Search This Blog

Monday, April 29, 2013

Sunset for reciprocating steam engines

Steam engine design peaked in the mid 20th century, when steam engines began being replaced by other technology.

There were a number of advances to the Corliss engine made before the end came.  Higher pressures were used.  Some advanced locomotives were using 800-1000 psi superheated steam.  Locomotives were "compounded", where the steam leaving a high-pressure cylinder would enter a low-pressure cylinder.  The Uniflow engine was invented and entered widespread use.  However other technologies surpassed the reciprocating steam engine, and the end was near.

At sea, the handwriting was on the wall after the steam-turbine powered "Turbinia" made an appearance.  She was capable of 34.5 knots (about 39 miles per hour).  I will turn the rest over to Wikipedia:

Turbinia was the first steam turbine-powered steamship. Built as an experimental vessel in 1894, and easily the fastest ship in the world at that time, Turbinia was demonstrated dramatically at the Spithead Navy Review in 1897 and set the standard for the next generation of steamships, the majority of which were turbine powered.


Parsons' ship turned up unannounced at the Navy Review for Queen Victoria's Diamond Jubilee at Spithead, on 26 June 1897, in front of the Prince of Wales, Lords of the Admiralty and foreign dignitaries. As an audacious publicity stunt, the Turbinia, which was much faster than all other ships of the time, raced between the two lines of large ships and steamed up and down in front of the crowd and princes with impunity, while easily evading a Navy picket boat that tried to stop her, indeed, almost swamping it with her wake.
In the automotive world, internal-combustion gasoline engines were far more practical and efficient than gasoline-heated steamers.  Internal combustion engines have the advantages of requiring no pre-heating and very little maintenance.  For fun, below is a picture of a Stanley Steamer 6 HP engine.  I would imagine it would take a fair amount of time to boil water, then heat the cylinders enough that steam wouldn't immediately condense in them.


On the rails, the end came a couple of decades later.  Diesel-electric locomotives began replacing steam locomotives in the 1930's.  Initial diesel-powered locomotives had been a disappointment.  Diesels operate at low speeds, so a heavy transmission and clutch was needed to adjust the speed of the train.  Eventually a design was developed where the diesel engine was connected to an electrical generator, and each wheel of the locomotive was attached to a motor. 

A pair of late-model steam locomotives (steam locomotives were often custom-made, with no two exactly alike):


The Great Depression and restrictions on liquid fuels during World War II delayed the inevitable replacement of steam trains.  However by the late 1950's, only a handful of steam locomotives were in operation, and in 1960 the last steam engine was removed from main line service.  The reasons for the demise were similar to those for automobiles... 

From wikipedia:

Steam locomotives, by comparison, require intensive maintenance, lubrication, and cleaning before, during, and after use. Preparing and firing a steam locomotive for use from cold can take many hours, although it may be kept in readiness between uses with a small fire to maintain a slight heat in the boiler, but this requires regular stoking and frequent attention to maintain the level of water in the boiler. This may be necessary to prevent the water in the boiler freezing in cold climates, so long as the water supply itself is not frozen.
Another useful feature of diesel-electric locomotives that might not be apparent at first glance is that one train crew can operate several locomotives.  If you need several steam engines to move a train, you will also need several crews.

Below is a diesel-electric streamliner design built in 1936.  I love the big radiator grille!

Union Pacific M-10000 and Burlington Zephyr, both Diesel-Electric.

Sunday, April 28, 2013

Mechanical Governors

Corliss steam engines were a huge improvement in efficiency over their contemporary rivals.  They also provided another great improvement: the "flyweight governor". The governor on the machine below is at the middle, sticking up, with the metal balls hanging off each side. A governor is what helps an engine maintain the set speed. You might think of it as a crude cruise control.

Why would a machine need a governor?  Let's do a thought experiment:

Let us suppose that our steam engine is running a lumber mill and that a really big log has just run into the blade. The blade bites in and slows down the blade (and our steam engine) due to drag.  Without a governor to increase steam flow to our engine, the blade would eventually to slow to a standstill, because until the blade bit into the log, only a tiny amount of steam was necessary to keep it moving.

With a governor though, as the sawblade (and steam engine) slow, the governor detects the loss of speed and increases steam flow to keep the engine running at the correct speed.


So How did these early governors work? A small shaft driven by the steam engine spun the balls. If the machine spun faster than desired, centrifugal force would make the balls swing outward. Since they were connected by a linkage to a collar. The collar lifted up. This collar would be connected to the central disc that controlled all the steam inlet and exhaust valves, to close them down.


Here is another image, which better explains how a governor controls the speed of an engine.



This was an important development for stationary engines in the era before the electrical grid, because each machine required a reliable means of maintaining stable speed. If not for a governor to increase steam flow, even a slight increase in load would eventually bring the machine to a stop. On the other hand, a drop-off in load without reducing steam flow could cause the machine to overspeed and damage itself.

