Sterling engine in a car question
Pete
If we take a normal car with an internal combustion engine.
And put a sterling cycle unit on the exhaust manifold where is should run
nicely with all that heat.
And use the sterling cycle to generate electricity which could run the
electric systems of the vehicle.
Would we get better fuel economy?
After all if you could generate enough power, you could in theory have an
electric a/c unit which would avoid the performance and fuel economy
disadvantages of staying cool. Also I mention the exhaust system as it has a
huge temperature differential compared to the outside world, but if you can
get usable energy from the large amount of almost boiling water in the
cooling sytem that would double the amount of free extra power.
As I say this is anoying me as I can't see a problem with the theroy barring
cost and/or the sterling cycle equipment being unable to generate useable
quantities of electric from a high grade heat source.
Can some on help me out please.
G. R. L. Cowan
It's "Stirling". An enthusiast was just recently touting
http://www.StirlingChat.com .
I suspect an exhaust heat-recovery Stirling installation
at the back of a car would have its front wheels off the ground.
You're not planning to do this to a front-wheel-drive car,
are you?
--- Graham Cowan
http://www.eagle.ca/~gcowan/boron_blast.html --
100 internal combustion watt-hours in a baby's fist
Steve Spence
be cost prohibitive to build.
--
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"Pete" <get...@toomuchspam.thesedays.com> wrote in message
news:YeDha.5202$qf7.34...@news-text.cableinet.net...
Don Libby
>
> in theory what you say would work. in practice, a 30-50 amp stirling would
> be cost prohibitive to build.
>
Still, might be fun to purchase a stirling off the shelf,
duct-tape it to the exhaust manifold, and use it to light an LED
on the dashboard. (Kids, don't try this at home: duct-tape may
be flamable).
Stirling Engines for sale:
http://www.stirlingengine.com/
-dl
Don Libby
Or try sticking a tiny turbine in the tail pipe (same disclaimers
apply). Of course, making your heat source do more work before
dumping to the sink will cost you at the gas pump. Whether you
would do better with stirling-electrical or conventional is a
matter of engineering economics, I suppose.
-dl
Pete
> apply). Of course, making your heat source do more work before
> dumping to the sink will cost you at the gas pump. Whether you
> would do better with stirling-electrical or conventional is a
> matter of engineering economics, I suppose.
First - Thanks for the replies.
Second, running a turbine from the exhaust flow is not the same as
scavenging power from the heat in the exhaust flow.
Don Libby
How different are they, in thermodynamic terms? Stirling cycle
and Rankine cycle are both heat engines, aren't they? If your
stirling engine is going to do useful work, then it is going to
nibble a little bit off the initial efficiency of the ICE,
right? Same problem if you run a little electric fan backwards
using the flow of exhaust gasses, right? How different are they?
-dl
Steve Spence
hence turbochargers add power at the expense of mpg.
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"Pete" <get...@toomuchspam.thesedays.com> wrote in message
news:OnGha.5394$RK7.35...@news-text.cableinet.net...
Steve Spence
is not interrupted.
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"Don Libby" <never...@tds.net> wrote in message
news:3E875C65...@tds.net...
daestrom
> and Rankine cycle are both heat engines, aren't they? If your
> stirling engine is going to do useful work, then it is going to
> nibble a little bit off the initial efficiency of the ICE,
> right? Same problem if you run a little electric fan backwards
> using the flow of exhaust gasses, right? How different are they?
>
Actually, they are different in some important ways.
Although it is true that Stirling and Rankine are both heat engines, both of
these ideas are *not* complete heat-engines. The Stirling idea is a
complete heat-engine using exhaust gasses as a heat source and the
environment as the heat sink. The working fluid is separate from the
exhaust gasses and the Stirling engine contains its own pump.
The turbine idea is only part of the cycle. The ICE contains the pump
(intake-stroke of cylinders) and the combustion chamber provides the heat
source. So the turbine is an adaptation to the Otto cycle of the ICE
already there. Sort of a combined-cycle system.
