Re: Motor Jets and thermojets.

On Sep 6, 6:27 am, "Keith Willshaw" <keithnos...@xxxxxxxxxxx> wrote:
"Eunometic" <eunome...@xxxxxxxxxxxx> wrote in message

news:539e1328-355d-4170-a055-8ae7eba9a805@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Sep 5, 6:09 am, "Keith Willshaw" <keithnos...@xxxxxxxxxxx> wrote:

Indeed and that is what piston engines do: throw away exhaust energy.

Not if fitted with a turbocharger, in that case some the energy is used
to drive the supercharger.
About 15% to 20% appears to be recoverable if the R-3350 is taken as
an example.

The R-3350 used turbo-compounding and didnt fly at 100,000 ft


R-3350 that were turbo-supercharged flew at 50,000ft (at 0.1 ata or
1.5psi) on a B-29's and aircraft: a respectable achievement for an
aircraft that had the compromises of being a combat bomber rather than
a pure high altitude cruiser.

Turbo-compounded engines i.e. those designed with 'power recovery
turbines' were designed to allow a better flexibility of utilization
of exhaust gas energy for aircraft flying at any altitude, the only
difference being that the energy was transferred to the supercharger
indirectly thereby giving more flexibility: the power can be
transferred to the main output of the aircraft not just the
supercharger.
The ultimate effect being that the turbo compound engine has the same
power at high altitude as the pure turbo supercharged engine
but more power at low altitude for takeoff and climb.


<snip>



Marginal at best , the formula in the simple case is jet
thrust=mass*velocity
The Merlin is dumping its exhaust into atmosphere whose pressure is at
about 0.5 atmospheres,  If it is dumping the same amount of exhaust
into air at 0.01 ata it is going to come out faster and produce more
thrust.

Feel free to prove it isnt marginal by doing the math - show all working

Feel free to prove that it is marginal, show all working.

Dump the exhaust into a small chamber which regulates pressure to 0.5
ata via a variable area nozzle into turbine.
Its fairly obvious that with 7psi in that chamber and effectively
0.15psi on the other side that there is a fair degree of
power available considering that combustion has added 2250kj or energy
to air at 330K and 1 ata with about
1/3rd extract by mechanical expansion in the pistons and another 1/3rd
via heat loss and friction to the cooling system, There is
still about 755kj in that 0.85kg of air to which has been added about
6% mass of fuel.

If we imagine it pushing a piston at a rate of 0.85kg air at 7psi
absolute (volume 0.85/1.2 x 2 = 0.1.4cubic meter with no pressure on
the other side we get a force
of 1600 inches area x 7psi = 11200lbs = 5000kg = 50000N. Work = Fv =
50000 x 1.4m/s = 70kW

So there is about 70kw extra in that exhaust. Assume we recover
another 20% and we have 14kW extra in the exhaust gas turbine= 20hp.




Of course the best way to use this lowered pressure is to use a turbo-
supercharger.

A simplistic assessment, In fact for high speed flight the jet thrust
might be more useful as it will not fall off in the same way the power
delivered by the propeller does
It depends, if the power is desired for a motor jet it might be more
useful

So instead of using the jet thrust directly you propose to drive a turbine
that drives a fan to produce jet thrust !

Pardon me while I larf

The fan-compressor of a motor jet will be able to augment the thrust
of the basic by fan-compressor by accelerating the
compressed fan air and may gain a more valuable increase in thrust and
there may be other engineering reasons,
such as the location of exhaust stacks.

Free piston engines driving turbines have been some of the most
efficient of all engines and were proposed for the B-36.





Also note that the ambient pressure is 0.15psi so the engine will also
recover pressure since there is essentially zero back pressure on the
exhaust.

Not much - try running a diesel engine on air at 15 psi

Diesels are started on less.

Indeed , look at the power output of an alternate electric starter

<snip>



The only practical way to do this would be install a steam turbine.
This is often done in land based diesel installations but has
been deemed a trifle impractical for aircraft
Several kW at 600C is a rather good heat source.

Not when considering the weight penalty

The power to weight ratio penalty is only in the radiator. If unused
cooling area (anti ice area on wing leading edges) is available it can
be used. The limit of 'free' radiator area such as wing leading
edges.



It don't take it too seriously but there are other cycles: the
stirling cycle or even the closed brayton cycle if other forms of
coolant than water are considered.

And practical issues are ignored.