Stationary Steam Engines

Now this is a subject near and dear to my heart!  Although I love steam trains and marine power plants, you don't get big power without a big engine.

Let's take a concrete example of the power output of mobile vs. stationary engines:  A really powerful modern diesel locomotive can produce 5000 horsepower.  Let's say you are moving a massive train over the mountains and require four big locomotives to move it.  So we need  20,000 horsepower.  Here is an online conversion calculator to watts.  If you don't want to follow the link, the four locomotives, running full blast, produce 14,913,997 watts, or 14.9 Megawatts.

Thats about what a really small gas turbine, hydro, or geothermal power plant makes.

Power stations didn't start out making huge power.  They started out with primitive low-speed engines that  used steam at atmospheric pressure.  These slow-moving engines drove lumber mills, grain mills, textile mills, and low-pressure air blowers for steel foundries.  They were even used for drawbridges.  See photo below.





A huge improvement on the atmospheric condensing steam engine was the Corliss Engine, which was invented in 1849.   There are several issues steam engines have that steam turbines do not have.  One of the big issues is intermittent steam admission into the cylinder.  Therefore valve design and timing are crucial to efficiency.

The Corliss engine greatly increased efficiency by using rotary steam valves (similar to today's ball valves), and introduced variable valve timing for both intake and exhaust.  Below is a cutaway of the cylinder of a Corliss steam engine.  It is a double-acting engine, meaning that steam pushes on the piston from both sides. 

This cutaway shows the inlet steam pipe (1), Rotary Steam Inlet valves (2), Rotary steam exhaust valves (3), Steam exhaust to condenser (4), Connecting rod (5), Piston (6), and Cylinder (7). 



Below is a drawing of a Corliss steam engine.  Steam enters the box containing the cylinder from the pipe at the top right.  The disc at the center of the box is connected by rods to four different rotary steam valves.  The timing of the steam valve opening is mechanically adjusted by the center disk, which in turn rotates back and forth based on the machine speed.  Thus the machine is efficient through a range of speeds.  This was the most efficient steam engine design until the invention of the Uniflow design, followed by the steam turbine.  There are still a few of these in operation today!


Below is a Corliss Engine that was on display in Philadelphia for the US Centennial Celebration.  Here is the Wikipedia entry about it:

The Corliss Centennial Engine was an all-inclusive, specially built rotative beam engine that powered virtually all of the exhibits at the Centennial Exposition in Philadelphia in 1876 through shafts totaling over a mile in length. Switched on by President Ulysses Grant and Emperor Dom Pedro of Brazil, the engine was in public view for the duration of the fair.


The engine was configured as two cylinders side-by-side. Each cylinder was bored to 44 inches (1.1 m) with a stroke of 10 feet (3.0 m), making it the largest engine of the nineteenth century. The Centennial Engine was 45 feet (14 m) tall, had a flywheel 30 feet (9.1 m) in diameter, and produced 1,400 hp.
 











Thursday, April 11, 2013

Steam Engine Progress - Transportation

Steam engines for transportation, which began with the original Trevithick locomotive in 1804, advanced continously until phased out by more modern technology.

Toward the end, steam locomotives were using high and low pressure steam, uniflow cylinders, superheated steam, and (due to massive steam production) mechanical stokers.

Below is a drawing and cutaway of a late-model steam locomotive.  I found a couple of things on the cutaway interesting:

Item #10, a superheater.  Takes advangage of heat remaining in the exhaust gas to increase efficiency.  Item #12, a blast tube.  Spent steam that is exhausted from the cylinders goes into a venturi.  The expanding steam entrains exhaust gas from the smoke box and pulls it out the stack.  This puts the fire side of the boiler at a negative pressure and pulls massive amounts of air into the firebox, burning the coal much faster than if it were allowed to smolder.  Much simpler than installing fans for the same purpose.



Elements of the locomotive 1. Firebox 2. Ashpan 3. Water (inside the boiler) 4. Smokebox 5. Cab 6. Tender 7. Steam Dome 8. Safety Valve 9. Regulator Valve 10. Superheater Header in smokebox 11. Piston 12. Blastpipe 13. Valve Gear 14. Regulator Rod 15. Drive Frame 16. Rear Pony Truck 17. Front Pony Truck 18. Bearing and Axlebox 19. Leaf Spring 20. Brake shoe 21. Air brake pump 22. (Front) Centre Coupler, 23. Whistle 24. Sandbox.


Meanwhile at sea, where there is a bit more room to indulge your need for power, a photo of RMS Titanic's starboard steam engine, and her boiler room:


This is about as far as piston-driven steam engines went, with regard to transportation.  Marine engines were replaced with steam turbines in the early 20th century, while it took until the mid-20th century for the steam locomotive to be replaced by the diesel-electric locomotive.


