response 26 of 49:

Sep 23 14:09 UTC 2003

Re #19: Good question.  My guess is either compressed air or a smaller
"pony" engine, but I'm not sure.  I remember finding a page once about
marine diesel technology but I can't locate it now.

Re #21: My guess is that the reason you don't see ceramics used instead
of piston cooling is that the marine engine market is probably pretty
conservative.  A single engine like this is often used to drive a
container ship, with no redundancy.  Reliability and long life are the
most important design criteria.

Ceramics aren't even showing up in car engines yet, as far as I know. 
In fact, many automotive turbodiesels oil-cool their pistons.

Re #22: Fuel cost may be an issue.  Marine diesels run on what's
varyingly called "marine residual fuel" or "bunker oil".  It's a very
heavy fuel oil (the gel point is as high as 70F for summer grades) and
is very cheap to produce, because it's essentially leftovers from the
refining process.  Turbine engines usually burn lighter fuels, like
kerosine or automotive diesel, which would be more expensive.  A turbine
design is going to be far more complex, as well -- you need reduction
gearboxes (which run at high input speeds, raising reliability issues
again), and since turbines can't run backwards you need some kind of
reversing gear to drive the ship aft.  By comparison, a low-speed diesel
can drive a prop directly.  Finally, turbines only run efficiently at
full output; you can't throttle them back without substantial losses.

response 28 of 49:

Oct 5 04:59 UTC 2003

For those who are still interested in this, the manufacturer's
web site is http://www.wartsila.com.

It's pretty dry and doesn't have any of the more interesting
(to a geek/gearhead) technical details, but it's there.
I'm still looking for details on things like compression
ratios, intake and exhaust pressures, inlet temperatures...
At least I've found that it does start using compressed
air.  (30 bar, it says.  1.5 megabytes of PDF to get that.)
And the exhaust temperature of their "flex" engine is so
low, I don't want to believe it:  285 degrees C.  (Where
does the excess heat go?  Out the cooling jacket?)

I'm wondering how well this 50%-efficient engine could be
operated on powdered coal, a la the University of Alaska
at Fairbanks cogeneration system.

response 30 of 49:

Oct 6 03:12 UTC 2003

It was my impression that auto turbos could run at TITs of
1800 F.  Don't the silicon nitride turbines run even hotter?

While digging deeper in the brochures from Wartsila, I found
that the figures I was looking at were for the flex-fuel
engine (fuel oil or natural gas).  This engine runs at a
fuel-air equivalence ratio of about 0.45, or way, way lean.
(They do this for NOx control.)  It no longer surprises me
that the exhaust is so cool.

The thermal efficiency of the 96C series attracts me, though.
It gets roughly 50%, and that is without using features like
insulated heads and piston crowns.  (According to an article
on a Caterpillar engine I read some time ago, an adiabatic
engine actually loses output from the lower volumetric
efficiency of the hot cylinder surfaces, but can make it up
due to the greater heat output through the exhaust which is
available to run a compounding turbine.

U of Alaska-Fairbanks is running a coal-burning diesel
cogenerator to heat and power the campus.  They expect to
run 41% efficiency to start, perhaps 48% once everything
is tuned to perfection.  Our typical steam powerplants run
closer to 30% efficiency, perhaps 33%.  If we could replace
them with diesels at 50% efficiency, that is 2/3 the coal
for the same useful energy.  If we can use better technology
to boost efficiency to 60% (turbocompounding and a steam
boiler to run a bottoming cycle might get that much), that
is roughly half the coal for the same output.  Half the coal
is half the carbon dioxide, among other things.

NOx is not a problem for stationary powerplants.  It is
easily reduced to N2 using a bit of ammonia and a catalyst.

response 32 of 49:

Oct 8 02:18 UTC 2003

If you've ever seen a dyno stand at an auto company, you'd know
that it doesn't take a turbo to have the manifolds and a fair
amount of the exhaust plumbing at a glow from dull red to orange.
And there's no air injected in the manifolds, so "afterburning"
has nothing to do with it; it's just metal that's exposed to
the exhaust flow and has neither insulation nor active cooling.

The combustion gases in any car engine are far hotter than
the melting point of iron, let alone aluminum.  But that's
neither here nor there.