The Carnot efficiency of the exhaust temperature to environment temperature
will be the upper limit for the Stirling cycle's efficiency. A properly
designed turbine can reach efficiencies *FOR THE TURBINE* of >80%. But a
turbine design will create a higher ICE back-pressure, causing the ICE's
efficiency to drop.
But just how much energy is available from the car's exhaust (assuming no
condensing of the water vapor)?? Of all the losses in a conventional ICE,
how much is this one?
daestrom
The Enlightenment
Stirling engines are reliable (fuel efficient especialy at part load
where IC engines fall of very rapidly) and clean (becuase of
continious combustion). They also run of any fuel.
They are however expensive becuase
1 High tolleraces required.
2 Expensive refractory alloys required. (IC engines have the
advantage of opperating a high temps but overcome material problems by
having this run only as a mommenatary burn)
There are problems with throttle response, which can be overcome.
Nevertheless stirlings have a niche, both hitech made out of nickel
alloys to low tech made out of ordinary material and charged with
compressed air.
Steve Spence
Engine driven CHP units hit 80% efficiency.
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"daestrom" <daes...@twcny.rr.com> wrote in message
news:k0Lha.6429$wD3....@twister.nyroc.rr.com...
Pete Lynn
> news:3E875C65...@tds.net...
> > Pete wrote:
> >
> > How different are they, in thermodynamic terms? Stirling cycle
> > and Rankine cycle are both heat engines, aren't they? If your
> > stirling engine is going to do useful work, then it is going to
> > nibble a little bit off the initial efficiency of the ICE,
> > right? Same problem if you run a little electric fan backwards
> > using the flow of exhaust gasses, right? How different are they?
> >
>
> Actually, they are different in some important ways.
>
> Although it is true that Stirling and Rankine are both heat engines,
both of
> these ideas are *not* complete heat-engines. The Stirling idea is a
> complete heat-engine using exhaust gasses as a heat source and the
> environment as the heat sink. The working fluid is separate from the
> exhaust gasses and the Stirling engine contains its own pump.
A turbocharger is effectively a gas turbine bottoming cycle, (open
cycle). A steam turbine operates on the rankine cycle, as such the
cycle is just as separate and closed as a Stirling cycle.
>
> The turbine idea is only part of the cycle. The ICE contains the pump
> (intake-stroke of cylinders) and the combustion chamber provides the
heat
> source. So the turbine is an adaptation to the Otto cycle of the ICE
> already there. Sort of a combined-cycle system.
>
> The Carnot efficiency of the exhaust temperature to environment
temperature
> will be the upper limit for the Stirling cycle's efficiency. A
properly
> designed turbine can reach efficiencies *FOR THE TURBINE* of >80%.
But a
> turbine design will create a higher ICE back-pressure, causing the
ICE's
> efficiency to drop.
>
Generalizing, small turbocharger turbines might be 70% efficient, very
large ones might get up to 90%, large gas turbines up to 95%,
compressors tend to be around 5% less efficient than the turbine. The
back pressure argument is questionable, exhaust volume/pressure might be
three fold that of inlet, increased back pressure reduces engine power,
but a properly designed exhaust turbine system should increase overall
power and efficiency. Ideally expansion should be greater than
compression and a separate turbine is an effective way of doing this
without getting into variable volume type crank systems. In practice
this extra energy is expended on valve losses and the like, increasing
effective power by getting more air in and out of the engine faster, the
advantages of an extra turbine are marginal.
> But just how much energy is available from the car's exhaust (assuming
no
> condensing of the water vapor)?? Of all the losses in a conventional
ICE,
> how much is this one?
>
Most of it, the radiator being the other major source. Depending on the
system, it might be possible to extract some of the energy of the
condensing water vapor, though this is of a very low quality, and
probably not worth the effort.
