Small Scale CHP Steam Engine System

Just sharing a project I've been working on slowly for a couple years. I am now testing a steam generator that will be used to power a small piston steam engine of a unique design. I previously assembled and tested a small wood gasification furnace that showed a very clean burn at high temperature. The steam generator will eventually be wood fired. But I am currently testing with a propane burner for convenience.

I've tested the unit over the last month making steam up to 1000F and up to 1200 psig. That noted, the engine specifications call for around 500 psig superheated steam up to about 700F. I'm just stress testing the unit. No problems so far. I will start assembling the steam expander after steam generator testing is completed.

The design philosophy of my project calls for minimizing costs (both parts AND fabrication requirements). To this end, the design is unique for repurposing existing mass-produced components in novel ways. Unfortunately, I cannot share specifics on the design. But if those active on the forum here show interest, then I will share any material progress and answer whatever questions I can.

Marcos Buenijo

Is this a monotube boiler?

That's pretty high operating pressures for a homebrew system (not that you aren't competent to build a high pressure system, but 1200 psig is right on up there).

I guess I could check steam tables.  Even though I should, I don't remember exactly where the critical point of water lies - where liquid and gas phases essentially merge and are indistinguishable.  It's been too long since I did any serious thermo stuff.  But, if that is below the critical point, any substantial volume of liquid water would expand quite vigorously as it flashes to vapor if the pressure dropped due to a leak.

At least monotube boilers have a comparatively small volume of water at the high pressure and temperature, so the consequences of a catastrophic failure are proportionally lower.

High pressure steam makes me nervous, but that's me, not you.

A few years ago, my brother was scheming on a sort of CHP system (scrap diesel dozer engine coupled to a generator head; waste heat to heat his house in winter, shaft power to electrical generation for net metering - kind of the opposite of what most people mean when they say CHP).  Given our local prices for electricity (among the highest in the Lower 48, and pretty dang high for the entire US), lots of power generating schemes look pretty reasonable if one is willing to make the upfront investment.  Unfortunately, his domestic situation changed and put the kibosh on his immediate CHP plans.  He now owns a side-hill property with a small perennial stream flowing through it, and seems to be aiming toward a micro hydro setup.  I haven't quite settled on what would be the best solution for me, as backup power for a grid down situation and to help mitigate the high cost of retail electricity.  For short term emergency use, we have a Honda generator, but I'd like to find a longer term solution (or even a defense-in-depth solution with multiple power sources).

Anyway, I, for one, am interested in what you have going with this CHP system.

Kevin Olson wrote:Is this a monotube boiler?

That's pretty high operating pressures for a homebrew system (not that you aren't competent to build a high pressure system, but 1200 psig is right on up there).

I guess I could check steam tables.  Even though I should, I don't remember exactly where the critical point of water lies - where liquid and gas phases essentially merge and are indistinguishable.  It's been too long since I did any serious thermo stuff.  But, if that is below the critical point, any substantial volume of liquid water would expand quite vigorously as it flashes to vapor if the pressure dropped due to a leak.

At least monotube boilers have a comparatively small volume of water at the high pressure and temperature, so the consequences of a catastrophic failure are proportionally lower.

High pressure steam makes me nervous, but that's me, not you.

A few years ago, my brother was scheming on a sort of CHP system (scrap diesel dozer engine coupled to a generator head; waste heat to heat his house in winter, shaft power to electrical generation for net metering - kind of the opposite of what most people mean when they say CHP).  Given our local prices for electricity (among the highest in the Lower 48, and pretty dang high for the entire US), lots of power generating schemes look pretty reasonable if one is willing to make the upfront investment.  Unfortunately, his domestic situation changed and put the kibosh on his immediate CHP plans.  He now owns a side-hill property with a small perennial stream flowing through it, and seems to be aiming toward a micro hydro setup.  I haven't quite settled on what would be the best solution for me, as backup power for a grid down situation and to help mitigate the high cost of retail electricity.  For short term emergency use, we have a Honda generator, but I'd like to find a longer term solution (or even a defense-in-depth solution with multiple power sources).