Mainly cost and maintenance and the limited amount of radiator area
(wing leading edge) that might be available.


Steam turbines and boilers suitable for aircraft use are in fact very
light and compact.

Thats a very strange definition of light and compact you have there.

steam turbines and boilers are very small in terms of their power
output
compared to piston and gas turbine engines. It is the condenser that
makes them unacceptably heavy. In ships this is not an issue given
the
availability of sea water cooling.


  It is the condensers that
are the problem so one could recover a little in say the wing surfaces
or leading edges if they were not yet in use.
Extracting mechanical energy from the coolant probably reduces the
radiator area.

No it doesnt. The  mechanical energy lost ends up as more heat which
has to be discarded. See Entropy

You've just extracted energy from the coolant, flashing it to steam,
expanding it through a turbine and letting the resultant steam
condense either inside a condenser or wing leading edge. Flashing it
to steam, without the turbine, directly isn't going to reduce the
condenser area.





If an intercooler is used such that after a compression of 10:1 the
air is cooled.to say 330K and only then further compressed 10:1 then
their is a considerable reduction in work required.

You'll have to demonstrate those figures are accurate, I dont believe em
and you'll still need an aftercooler.
Inter coolers are a very accepted and widely used in both piston and
gas turbine engines.

No *** sherlock

And they work and are in use, so your fuss over pressure loss in the
inter cooler is a red herring.


Just repeat my calculations only for two 10:1 compression ratios in
series instead of one 100:1.

Repeat after me 'the physical laws governing the energy required to compress
gas dont care how many stages you use'

Unless one requires the compress gas at a given, lower temperature,
then you need to break your compression into two stages since an inter
cooler with after cooler is far far more efficient than an after
cooler alone.


Assume that intake air is at 240K in both cases and assume that the
intercooler cools the exit
air of the intermediat stage.

Bad assumption number 1, the air temperature at 100,000 ft is
less than 240k, at 70,000 ft its -57 C so the value is closer to 210 K

Actually there air starts to rise again and then falls again. At
105,000ft it is at 218K
Of course if the air is 10% colder then the compressor needs 10% less
power
so I'm happy to use your 210K as it nets me another 70hp.

Data here:
http://en.wikipedia.org/wiki/Air_pressure


The original for a 100:1 ratio:
Equation 1:
Power required to compress gas is
W = Cp(T2-T1)

WRONG.

No you are wrong, embarrassingly so for you.


There are no mass or time terms here, this cannot be valid formula for power

Duh, assume the figures are per second and all is right in the
world. The Cp term is in kJ/degree/kg. Maybe you haven't done
thermodynamics since imperial units were abandoned?

and you are ignoring Cv so this IS assuming isentropic compression

L = Cp/Cv = 1.4, so I didn't ignore it. The ratio is incorporated as
I stated.


This is a lot less than the original 880hp required admittedly there
are slight pressure losses in the inter cooler and after cooler due to
friction but they are considered worthwhile.  It should be possible to
circulate coolant water in the stator blades thus avoiding pressure
loss of an inter cooler entirely.

Guess what happens when you cool a gas sherlock - the pressure
DROPS. You cant apply formula for adiabatic compression
when the heat generated is being extracted from the system

to borrow your term WRONG!

the gas is cooled and the volume it occupies is concurrently reduced
then there is no pressure loss from the cooling. This is exactly what
inter coolers do; the gas goes through a pipe at constant pressure but
reduces in either velocity or cross sectional area there being some
effects as the kinetic energy is reduced but mass flow stays the same
that will manifest themselves in minor and not always desultory ways.



Your statement would get you a fail on a thermodynamics course

You're very boastful about your qualifications yet I see no evidence
of a great deal of technical skill but a lot of hubris.

Did you ever actually pass a thermodynamics course? Perhaps you
haven't opened a book in 10-20 years?

I actually bothered to consult some PV and QT diagrams of inter
coolers in various cycles: they are NOT shown as causing an
appreciable pressure loss.

I've treated you with respect up until now and ignored your insolence.



The gas equations dont change just because you do
the compression in two stages
The work done is purely a ratio of the inlet temperature, therefore if
you can lower inlet temperature you reduce work.
If the work is divided up between 12 stages of 1.46 compression with
an inter cooler between each stage to keep temperature below 330K  the
power required is even lower.  I get 34kW per stage and only 408kW/
550hp.

WRONG  in oh so many ways

Name one that is substantive and not nit picking.



