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Default How Hot should an alternator get?

Ruskie wrote:
On Sat, 15 Jul 2006 17:11:08 -0400, Larry wrote:


Way too many boat diesel books are being sold.....




Speaking of diesel engine books. I read that cruising sailbooats with
diesel engines should have a heavy-duty blower installed in the engine
compartment, with proper venting, to extend longevity of all related
components.

Sounds like a good idea. Yet, as far as I know, not even Baby-Blake
endowed Swans bother with this.


Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running

bob
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Default How Hot should an alternator get?

On Thu, 20 Jul 2006 07:49:13 -0700, RW Salnick
wrote:

Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running


Yes. The exhaust blowers are mostly for after the diesel engines have
shut down.

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Default How Hot should an alternator get?

RW Salnick wrote in news:e9o55a$2hq$1
@gnus01.u.washington.edu:

Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running



That's true in a Hatteras with twin turbo 8V92TA's in it....but not in a
sailboat with a two-cylinder Yanmar idling slow. Even wide open, it's
still two little diesel pistons pumping slowly up and down, not much of a
threat to pumping out the stinky head hose smell on other threads at all...
(c;
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Default Diesels - How Hot should an alternator get?


"Larry" wrote in message
That's true in a Hatteras with twin turbo 8V92TA's in it....but not in a
sailboat with a two-cylinder Yanmar idling slow. Even wide open, it's
still two little diesel pistons pumping slowly up and down, not much of a
threat to pumping out the stinky head hose smell on other threads at

all...
(c;


Many diesel powered sailboats do have exhaust blowers, whether they need
them or not. I have owned 4 inboard sailboats and three had blowers - not
sure about the other, but it was a saildrive in it's own box.

But, I have to admit I hardly ever turned the blower on. Usually the engine
only ran for 15 or 20 min, to exit harbour, so no need. But on long windless
trips, I sometime remembered to turn it on, if it was getting steamy down
below.

It may be a good idea to wire the blower into the starter switch circuit so
it is always running when the engine runs or add a thermal switch set at 35C
or so. This would perhaps help the refrig unit too, because it exhausts into
the cockpit lockers which are open to the engine compartment.

GBM


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Default How Hot should an alternator get?

Larry wrote:
RW Salnick wrote in news:e9o55a$2hq$1
@gnus01.u.washington.edu:


Don't forget that a diesel engine, which has no throttle butterfly, is
moving a lot of air out of the compartment all the time it is running




That's true in a Hatteras with twin turbo 8V92TA's in it....but not in a
sailboat with a two-cylinder Yanmar idling slow. Even wide open, it's
still two little diesel pistons pumping slowly up and down, not much of a
threat to pumping out the stinky head hose smell on other threads at all...
(c;


Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...

bob


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Default How Hot should an alternator get?


"RW Salnick" wrote
Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...

bob,
If the 2GM is a 4-cycle engine, is the above correct if it only draws in
air every other revolution?

Shouldn't air flow to engine room be calculated to keep temperature down ?
As the combustion air temperature goes up, engine efficiency goes down - I
read somewhere that power loss could be 11% if temperature rises from 80F to
150F.

Perhaps having the exhaust fan run all the time the engine runs would be a
good idea?

GBM





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Default How Hot should an alternator get?

GBM wrote:
"RW Salnick" wrote

Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...


bob,
If the 2GM is a 4-cycle engine, is the above correct if it only draws in
air every other revolution?

Shouldn't air flow to engine room be calculated to keep temperature down ?
As the combustion air temperature goes up, engine efficiency goes down - I
read somewhere that power loss could be 11% if temperature rises from 80F to
150F.

Perhaps having the exhaust fan run all the time the engine runs would be a
good idea?

GBM


Correct - that is why I divided by 2 in the equation. I doubt that the
engine room temperature would reach 150 F under normal conditions
(although the engine external surfaces certainly could). If it did get
this hot, improved ventilation is certainly in order!!

The amount of air we are discussing here is a little more than what
would fill a 2' x 2' x 2' cube. On the small boat we are discussing
here, I am guessing that the engine compartment is pretty small and
crowded, and that the 10 CFM flow, at engine idle, would completely
replace the air in the engine compartment every minute or two, or less.

bob
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Default How Hot should an alternator get?