I take it that the potential of this diesel technology for
solving other problems doesn't interest you that much?  I
find it fascinating for stationary powerplants; among other
things, it should be possible to start and stop one of
these engines in less than a minute, perhaps only seconds.
When you compare with the very long ramp up/ramp down times
for many steam powerplants, and the reasons why it took
Michigan so long to get back on the grid after 8/14, the
advantages are obvious to me.

One problem with burning coal is the mercury content.  I did
some research on-line but nothing popped out with the usual
mineral form of mercury as present in coal, although I did 
find a mention that coal washing can reduce it.  Of course,
reducing the amount of coal used reduces the mercury too.

response 34 of 49:

Oct 8 14:46 UTC 2003

Re #32: It's an interesting idea, but I think gas turbines have higher
efficiencies when used for power generation.  The throttling and
gear-reduction issues aren't as important in a stationary application.

response 36 of 49:

Oct 9 02:23 UTC 2003

Re #34:  Gas turbines fueled by what, though?  The Wabash River
plant is a coal-fired, integrated-gasifier combined-cycle plant
and just barely hits 40% efficiency overall.  That's not much
better than a typical steam plant at 33%; if you can use a
diesel topping cycle to boost that past 50% you've got a big win.

If you think about it (and work the thermo), the gas turbine is
at a disadvantage because it does not do the combustion in a
(nearly) constant volume.  The entropy of an ideal gas is
proportional to the log of the specific volume, and the gas
turbine gets nothing from that expansion in its combustion
systems.  The diesel can harness the pressure increase and
turn more of the heat into work.

If I had a decent thermodynamic model I'd try to get the work
available from a more-complete-expansion cycle, perhaps with
a tuned exhaust system to maintain the turbine inlet at a
higher pressure than the turbocompressor.  I'd like to have
a better idea of the possibilities than I've been able to
get thus far, but with the lousy info I've got I can't be
sure that my calculations relate usefully to reality.

response 38 of 49:

Oct 10 03:05 UTC 2003

I knew that mercuric sulfide was not very soluble (I found
it was used as a tatoo pigment), but I can't believe I
mis-spelled "sulfur".  I've tried finding the reaction used
to convert H2S to pure sulfur, without success; I wonder if
it yields anything useful, like H2.

No suggestions for engine simulations?

response 40 of 49:

Oct 11 13:31 UTC 2003

So it starts with the reaction

        H2S + O2 = H2 + SO2

right?  So some free hydrogen is produced?

response 42 of 49:

Oct 11 23:10 UTC 2003

Yeah, I remembered that later.  It takes a little bit of heat to start the
hydrogen-oxygen reaction, but the reaction is exothermic, so it provides the
heat necessary to keep itself going.

response 44 of 49:

Oct 12 05:00 UTC 2003

There isn't much H2S around to use as a fuel. It is also more toxic
than HCN. I don't think it will be an optimal fuel. 

The more common bacterial use of sulfur compounds is of SO4(-2, sulfate),
which they use as an oxidant, reducing the sulfur from +6 to -2 (as H2S).
This is the source of H2S in much of deeper Michigan groundwater.

response 46 of 49:

Oct 12 14:46 UTC 2003

Have you said how you are going to get H2 from H2S?

Yes, sulfur from desulfurization is supplying most of our needs for sulfur
- much more than from Frasch plants. But you cannot yet economically
recover H2 from H2S, although there is ungoing research
(http://members.tripod.com/sulfotech/h2scrack.html). 

The main use for all that sulfur is for producing sulfuric acid. I don't
think there is any surplus that needs to be thrown away. 

response 48 of 49:

Oct 12 18:38 UTC 2003

In #45 you said "the yield of hydrogen would be about 625 tons a year or
1.7 tons of H2 per day". That sounded like getting H2 from H2S. What did
you mean, then? 

"As long as there was H2S present, the environment would be too reducing
to allow SO2 to form" means that SO2 is formed, but reacts immediately
with the excess H2S. This is the process I described earlier (I now recall
it is a form of the Claus process, which is conducted in the liquid phase
and does require a catalyst to be practical. No electrolysis is required.