When you compress a gas you increase its internal energy.
This shows up as an increase in pressure and temperature

yep


See the ideal gas laws

yep


You have been using formulae based on isentropic compression
where the assumption is that no heat flow outside the system
occurs and thus the internal energy is a constant

However when you cool the gas in those intercoolers you
throw away some of that internal energy, the net effect is
to INCREASE the energy required to reach the final state

See what happens when you make bad assumptions

Keith, this is simply avoiding the issue and to be quite frank
gobbledygook.

The equation for the work required to produce a given quantity of
compressed gas is well known. The equation easily incorporates a
factor for the compressor efficiency. The equation I used included the
an efficiency ratio of 0.85 to account for the fact that compressors
are not ideal. The effect of after coolers and inter coolers is also
well known: hint they don't cause but minor parasitic pressure loss
whose effect is minimal.

The power required to compress 0.85kg or air starting at 230K and
0.15psi (about 0.0105 ata) and finishing at 15psi (about 1.05 ata) is
880hp assuming that the compressor is 85% efficient. Higher
efficiencies are possible. The air is at a temperature of around
600K and must be reduced to about 330K (57C) by an aftercooler in
order to be usefull in a piston engine. That amount of air (0.85kg
at 1.05 ata and 57C) is sufficient to produce 1000hp in a fairly
ordinary gasoline engine at sea level. The pressure losses in the
aftercooler are fairly minor. At sea level an exhaust gas turbine
could be expected to be able to recover an additional 200hp. Because
the piston engine is dumping into an atmosphere at 0.15psi instead of
14.2 psi the engine will have substantially more power to recover from
the exhaust gas.

A better approach to using an aftercooler is to use an inter cooler
this reduces power consumption to less than 709hp or better still an
integrally cooled compressor which reduces power consumption to 550hp.

Even if we assume a 10% pressure drop in the inter cooler and after
cooler thereby requiring 2 x 11:1 compressor instead of 2 x 10 the
power reduction is still minimal.








There are some pressure losses but they are not so
significant. This gives us a net power of 1000-671 = 330hp.
Intercooling is worthwhile and even gas turbines can benefit from it..

Inter cooling is worthwhile because it reduces the outlet gas
temperature which is essential for a piston engine and it reduces
the physical size of the compressor as the density in secondary
stages and burners is higher. This can increase power output but unless
you can recuperate that heat the energy is lost reducing thermal
efficiency

We've already given it away so no need to recuperate, the limitation
in petrol engines is octane rating and the limitation in gas turbines
is inlet temperature.   Diesels are more tolerant of high inlet
temperatures.

Lots more errors

Name one Mr 'Expert'



1) Look up the word recuperate - it means recover and use the
heat instead of throwing it away

2) Diesels are HIGHLY sensitive to inlet temperature
thats why turbodiesels have intercoolers and aftercoolers

Spark ignition engines are even more 'highly sensitive' to inlet
temperature because of pre-ignition issues.


In an ideal world the gas turbine doesn't need inter cooling but Gas-
turbines with high pressure ratios can use an intercooler to cool the
air between stages of compression, allowing you to burn more fuel and
generate more power.

Just like internal combustion engines

Remember, the limiting factor on fuel input is
the temperature of the hot gas created, because of the metallurgy of
the first stage nozzle and turbine blades.  One turbine using this
cycle is the General Electric LM1600 / Marine version

A well known phrase or saying involving Grandmothers Sucking Eggs
springs to mind.



As for their usefulness for gas turbines while they are widely
used in land and marine based applications their weight rules
them out of aviation usage

You'd bet wrong

I bet its more a maintenance issue than a weight issue.   Imagine a RB.
211 or Trent.  If the IP compressor stator
blades are hollow and water cooled then the pressurized water can be
flashed into steam in the hollow cowling to take advantage of all of
that bypass air, alternatively sodium-Potassium cooling or heat pipes
might be used to 'wick' the heat to the inner cowling.

Trouble is none of those assumptions are even close to reality

Take a look at such an installation - I have installed several

Installed several 'what's?

I take it that you do know that there are proposals to cool HP
compressor bleed air in the cowlings of High BPR turbofans prior to
using the air for turbine blade cooling.


Ok, I did make an minor error in the scenario of a purely after cooled
engine, the compressor power is 880hp leaving only 120hp.

