Re: "Jakuba's Compounding article in the Bulletin"
August 12, 2014 08:06PM
Hi Kerry,

Let's see if I can't transfer the file to this discussion. It should have opened just by clicking on the link, I tried it at work and at home on my laptop and desktop computers.

I agree, the Doble draft booster was effectively a form of compounding. If the turbo is picking up a load so that the main engine doesn't have to carry it you've increased effective output at the driveshaft anyway you care to look at it. Back in the 50's there were some commercial marine plants with a steam supercharger --- the recip exhaust steam flowed through a turbine and to the condenser as you'd expect. The turbine operated a centrifugal compressor that was in the steam line just before the engine to boost the steam pressure going into the engine. As I understand it, they found mechanically mating the turbine to the reciprocating plant to be a bit of a pain in that it was unlikely that both expanders would be wishing to turn at the same rpm all the time---to avoid the mismatch they had the turbo increase the recip power output so that all the output would be realized on one shaft.

open | download - Engine_Balance_2003.pdf (623.6 KB)
Re: "Jakuba's Compounding article in the Bulletin"
August 12, 2014 08:49PM
Thanks, Ken

This is going to be a great read.

Re: "Jakuba's Compounding article in the Bulletin"
August 13, 2014 01:56PM

Actually the Doble fan turbine and the draft booster turbine were a form of compounding.
Reading Warren's notes and the engineering notebooks, their reasoning was apparent and logical.

1) When just cruising along, the draft booster took over the load from the Bosch generator at about 30-35 mph, reducing the electrical load on the generator and thus the shaft power needed to drive it.

2) Seeing that Abner always wanted high performance, the draft booster created a higher draft pressure for the burner and as they used a carburetor burner, the evaporation rate went to almost double at high load. going from some 3"-4" draft on the motor alone, to 19" when the booster was really screaming along.
When describing the effect in a telegram to Dr. Mudd and selling him a new booster for his E-14, Abner wrote that he flew up California St. in San /francisco so fast he flew half way across Stockton St. before landing and the steam pressure stayed at 1200 psi. Dr. Mudd was sold and ordered one for his Doble.
Duplicating this stunt one early morning at 2:00 AM, it took 80 mph on the Dodge to duplicate this aerial antic. Yes, the front end was in need of serious alignment.

3) When hill climbing or accelerating, the air flow through the condenser was a lot less than when running on the highway. Since under those conditions, a higher air flow was really needed to try to condense all the exhaust steam, driving the fan with a turbine was the logical step. It also took energy from the exhaust steam and helped the condenser do its work. Later versions had a feed heater coil built in.

The downside was as the Series E engine was a compound, both turbines added backpressure to the LP exhaust, sometimes observed as high as 15 psig. This hurts the PV diagram.
When in use, both turbines extracted otherwise wasted heat and in their way returned it back into the cycle.

Re: "Jakuba's Compounding article in the Bulletin"
August 13, 2014 07:18PM
If you wont to use an exhaust turbine. You should look into what the modern electrics are doing. They have develop some vary high effecient electrics. So use the exhaust turbine to run a generater and cooling fan on the condenser.

Just A thought.

But I do think there is a lot of advanced tech already developed or being developed we could be using to advantage.

Re: "Jakuba's Compounding article in the Bulletin"
August 14, 2014 11:46AM

This is exactly something that I avoid like the plague. Stacking energy conversion system in series.
Using otherwise wasted heat to run something directly like fan turbines, draft boosters, turbochargers, power recovery turbines, is one thing. Going from creating extra backpressure on the prime mover and influencing the PV diagram to charge the battery, then to power an electric motor, then to run something, is what I avoid.
These electric motor driven superchargers do not generate the boost pressure a straight turbo or evan a belt driven supercharger can generate much more efficiently and they add weight and bulk. Short duty too unless you want to carry extra batteries.

Re: "Jakuba's Compounding article in the Bulletin"
August 15, 2014 10:20AM
I would think of a turbine driving a generator that powers a motor as just another transmission system. It's especially useful where there are large speed variations between the driver (in this case, a turbine) and the desired output. Electric motors have huge low rpm torque as well. Batteries are getting better as an energy storage system. However, a turbine driving a fan shouldn't need much variation in speeds or reduction. There will be a need to run all the other accessories, and electric power is the modern choice. My car has electric power steering as well as all the other electric gadgets. I can't imagine any modern car without extensive needs for electric power. I've been involved with the design of one electric power project that was very challenging and successful.