The amount of air we are discussing here is a little more than what
would fill a 2' x 2' x 2' cube. On the small boat we are discussing
here, I am guessing that the engine compartment is pretty small and
crowded, and that the 10 CFM flow, at engine idle, would completely
replace the air in the engine compartment every minute or two, or less.


bob,
I have the same size engine (older model) - The engine compartment is
3'highx2.5'wide and is open aft to the cockpit lockers etc, so enclosed
space is quite large. Nevertheless, after a long run (without blower
running), the engine "room" IS quite hot - I must measure it, but it must be
20-40F above the cabin temperature. Most of this is likely due to radiation
from the block which is at 150-160F, the exhaust manifold and the
alternator.

Because the refrig unit is nearby, I plan on rewiring so my exhaust fan will
run whenever the engine is running (so I don't have to remember to turn it
on). I have already insulated the wall between the engine and the refrig
unit. Hopefully these two things will keep the engine from adding further to
the already high refrig heat load.

GBM



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Default How Hot should an alternator get?

Larry,

In order to produce power, a diesel needs fuel and it needs oxygen.

If it is starved of oxygen, power is reduced.

Most normally aspirated diesels will run at high efficiency with 80F air. If
the air is hotter, it also has lower density. Therefore at higher
temperatures, less air (and therefore oxygen) is sucked in because the
engine sucks a fixed volume.

By the way, I am definitely not an expert! My total knowledge of diesels
stems from owning an old diesel car and having had 3 or 4 diesel sailboats.
But, check the above out on Google - I am sure it will come up with a few
pages explaining this. If not, maybe I will learn something

GBM

"Larry" wrote
Huh?? That might be true for gas engines, but diesel engines RUN on air
temperature. That's what the 22:1 compression ratio is for! You have to
raise the temperature of the incoming air up high enough to make the fuel
spray explode when it's injected....knock, knock, knock, knock.

The higher the intake air temperature, the better. The hotter the engine,
the better! Another great idea that got buried, probably by big oil, was

a
ceramic diesel engine invented by Mitsubishi, I think. The engine had NO
LUBRICATION and NO COOLING SYSTEM to increase the temperature of the

engine
into the glowing zone. The engine was even wrapped in an insulating
blanket to make it even hotter. Efficiency was amazing, hence my

suspicion
of another oil burial of the technology. Thermal efficiency was near 50%!

Funding was mysteriously pulled, like anything that is efficient, and
"reliability of ceramic parts" was the excuse to stop it, the cover story.

It has a 40:1 compression ratio, by the way....

80-150F mean nothing.



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Default Diesel engine inlet temperatures - was:How Hot should an alternator get?


"Larry" wrote



Altitude makes much more difference than temperature on a diesel without a
turbo or supercharger. Yes, temperature changes the density altitude, but
in comparison to the 22:1 compression just before the fuel sprays into it,
it's quite insignificant. Of course, altitude isn't much of a problem for
boats at sea.


The compression ratio causes the temperature to rise, but it would do this
even if there was no oxygen present.

Air density (and therefore oxygen content) is affected by temperature and
pressure. If my high school physics is correct (and it may not be), the
affect of going to an altitude of 4000ft, is about the same as changing the
temperature from 80F to 150F at sea level. Both will reduce the oxygen in
the cylinder by about 11%. Most engines have no fuel management system to
handle this so they over inject fuel which causes environmental problems
(trucks/stationary diesels).

If we want more power out of a diesel, we can use a turbo compressor to
raise density, but it also causes air to heat up. Therefore, intercoolers
are sometimes added to reduce air temperature and get density back up. If we
overdo boost, exhaust temperatures get too high and we risk ruining the
turbo and the engine (My car has 3 safety systems just to prevent
over-boost!)

If my 14BHP non-turbo boat engine loses 11% power because the engine intake
air is hot, it WOULD be significant - Now I only have 12.5BHP and if my
alternator takes another 2BHP I am down to 10.5. But this is at max RPM! At
cruising speed, I may lucky to get 8BHP!

In reality, I won't see 150F at the engine intake and I won't be motoring at
altitude unless I go and cruise Lake Titicata.

It is something to be aware of but can be controlled by good ventilation.
Having a clean filter and unrestricted inlet air flow is also important
because the pressure loss also causes lower inlet air density. Maybe someone
sells a performance kit for Yanmars

GBM


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