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.
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.
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].
---
Mainly Anonymous (with some extra translation from Pete)