Lohring Miller
Re: "Jakuba's Compounding article in the Bulletin"
August 15, 2014 02:05PM
It is another two stage transmission system, one that adds cost, weight, inefficiency and bulk to the system, when direct connection is desired and used to minimize these things.
Both the fan turbines and the draft booster turbines definitely need variable speed to do their tasks in relationship to the condensing loads and the amount of heat release wanted. All which work in concert with the main expander load and thus the amount of exhaust steam being generated.

A very careful and detailed energy balance always displays the most efficient and compact way to take care of the parasitic loads.

Re: "Jakuba's Compounding article in the Bulletin"
August 15, 2014 10:23PM
There is a lot to be said here about system design and integration. Almost every steam car I have ever seen is a conglomeration of parts flying in loose formation. The engine here, boiler over there, feed pump in that corner, fuel pump in the other, blower underneath that doohickey and control systems stuck in the middle of all the piping. Modern IC engines are integrated to the point where the block casting acts as the oil and water pump housings, the turbo is built right into the exhaust manifold, some intake manifolds are cast into the head, coolant fittings are no longer bolted on but rough cast into the head and machined to profile, most of the sheet metal brackets for power steering and brake pumps, AC compressor, alternator and so on are now gone...again they are part of the cylinder block. All this stuff saves a ton of money, it is extra hardware you don't have to make. It makes for a more compact unit and is more rugged because it is built in and can't become deranged.

This sort of integration might not be practical for a steam car because the boiler and its associated hardware have to sometimes run independent of the every time you start from cold iron. On the other hand, I don't see why a very compact, rugged and integrated auxiliary package shouldn't be possible. It could be both electrically and engine driven either through over running clutches, differential mating gears or other methods. From a manufacturing standpoint it would be a real boon...part of the reason front wheel drive is popular is that the entire powertrain is one package that can be bolted straight in.

Anyhow, that's the kind of refinement I think you would need to see to make a production steam car even reasonably viable. Thermodynamic cycles notwithstanding, a car is a massive set of both synergistic solutions and compromises. To rip off Bing Crosby, "You gotta accentuate the positive, eliminate the negative".

See you all after the weekend, it's the biggest event of the year for a huge number of motoring enthusiasts. The DREAM CRUISE ON WOODWARD! When you see cars from California and Florida, that is kind of neat. When some guys ship their cars in from Austria and Australia just to drive down Woodward, that's an event.
Re: "Jakuba's Compounding article in the Bulletin"
August 17, 2014 01:38PM
Well People,

Have we killed off the compound entirely? Will it remain dead for a modern steam car forever? Should we have a funeral and just bury the poor thing?

This makes me laugh. Only a compound (at least a two stage one) can give the expansion ratios needed for high efficiency. Mediocre efficiency might be had with a properly designed single stage engine, but now thoughts go toward adding some kind of secondary expander such as an exhaust turbine.

For efficiencies sake we require higher temperatures. Higher temperatures necessitate higher pressures which necessitates larger expansion ratios than one can get with single stage engines. Due to materials limitations 1,200 deg F. seems to be a decent limit for now. That puts the pressure at about 1,000 psia. and to take advantage of that with a uniflow engine the expansion ratio should reach 40 : 1 to just get to 15 psia saturated to exhaust into a condenser and that is doable.

May I remind people that a uniflow engine can NOT over expand! If it does because of throttling or short cutoff it will not exhaust and from little to no steam goes through it. Power goes down to nothing as it begins to suck steam or air into the exhaust ports and re-compress that.

The best I could design for a single stage engine was a 12:1 expansion ratio at full power. This makes for a large engine; 260 cubic inches for 168 hp. Cutoff is about 5-6% at 27 deg past t.d.c.. Valves take time to close. They take time in crankshaft degrees. The best I could do is 15 deg to 30 deg. The valve is de-accelerating toward the end of the closing so wire drawing comes into play with the P-V curve and this would vary the exact closing to end up with an effective 5-6%. Because of the interplay between cutoff timing and valve closing timing at shorter cutoffs the engine is effectively just throttled at less than 27 deg after t.d.c..

It's not a shabby engine, at three cylinders double acting it should have an engine efficiency of about 25%. Minus other losses, however, it is not going to quite compete with the gasoline IC. And again because of the interplay between cutoff timing and valve closing the expansion ratio is effectively limited to around 12:1. This engine would run on steam at about 900 deg F. and 900 psia. Due to the limited expansion ratio it can't take advantage of much higher. Its big advantage; it's a simple buildable engine and would be a great ground work for further development.