Stirling cycle engines are great in theory but lacking in practice, high
power to weight ratios and efficiencies of 60% have been achieved,
though 40% is more realistic, small practical engines might typically be
25% efficient, price might typically be around ten times that of an ICE.
A Stirling engine operating off a trucks exhaust might achieve 15%, (a
friend looked into this around a decade back before pursuing home SCE
CHP).
The approach that makes greater sense is to use a steam turbine type
system, greater practical efficiency should be possible at a far lower
price, the cold end heat sink is still a problem, though no different
than a SCE, I figure such a combined cycle might be capable of 50%
efficiency, maybe 25% out of the steam turbine. Clever design and a
great deal of time and effort would be required to turn this into a
practical system, I am not sure that the economics justify it just yet,
obviously, it comes down to cost, and there are other methods...
Pete.
> daestrom
>
>
Richard Bell
Steve Spence <ssp...@green-trust.org> wrote:
>correct. adding backpressure creates load on the engine, using more fuel.
>hence turbochargers add power at the expense of mpg.
>
turbine is used to run accessories that are normally driven from the
serpentine belt, then mpg goes up. The decrease in power from the
engine is less than the parasitic load of the accessory (or why turbocharged
cars get better milage than supercharged cars, all else being equal).
Bottoming the cycle extracts more energy from the fuel, so the overall
efficiency is higher, which translates to higher mpg over a similarily
equipped vehicle without a heat recovery turbine.
The Enlightenment
The correct term for a gas trubine cycle is "Brayton Cycle". There
are two types "open cycle" and "closed cycle". Open cycles are more
common but in automotive applications require an exhaust gas heat
regenerator to be efficient under part load. They also require
expensive refractory alloys which is the only thing making them
expensive.
Closed Cycle Brayton engines are like stirling engines extremely
efficient under part load but require highy stressed heat exhager
walls. Unlike Stirling engines they are very light; as light as
normal gas turbines.
Some piston engines like the Trubo-Compounded R2800 for aircrart had
turbines that drove the main shaft of the engine via torque
convererts. They were among the the most efficient ever and did not
sufer form exhaust gas back pressure.
Some diesels, particularly big stationay low speed and marine diesls
can achieve a 57% efficiency, in part by putting turbo-generators on
their exhausts or turbosuperchargers. Some like piston engines even
dispense with a crank shaft altogether and recover all the hot gases
energy by expansion through a turbine. The japanese have built cars
like this with normal gasoline engines (Diahatsu and Hitachi I
believe). I imagine this will become a good idea for hybrid cars.
Napier's Nomad aviation diesel was to be turbo-compunded this but the
jet engine proved cheaper becuase of its lighteness.
Paul E. Bennett
get...@toomuchspam.thesedays.com "Pete" writes:
> This is annoying me.
>
> If we take a normal car with an internal combustion engine.
>
> And put a sterling cycle unit on the exhaust manifold where is should run
> nicely with all that heat.
Probably better to ditch the IC engine altogether replacing it with
a Stirling Engine driving a generator to recharge batteries and run
electric drive motors. You could use almost any clean fuel to provide
the heat.
--
********************************************************************
Paul E. Bennett ....................<email://p...@amleth.demon.co.uk>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
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********************************************************************
Steve Spence
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""Paul E. Bennett"" <p...@amleth.demon.co.uk> wrote in message
news:104904...@amleth.demon.co.uk...
daestrom
"The Enlightenment" <bern...@yahoo.com.au> wrote in message
news:39556695.03033...@posting.google.com...
> "daestrom" <daes...@twcny.rr.com> wrote in message
news:<k0Lha.6429$wD3....@twister.nyroc.rr.com>...
> > "Don Libby" <never...@tds.net> wrote in message
> > news:3E875C65...@tds.net...
>
> are two types "open cycle" and "closed cycle". Open cycles are more
> common but in automotive applications require an exhaust gas heat
> regenerator to be efficient under part load. They also require
> expensive refractory alloys which is the only thing making them
> expensive.