You made lots more errors than that


That's the only a minor arithmetic error in one of three inter cooling
scenarios I pointed to that doesn't change the fact that there is
still net power available.

You haven't been able to point out to one single error that fatally
dams that piston engines can't produce power at 100,000ft.


However in the case of effective inter cooling between 10:1 and 10:1
stages only between 700hp is required if perfect inter cooling is used
the power requirement is only around 550hp

The errors in your assumptions have been displayed

No they haven't.

Your obfusifcating and don't even understand your own reply.



Perfect inter cooling is the situation where the gas is never allowed
to rise in temperature in subsequent stages.

And is non existent as it would require 100 efficiency in the
exchanger. If your cooling air is at 210 K there is no way you
can cool the compressed air enough to reach the same
temperature.

Yes but in my estimate I showed that and assumed that the temperature
would be allowed to rise from 230K to 330K in the first 4 stages of a
13 stage compressor (no cooling) and then in the final 9 stages they
would rise from 330K to 360K in each stage but would be cooled back to
330K by hollow water cooled stator blades, a water jacket in the
compressor casing and stator core before passing to the next state.
The compressor blades themselves could even be water cooled.

You know of course that the casing of the Merlins centrifugal
supercharger was water jacketed to remove heat. An axial compressor
offers vastly more area for heat transfer.




It can be accomplished by integral inter cooling of an axial
compressor.  Cooling a water jacket is normal on an
axial compressor, in this case cooling of the stator blades would be
required as well.   This can be accomplished with no
pressure loss at all.

This is ludicrous, you are no claiming to be able to make a machine
with 100% efficiency that can cheat the gas laws

I'm not cheating any gas laws. I'm applying them: correctly.



<snip>



Lets get back to reality. The single stage supercharger on the Merlin 20
required almost 150hp to drive it at full power and even then the power
output fell off rapidly at altitude.
Actually it gained power before falling off with the fall off not
becoming rapid until after full pressure altitude which in itself
varied as to supercharger gearing and settings.

You are confusing engine  power output with the power demands of the
supercharger

No, I'm merely pointing out that the supercharger was choked of at sea
level, thus wasting a lot of power due to gear settings.
Max power of the Merlin 66 was at 5750ft not sea level.




The two stage supercharger at full output in high altitude flight
absorbed
around 400 hp and its power output at 35,000 ft was still much lower
than at sea level

The Merlin 61 supercharger required 800hp to deliver air with
24" boost. You are specifying close to 29" boost
Of course an engine running at 24 inches boost is delivering more than
1 atmosphere boost and the Merlin is more than a 1000hp engine.  In
English units: 1 inHg = .491098 psi, or 2.036254 inHg = 1 psi so this
is 12 inches boost on top of 14 ie 1.88 ata.

Wrong

You claim to be a 'qualified' technical person but nothing you write
is at all professional and clear that would be befitting that claim.
Nor do you maintain a professional level of politeness or respond in a
numerate or technical way. Rather inconsistent,

You demand very high levels of proof of others that involved worked
equations, which I have provided, yet the the level of proof you offer
in return is of a inversely correspondingly low level. Merely a form
of heckling when you say 'wrong' or 'wrong assumption'. You simply
don't support your assertions with any argument and are too either too
lazy or too incapable of constructing one.

For instance in you above example of Merlin supercharger consuming
800hp you fail to specify what the intake pressure to the supercharger
is so we have no idea of the compression ratio which along with intake
temperature are the key parameters. You then provide a manifold
pressure but fail to indicate whether this is relative or absolute.
You fail to give full data and then merely heckle when having forced
me to make assumptions due to incomplete data you proclaim "wrong"
because they don't conform to your 'secret' assumptions. Very
professional.

Firstly I don't trust you at this point or your claim of 800hp to
deliver 24" boost absolute, secondly it hardly makes sense.
Americans speak of boost in terms of inches of Mercury normalized with
0 inches of Mercury being zero pressure and assuming that 30 inches
equaling one sea level atmosphere while the British speak of psi
normalized to a sea level pressure of 14psi

Thus 24 inches mercury boost on a Packard Merlin V-1650-7 is actually
below ambient sea level pressure and is referred to as -2.8psi boost
in a similar Merlin 66 (absolute pressure 11.2psi) with the brits
normally assuming the negative sign as implicit.

So are the above American or British figures that you supplied based
on pressures absolute to vacuum or relative to sea level. Be as
'rigourous' and as professional as you claim to be.