My compound engine is more complex, granted. In thermodynamics it is a given that after an engine of any kind ,not micro, reaches a decent development stage in efficiency, the only way to higher efficiency for the same given temperature parameters is to make it bigger. A bigger engine with less power output per unit volume. Heat exchangers are added also and it heads toward an engine so big and super efficient that it barely runs. When friction and pumping and thermal losses are entered into the design the size shrinks quickly. So, of necessity, to expand to a larger volume the engines displacement is larger.

At a 16:1 expansion ratio for full throttle the cutoff is at 66 deg after t.d.c.. To go from long to short cutoff is to go from 66 deg down to 15 deg without much wire drawing. Throttling below that. A 40:1 expansion ratio is there if conditions can use it. This is a modern, advanced compound design, not a takeoff on the old stuff. The engine is almost receiver-less with re-compression between the two stages since the very small receiver is just a small clearance volume for the last stage. On a T-S chart there is no bump in the expansion line which tapers down and to the right to compensate for 5% overall expansion losses. Full throttle engine efficiency looks like 30% and cruise goes up to 35%.

Advanced also is the "how to use reheat in a car engine" . A higher pressure stage can be added easily making it now a three stage compound. The first stage exhaust goes back to reheat in the boiler. A way has been thought out to easily control the reheat steam cycle. Andy pointed out the need to add lower pressure steam to the system because the ratio of inlet steam to the high pressure stage to that of the lower pressure stages varies with engine output conditions. This requires "make up steam". Fixed that.

Now the efficiency of the three stage compound steam engine with first stage reheat is looking more like 42 -46% and can compete with a Diesel engine. No computer control need apply.

As far as the "excess" friction of the more cylinders; With a piston rod engine we don't get piston skirt friction, nor side thrust on the piston. The cross slide (or the "what ever" in my case) takes up the side thrust and is in a position to do that with little boundary lubrication friction as it is in a well oiled environment and the cross slide sliders can be shaped to much maintain hydro-dynamic lubrication. The piston proper should never touch the cylinder walls, just the rings. The c.o.f. for boundary lubrication is about 0.1 while the c.o.f. for hydro-dynamic lubrication with the synthetic oils is in the area of 0.008 or less. This is a big factor of 125. Design of the cylinder walls and piston setup is more important than the size or number of cylinders as far as friction goes.

So there. The only way to get competitive, high efficiency is going to be with an advanced compound engine with reheat. I say it is doable. And that also includes a six thousand hp train engine, thank you!

I'm not ever going to bury the compound.


Bill G.
Re: "Jakuba's Compounding article in the Bulletin"
August 17, 2014 11:55PM
Not speaking to anyone in particular here- just making sure we don’t have issues with semantics. With a simple reciprocating steam engine, expansion ratio is the difference in cylinder pressure between the moment the intake valve is fully closed and the moment the exhaust valve or ports begin to open. Any work done on the piston before the intake valve is fully closed is not expansive work. Whatever pressure remains in the cylinder at the moment of release is wasted unless it be used to induce a draft as in a steam locomotive (and that was very inefficient). It took me a long time to realize that expansion ratio is NOT the ratio of boiler pressure and exhaust pressure. It took me longer still to realize that swept cylinder volume and dead volume are not factors.

I spend a lot of time reading historical stuff. Many American railroads gave compounding a try between 1880 or so and 1905. There were several superheating schemes that did not provide much superheat and were found to be ineffective- really they were not much more than steam dryers. By 1905 the Canadians had demonstrated that the German Schmidt superheater was very effective under American conditions.

From that point forward, most people realized that compound locomotives were not worth the trouble. Compound locos were converted to simple super heaters as fast as they could be run through the shops. The only exceptions I know of were locos which were not worth rebuilding and the N&W Mallet Y class. The Mallet configuration is the most friendly to compounding, and the Y class was used in work that best suited compounding.

Bill- Given the number of expansions (as defined in the first paragraph of this post), how many stages do you need to get the total expansion ratio you want?

I began my last missive with words about the difficulty of getting low pressure steam out of a cylinder. How big will your LP cylinder (or cylinders) be? What size are the valves and ports? Now work it backwards. How small will the high pressure cylinder be? What specific output (horse power/engine weight) do you expect?

