Text 1590, 140 rader
Skriven 2005-05-20 09:00:00 av TOM WALKER (1:123/140)
Ärende: AIP and Submarines    1/3
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Here is something I found Interesting having served on Submarines some 9
1/2 years. And having been associated with them Most of the rest of my
Naval Career.

*****
AIP(Air Independent Propulsion)

*AIP - The Early History
Despite their initial successes, submarine pioneers were still eager to
find some means to free their boats from the necessity of surfacing
frequently for access to the atmospheric oxygen demanded by the gasoline
or diesel engines that charged the batteries. A number of approaches
were tried, but eventually, open-cycle diesel engines, lead-acid
batteries, and electric motors for submerged propulsion became the
standard submarine engineering plant that served well through two world
wars.

In the early 1930s, however, a brilliant German engineer, Dr. Helmuth
Walter (ca. 1900-1980) of Kiel's Germaniawerft, proposed a radical new
submarine propulsion plant based on the use of high-purity hydrogen
peroxide (H2O2) as an oxidant. In Walter's system, hydrogen peroxide
from an onboard supply was decomposed using a permanganate catalyst to
yield high temperature steam and free oxygen. Into the reaction chamber
was injected diesel fuel, which combusted with the oxygen to yield a
mixture of steam and hot gas that drove a high-speed turbine. The
exhaust and condensed steam were then expelled overboard. Walter's
primary design goal was high underwater speed, rather than long
endurance, and indeed, his first submarine prototype, the experimental
V80, reached 28.1 knots submerged in its 1940 trials - at a time when
conventional submarines were limited to 10 knots or less. Thus, V80,
only 76 tons and 22 meters long, also served as an early test bed for
studying the dynamics and control of high-speed underwater vehicles.

Later in the war, the Kriegsmarine attempted to scale Walter's prototype
up to a useful operational size, but although seven Type XVIIB H2O2
coastal boats were completed before Germany's final defeat, none saw
combat. These Type XVIIs displaced 300 tons and were powered by two
2,500 horsepower turbines, in addition to a conventional diesel-electric
plant. More ambitious plans to build larger Walter-designed ocean-going
submarines, such as the 800-ton Type XXVI and the 1,600-ton Type XVIII
were thwarted by the unsuccessful course of the war and the realization
that the industrial capacity needed to supply sufficient quantities of
hydrogen peroxide could never be achieved. However, the Type XVIII was
modified into the highly successful Type XXI "electro-boat," in which
larger batteries provided a submerged speed of 17 knots, which could be
maintained for 90 minutes. That innovation, and the adoption of the
snorkel, yielded a potent combination that strongly influenced the
postwar design of conventionally-powered submarines on both sides of the
Iron Curtain.

*AIP Fallout from World War II
After the conflict, several nations sought to exploit Dr. Walter's
revolutionary propulsion concepts. As war prizes, the United States and
Britain received the scuttled Type XVIIBs, U-1406 and U-1407,
respectively, and the latter was resurrected for experimental purposes
as HMS Meteorite. Additionally, Walter himself and several of his key
staff were brought to England and there collaborated with Vickers, Ltd.
for several years in the design of more advanced hydrogen peroxide
systems. The result was two 1950s-era high-speed boats, HMS Explorer and
HMS Excalibur, whose design was heavily influenced by that of Walter's
wartime Type XXVI. While both boats achieved stated design goals for
high underwater speed, their highly-concentrated hydrogen peroxide fuel
created such a safety hazard that the two boat became known as "HMS
Exploder" and "HMS Excruciator." Both were decommissioned in the 1960s.

The Soviet Union built a single, semi- successful exemplar of a
Walter-cycle boat, known in the West as "the Whale," but their most
serious AIP efforts were focused on a closed-cycle diesel plant based on
the German Kreislauf system and their own researches prior to the war.
Eventually, this led to the 650-ton Soviet QUEBEC class (1956) that used
stored liquid oxygen to sustain closed-cycle operation for diesel
engines on three shafts. Although 30 were built between 1953 and 1957,
their safety record was so dismal that they were known by their crews as
"the cigarette lighters" and withdrawn from service by the early 1970s.

Meanwhile, the United States had salvaged a 2,500-horsepower Walter
turbine from U-1406, as well as a 7,500-horsepower version planned for
the Type XXVI, and set them up at the Naval Engineering Experiment
Station at Annapolis, Maryland. Subsequently, the Navy funded research
on several alternative submarine AIP approaches, including variants of
the Walter-cycle and Kreislauf systems. Eventually, unacceptable growth
in the required size and weight of the corresponding engineering plants
- plus the growing prospect in the late 1940s of submarine nuclear
propulsion - soon brought these efforts - and those of the British and
Russians - to a close. USS Nautilus (SSN-571) got "underway on nuclear
power" in January 1955.

*X-1 - The U.S. Navy's First Midget Submarine
However, in September 1955, the U.S. Navy's first midget submarine, the
one-of-a-kind X-1 (SSX-1), was launched on Long Island with a
closed-cycle hydrogen peroxide/diesel plant! Inspired by the success of
the British "X-craft" of World War II, X-1 was intended for
shallow-water commando operations. Displacing 36 tons submerged on a
length of some 50 feet, X-1 was powered by a heavily modified commercial
diesel engine with a small battery-powered electric motor as a backup.
On the surface, the ambient atmosphere charged the engine, but
underwater, the oxygen required for combustion was derived from the
catalytic decomposition of hydrogen peroxide in a reaction chamber. Both
engine exhaust and water condensate were compressed and discharged
overboard. Four hundred gallons of peroxide could be stored in a
flexible polyvinyl-chloride bag forward, and the craft could accommodate
four crewmembers.

After several engine failures and subsequent design modifications, X-1
finally achieved acceptable performance in February 1957 and undertook a
series of operational trials based at the Portsmouth Naval Shipyard.
Unfortunately, in May 1957, an explosion in the hydrogen peroxide
storage system blew off the whole bow section, and although no one was
injured, X-1's closed-cycle capability was never replaced. Instead, the
boat was rebuilt with a small, conventional diesel-electric/battery
plant, and after being laid up for three years, it was reactivated in
late 1960 and subsequently used until 1973 for a variety of research
studies in the Chesapeake Bay. Later, X-1 was put on static display at
the U.S. Naval Academy in Annapolis, and more recently at the Nautilus
Museum in Groton, Connecticut. Significantly, her former
Officer-in-Charge later wrote, "The most important lesson learned from
this experimental program was_ that high concentration unstabilized
hydrogen peroxide has no place on a fighting ship.

*Current Efforts in AIP
Although major naval powers like the United States, the United Kingdom,
and the Soviet Union turned quickly to submarine nuclear propulsion as
soon as it became technically feasible, smaller navies have remained
committed to conventional diesel-electric submarines, largely for
coastal defense. Many of these have incorporated innovations originally
pioneered in the German Type XXI, but more recently, growing demand for
longer underwater endurance has generated increasing interest in
promising AIP technologies, both old and new. Currently, system
developers are actively pursuing the following generic approaches for
achieving "closed cycle" operation:

    * Closed-cycle diesel engines, generally with stored liquid oxygen
    (LOX)
    * Closed-cycle steam turbines
    * Stirling-cycle heat engines with external combustion
    * Hydrogen-oxygen fuel cells
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