>
Yes, I'm quite familiar with Brayton as well as other cycles. But the topic
of discussion wasn't a complete cycle, it was adding an exhaust turbine to
the already existing ICE (Otto cycle). As such, this addition isn't a
complete cycle at all. Rather, it is just a modification to the Otto cycle
where some of the expansion is done in the cylinder and the rest in an
exhaust turbine.
Personally, I have my doubts that this design would be of any improvement at
all. The only expansion through the turbine would come at the cost of
higher discharge pressures in the cylinders.
> Closed Cycle Brayton engines are like stirling engines extremely
> efficient under part load but require highy stressed heat exhager
> walls. Unlike Stirling engines they are very light; as light as
> normal gas turbines.
>
> Some piston engines like the Trubo-Compounded R2800 for aircrart had
> turbines that drove the main shaft of the engine via torque
> convererts. They were among the the most efficient ever and did not
> sufer form exhaust gas back pressure.
>
> Some diesels, particularly big stationay low speed and marine diesls
> can achieve a 57% efficiency, in part by putting turbo-generators on
> their exhausts or turbosuperchargers.
And many large diesels are only two-stroke and use the turbo-charger design
to supply the 'pump' needed to drive the working fluid (air) into the
cylinders. Such designs have over-running clutch and drive shaft to spin
turbo-charger from crank-shaft on startup. Once up to about 40% load, there
is enough energy in exhaust gasses that the turbine can drive the charger
without aid from the mechanical drive-shaft.
But I question your numbers for 57% efficiency. Got any citations for this?
Some like piston engines even
> dispense with a crank shaft altogether and recover all the hot gases
> energy by expansion through a turbine.
If they have no crank or at all, then what are pistons for? If it's just a
matter of compression, combustion and expansion, that's sounds a lot more
like a Brayton cycle than Diesel (constant pressure combustion).
daestrom
Richard Bell
The Enlightenment <bern...@yahoo.com.au> wrote:
>
>Some piston engines like the Trubo-Compounded R2800 for aircrart had
>turbines that drove the main shaft of the engine via torque
>convererts. They were among the the most efficient ever and did not
>sufer form exhaust gas back pressure.
The engine in question was actually a variant of the R3350 and it was only
efficient when compared to other low compression engines blown by very
large superchargers (IIRC about twenty pounds of boost, maybe more).
Supercharged engines trade efficiency for reduced weight and volume and,
for aircraft, there is a balance point where the reduced fuel consumption
of a more efficient engine is offset by its increased weight. It did not
suffer from back pressure from its turbines due to the exhaust gases being
well above ambient pressure.
[Obligatory useless trivia]
The DC-6 Northstar (?) ran on four supercharged Lycoming 1710 V12 (or
merlin derivatives) and the flight attendants spent alot of their time
convincing the passengers that the flames shooting out from the engines
were normal and of no concern. That wasted energy is what turbocompounding
was meant to capture.
An engine designed for maximum efficiency, in absolute terms, was the Napier
Nomad. It looked like the bizarre marriage of a turbojet engine and a
flat-12 diesel. The turbocharger, which was geared to the crankshaft, had
an axial flow compressor and turbine, with the option of reheat for power
boosting. It supplied a boost of 89 psi to a two-stroke diesel with a
compression ratio of a mere 3.5:1. Intended for the Shackleton maritime
patrol aircraft, but never produced, its efficiency at cruise was a staggering
45%.
Paul E. Bennett
ssp...@green-trust.org writes:
> have you priced 100 hp stirlings lately?
So, pray why would we need that much power?
I was not thinking of this treatment for the enourmous gas guzzling
monsters that seem to be favourite in the USA. I was considering the
smaller electrically propelled run-about vehicle.
If the Stirling engine ran a generator at a constant rate that was
set to charge the batteries when cruising (or at less demanding speeds
and accelleration) the range of the electric vehicle is improved. It
should be easy enough to stop the Stirling engine so that complete
ZEV status could be claimed when in city centre zones that demand it.