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 09:57AM
Jim Crank Wrote:
> Andy,
> This is exactly something that I avoid like the
> plague. Stacking energy conversion system in
> series. ...
> Jim

I think you misunderstood me. I was not advocating a steam-electric hybrid. It's really nothing that you are not already doing. You already have a generator to keep the battery charged. I am just saying use the turbine to run the generator. Look at the motors developed that have extremely high efficiency over a wide RPM range for the burner blower.

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 11:19AM
I’m with you. In Walton’s book Abner did a study between a triple and a compound, the compound won out.
And besides I like compounds. I never built my three-cylinder compound, one high and two low. High outside admission, two low’s inside admission. 120 degrees.
Maybe some day.

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 12:14PM

Better yet, read the first 40 pages of the notebook on engine design that Abner did just before going to work on the McCullogh car project. SACA stores. He examined every single layout he could think of.
The eventual winner was the same design as the Skinner tandem compound and an engine called the Acme, which was the same.
He even gives rightful credit to the Farquart (sp) tandem compound first proposed around 1885 or so. I have that book in my library.

Brobeck's bus engine was that three cylinder compound you mentioned. Abner's design for the second Sentinel truck was a V-4 triple wit two lows. What killed his whole line of thinking about reheat was that in a vehicle reheat temperature was not controlled and the oil turned to carbon. He never mentions using normalizers to control the reheat..

My whole outlook after living with compounds in cars is that there are more and better ways to recuperate the otherwise lost energy than dragging a larger piston along.

The exhaust turbine speeds under varying loads and the condenser/radiator fan needs are the same.
The batteries providing the electrical supply when the generator is not running does all that is needed.

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 01:23PM
Thanks for a little support Rolly. It is appreciated.

Kerry, The compound I am talking about with 16 -40: expansion ratio is a two stage. That is two pistons, both unaflow in it's simplest form. The low pressure piston re-compresses as I said using the little receiver volume like a clearance. The pistons are 120 deg offset on the crank and the exhaust port of the first stage is 120 deg after t.d.c. At first stage exhaust the second stage is at t.d.c., so there is 120 deg crank to get the steam from the first stage to the second. I don't disagree with you as to what the expansion ratio is defined as. This engine setup could do higher expansions but there is no reason to. The second stage is also unaflow exhaust starting at 120 deg after its t.d.c. So I hope you can see that the steam flow through the engine is much unimpeded. Exhaust pressure is in the neighborhood of 40 psia at full throttle going into a condenser. The first stage inlet valve is desmodromic good to 4,000 rpms. 1 1/8" diameter.

I'm not worried about my design work.

I don't think people on the Phorum are much interested in what I have to say, so I'm not going to post anymore.

Bill G.
Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 02:44PM
First with a compound the low-pressure cylinder should not be being dragged around by the high, it should be designed to do its own work. It’s there to increase the overall expansion. The cutoff in the high has to be balance with the low for the maximum expansion and balance both cylinders.
Any carbonizing of oil is the result of a very pure overall design. There is no reason to design above what the oil can handle.
It is my opinion there is no need to superheat above 200F over the saturated design. Nothing is gained at that point with volume of expansion verses fuel and material.
The oil we use today will separate from the steam/water very well and not screw up the condenser in any way. Where not in the pre 1940 any more.
I see the largest problem in the condenser design for a modern steam car. We can build great expanders and generators. It’s the overall combination of all components that needs the most work.
I am still under the opinion that steam over electric would be the best approach as I believe the steam plant should need to run at a constant load. And I still believe the scroll expander compounded would make the best power plant.

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 06:27PM
Bill, I'm doing virtually the same thing as you it seems. The second cylinder is actually responsible for more net torque out as the first is doing significant compression work. I too think compounding has lots of merit and thermodynamic advantages.

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 07:43PM

I am sorry to have offended you. I wish I was better at communication.

I really am interested in what you are doing and was asking questions that I might learn. I spent considerable time re reading this convoluted thread before posting.

If people on the Phorum are much interested in what you have to say, they would not bother to respond.

Tell you what- You continue to post and I will remain silent. I think it will work better for everyone concerned.

Re: "Jakuba's Compounding article in the Bulletin"
August 18, 2014 10:18PM
The thing of note that everyone should be thinking about is the power range. The engine must operate from near 0 output to what ever is needed at max speed. There would be an infinite number of Rankine cycles between those operating points.