Anyway, I, for one, am interested in what you have going with this CHP system.

Hi Kevin. Yes, this is a monotube formed from 1/4" 316SS tubing. It gets up to temperature in less than 5 minutes from cold. The dangers presented by steam engine systems are primarily from traditional boilers for two reasons: (1) they maintain a large mass of saturated water under pressure, and (2) they fail catastrophically (the boiler shell rips apart to expose the saturated water to atmosphere - BOOM!). By contrast, a monotube has a relatively small mass of saturated water, and failures take place in a localized point. It takes time for the contents of the tube to move through the long tube and escape. So, no explosion. What scares me is getting burned with superheated steam. So, I shield the steam fitting, and I used goggles, face shield, long sleeves, and high temperature gloves.

Thanks for sharing your brother's story. I would not hesitate to develop micro hydro if I had suitable property. That's the holy grail for off grid power.

I previously built and tested a small wood gasification furnace as a proof of concept before I started developing the steam engine system. The temperature was high (on the order of 2000F), it was very clean (no odor and I could place my face a couple of feet above the combustion chamber with no tearing of the eyes), and I was able to precisely control the burn rate from a low of about 15,000 btu/hr up to about 50,000 btu/hr using a blower fan on a variac. A final prototype system calls for controlling the furnace blower with steam line temperature feedback possibly with a PID controller (TBD). The furnace used dry wood chunks up to 2" across. But it would have worked well on dry wood chips as well.

One aspect of my design might interest some. I put emphasis on harvesting otherwise wasted heat (the "CHP" aspect). Steam exhausted from the engine is condensed in a compact water-cooled heat exchanger to provide heated water for a hydronic heating system. But I also designed the system to generate low pressure steam without having to operate the engine. This requires only a low power DC blower for the furnace and a low power DC pump to distribute the heated water.

My system might be considered as a wood gasification boiler that can also provide all electricity demanded by the home. Configuring the system for battery charging requires only closing a couple of small valves.

M Buenijo wrote:Just sharing a project I've been working on slowly for a couple years. I am now testing a steam generator that will be used to power a small piston steam engine of a unique design. I previously assembled and tested a small wood gasification furnace that showed a very clean burn at high temperature. The steam generator will eventually be wood fired. But I am currently testing with a propane burner for convenience.

I've tested the unit over the last month making steam up to 1000F and up to 1200 psig. That noted, the engine specifications call for around 500 psig superheated steam up to about 700F. I'm just stress testing the unit. No problems so far. I will start assembling the steam expander after steam generator testing is completed.

The design philosophy of my project calls for minimizing costs (both parts AND fabrication requirements). To this end, the design is unique for repurposing existing mass-produced components in novel ways. Unfortunately, I cannot share specifics on the design. But if those active on the forum here show interest, then I will share any material progress and answer whatever questions I can.

Marcos Buenijo

Do yuo have any info on the gasifier heat source?
Thanks,  David

David Baillie wrote:
Do yuo have any info on the gasifier heat source?
Thanks,  David

David, the "gasifier" was a small wood gasification furnace that I assembled. The fuel was small wood chunks 1-2" across. Mostly pine, but some eucalyptus as well. I made this furnace and tested it before I began working on the steam engine system. I did this to first verify that I can make a clean burning high temperature wood furnace with a controllable heat rate.

The following taken from a previous comment:

M Buenijo wrote:I previously built and tested a small wood gasification furnace as a proof of concept before I started developing the steam engine system. The temperature was high (on the order of 2000F), it was very clean (no odor and I could place my face a couple of feet above the combustion chamber with no tearing of the eyes), and I was able to precisely control the burn rate from a low of about 15,000 btu/hr up to about 50,000 btu/hr using a blower fan on a variac. A final prototype system calls for controlling the furnace blower with steam line temperature feedback possibly with a PID controller (TBD). The furnace used dry wood chunks up to 2" across. But it would have worked well on dry wood chips as well.

BTW, my wood furnace and steam generator design was inspired by rocket mass heater design. However, as a wood gasification furnace, it generates the fuel gas and heated secondary air (for complete combustion) separately. And it uses a blower fan to vary the heat output.