Current availability of Stirlings in even this range is nothing to
shout home about. However, with a move in such a direction the Stirling
solution might actually look quite attractive.
I suppose for the out and out speed demons who like monster engines
in their chariots the Stirling would not suit at all.
Incidently, my research was more in the direction of power plant for a
largish boat and would be approximately 10 to 15kW.
Steve Spence
expensive. see http://w1.166.telia.com/~u16602240/MainV160.htm
check out the st-5 a 5 hp stirling.
--
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""Paul E. Bennett"" <p...@amleth.demon.co.uk> wrote in message
news:104915...@amleth.demon.co.uk...
Paul E. Bennett
ssp...@green-trust.org writes:
> 20hp won't power any legal road car. a 20 hp stirling is going to be quite
> expensive. see http://w1.166.telia.com/~u16602240/MainV160.htm
>
> check out the st-5 a 5 hp stirling.
In Europe we have many cars that operate on 35 to 85hp engines. They
may not be sparkling performers but are good run-abouts (even the
ones with 35hp engines).
If we were to utilise the best electric motor and control technology
with decent, light-weight deep-cycle batteries, and a Stirling engine
generator of maybe just 12hp the same sort of duty as the run-about
could probably be realised relativly easily. I would need to do some
calculations to be sure of the power ratings but I am sure that the
above is somewhere in the right ball-park. Remember that the batteries
will provide most of the accelleration energy requirements. The Stirling
is only recharging the batteries during operation at cruising or low
speeds.
Anyway, I am looking at Stirling Engines this weekend at the Stirling
Engine Associations rally at Kew Bridge, London. I'll try and let you
know whatI find there.
Steve Spence
Not when you have 50 feet of onramp to hit 70mph, or you get run over.
--
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""Paul E. Bennett"" <p...@amleth.demon.co.uk> wrote in message
news:104940...@amleth.demon.co.uk...
steves
> If we take a normal car with an internal combustion engine.
>
> And put a sterling cycle unit on the exhaust manifold where is should run
> nicely with all that heat.
>
> And use the sterling cycle to generate electricity which could run the
> electric systems of the vehicle.
>
> Would we get better fuel economy?
You could try a Peltier thermoelectric generating device.
They might be lighter than a stirling at given power output,
they certainly have less moving parts :-)
There's some interesting info at
http://www.thermoelectrics.com/introduction.htm
I wonder if reducing the temperature of the exhaust would decrease the
engine's efficiency?
Cheers,
Steve
steves
> If we take a normal car with an internal combustion engine.
>
> And put a sterling cycle unit on the exhaust manifold where is should run
> nicely with all that heat.
>
> And use the sterling cycle to generate electricity which could run the
> electric systems of the vehicle.
>
> Would we get better fuel economy?
You could try a Peltier thermoelectric generating device.
Steve Spence
the exhaust increases overall efficiency. we do that in CHP applications.
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"steves" <ste...@steves.com> wrote in message
news:3E929D30...@steves.com...
Paul E. Bennett
> You could try a Peltier thermoelectric generating device.
> They might be lighter than a stirling at given power output,
> they certainly have less moving parts :-)
Did you really mean Seebert(sp?) device? I found a couple of links through
Steve Spence's web-site that were interesting and reported on some
experiments in Sweden (waste heat from cooker range flue).
> There's some interesting info at
> http://www.thermoelectrics.com/introduction.htm
--
The Enlightenment
> "The Enlightenment" <bern...@yahoo.com.au> wrote in message
> news:39556695.03033...@posting.google.com...
> > "daestrom" <daes...@twcny.rr.com> wrote in message
> news:<k0Lha.6429$wD3....@twister.nyroc.rr.com>...
> > > "Don Libby" <never...@tds.net> wrote in message
> > > news:3E875C65...@tds.net...