Rolly is right. The engine design should not be such that you have dead cylinders being drug around. But that is not an easy thing to do with a compound.

In theory it can be done. I have MathCad work sheets that do calculates hundreds of cycles for a triple expansion engine. it figures cutoff and compression etc. But just have not figured out the engine design to implement it. I have bits and peaces.

Each stage is outputting 1/3 of the total work.

In figuring the cycles each stage mus ise (by weight)t the same amount of steam.

It is extreamly hard to design a compound having a wide power range.

Re: "Jakuba's Compounding article in the Bulletin"
August 19, 2014 01:29PM

Most interesting discussion for sure. Maybe we should retitle this as "Thoughts on Modern Steam Car Design."
Rolly, in a car the condensing problem has been solved. The best steam generator and it's control system for vehicle use has been identified, the main expander sure has not, the burner still is questionable, .

Now, just for my education, please answer me this, vehicle use only. Boats are easy as they operate more or less at one speed all the time.
1) With a triple or quad and with the high pressure cylinder stopped on either TDC or BDC, how do you
propose to get it going reliably and quickly every time in heavy traffic? Some automatic simpling valve
or just how? Everyone worked on this and as yet none have succeeded.
2) If reheat is used and it should be, how do you propose to control the reheat temperature?
3) Unless every cylinder has it's valve gear independent and yet interlocked with the others, how do you
propose to have a balanced torque output from each cylinder at all times with varying throttle and
cutoff percentage?
4) Championing compounds or triples is certainly one way to go; but let us not ignore the flow losses,
added bulk and weight and the radiation heat losses. There are other ways to get good expander
efficiency and reliable and smooth operation. The Mccullogh was a very good concept.

A lot of good people have fought these problems when real hardware was there and not just paper theories.
The stuff that makes steam car building so much fun.

Re: "Jakuba's Compounding article in the Bulletin"
August 19, 2014 03:27PM
First of all I would not invest in a piston expander, I would go with a scroll expander as stated in my previous post.

No car built today would be built without electricity.
Modern controls would dictate it. With a 90-degree compound I would use a position indicator for the top or bottom of the high-pressure cylinder only when in the stopped position, which would open a solenoid to pass steam to the receiver of the low-pressure cylinder as with any compound on startup.

(2) If reheat is used and it should be, how do you propose to control the reheat temperature?
With moden thermocouples and solenoid valves with digital controller.

(3) Unless every cylinder has it's valve gear independent and yet interlocked with the others, how do you propose to have a balanced torque output from each cylinder at all times with varying throttle and cutoff percentage?
It would not be necessary except at cruising speed. Fixed valve gear or digital controller.

4) Championing compounds or triples is certainly one way to go; but let us not ignore the flow losses, added bulk and weight and the radiation heat losses. There are other ways to get good expander efficiency and reliable and smooth operation. The Mccullogh was a very good concept.
As I stated before I would go with a scroll expander, cast in Invar 36 as a start for my testing. No expansion up to 600F or so small it would not count.
Re: "Jakuba's Compounding article in the Bulletin"
August 20, 2014 07:26AM
I should have mentioned I am not in favor of reheat; it defies the whole concept of expansion, or the proper design of the phenomena of the natural expansion of the steam.
The bases of any good design in my opinion is to charge the cylinder with the correct charge of superheated steam and let it expand as it cools to a point just before it collapse for the exhaust and use the collapse on the other side of the piston for the vacuum.
A 90-degree compound screws this all up as you need 3.5 to 4 times cylinder volume for the receiver. The advantage is it allows you to have a self starting and reversing engine.
That is the beauty of Abner’s E engine each side was a 180 degree compound allowing for continued expansion and the two sides were 90 degrees to each other allowing for self starting. Nice.
Re: "Jakuba's Compounding article in the Bulletin"
August 20, 2014 03:42PM

If you think the Doble Seres E engine is nice by any respect, think again.