M Buenijo wrote:BTW, my wood furnace and steam generator design was inspired by rocket mass heater design. However, as a wood gasification furnace, it generates the fuel gas and heated secondary air (for complete combustion) separately. And it uses a blower fan to vary the heat output.

Thank you. I am aware of gasifiers I was wondering if you had documented the build.

David Baillie wrote:
Thank you. I am aware of gasifiers I was wondering if you had documented the build.

Here is a pic of the old test furnace. I did not document the build as there are aspects of the design I am unwilling to share.

I gladly note the OP's awareness of the hazards involved. I have worked in industries involving high pressure processes and steam generated electricity. Steam is unforgiving, and steam accidents are potentially life-altering.

May I flip the question? What is the rotational energy intended for? Is there a safer and more friendly technology like a Stirling engine that could solve the problem without the hazards?

Douglas Alpenstock wrote:I gladly note the OP's awareness of the hazards involved. I have worked in industries involving high pressure processes and steam generated electricity. Steam is unforgiving, and steam accidents are potentially life-altering.

May I flip the question? What is the rotational energy intended for? Is there a safer and more friendly technology like a Stirling engine that could solve the problem without the hazards?

The concerns about safety always come up with steam power - and for good reasons. A lot of people have been hurt by steam energy. The vast majority of injuries and deaths were caused by boiler failures or failure in some other form of large pressure vessel. This is precisely why I am using a monotube steam generator made from small diameter tubing. I have a good basic foundation in steam power (U.S. Navy nuclear power steam plant operations as well as formal training and work experience with high pressure air systems and hydraulics).

The potential hazard here is getting burned by superheated steam. Also, this should not be operated in a confined space. But concerns about an explosion hazard are simply misplaced. A final system will have a pressure relief on the steam side as well as a high pressure cutoff switch to de-energize the furnace blower. This is not to protect personnel from an explosion due to high pressure, but to protect the system from failure due to high pressure.

The engine crankshaft will directly couple to an alternator to maintain charge on a battery system. Most of the heat in the steam exhaust will be used to heat water for heating applications. I've done a lot of research into Stirling engines. A steam engine system based on my design is superior for many reasons.

Back in 2010 - 12 I built a working low pressure steam generator also using an alternator to make electricity. It was also made from repurposed parts. A twin cyl air compressor made by Emglo IIRC.  My steam valve was a log splitter valve which worked brilliantly.  100psi supplied about 40 amps at 14 volts. I built it and posted a couple short clips on youtube and then gave it up as to dangerous to let unknowing people copy it, as was my original purpose. To share the knowledge is what I was after and then decided most people didn't have the sense to be safe! So I packed it away. I could get it going again in a day or three if ever needed.

My point is be CAREFUL with what you share so anyone who doesn't understand gets maimed or killed!

larry kidd wrote:Back in 2010 - 12 I built a working low pressure steam generator also using an alternator to make electricity. It was also made from repurposed parts. A twin cyl air compressor made by Emglo IIRC.  My steam valve was a log splitter valve which worked brilliantly.  100psi supplied about 40 amps at 14 volts. I built it and posted a couple short clips on youtube and then gave it up as to dangerous to let unknowing people copy it, as was my original purpose. To share the knowledge is what I was after and then decided most people didn't have the sense to be safe! So I packed it away. I could get it going again in a day or three if ever needed.

My point is be CAREFUL with what you share so no one who doesn't understand gets maimed or killed!

I AGREE. This is partly why I will not share specifics about the project. The vast majority of people are not qualified to work with steam power safely. That noted, even with my previous training and experience, I would never attempt to assemble and operate a large steam boiler. I think I could do it safely. But the consequences of a failure are too severe.

NOTE: Part of the reason for using a compact steam generator is safety. But higher efficiency is another reason. A good steam generator can be a great deal more efficient than traditional boiler designs. But even more important for efficiency in a small engine is the ability to safely generate steam at much higher pressure and temperature. A small steam engine limited to saturated steam at modest pressure will not be efficient. The engine I am working on is targeting 20% cycle efficiency.