> >
> > The correct term for a gas trubine cycle is "Brayton Cycle". There
> > are two types "open cycle" and "closed cycle". Open cycles are more
> > common but in automotive applications require an exhaust gas heat
> > regenerator to be efficient under part load. They also require
> > expensive refractory alloys which is the only thing making them
> > expensive.
> >
>
> Yes, I'm quite familiar with Brayton as well as other cycles. But the topic
> of discussion wasn't a complete cycle, it was adding an exhaust turbine to
> the already existing ICE (Otto cycle). As such, this addition isn't a
> complete cycle at all. Rather, it is just a modification to the Otto cycle
> where some of the expansion is done in the cylinder and the rest in an
> exhaust turbine.
It's a hybrid cycle Otto-Brayton. You can view it as a brayton with
the combustion chamber replaced with an IC Otto engine.
>
> Personally, I have my doubts that this design would be of any improvement at
> all. The only expansion through the turbine would come at the cost of
> higher discharge pressures in the cylinders.
You gain much more than you loose. A matter of equations. Besides in
the real world you need to muffle the exhaust and a turbine is a good
silencer.
It works, the technique was used on the R3350 turbo-compound engine
famous on Lockheed constelations. This drove the power back in via
hydralic torgue convertors.
Isuzu used exhaust gas turbine little generators to feed back power to
the main engine via an integral motor/generator/flywheel that replaced
the seperate alternator, starter and flywheel. (these ISAD integrate
starter alternator damper assist devices are apparently expected to
become the norm)
http://www.livedevices.com/pdf/conti_release.pdf
The technique is more amenable to diesels, where it is widely employed
since they don't throttle their air intake and aircraft because of the
high power settings they run on.
>
> > Closed Cycle Brayton engines are like stirling engines extremely
> > efficient under part load but require highy stressed heat exhager
> > walls. Unlike Stirling engines they are very light; as light as
> > normal gas turbines.
> >
> > Some piston engines like the Trubo-Compounded R2800 for aircrart had
> > turbines that drove the main shaft of the engine via torque
> > convererts. They were among the the most efficient ever and did not
> > sufer form exhaust gas back pressure.
> >
> > Some diesels, particularly big stationay low speed and marine diesls
> > can achieve a 57% efficiency, in part by putting turbo-generators on
> > their exhausts or turbosuperchargers.
>
> And many large diesels are only two-stroke and use the turbo-charger design
> to supply the 'pump' needed to drive the working fluid (air) into the
> cylinders. Such designs have over-running clutch and drive shaft to spin
> turbo-charger from crank-shaft on startup.
Its interesting when sleeve valves are used or horizontaly opposed
engines with two gear driven cranks and piston boxing inwards. This
ensures excellent scavenging.
> Once up to about 40% load, there
> is enough energy in exhaust gasses that the turbine can drive the charger
> without aid from the mechanical drive-shaft.
>
> But I question your numbers for 57% efficiency. Got any citations for this?
Lost my link, but it was a MAN low speed diesel power station. Try a
serach on:
"low speed diesel" efficiency -organic -seed.
50%+ efficiecy is common for a low speed marine diesel. To get to 57%
the engine is turbo-compunded with a steam cycle added in after that.
It makese economic sense on a 25MW generation system. There is maybe
2MW of energy to recovver in the turbine and 500KW in the steam.
>
> Some like piston engines even
> > dispense with a crank shaft altogether and recover all the hot gases
> > energy by expansion through a turbine.
>
> If they have no crank or at all, then what are pistons for?
The pistons are just reciprcating compressors as opposed to rotating
compressors. The cylinder is the compression chamber. These engines
are extremely efficient and exhaust gas conditions on the turbine are
nowhere as severe as in a jet engine.
> If it's just a
> matter of compression, combustion and expansion, that's sounds a lot more
> like a Brayton cycle than Diesel (constant pressure combustion).
Exactly correct. It's called a free piston engine and through the
turbine it recovers energy throgh expansion more completely than a
piston which has a fixed stroke.
