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Some stupid questions...

Posted by steveinky 
Some stupid questions...
February 20, 2023 03:37PM
I'm a new SACA member and am enjoying the very technical stuff in the bulletins.
Question #1 What is the advantage of a 4 cylinder triple expansion engine? The Titanic sister ships and USN Montana Class Cruisers apparently used engines of this design. I'm familiar with quadruple and triple expansion engines from the Juniata/Milwaukee Clipper and the SS City of Milwaukee, but I've had never heard of a 4 cylinder triple expansion engine before.
Question #2 How is it possible to have exhaust from a steam turbine, or a low pressure cylinder exhaust at a "near vacuum?" This is not only true of the Titanic class ships, but claimed by the Skinner unaflow engines as used in some C&O Carferries like the SS Spartan. It would seem to me that atmospheric pressure would blow up the tailpipe of such engines.
Thanks for your input.
Re: Some stupid questions...
February 21, 2023 09:47AM
Answer #1: A quadrupedal (4) expansion engine is not feasible. No advantage, not possible in the working parameters of most steam engines, even the most sophisticated ones. The benefit of using multiple expansion is to utilize the most energy in the steam. This equates to better efficiency.

Answer #2: The steam exhaust is into a chamber (condenser) cooled by a body of water. If you have a vessel that is kept cool, it will have an atmosphere lower than that of standard atmosphere all around us. This creates the vacuum.

I recommend buying the Doble Steam Car book through SACA. Read it and then ask more questions.

Re: Some stupid questions...
February 21, 2023 10:48AM
Hi Steve,

Your first question regarded a 4 cylinder, triple expansion engine, such as was found in the USS Texas (BB-35) which is a New York class battleship and now a naval museum in Houston (albeit closed at the moment since Texas is undergoing a well-publicized drydocking in Galveston, you can see details on the USS New Jersey You Tube channel). A similar engine type was found on RMS Titanic -- although we can get caught in semantic knots since there was a 4th level of expansion in the Parsons turbine situated between the reciprocating engines. Since the two engines shared this expansion stage, things get a bit cloudy, terminology-wise.

There really isn't a big mystery as to why they split the third stage into a pair of cylinders, it was for mechanical convenience. This allowed the designers to keep the pistons and cylinders to a more reasonable diameter. The smaller pistons also weighed less and allowed for better engine balance and smoother operation.

Quadruple Cylinder, Triple Expansion, Engine

As for your second question, the water cooled condensers provide a vacuum that allows for expansion of steam below atmospheric pressure. The condensers work on the principle that steam occupies a far greater volume than water. If you condense the water in an air-tight chamber, nothing can fill the space occupied by steam before condensation, and you get a vacuum. Things aren't that simple, in real life, since air and other noncondensable gasses are entrained in the steam. Given time, these will gather in the condenser and raise the pressure. Therefore, some sort of air pump is fitted to the condenser to reject these gasses to the atmosphere. In earlier systems, this would be a piston pump. In modern turbine setups, such as the ones with which I worked on an aircraft carrier, they use two-stage steam ejectors (jet pumps). The ejectors also serve to establish a vacuum upon engine startup. In some instances, your steam system may also have some sort of deaerating feed tank which serves to remove the majority of entrained air and gasses before feeding the water to the boiler (in our case, it was a reactor). Submarines were too small to have DFTs, aircraft carriers had the room.



There were a number of quadruple expansion engines built but, generally speaking, the added friction losses and low superheat temperatures tended to make these an example of diminishing returns. In some cases the quad expansion engines had five cylinders. Quadruple Expansion

Edited 1 time(s). Last edit at 02/21/2023 11:13AM by frustrated.
Re: Some stupid questions...
February 21, 2023 11:00AM
I think you misunderstood the first question. A FOUR CYLINDER, TRIPLE EXPANSION engine limits the low pressure cylinder to a reasonable diameter with two cylinders of half the displacement. It also allows better balance than in a three cylinder engine at the expense of a longer engine.

Lohring Miller

Re: Some stupid questions...
February 22, 2023 05:17AM
Thanks for the replies. I do see an advantage to the 4 cylinder triple expansion engine in that the low pressure cylinders have staggered crank throws. I think this would allow for greater expansion and smoother operation.
There may be little advantage to a quadruple expansion engine, but the SS Milwaukee Clipper has one. Here is a picture I took of the boat a few years ago. The tours don't include the engine room anymore for "safety" reasons.
Have a nice day

Edited 1 time(s). Last edit at 03/01/2023 02:56PM by steveinky.

Re: Some stupid questions...
February 28, 2023 12:30PM
Hi Steve,
I learned something regarding a triple expansion engine that uses 4 cylinders. Two of which are used for the 3rd expansion. The benefits as Ken say are with the mechanical commonality with the size and with you, the crank angle with smooth running. I didn't know this or wasn't aware of it.

After some research regarding the Titanic, it used a triple expansion engine with 2 LP cylinders. The second expansion is referred to as the IP cylinder as I'm sure you already know. Then the exhaust steam from the reciprocating engine went to the steam turbine at 9 PSI. The steam pressure started at 215 PSI. Not sure what the vacuum was from the condenser...maybe someone can elaborate.

In summary, I would say that this is very efficient use of the steam at the initial pressure and temperature. I would imagine that a quadruple expansion engine would need much more initial pressure to complete the stages and perhaps a turbine after that. Not sure if any re-heat was applied. Maybe someone can elaborate. Again, very efficient use of the steam.