Steam Engines for transportation

The steam engine that James Watt designed significantly improved the efficiency of stationary engines used for pumping water out of mines.  However, since it was an "atmospheric" engine (meaning the steam supplied to the cylinder was at normal air pressure), the cylinder had to be quite large to accomplish meaningful work.

Below is an example of a steam-powered blowing engine, used to provide low-pressure compressed air for use in steel furnaces.  The cylinder on the left is the steam engine, and the one on the right is the air compressor.



In order for a steam engine to be practical for powering a vehicle (ship, tractor, or train), cylinder size would need to be shrunk, and so steam pressure and temperatures would need to increase.

By 1800 metallurgy had come far enough along that steam could be contained under significant pressure.  In 1804 a steam engine using 145 psi steam pressure hauled a load of 10 tons for 10 miles in England.  This was proof that steam power could be used to move significant amounts of goods.

Here is a photo of the first practical steam locomotive. 



This design is quite complicated-looking, but not too difficult to understand.  The driver stands on a separate railcar (not shown) to the right.  Fire passes through tubes and out the stack at the left.  The fire and hot gas passing through the tube bundle boils water that surrounds the tubes and makes steam.  The steam pushes a piston - which cannot be seen because it is inside the body of the boiler. 

The piston goes in and out of the front of the front of this engine like a giant slide trombone.  Connected to the piston rod is the diagonal connecting rod, which is hooked to a crank at the rear (upper right) of the engine.  A huge flywheel on the opposite side of the engine smoothes the pulses (and wheelspin on the steel tracks) caused by the pulsed power delivery.  A pair of the wheels are then driven by using a series of gears, again to reduce wheelspin. 

Here is a video of the original locomotive in action.  Looks a bit dangerous to be the engineer ;)



Steam Safety:

Early problems (fatalities) with using higher steam pressures usually involved loss of water level and overpressure conditions. 

Loss of water level would leave the boiler tubes uncovered by water, allowing them to melt and release massive volumes of steam into the firebox, blowing ash and steam everywhere.  It may not be obvious, but water can absorb enormous amounts of heat, but steam cannot.

Steam overpressure is bad for equally obvious reasons - boiler rupture and explosion. 



The low water level condition was solved by adding a lead plug in the boiler at the lowest allowable water level.  When the water dropped below that level, the lead plug would be uncovered, it would melt, and release steam pressure (and excess energy) in a safe direction.  The lead plug would be installed at a slightly higher level than the bundle of boiler tubes, to prevent uncovering a tube and rupturing it.

The steam overpressure condition was corrected by fitting safety valves to the boiler, allowing excess steam to be safely vented off, in the event that there was too much fire for the amount of steam needed for the engine.

With these problems more or less resolved, the tranportation side of steam technology could march on.


Early Steam Engines

The first commercial piston-type steam engine was produced in 1698.  It was a primitive device that was used to remove water from underground mines. 

In 1712 a successful steam engine (again using up-down motion to pump water from mines) was invented by Thomas Newcomen, called the "atmospheric engine".  Below is a diagram showing operation of this engine.  The boiler is to the bottom right.  Water is blue, and steam is pink in this animation. 

What is not obvious to modern eyes is that the power stroke on these early engines was not due to steam pressure from the steam entering the cylinder.  The boilers of the day were not able to contain enough steam pressure to push anything.  The steam used in these engines was at atmospheric pressure, same as your tea kettle.  The power stroke on this engine occurs when the steam condenses and creates a vacuum underneath the piston.

Here is how it operates:  A valve at the top of the boiler opens, and the cylinder fills with steam at atmospheric pressure.  The reason the piston moves up is due to the weight of the pump assembly (not shown) pulling down the rod on the left.

The steam valve closes and a second water valve opens.  This valve sprays gravity-fed water into the cylinder, condensing the steam.  As the steam suddenly condenses, it creates a vacuum.  This vacuum pulls the piston back to the bottom of the cylinder, and the process repeats.  The steam and water valves would be operated by linkages connected to the piston, so that they would open and close at the correct point in the cycle.  Very clever! 

There was also a third valve to drain water from the bottom of the cylinder that is not shown in this animation.



But while this engine worked well enough, there was a great deal of room for improvement. 

The biggest problem with this design is that the cylinder and piston are cooled down a great deal by the spray of water on the down-stroke.  Thus when steam is admitted for the next cycle, a lot of the steam condenses on the cold metal parts.  This design, while very creative, wasted a great deal of steam re-heating the cylinder/piston assembly each stroke, and was therefore very inefficient.

Meet James Watt.

His brilliant contribution to steam power was to condense the steam in a different vessel.  He did this by connecting the bottom of the cylinder to a separate vessel called a condenser.  His condenser was a large pipe submerged in water

Another huge improvement he made was to keep the cylinder at the same temperature as the incoming steam by surrounding it with a "steam jacket" - passages in the cylinder wall that steam continously flowed through and heated.