"In 1940 Hobbs of Pratt & Whitney was discussing with Andrew Kaltinsky
of the MIT the best way to power the future giant transatlantic bomber
that matured as the B-36. Kaltinsky showed that whereas the
forthcoming R-4360 Wasp Major could not expect to better a specific
fuel consumption of 0.42 ... a free-piston plant could cruise at
better than 0.34 and possibly as low as 0.27. ... Pratt & Whitney put
$3.3 million of their own money into the PT-1 [free piston engine].
... The PT-1 was given up soon after the war, and never seriously
affected the design of the B-36..."
(Bill Gunston, "The Development of Piston Aero Engines", 1993)
(specific fuel consumption is measured in this case in hp/lb/hour)
The Enlightenment
> In article <39556695.03033...@posting.google.com>,
> The Enlightenment <bern...@yahoo.com.au> wrote:
> >
> >Some piston engines like the Trubo-Compounded R2800 for aircrart had
> >turbines that drove the main shaft of the engine via torque
> >convererts. They were among the the most efficient ever and did not
> >sufer form exhaust gas back pressure.
>
> The engine in question was actually a variant of the R3350 and it was only
> efficient when compared to other low compression engines blown by very
> large superchargers (IIRC about twenty pounds of boost, maybe more).
> Supercharged engines trade efficiency for reduced weight and volume and,
> for aircraft, there is a balance point where the reduced fuel consumption
> of a more efficient engine is offset by its increased weight. It did not
> suffer from back pressure from its turbines due to the exhaust gases being
> well above ambient pressure.
>
> [Obligatory useless trivia]
> The DC-6 Northstar (?) ran on four supercharged Lycoming 1710 V12 (or
> merlin derivatives) and the flight attendants spent alot of their time
> convincing the passengers that the flames shooting out from the engines
> were normal and of no concern. That wasted energy is what turbocompounding
> was meant to capture.
The V1710 was actualy bench tested as a turbo-compound but never
entered production. Strategic refractory alloys were preserved for
bomber super-chargers with some set aside for P38s and P47s. The
Merlin with a two stage intercooled supercharger could on a P51
mustang or spitfire recover exhaust gas energy without a turbine: the
jet thrust of the exhaust added well over 300hp equivalent jet thrust
at 350mph. Rolls-Royce just didn't want to give up that thrust on a
high speed aircraft for a few extra hp. It made sense on a slow speed
bomber but in a fighter at 400mph jet thrust was more valuable.
>
> An engine designed for maximum efficiency, in absolute terms, was the Napier
> Nomad. It looked like the bizarre marriage of a turbojet engine and a
> flat-12 diesel. The turbocharger, which was geared to the crankshaft, had
> an axial flow compressor and turbine, with the option of reheat for power
> boosting. It supplied a boost of 89 psi to a two-stroke diesel with a
> compression ratio of a mere 3.5:1. Intended for the Shackleton maritime
> patrol aircraft, but never produced, its efficiency at cruise was a staggering
> 45%.
Marvelouse. They had sleeve valves and were expected to have a
service life of over 5000 hours.
Did you know that sleeve valves reduce friction and double engine
life? I saw a we site a year agoi that talked of poppet valve engines
with a sleeve added just to reduce the friction.
daestrom
> "daestrom" <daes...@twcny.rr.com> wrote in message
news:<_54ia.1174$YQ2....@twister.nyroc.rr.com>...
design
> > to supply the 'pump' needed to drive the working fluid (air) into the
> > cylinders. Such designs have over-running clutch and drive shaft to
spin
> > turbo-charger from crank-shaft on startup.
>
> Its interesting when sleeve valves are used or horizontaly opposed
> engines with two gear driven cranks and piston boxing inwards. This
> ensures excellent scavenging.