The Woolf compound idea is bad from the start. Why Abner didn't add two more valves we never could understand. It still is an unbalanced engine and you feel the torque pulses when starting.
The water rate is still 11-13 lbs/hr compound or not.
After his success with the White type of Joy valve gear why it wasn't used again is just bad designing. They even changed the eccentric bearings from ball to roller, for some unknown reason.
Seeing twenty leftover cylinders at Gawors place after he bought all the junk parts left at Beslers, every one was split between the HP and LP bores, the wall was too thin.
11 new cylinder sets had to be made. The coring is so complicated that the patterns and core boxes cost $26K.
The grandson of the original foundry owner who cast the Doble cylinders had the records. the scrap rate due to core shifting was 80%.
The flow losses are bad through the valve. That valve cools the incoming steam, bad practice.
All remaining original crankcases are cracked because I had a metallurgical analysis done and they are 30% zinc. I had to make 11 new ones, completely redesigned.
The center main bearing caps are badly supported and if the thru bolts get a bit loose the crankshaft wobbles and breaks. Also completely redesigned.
The crankshaft hardening was horrible and shafts do break. Again new ones had to be made.
In spite of all the delusions and fairy tales people have about the Doble, I will take a late White any day.

It is a huge and heavy engine and as far as I am concerned I wouldn't touch such a double acting engine in a car for all the money in the world. Only a single acting, unaflow with poppet valves.
Enough of this, it's going nowhere.

Re: "Jakuba's Compounding article in the Bulletin"
August 21, 2014 06:38AM
Dear Jim
I’m sorry you feel the way you do after spending half your life edifying Abner’s work.
I was only referring to the expansion cycle of a 180-degree compound verses a 90-degree compound.
The subject is compounding. It’s really designing an engine that utilizes the expansion cycle of the cooling of steam after cutoff. An expanding cone would be nice. I believe you get the same effect from the scroll expander. They’re building them that pump over 10,000 psi as a compressor, for now I would be happy with 600 psi as an expander.
Re: "Jakuba's Compounding article in the Bulletin"
August 21, 2014 09:22AM
A Wankel can be made a compound. The Wankel is a type of piston engine. A chamber volume varies
from a min displacement to a max isplacement and back again. But unlike a reciprocating engine the
stroke of a Wankel engine is 270 degrees of crank rotation. That is 180 + 90 degrees. It wold be
a ground up design. It would have two chambers and two rotors. Lake a piston compound the expander
would have a small high pressure and large low pressure expander. The displacement would be
designed the same way as a piston engine. The sizes determined for best compound expansion. The
chambers would be at 90 degrees to each other and the crank throws 180 apart. That would make for
the simplest nter connections. The exhaust of the high pressure would directly feed the low
pressure side. The above arrangement has the compression stroke of the high pressure expander
exactly aligned with the low pressure power stroke.

Jim, What you said about a compound having to be larger than single expansion make me wonder why
you would wont to give up half the displacement of a Wankel using only one side.

Following one rotter face. Starting with it at min displacement. The crank throw is pointing at
the face having min displacement.The line runs throw the narrow width of the chambers. If you
rotate the crank 270 degrees it is now pointing at the rotor apex opposite the rotor face were it
started. The rotor has rotated 90 degrees as the chamber that was at min displacement is now at
max displacement.The exhaust stroke begins. It takes 270 degrees of crank rotation and the same
rotor face is now at min displacement opposite the point where it started. One cycle is 540
degrees of crank rotation. Every 180 degrees of crank rotation we have a rotor surface at min

Why would one not wont to have a power stroke ever 180 degrees of crank rotation? Why wast that

The compound Wankel with the chamber at 90 degrees would have a power stroke starting every 90

Re: "Jakuba's Compounding article in the Bulletin"
August 21, 2014 05:22PM
If a scroll expander is so good and can be sealed, why not get one and try it out?
On a dyno and report the water rate. Curious if they are sealed with no oil or if they need to be flooded?

The big problem with Series E Doble engines, is that they were designed for 750 psi and owners ran them at 1500+ psi putting stress on the engine it was never designed to see, so they break. Also, Dobles constantly changed things so spare parts do not fit. New parts are the only way to restore one, so collecting old parts is pointless, they don't fit. Expensive too!!!
Thus the total redesign and 11 new engines made to keep these prize cars on the road and not sitting dead and broken in museums. Jay Leno's E-20 has one of the new kits and he runs the wheels off it.

I have a 13-B apart and a big design file on them and know full well what can be done with a Wankel. It all hinges on if Mazda really does come up with oil free seals, that is the key. Ken and I may have an alternate way to do this.
When you actually have a housing, rotor and eccentric shaft in front of you, then it is clear what can and cannot be done. I still like it. It definitely would be compounded.
Re: "Jakuba's Compounding article in the Bulletin"
August 22, 2014 08:19AM
Jim there is a lot more experiments going on with Scroll steam expanders then I could ever afford.
What I see is they’re using off the shelf compressors converted to run as expanders and not designing one specifically for superheated steam.
You can search the internet and find many more, even stuff on U-tube.