Secondly it sounds like the claim is that 800hp of power is absorbed
by the Merlins supercharger is based on the assumption that if the
Merlin was producing 1700hp at sea level then if it is producing 900hp
at say 20000ft then 800hp difference is being absorbed in the
supercharger. This would be an incorrect assumption. At near sea
level the Merlin's power is coming from over boosting ie 15psi over
boost which is relative to sea level, ie 32psi or 44 inches mercury(US
method)


One atmosphere = 29.92 inches hg

24 inch of boost is less than one atm

The datum for boost for American terminology is normally 0 inches =
vacuum and 30 inches = 1 ata. If the Brits were creating these
figures (and it is Merlin 61 not a Merlin 261) from Manometers 24
inches could mean 1.88 ata, something the Merlin was quite capable of
running at.

When for instance an American says his packard Merlin V-1650-7 in a
spitfire was running a boost of 66 inches his british counterpart with
a packard merlin 266 (exactly the same engine) was producing 18psi and
would have measured 48inches on his manometer working on absolute
pressure in inches of Hg instead of psi.

The difference being the Americans used absolute pressure and the
British used relative(to sea level pressure)



The Merlin engine is not that optimized for high altitude as it is set
up for power from a small block, it has a relatively low compression
ratio of 6.3:1 which limits its expansion ratio and on top of that
while the two stage supercharger was supposedly efficient for its day
it is unlikely to have exceeded 70% by much.

Another ASSumption

Very elegant.

Compression ratio of Merlin single stage 6.1
Compression ratio of Merlin 61 and 66. 266 and V-1650-9 also 6.0

http://www.unlimitedexcitement.com/Pride%20of%20Pay%20n%20Pak/Rolls-Royce%20Merlin%20V-1650%20Engine.htm

DB605 Compression ratio: 7.5/7.3:1 with 87-octane fuel; 8.5/8.3:1 with
100-octane fuel types. The side with the king rod had slightly more
compression and in the German engines was fed air from the longer
manifold to ensure manifold pressure on the bank with the higher
compression ratio was slightly lower.

No assumption there.
http://www.spitfireart.com/merlin_engines.html



You also haven't
specified the operating altitude,

I dont need to, the power to provide 24" boost doesnt vary that much
it just wasnt usable low down

This gets down to an oddity to with the Merlin: its supercharger
gearing ratios could be varied and that excess pressure was simply
throttled of which means that the superchargers was far from its
optimal operating point in many cases. The Merlin also produced it
lowest fuel consumption at -3psi for the Spit.


 Even the Merlin supercharger wasn't
that powerful.   When the Germans finally introduced two stage
superchargers DB605L and Jumo 213E1 they had critical altitudes of
around 9600m (nearly 32,000ft)

A LONG way short of 100,000 ft

Indeed, but these superchargers weren't designed for that. Merlin
100's nearly matched these critical altitude


Once you figure in all the losses the power required to deliver sea
level pressure air at 100,000 ft going to require more power
than the engine can produce.
With inter cooling we have around 291hp net available, assume some
additional parasitic losses in pumping coolant water and some pressure
losses and we are down to say 200hp.

Only if you use the wrong formulae and ignore the fact that you
dont have isentropic compression. In the real world this is
simply the wrong answer

I assumed an isentropic compressor efficiency of 0.85 thus I have a
factor to account for the inefficiency of the compressor.



We still have 300lbs jet thrust or 200hp that can easily be recovered
by an exhaust gas turbine.

You might if the engine could run - it cant



I don't think their is going to be a problem achieving

85% efficiency in the supercharger and even if that efficiency isn't
quite achieved the use of inter-cooling will substantially cut the
work required down

The work done compress n kg of gas from Pressure 1 to Pressure
2 doesnt change just because you use an intercooler.
It does for the subsequent stage because the work of compression is
always dependent on the absolute inlet temperature.

Not when dealing with non isentropic compression

Gobbledygook







What it does do is help the efficiency of your compressor
by increasing density.
Yes it reduces the size of the turbo machinery and allows it to run
slower but it also reduces the work required of any down stream stage
in achieving a certain compression ratio.

Wrong, you have not accounted for the energy lost by throwing away
energy in the intercoolers

Yes I did. 550hp, 709hp or 880hp were thrown away depending on the
type of inter cooling (integral, intercooling half way during
compression, and only after cooling)



If you need to produce compressed air at a certain temperature it is
better to intercool than aftercool.