>
Yes, that sounds like the 'submarine' Fairbanks-Morse, opposed-piston
engine. One crank 'leads' the other and thus the power generated is split
something like 60-40. Eases requirements on the connecting drive train. No
separate valves, just cylinder ports (the offset in crank angles provided
for exhaust/intake timing). Simple 'Paxton' blower provided supercharging.
Extremely reliable engine (personal expierence there :-)
> 50%+ efficiecy is common for a low speed marine diesel. To get to 57%
> the engine is turbo-compunded with a steam cycle added in after that.
> It makese economic sense on a 25MW generation system. There is maybe
> 2MW of energy to recovver in the turbine and 500KW in the steam.
>
Perhaps you ment 2.5 (two point five) MW? That would be 2MW turbine and 0.5
MW steam?
> >
> > Some like piston engines even
> > > dispense with a crank shaft altogether and recover all the hot gases
> > > energy by expansion through a turbine.
> >
> > If they have no crank or at all, then what are pistons for?
>
> The pistons are just reciprcating compressors as opposed to rotating
> compressors. The cylinder is the compression chamber. These engines
> are extremely efficient and exhaust gas conditions on the turbine are
> nowhere as severe as in a jet engine.
But the pistons are actually driven by a crank, right? Just don't extract
any power. And the crank is driven, indirectly, from the turbine?
daestrom
The Enlightenment
>
> "The Enlightenment" <bern...@yahoo.com.au> wrote in message
> news:39556695.03040...@posting.google.com...
> > "daestrom" <daes...@twcny.rr.com> wrote in message
> news:<_54ia.1174$YQ2....@twister.nyroc.rr.com>...
> > > And many large diesels are only two-stroke and use the turbo-charger
> design
> > > to supply the 'pump' needed to drive the working fluid (air) into the
> > > cylinders. Such designs have over-running clutch and drive shaft to
> spin
> > > turbo-charger from crank-shaft on startup.
> >
> > Its interesting when sleeve valves are used or horizontaly opposed
> > engines with two gear driven cranks and piston boxing inwards. This
> > ensures excellent scavenging.
> >
>
> Yes, that sounds like the 'submarine' Fairbanks-Morse, opposed-piston
> engine. One crank 'leads' the other and thus the power generated is split
> something like 60-40. Eases requirements on the connecting drive train.
No
> separate valves, just cylinder ports (the offset in crank angles provided
> for exhaust/intake timing). Simple 'Paxton' blower provided
supercharging.
> Extremely reliable engine (personal expierence there :-)
Yes used in trains and USN submarines. The German Jumo Aero Piston Engines
(jumo 206 I believe) used a similar arangement with an fascinating
injection sytem that collided the injector inpulses to increase mixing. The
British Napier ero diesel used sleeve valves to achieve stupendous duel
efficiency and opperating life. But for jets air travel would be the
'diesel age'
>
> > 50%+ efficiecy is common for a low speed marine diesel. To get to 57%
> > the engine is turbo-compunded with a steam cycle added in after that.
> > It makese economic sense on a 25MW generation system. There is maybe
> > 2MW of energy to recovver in the turbine and 500KW in the steam.
> >
>
> Perhaps you ment 2.5 (two point five) MW? That would be 2MW turbine and
0.5
> MW steam?
25MW diesel, 2MW exhat turbine and 0.5MW steam. (approximetly)
>
> > >
> > > Some like piston engines even
> > > > dispense with a crank shaft altogether and recover all the hot gases
> > > > energy by expansion through a turbine.
> > >
> > > If they have no crank or at all, then what are pistons for?
> >
> > The pistons are just reciprcating compressors as opposed to rotating
> > compressors. The cylinder is the compression chamber. These engines
> > are extremely efficient and exhaust gas conditions on the turbine are
> > nowhere as severe as in a jet engine.
>
> But the pistons are actually driven by a crank, right? Just don't extract
> any power. And the crank is driven, indirectly, from the turbine?
>
> daestrom
>
Free Piston Engines usualy float on cushions of air. Cranks are possible.
In some cases free piston engines have been built using linear generators.