M Buenijo, I think your responsible cautions need to be heard. Too often there is somebody trying to build steam in a discarded propane tank. This is also known as shrapnel. Not good.

How do you propose to maintain a constant heat and constant flow to power the shaft?

Douglas Alpenstock wrote:M Buenijo, I think your responsible cautions need to be heard. Too often there is somebody trying to build steam in a discarded propane tank. This is also known as shrapnel. Not good.

How do you propose to maintain a constant heat and constant flow to power the shaft?

I've seen such contraptions on YouTube, and I cringe every time. They're not only dangerous, but these nonsense projects produce no useful output. And they never will.

My test rig is designed to develop the steam generator and steam expander. I am operating a plunger pump at a precise speed using a gearmotor on a PWM controller. The steam generator is heated with a propane burner. I have temperature indication of the steam line. In practice, I just fire up the propane burner to the desired output, then I adjust the pump speed to keep steam line temperature in the desired range. I control system pressure as follows:

The steam line connects directly to a tubing coil (also 1/4" stainless tubing) placed inside an 8 gallon stainless pot still and submerged in water. This condenses all the steam. The steam line fitting is well inside the pot still. The steam line is insulated with three ceramic sleeves, and the line extends through a hole in a stainless pot that serves as a shield in case the fitting leaks (which happened once previously because I did not install the fitting correctly). The condensate end of the condenser coil has a needle valve and pressure gauge that I use to set system pressure (I installed these where the heating element for the still normally is placed). An adjustable relief valve would be better. But these are rather expensive. Last time I ran it, I operated for one hour without intervening. It was very stable. The pressure was about 550 psig, and the temperature stayed between 750F and 800F.

Interesting! Though assuming this end of the tea kettle works, how do you propose to connect it to the wood fired side? Quite a lot of variables.

M Buenijo wrote:

Douglas Alpenstock wrote:I gladly note the OP's awareness of the hazards involved. I have worked in industries involving high pressure processes and steam generated electricity. Steam is unforgiving, and steam accidents are potentially life-altering.

May I flip the question? What is the rotational energy intended for? Is there a safer and more friendly technology like a Stirling engine that could solve the problem without the hazards?

The concerns about safety always come up with steam power - and for good reasons. A lot of people have been hurt by steam energy. The vast majority of injuries and deaths were caused by boiler failures or failure in some other form of large pressure vessel. This is precisely why I am using a monotube steam generator made from small diameter tubing. I have a good basic foundation in steam power (U.S. Navy nuclear power steam plant operations as well as formal training and work experience with high pressure air systems and hydraulics).

The potential hazard here is getting burned by superheated steam. Also, this should not be operated in a confined space. But concerns about an explosion hazard are simply misplaced. A final system will have a pressure relief on the steam side as well as a high pressure cutoff switch to de-energize the furnace blower. This is not to protect personnel from an explosion due to high pressure, but to protect the system from failure due to high pressure.

The engine crankshaft will directly couple to an alternator to maintain charge on a battery system. Most of the heat in the steam exhaust will be used to heat water for heating applications. I've done a lot of research into Stirling engines. A steam engine system based on my design is superior for many reasons.

It's good to hear you have the training to keep it safe. Historically the reason stirlings became so popular for small scale jobs was due to the danger of wet steam large volume steam boilers and even then peoples' fear of wet steam disasters which were very real. The Monotube is certainly a good choice which most of the steam cars evolved to back in the day. When I did all my experimentation the conclusion I came to was that efficiency wise I was better Running engines directly off the gasifier and recouping the gasifier heat for water. That was before the price of solar panels dropped to their ridiculously low cost now which destroyed a lot of the economic argument for alternative power either wood or wind.  There are quite a few steam enthusiasts on the site www.driveonwood.com  As well as a lot of open sourced gasifier designs. It looks like you have made a fema derivative type unit which as a good solid design for basic heat applications. I ended up going the charcoal gasifier route myself for powering small engines. The small engine section has a lot of good test examples to consider.  I look forward to seeing how the project goes forward and what kind of end efficiency you achieve.
Cheers,  David Baillie

Douglas Alpenstock wrote:Interesting! Though assuming this end of the tea kettle works, how do you propose to connect it to the wood fired side? Quite a lot of variables.

