-  to exhaust/expel gas in the seawater, and

-  to expel gas out of the snorkel into the surface air.

4.  Other diesel requirements are:

-  the capability to match/balance intake and exhaust pressures (in a snorkel), and 

-  an efficient safety device to stop the diesel for stops, reversals or other high stress needs.

For example when snorting if either the tube drawing in air or the exhaust tube were blocked valves must be sensitive enough to stop before damage to the submarine or to the crew (avoiding atmosphere vacuum within the hull :( is done

Anonymous’ Comment

Submarine diesels are quite different from ship diesels. Sub diesels require superior material as well as very robust design capabilities. In submarine/shipyards submarine diesels need to be capable of easy dismantling:

-  in order for some engine parts to be passed through the submarine’s small hull hatches, and

-  for quick and easy maintenance in the yard.

[1] Ships Of The World, 7, 2017.No.862, page 104, “Today’s Submarine” by Masao Kobayashi, Ex-Commander, Japanese Submarine Fleet and former Vice-Admiral (JMSDF).

[2] “Perfect Guide of Mechanism in Submarine” by Tadashi Sano, Ex-Director, Sub Design, KHI.

[3] “Warming up on a ship” (in Japanese, but right-click mouse translatable)

Unlike trucks and small ship diesels, a large ship [or submarine] diesel takes time until the whole large diesel has evenly warmed up across all parts. Without a warm up period large temperature differences can remain long enough to break some parts. Distribution of warm air (from dockside starter motors) can warm many submarine parts successfully.

Coolant and oil should also be circulated by dockside or internal pumps. Dockside motors might also need to "turn" the engine to warm the cylinders. The larger the engine the longer the warm-up required, eg. 30 minutes for large ship diesels.

[4] http://www.dieselhub.com/tech/warm-up-cool-down.html

All turbochargers are lubricated via the engine's pressurized oil system, meaning that engine oil is constantly circulated through passages entering and exiting the bearing cartridge. While a vehicle is driving ([or submarine moving] and the turbocharger is functioning, it becomes hot - the temperature of the turbocharger is relative to load. When a vehicle has been driven and is abruptly shut off (and the oil flow to the turbocharger ceases), engine oil contained in the turbocharger absorbs heat from its surroundings. If the temperature of the turbocharger prior to shut down is great enough, the oil risks burning and will have a tendency to create deposits in and around the turbo bearings in addition to contaminating the engine oil supply [not good if you are crewing a submarine on an (almost always) isolated mission].

A nice roomy engine room - or is that for the tourists? These are opposed-piston Fairbanks-Morse diesel engines on USS Pampanito (SS-383) which is permanently docked in San Francisco and can be toured as part of the Maritime Museum. (Photo courtesy Wikimedia)

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Not so roomy looking engine room of an Oberon "O-class" submarine. The 2 x 1,840 hp Admiralty Standard Range V16 diesels (same as?) were still very reliable I hear! (Photo courtesy Sandy McCearn via Haze Gray & Underway).

Mainly Anonymous (with some extra translation from Pete)