For mechanical reasons

No for the reasons of reduced power consumption. I really can't
believe this.

The following equation is from Gas Turbines, second edition by V
Ganesan. Its available on Google books. It is based on exactly the
equations I used before only the equations are collapsed into one so
that the heat rise is not a seperate term,

Wc = CpTi/Nc x (r^0.286 -1)

where
Wc = work per kg.
Ti = Inlet temperature
Cp = 1.005 (it varies little between 0C and 500C) specific heat in kj
per degree at constant pressure
Cv = 0.7 (it varies little between 0C and 500C) specific heat in kj
per degree at constant volume
L = Cp/Cv = 1.4
Nc = the polytropic efficiency of the compressor 0.85 my example
r compression ratio.

The term 0.286 comes from (L-1)/L = 0.286

As you can see the lower the inlet temperature the lower the power
required to compress a gas.

A compression ratio of 1.66:1 then r^0.286-1 = 1.15-1 = 0.15
multiplying by CpTi of 1.005 x 300K gives 45Kj/sec (ie 45kW) to to
compress one kilo air.
A compression ratio of 2:1 then r^0.286-1 = 1.22-1 = 0.22
multiplying by CpTi of 1.005 x 300K gives 66Kj/sec (ie 66kW) to to
compress one kilo air.
A compression ratio of 2.5:1 then r^0.286-1 = 1.30-1 = 0.30
multiplying by CpTi of 1.005 x 300K gives 90Kj/sec (ie 90kW) to to
compress one kilo air.
A compression ratio of 3:1 then r^0.286-1 = 1.37-1 = 0.37
multiplying by CpTi of 1.005 x 300K gives 111Kj/sec (ie 111kW) to to
compress one kilo air.
A compression ratio of 10:1 then r^0.286-1 = 1.93-1 = 0.93,
multiplying by CpTi of 1.005 x 300K gives 280Kj/sec (ie 280kW) to to
compress one kilo air.
a compression ratio 100:1 then r^0.286-1 = 3.73-1 = 2.73
multiplying by CpTi of 1.005 x 300K gives 45Kj/sec (ie 823kW) to to
compress one kilo air.

You will note that it doesn't take ten times more power to compress
air 100:1 as opposed to 10:1. Its not linear.

This is elegant and explains why inter cooling works and why the
energy required to compress gas 100:1 is not much more than that
required to compress gas 10:1

Given a Merlin was a 26Litre swept volume engine 4 stroke engine
capable of 3000rpm (50 cycles sec) then the volume of air it processes
per second is
theoretically 26 x 0.5 x 50 = 650L which is 0.65 x 1.2kg/cubic meter
or 0.78kg or air. This doesn't include factors for over boosting or
scavenging produced by overlapping the inlet and outlet slightly.

Assuming 70% supercharger efficiency, assuming 0.78kg air consumption/
sec, assuming 3:1 compression ratio requiring 111kW/kg then at 26000ft
the Merlin HF
required 1/0.7 x 0.78 x 111kW = 124kW = 164hp.

At low altitude at say 5750 feet where pressure was 0.8 atmosphere and
at 18psi boost (2.3 ata) where the Merlin was optimized the
overboosting would tend to double the mass flow through the engine but
compression ratio would also be 2.3/0.8 ie about 3:1 but at over twice
the mass flow.
ie 1/0.7 x 1.56 x 111kW = 247kW = 330hp.

This is in agreement with the 400hp attributed on this web site:
http://www.madabout-kitcars.com/kitcar/kb.php?aid=48
The two-stage Merlin was loosing 400 hp (300kW) to turn the
supercharger but developing between
1500 and 1700 hp (1125 to 1275 kW) at the propeller shaft, depending
on model.









On top of that we have hundreds of hp available in the exhaust for use
in either a turbine for either turbo compounding or turbo-
supercharging that would boost our power from 220-330 by about 20% of
1000hp ie 200hp to 440hp-530hp as exhaust gas turbines in turbo
compounded engines recover about 20% of exhaust gas energy which is
almost the same as shaft hp. In our case I think this would be much
more due to the very low backpresssue,

Nonsense, you have already accounted for that energy by giving yourself
the extra 100hp in the engine and you have already boosted the inlet
pressure with your supercharger. The very act of fitting a turbocharger
RAISES the backpressure. This negates your hoped for 100hp
and also loses you the jet thrust
Let me repeat:
worst case scenario with an 85% efficient compressor and aftercooler
is 880hp required power which leaves 120hp net power.