The wood furnace will be incorporated after the expander is working (assuming I ever get it working). The wood furnace test unit could be controlled as easily as a propane burner (no BS - it was HOT, clean, and very precise from about 15,000 btu to 50,000 btu max).

David Baillie wrote:It's good to hear you have the training to keep it safe. Historically the reason stirlings became so popular for small scale jobs was due to the danger of wet steam large volume steam boilers and even then peoples' fear of wet steam disasters which were very real. The Monotube is certainly a good choice which most of the steam cars evolved to back in the day. When I did all my experimentation the conclusion I came to was that efficiency wise I was better Running engines directly off the gasifier and recouping the gasifier heat for water. That was before the price of solar panels dropped to their ridiculously low cost now which destroyed a lot of the economic argument for alternative power either wood or wind.  There are quite a few steam enthusiasts on the site www.driveonwood.com  As well as a lot of open sourced gasifier designs. It looks like you have made a fema derivative type unit which as a good solid design for basic heat applications. I ended up going the charcoal gasifier route myself for powering small engines. The small engine section has a lot of good test examples to consider.  I look forward to seeing how the project goes forward and what kind of end efficiency you achieve.
Cheers,  David Baillie

The main value of my limited training and experience is appreciating the potential for danger and understanding basic thermodynamics. But very little actually carries over to small scale steam power which is a lost art. People who think they understand it often do not. My research led me to appreciate the old school engineers. They had to be SMARTER because they had access to fewer resources.

On "efficiency": My primary design goal is mechanical simplicity, reliability, and ease in repairs. Efficiency is important only in the sense that is has to be EFFICIENT ENOUGH to be useful. I believe an overall efficiency of 10% can be achieved (fuel lower heating value to DC battery charging). But I consider the HEAT from the unit as more valuable, and this is why I designed the unit to generate low pressure steam without running the engine. It makes the most sense in regions that see extended and very cold winters. But absolutely use solar panels when the sun is available! Why run the engine unnecessarily?

I have two expander designs. The first does not require oil lubrication. The second is a more traditional design with oil lubrication and an oil separator. I already built the oil pump and I have a separator design. I expect the oil lubricated version can be more efficient. But I would prefer to see the oil free expander work well.

Oh, I realized I didn't mention this previously. I came upon a very simple diesel burner design a while back that I believe can be retrofitted fairly easily into my steam generator design. The ability to make use of fuel oils makes sense as these fuels store for long periods, they have very high energy density, are a lot safer than gasoline or propane, and they are sometimes available at very low cost.

Plans for a small monotube boiler may be found near the bottom of the page, here:
http://www.firedragon.com/~kap/Educator/
It's made from 1/4" copper tubing, not capable of such high pressures as yours, I'm sure, but easier to bend, and cheaper than 300-series stainless, too.  So, maybe still useful for someone.

This monotube boiler was for intended for the small steam runabout described at the top of the page.  The whole thing was a high school shop project, hence the "Educator" name.  The designer, Richard J. Smith, had several US patents for steam related inventions, including automated controls for the monotube boiler, a rotary valve design, and one for the steam generator itself.  With the controls system, Smith was trying to provide better responsiveness of a monotube boiler to variable load.

I haven't built this, so have no direct experience.  But, it got stashed away on the terabyte archive of potentially useful ideas, in case the need (or opportunity!) arises.  I'd thought that I might be able to run a line shaft shop with it under exigent circumstances, using a small horizontal shaft gasoline engine, converted to a bump valve steam engine, should the need ever arise.  (A bump valve engine uses an inlet check valve in place of the spark plug, with a pin or screw in the crown of the piston to "bump" open the check valve when near top dead center).  Crude, simple, inefficient, but possibly achievable under duress.  My machine tools are somewhere between vintage and ancient, so quite amenable to this scheme.

