I would suggest that for an Engine that the intake and exhaust
are 2” minimum and that the intake air (snorkel) has a float valve on it
then goes into the cabin with a 2” Ball valve. The engine should
then suck from the cabin air which keeps the cabin air fresh again through a 2”
ball valve to the engine chamber/pod. Wet exhaust is the most sensible
with a loop extending above the water-line before the exhaust valve again 2”
but the placement of the exhaust outlet is best just under the water surface as
if it is too low it will create backpressure. If the exhaust is facing
backwards then there will tend to be a slight venturi action to lower the
exhaust pressure when at max forward speed which should coincide with max power
requirement. Underwater exhaust will save having to put in a muffler. Wet
exhaust also reduces noise. Chs, Hugh
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Antoine
Delafargue
Sent: Monday, 21 December 2009 9:50 a.m.
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Engine intake and exhaust-Carsten?
Hello all,
I have been wondering about this issue too. I don t know what Carsten uses on
his sub, but here is what I found on the web:
If you go for a 'dry' exhaust where there is no cooling water injected at the
exhaust manifold of the engine, then the gases will be way too hot (450+
degrees celsius) for the typical elastomer seals located in isolation valves. The
inside of the sub would be hot and noisy too.
If you go for a 'wet' exhaust with cooling water injected in the exhaust
manifold, you d have a sea water loop to look after (which I think Carsten does
not have any of in his boat) but the temperature at the isolation valve of the
exhaust should be lower, in the range of 80-90 degrees celsius (still high
enough to wonder about thermal stress and fatigue issues).
The other thing is that the exhaust including the isolation valve on the hull
need to be of a large diameter (1-2" ?) to prevent a raise of back
pressure at the outlet of the engine, detrimental to its life and performance.
regards
Antoine
On Sun, Dec 20, 2009 at 12:38 AM, Brian Cox <ojaivalleybeefarm@dslextreme.com>
wrote:
Hi Frank, Just a few thoughts, I was thinking that if
I made downward U turns at the end of the pipes and then put a valve there, I
wouldn't have to worry about draining any water since it could not get
in. Except for the point you made about condensation. On the diesel
lines, maybe a fuel bladder so no water vapor would be present. I like
your idea using the outboard and I think that is a good approach - except I
want more power !! I was going to put a stack fairly high up
in the air to get away from any splash. The cooling system, the
lines would not need to be locked out, as they would not be open
the outside pressure, although it would be easy enough to do.
Hi All,
I'm looking into schemes to handle the
intake and exhaust
Hi Brian. Not expert advice but just a couple thoughts.
I think I remember hearing about a double valve system on the
application. There was a poppet valve to prevent "splash" from
getting sucked into the intake side, and it makes sense to have a similar
set-up on the exhaust.
There was a hard "gate" valve for actual diving to lock
out the pipes much like any other hull penetration.
These valves were coupled with a "drain" bypass to dump
any water that gets in there before starting up the motor. Maybe like a water
trap on a compressed air system in a shop.
Depending on how deep you go, the intake and exhaust
"pipes" need to be sufficiently thick to withstand the pressure.
The water cooling system also has a set of valves to
"lock-out" the system when submerging.
If the fuel system is diesel then you need a means of evacuating
water from the lines, as the environment will be conducive to condensation with
the heating and cooling cycles experienced between surface ops and submerged
ops. Big temperature changes there.
A diesel motor vibrates and the vibration would need to be
isolated from the hard piped thru-hulls.
On the exhaust side, the temperature changes from a "long run
time" to "shut off and submerging" will make the exhaust pipe
exposed to salt water corrode fairly quickly. The exposed parts will need to be
designed for replacement when they get corroded. Even if it's stainless, the
many cycles from hot to cold will reduce the anti-corrosion properties of the
metal. Bolt-up stuff so it can be replaced without using a torch and welder.
The valves on the exhaust side will need to have seats and seals
that can take the many heat cycles.
It's fairly complicated but should be do-able.
On my little boat, I'm going with an outboard motor that will be mounted
and un-mounted so no extra thru-hulls are needed. The steering is controlled by
the same actuator that controls the submerged steering rudders. Throttle will
be another simple actuator or maybe just a quick disconnect cable running
through a small ( 3/8 inch ) thru-hull with a ball valve.
The outboard is small enough to fit through the hatch, and the
fuel tank ( gasoline ) will be small too.
A 20 horse Mercury outboard looks to just fit, and is light
enough to pick up easily.
Typically the outboard will not be carried inside the sub but I
want it to fit just in case. I expect to always have a surface boat with me,
unless it's just playing around in a lake for the day. The outboard would be
un-mounted from the sub and placed in the surface boat when diving.
I've often thought about how to add a diesel powered
"module" to my sub that would be more or less self contained in it's
own pressure vessel but connected by a couple of electrical thru-hulls for
engine controls and system monitoring. In the current design it would be
basically a pressure vessel split in half with mating flanges, hard valves on
intake/exhaust/cooling water, and the prop would be on a magnetic
coupler.
Of course, being the dreamer that I am, the concept quickly
evolved into a pressure cabin, fuel tanks, gen set, extra battery banks, bunks,
galley, and head stretching the thing to 24 feet long !
I think I showed you the concept sketch once when you visited.
Anyway, good luck with the diesel and keep us informed as the
design progresses. It sounds very interesting.
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