Re: Some stupid questions...
February 28, 2023 12:55PM
Titanic had reasonably good condensers. The literature says that they were capable of producing a vacuum at 28 or 28.5 inches Hg. That's one of those figures that you always take with a grain of salt since condenser vacuum is dependent upon steam flow, and water temperature. I've seen better than 29 inches on an aircraft carrier and also around 26 -- depending upon the speed we were making and the water temperature. At flank speed, we were using vastly more steam than Titanic, and our condensers would have to work harder. Operating on the Equator usually involved a bit higher condenser pressure than you would see above the Arctic Circle. What was really weird was passing in and out of the Gulf Stream -- the temperature difference was enough that you could see the temperature change on the thermometer installed on the condenser scoop injection manifold. Honestly, I believe barometric pressure may have played a part in the readings since I think we were reading gauge and not absolute pressure. But, it's been a little over 40 years and that sort of picayune detail kind of faded from memory.



Edited 2 time(s). Last edit at 02/28/2023 12:59PM by frustrated.
Re: Some stupid questions...
February 28, 2023 01:05PM
Rick the water under a boat works great on the keel condenser.
I always ran 30 inches of vacuum on my boats.


Re: Some stupid questions...
March 09, 2023 07:19AM
Hi Rolly,
30 inches of vacuum is significant. Is this in Florida waters or in the Northeast where you used to live? Do you find there is a difference.

That is a sweet looking boat!

Kind regards,
Re: Some stupid questions...
March 09, 2023 09:44AM
The entire keel of thirty feet is the condenser. All aluminum Sea water never gets much above forty in New England. Works great.
Re: Some stupid questions...
July 01, 2023 08:00AM
I was reading about condensing boilers used in heating systems. It seems that to achieve 90% efficiency, the return steam must cool below 130F to condense the water and get that last bit of latent energy out of the steam. The exhaust is so cool that they use plastic vents for the exhaust. It didn't seem like this would have any application in a propulsion system.
It dawns on me that the exhaust steam from a reciprocation steam engine could possibly be used in a condensing steam engine, either as the final stage on a compound engine, or as a stand alone aux power unit using waste steam as the power source. Maybe too cumbersome for an automobile with no ready source of cold water, but might have a use in marine or power plant applications.
I'm sure this is not a new idea. Has this been tried?
Just pondering
Re: Some stupid questions...
July 03, 2023 04:29PM
Hello Steve,

The condensing boiler used for heating is a boiler that is condensing the combustion exhaust and removing the latent heat from that exhaust.
All that would require is an hydronic system which has a return water temperature of less than 212 deg F. Less is better. This return water then goes through a water to exhaust heat exchanger.

Don't think that they can't mess this up with enough sales talk. I have watched the result of the new, super efficient condensing boilers in a set of apartment buildings where I used to live. There was an unbelievable amount of steam coming out the exhaust in the winter time.

Baseboard heat requires a temperature of 190 deg F for best output and normally that is the temperature that should reach them with a return temperature of say 150 deg F. Cast iron radiators should be sent water at 140 deg F and the return might be 120 deg F. So one can see which would work better with a condensing boiler.

Steam heating boilers send wet steam out at 212 deg F and the return condensate is about 180 to 200 deg depending on the heat losses in the return line or mains. Below boiling temperature is needed for good operation but no where to use a condensing system.

Notice that all these temperatures are around or below that of a condenser operating near full engine output considering an efficient engine.

So conclude that a condensing exhaust boiler in a car is not going to add efficiency. The exhaust can, however, be used to warm things up during startup in cold or freezing conditions. Pumps may need to be unfrozen as well as the water tank. Running a boiler on low while empty shouldn't be a problem.

And always remember that a good, well designed compound engine will blow snow out the exhaust. spinning smiley sticking its tongue out

Best Regards,

Bill G.
Re: Some stupid questions...
July 04, 2023 02:26PM
Thanks Bill:
I guess those condensing boiler efficiency claims are wildly optimistic, based on ideal conditions.
What I failed to convey in my question, is that I'm thinking about using the engine exhaust steam in a auxiliary atmospheric engine, or as the final stage in a compound engine.
With a steam turbine exhausting into a vacuum, I can see the added efficiency of using a water cooled condenser. On a uniflow engine, having the steam exhaust into condenser probably helps scavenge the exhaust, but there is still a lot of hot steam going into the condenser with a lot of latent heat. So I wonder if anyone has ever added an atmospheric (Newcomen condensing contracting) cylinder to a compound engine, or alternately as a aux power unit. Obviously this is not practical in a car but might be in marine or stationary engines.
One OLD steam guy told me that there are no new ideas, so I suspect this has been done before.
My idea for a Stanley car type engine would involve using a power recovery turbine. Probably not a new idea either. The PRT could drive various accessories and could improve efficiency a bit.
Have a nice day
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File Name File Size   Posted by Date  
Titanic Engine.jpg 180.3 KB open | download lohring 02/21/2023 Read message
Battledhip Oregon Engine.jpg 475.9 KB open | download lohring 02/21/2023 Read message
MilwaukeeClipper.jpg 50.1 KB open | download steveinky 02/22/2023 Read message
Tryall-1.jpg 120.2 KB open | download Rolly 02/28/2023 Read message