Kevin Olson wrote:Plans for a small monotube boiler may be found near the bottom of the page, here:
http://www.firedragon.com/~kap/Educator/
It's made from 1/4" copper tubing, not capable of such high pressures as yours, I'm sure, but easier to bend, and cheaper than 300-series stainless, too.  So, maybe still useful for someone.

This monotube boiler was for intended for the small steam runabout described at the top of the page.  The whole thing was a high school shop project, hence the "Educator" name.  The designer, Richard J. Smith, had several US patents for steam related inventions, including automated controls for the monotube boiler, a rotary valve design, and one for the steam generator itself.  With the controls system, Smith was trying to provide better responsiveness of a monotube boiler to variable load.

I haven't built this, so have no direct experience.  But, it got stashed away on the terabyte archive of potentially useful ideas, in case the need (or opportunity!) arises.  I'd thought that I might be able to run a line shaft shop with it under exigent circumstances, using a small horizontal shaft gasoline engine, converted to a bump valve steam engine, should the need ever arise.  (A bump valve engine uses an inlet check valve in place of the spark plug, with a pin or screw in the crown of the piston to "bump" open the check valve when near top dead center).  Crude, simple, inefficient, but possibly achievable under duress.  My machine tools are somewhere between vintage and ancient, so quite amenable to this scheme.

I'm familiar with that project. Karl Peterson worked with Smith to design and build that vehicle. I'm pretty sure Karl is still with us. He might still be with the Steam Automobile Club of America. http://kimmelsteam.com/smith-petersen-work.html

This video shows what is perhaps the simplest possible way to assemble a monotube steam generator. It uses 300 feet of 3/8" ACR copper tubing. The output is significant with roughly 3 KG of water vaporized each minute! This would be suitable for generating saturated or very slightly superheated steam at modest pressures. A good compound engine can make a reasonably efficient system if everything is optimized.



NOTE: Steam power can be dangerous. But most of the danger is eliminated by simply going to a monotube steam generator in lieu of a traditional boiler.

BUMP VALVE EXPANDER: These can be highly efficient. Two of the best examples include the Jay Carter engine and the White Cliffs Solar Steam engine. Both were measured at up to 23% cycle efficiency (meaning 23% of the heat added to the feed water to make steam was converted to shaft work). My steam expander design is similar to the Jay Carter engine. The White Cliffs engine used ball bearings.

White Cliffs engine: https://wiki.opensourceecology.org/wiki/Steam_Engine_Design/White_Cliffs

Jay Carter engine: https://www.steamautomobile.com/wsa/tutorial/index_18.htm

Thanks for the links.  This is great stuff.

Kevin

Two quick points from me.  1)  I know nothing at all about this subject 2)  I'm fascinated by it, and would love it if someone comes up with a safe, relatively simple, DIY steam engine, powered by wood, for home use.

I'm very interested in hearing more about this.

Yet another rabbit hole, down which to fall...

Some additional details and photos of Jay Carter's setups can be seen in this NASA publication:
https://ntrs.nasa.gov/api/citations/19830002255/downloads/19830002255.pdf

Trace Oswald wrote:Two quick points from me.  1)  I know nothing at all about this subject 2)  I'm fascinated by it, and would love it if someone comes up with a safe, relatively simple, DIY steam engine, powered by wood, for home use.

I'm very interested in hearing more about this.

There is one small company in Australia developing a very good engine designed by the late Ted Pritchard. I don't know a lot of specifics about their design. But I do know it is high compression double-acting uniflow. Fully recompressing the residual exhaust steam up to steam generator pressure before the steam inlet valve opens does a lot to optimize efficiency. The bump valve design only partly compresses the steam. Therefore, the relatively low pressure and lower temperature recompressed steam mixes with the incoming steam when the inlet valve opens. This reduces the temperature of the steam charge before expansion begins thereby reducing the efficiency somewhat (this is called "clearance volume" loss). It is one of the seven losses of a steam engine. The steam pressure in that engine is around 300 psig and highly superheated to 750F. The cycle efficiency is at least 20% (does not include thermal losses from the steam generator or alternator losses).