The animation below shows the improvements.  Steam from the boiler enters the "steam jacket", a space between and inner and outer cylinder.  It enters the bottom of the cylinder when the upper valve is open and the lower valve is shut.  The piston moves up (again due to the weight of the equipment on the left side of the rocker arm, not steam pressure).  When the piston reaches top of travel, the steam valve shuts and the valve to the condenser opens.   As the steam condenses in the condenser, it places the bottom of the cylinder under vacuum and pulls the piston down - the power stroke.  The process then repeats.





Lastly, to have practical, useful power, we need to have rotary motion.  If we attach a large wheel with lots of mass to keep it in motion between pulses, we have the basic technology for the industrial revolution!





Very Basic Steam Turbine

Steam Turbines come in an infinite number of sizes and designs.  It's amazing how many ways a machine can be designed to extract energy from expanding steam.

The oldest known design dates from the Greeks about 10 yrs A. D., and is known as Hero's Aeolipile (How you pronounce that, I am not sure).  Here is a drawing of one from antiquity:




Apparently a few of these were made from bronze, and were simply curiousities.  Heat from the fire below boils water in the bronze reservior.  Steam from the boiling water is carried up in pipes to a hollow ball at the top.  The pipes that carry the steam up to the ball support it, but also allow the ball to rotate freely on the axis.  The steam is then allowed to escape from the ball via two nozzles, spinning the ball.

A couple of interesting things to note about this design: 
  1. This design would not be useful as anything other than a curiousity because it has no output shaft.
  2. The very first steam turbine design is a reaction turbine.
Item #1 probably prevented the steam age from happening for 1800 years.

Item #2 is interesting because although Issac Newton didn't explain the Third Law of Motion until 1687, the process was understood long before then!  Newton's third law is usually paraphrased as "For every action there is an equal and opposite reaction", thus the term "reaction" turbine.

Reaction turbines achieve movement (and actual work) by squirting steam through nozzles, like our Aeolipile above.  The steam squirts out, and the reaction force causes the ball to spin in the opposite direction from the steam jet.

The other type of turbine is called an impulse turbine.  In this design, steam is directed at a set of blades on a shaft and bounced off of them.  This provides an "impulse" to move.  Below is a simple diagram showing the difference between the two basic designs.


In other posts I will decribe a little of the evolution of piston steam engines, steam turbines, and show some intersting modern designs and cutaways.

Wednesday, April 10, 2013

Beer and Deer

We have a few families of deer (fawns and does) that we have been feeding through the winter months.  They come around for breakfast and dinner, when we pour out a pitcher of corn.  They are not quite tame.  You cannot get very close to them, but they are also not too concerned when they see a human nearby. 

The brew is a Blue Moon Seasonal called Valencia Grove Amber.  Quite a tasty orange-wheat flavor.

Tuesday, April 02, 2013

Another Gas Turbine Cutaway

Since the Gas Turbine Cutaway post appears to be one of the most-viewed on the blog, here's another one.  This is a really odd design that Alstom came up with back in the 1980s. 

It's a pretty cool design, and it kind of reminds me of a model airplane engine.  This is the Alstom GT11N.  I think it puts out about 100 Megawatts.  What's interesting about this design is that combustion occurs outside of the turbine proper, in a "silo combustor". 

Air is drawn in at the right side in this picture, compressed in several stages, and then it flows up just inside the wall of the the large cylinder at the center.  This pre-heats the combustion air while keeping the inner combustion liner cool and preventing it from melting.  The air is blended with natural gas (or fuel oil) at the top of the silo combustor.  The fuel/air mixture is burned as it travels down in the silo, then the hot gases are routed into a donut called the hot gas casingthat spreads them all around the turbine shaft, where they are allowed to expand and drive the turbine.


Here is another picture (actually an advertisement) that shows some of the parts in the gas flowpath.
I don't know much more about this machine than this.  It doesn't appear to have been too successful commercially, because there isn't much on the web about them, and the axial combustion scheme appears to be the dominant technology.  Still, I thought this was a cool idea...

 


Still exercising!

Yep, I am still exercising.

And still brewing beer.

I've decided there isn't a lot of synergy with these two hobbies.  That is to say, one doesn't really add to the strength of the other. 

My other hobby is riding motorcycles, and there isn't much synergy there either.  I do fit into my leather jacket a lot better this year however :)

Speaking of which, I rode the bike for the first time this season today.  Commuted to work on it - boring!!! (no twisties to wind through).   It didn't want to crank either.  Guess that cool lithium ion battery wasn't quite the bomb I thought it was.  It is light though.  Just feels like an empty plastic battery case.

Anyhoo...  I needed to get a post up!  Here's a gratuitous bike pic :)