Re: "Jakuba's Compounding article in the Bulletin"
August 28, 2014 10:49AM
It seems to me that the majority on this Phorum agrees with my reasoning that multi-stage expansion is useful in marine and stationary application only. I pointed out that even in steam locomotives compounding was rare by the time railroading has progressed far enough to make accurate comparisons of performance and service duty possible. In the US, no serious manufacturer designed a compounded loco after 1930. After WW2 the compounding disappeared from the drafting boards of all manufacturers, except French. It is interesting to observe why that was so.

Unlike elsewhere, in France a loco engineer had been assigned to “his” locomotive “for life,” and vice versa. This familiarity of man and machine was apparently a prerequisite for operating compounded locomotives successfully for they were known everywhere as fussy in operation. We mentioned here some of the problems like starting, distributing power evenly among stages, complexity and cost. To acquire that needed skill apparently required that one-one commitment. It included also that the engineer participated in maintenance, repairs and rebuilding of his loco. In this arrangement, the engineer learned how to take advantage of the compounding on his route and how to tweak the various valves and levers to realize the loco’s potential.

Nevertheless, even in France, compounded locomotives were common only on routes requiring long runs at a relatively high and steady load. Eventually, after WW2, the new designs reverted to single expansion even in France. The steam locomotive era ended with only the single-expansion marvels, two cylinders outside. We will never know as much about steam engines as the engineers of that by-gone era did.

I do not dispute the aesthetics of the compounded models on one’s office desk. But I’d classify that as a stationary application, just within the scope of the reasoning.

Re: "Jakuba's Compounding article in the Bulletin"
August 29, 2014 05:51PM
I haven't seen it mentioned in this thread, but it should be noted, without compounding on a uniflow, to get decent expansion requires rods, bearings and crank strength about 3x greater than a compounded arrangement. All the pressure is available at TDC,where it can't do much good and dimineshes from there. i think Jim used a term grenade engine a couple times and the term comes to mind. I agree that for a transmissionless auto one would need to work hard at a decent compound arrangement. I have big hopes for a modern compound. Keith
Re: "Jakuba's Compounding article in the Bulletin"
August 29, 2014 08:46PM
Hi Keith,

"All the pressure is available at TDC, where it can't do much good and diminishes from there."

I don't think I can agree with that, what you are describing is an engine with high initial pressure and low MEP because the working fluid has been greatly expanded. This is exactly the same description as a Diesel engine and they are the epitome of efficiency. The force applied longitudinally on the connecting rod, in my opinion, isn't relevant in and of itself. The goal of an engine is to produce work, which can be defined as the output force applied to a load through a distance. At exactly TDC the pressure is at peak BUT there is zero motion of the piston, since the force isn't applied to a load over a distance there is no work being done. At the same time, there is no mechanism removing the potential energy from the steam (ignoring thermal losses to the cylinder wall)....non condensable gasses can be pressurized into containers and the force does not dissipate even though it is working against the wall because the wall is not moving. As the crankshaft passes TDC, the pressure is still great, but the piston is barely moving. The work performed is small relative to the pressure but the only potential energy lost is that applied to actually move the crank. As the crank keeps rotating the piston moves greater distances and the force is applied across these larger distances, extracting more potential energy from the steam. Since most piston engines average mechanical efficiencies between 80 and 90 percent and since friction is always a given, it follows that the piston-crank-rod configuration is about as efficient as anything else regardless of the peak pressure.

I'm sorry if I beat this topic to death. It had very little to do with the initial observation and a lot to do with any number of websites and patents I have seen promoting some engine scheme designed to get rid of losses due to the peak pressure being at TDC. Lots of money gets invested in this but to date none of the alternative schemes have worked out as well.

Re: "Jakuba's Compounding article in the Bulletin"
August 30, 2014 07:13AM
All I meant to point out is that for a given output engine, if it isn't compounded, the single cylinder must be larger to do the same work. Now that means larger bearings, rods etc., as the work isn't distributed across 2 cylinders and their associated assemblies working in their prime positions to extract work. I believe a lighter assembly can produce the same work if compounded. i like having peak pressures at about 75 degress of crank rotation, about the maximum work extraction level for my stroke/rod length combo. The ICE has quite different dynamics with the necessity to contain a controlled explosion, shifting the peak pressure as it must.
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