My design attempts to address some of the problems I perceive with this unit. Don't get me wrong. The engine is better than anything I can make. But I consider it to be too bulky, too complicated, and more powerful than necessary for most applications. I'm trying to make something that is compact - even portable - and extraordinarily simple mechanically.

Kevin Olson wrote:Yet another rabbit hole, down which to fall...

Some additional details and photos of Jay Carter's setups can be seen in this NASA publication:
https://ntrs.nasa.gov/api/citations/19830002255/downloads/19830002255.pdf

Yeah, I read about these tests a while back. I recall the engine showed a peak overall conversion efficiency of slightly more than 20% in generating AC electricity (the auxiliary loads were driven by electric motors, so these loads were deducted to yield a net figure). Other systems showed higher efficiency. But this system was easily the simplest and the most compact. Personally, I don't see a small solar heat engine as competitive with photovoltaics. But a medium scale system that uses low cost thermal storage could be competitive. The real potential for a small steam engine system is residential scale CHP with primarily locally obtained biomass fuels.

A guy did his Engineering thesis on the White Cliffs engine in 2010. I have the document. Good pics and description of the unit. It's really funny that the premise of his thesis was to investigate failure of the valve lift pins attached to the pistons. But later in the document he mentioned that they found a set of lift pins that were TOO LONG. They concluded that the installed set of pins were almost certainly too long when they were first installed. The "failure" was caused by the starting motor forcing the pins against the mechanical stops which crushed the ends of the pins. Kinda hilarious actually. By all accounts I've been able to find, the expander was reliable for the 5 years or so that it operated. Although, the complete system had intermittent problems (after all, it was experimental). We now have better ways to configure such things.

https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?13

http://kimmelsteam.com/smith-petersen-work.html

If you reference this page and scroll down a bit, you will see some data on testing a Mercury outboard two-stroke engine converted to a steam engine using bump valves. The data provided is as follows:

“Merc” 4 cylinder Engine on
cradle type E, Fan Brake for test,
Pressure: ~200 psig
Temp:     ~390° F.
RPM:     ~200
Exhaust Pressure – Atmospheric: (14.7)
Water Rate this test: 23.7 lbs/H.P. HR
—R.Smith

Assuming the data is accurate (and based on Smith's work I imagine it's reasonable), this puts the cycle efficiency at around 10.5% which is approximately 75% of theoretical maximum Rankine cycle efficiency. The reader may not likely appreciate this, but I'll just say this is pretty nuts for a small steam engine. A typical double-acting slide valve steam engine expander would show around 50-55% of theoretical maximum under these conditions. So, a good single-acting uniflow can provide 50% MORE work from the exact same steam source. Furthermore, the uniflow design is simpler mechanically.

The White Cliffs engine using saturated steam at around 550 psig (about 480F) and exhausting to a partial vacuum at around 5 psia showed around 73% of theoretical maximum (actual cycle efficiency was 16%). The cycle efficiency increases as the steam temperature increases (i.e. more superheat). However, the % of theoretical maximum tends to fall mostly due to clearance volume losses. For example, the White Cliffs engine showed about 65% of theoretical maximum efficiency when the steam temperature increased to 780F (cycle efficiency was measured at 21.9%). Furthermore, the efficiency gains start to flatline after about 150F superheat.

The lesson I got from this is don't bother trying to use crazy hot steam. You get diminishing returns and the additional thermal stress on the engine isn't worth it. I plan to operate at about 500 psig and no higher than 700F. This can yield a cycle efficiency of 20%.

ADDENDUM: My strategy is to adopt certain criteria that provide (1) increased safety, (2) increased efficiency, (3) increased mechanical simplicity, and (4) lower cost. The criteria include:
1. Gasification furnace - Cleaner and much higher temperatures for more efficient heat transfer
2. Monotube steam generator - Far safer than a firetube boiler, and a lot more efficient. A typical firetube boiler is often 60-70% efficient. Whereas, the monotube can be 80-90%.
3. Single-acting bump valve uniflow - See previous discussion. These are both simpler and more efficient than simple traditional steam expanders.
4. Engine designed for a constant relatively low output for battery charging (i.e. no load following and no speed control)
5. Repurposing existing low cost mass-produced components where practical.