<snip repeated nonsense>

http://www.wipo.int/pctdb/images1/PCT-PAGES/1997/371997/97031192/9703...

Did you actually read this paper ?

It clearly refers to the use a heat recuperation system
to recover the energy for efficiency. This is a LAND BASED system
and they are suggesting using the heat from the intercoolers via
a recuperator with augmentation to recover the heat energy extracted
in the intercooling process.

However they point to a highly efficient form of integrally
intercooled compression.





So at 100,000ft it is possible to produce usefull levels of power
albeit with superchargers and radiators and even more with a turbo.
The supercharger isn't going to be to big and heavy as the IC engine
doesn't need to much air and the lightly loaded first stages aren't at
too much pressure.

More wishful thinking.
I've done the maths,

Using the wrong assumptions and formulae

Utterly correct formulae.



 > without inter cooling there is just enough power

to produce a tiny net output of 12% which would reduce a little when
after cooler pump losses are considered.  With inter cooling there is
a significant net output of around 29% of sea level output with 45%
being the theoretical limit.
parasitic pressure losses in the inter cooler are not that significant
while the water pump power required is no more than the coolant
required in normal engine cooling as it is in the same order of
magnitude.

Statements made with absolutely zero basis

<snip>

While we are talking about intercoolers bear in mind
that the intercooler on the Merlin XX required around 30 gallons of
water per minute to reduce the charge temperature to a reasonable
level.
Merlin XX is a single stage Merlin?

With a relatively small supercharger

How much did the coolant pump for the remainder of the engine require?

An irrelevant question when discussing th supercharger



Feel free to list the engines with mechanical superchargers and
exhaust turbines that produced significant jet thrust
CW R-4360 VDT (Variable Discharge Turbine) several hundred pounds jet
thrust
http://www.time.com/time/magazine/article/0,9171,887932,00.html
Napier Nomad 2 (without reheat) about 318lbs

Interesting example. The Nomad 1 had 300 lbs of thrust from a 3000hp
engine with a ceiling of 35,000 ft so a pro-rata conversion would
suggest 100lbs of thrust and of course not even Napier claimed a
ceiling of 100,000 ft

Nomad was a diesel with little energy in the exhaust: it was 45%
efficient not 33% so the exhaust energy had a 18% residual not a 33%
residual seen in a petrol engine yet is still produced jet thrust.

The R-4360 VDT was attributed with over a thousand pounds thrust for
its 4000hp.


The Nomad 2 was given an extra row on the exhaust turbine to provide
more power for the 12 stage axial compressor and so lost that jet thrust.

Perhaps, still the Nomad 1 created jet thrust.


The engine was so complex and heavy compared with the turboprop alternatives
that its development was abandoned

It seems that all that is required is a variable area nozzle.

Not to any sane individual



Now take a look at the combined weight of your diesel
engine, intercoolers and compressor and compare that
with a gas turbine of the same power
Sure, the gas turbine might be better but there is not indication that
for subsonic aircraft that piston engined aircraft can't fly as high
as jets though they do seem to use turbochargers. Technically the
heat exchangers/radiators are probably the most challenging task.

There is one indication - NONE OF THEM DO
66000ft for the boeing condor and 80000ft for the Grob Strato 2C

Both well below 100,000 ft, note that the F-15 reached 103,000 ft
and for the last 10,000 ft it was reliant on pure momentum

Streak Eagle was specially lightened version in a ballistic climb.
Effectively the stabilized service ceiling of jets is max 85000ft eg
U2 and SR-71 and these aircraft have compromises designed into them
around achieving a certain rane etc.

Aircraft that can loiter at high altitudes for long periods are in
demand. Streak eagle isn't that aircraft is it?

We are of course talking about what is possible not whether it is the
ideal case.

Piston engines can produce a useful output power at 100,000ft so the
possibility that they might be able to generate enough power to fly at
that altitude has to be conceded.





The max altitude at which a turbo/supercharger system can deliver
sea level pressure air is called the critical altitude. Typically for
late piston engines this was around 25,000 ft and they required several
hundred hp to do this. You seem to think that you can do better and
take it up to 100,000 ft
It can be done.   Key is
1 Highly efficient compressor
2 Effective Intercooling.

3) Coupled with an active imagination and a disregard of physical laws

Keith

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