M Buenijo wrote:https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?13

I tried to follow this link, but it didn't work for me ("Database connection failed...").  I tried site searches, and also dumped that URL into the Wayback Machine, but still no joy.

Any thoughts?

Anyway, thanks for sharing your obviously deep practical knowledge on this sunject.  I've only ever played with toy model steam engines, though we do have a small 0-4-0 saddle tank switcher locally which was operable, but is currently laid up for repairs.

Kevin Olson wrote:

M Buenijo wrote:https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?13

I tried to follow this link, but it didn't work for me ("Database connection failed...").  I tried site searches, and also dumped that URL into the Wayback Machine, but still no joy.

Any thoughts?

Kevin, it's not coming up for me at the moment either. However, it was available when I posted it. If it takes you to a page with any links, then try the "steamstuff" link as this happened to me. I will try to find a better link or download it as it's a good resource.

https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?1

Looks like the document is available now. I think the forum where it was available was down for maintenance. Anyway, the main value of the document in my opinion are the few pics that illustrate the expander configuration.

Kevin Olson wrote:

M Buenijo wrote:https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?13

I tried to follow this link, but it didn't work for me ("Database connection failed...").  I tried site searches, and also dumped that URL into the Wayback Machine, but still no joy.
Any thoughts?
Anyway, thanks for sharing your obviously deep practical knowledge on this sunject.  I've only ever played with toy model steam engines, though we do have a small 0-4-0 saddle tank switcher locally which was operable, but is currently laid up for repairs.

 I tried the link and it is working well.  I clicked on the word "steamautomobile" which highlighted but the rest didn't.  An interesting read.

Here is the "big dish" described in the document:

M Buenijo wrote:https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?1

Looks like the document is available now. I think the forum where it was available was down for maintenance. Anyway, the main value of the document in my opinion are the few pics that illustrate the expander configuration.

Thank you.

Retrieved and saved.  Patience is indeed a virtue...

So, this expander/engine used 3 bump valves per cylinder, operated in parallel, with pretty typical looking ball bearing check valves.  Perhaps I should dig into the paper (I haven't yet, so I may be demonstrating my willful ignorance, now!), but was this a conscious choice on performance grounds, versus the Jay Carter "Chinese hat" style of valves?  Obviously, the ball style is easier to manufacture (assuming you can just buy carbide balls from McMaster Carr or wherever).  A quick internet search didn't turn up carbide countersunk washers to use as seats, but maybe hardened steel would be adequate.  I thought someone might have commodity kinematic ball supports with a conical contact available, but I didn't spot any on the quick - just Vs and flats.  I'm guessing that a bit more fine tuning of steam admission could be had be using differing pin lengths for each valve.  Maybe not usefully so, but possible, nonetheless.

Do you have direct experience with the ball style of valve, versus a conical lightweight Carter-style valve, especially as regards durability?  I'd seen some chatter indicating ball valves should be serviced every few hundred hours of operation (the exact figure varied from source to source, but this is the referenced order of magnitude).  For my current daily driver, that would be roughly twice per year.

I am now somewhat taken with this idea of using a high speed engine like the Carter setup to drive a conventional automobile through a manual transmission driveline.  Previously, I'd only considered low speed, high torque, direct drive for motive power, with all reversing in the valve gear, a la locomotive.  Of course, you could just select a gear appropriate for the immediate circumstance at hand, then drive, like with a tractor, with a low speed engine, but for a road vehicle, this isn't as convenient.  Mimicking the speed characteristics of the original IC engine (and making power by turns rather than brute force torque) seems more straightforward, and better suited to road use.

Work trucks with blown engines or smoked automatic trannies are readily available (e.g. my brother has a 4WD one ton with an automatic with bad dentition, just sitting, right now - an old Borg Warner 4-speed replacement could be had reasonably, is dump truck grade with the larger input shaft and beefier clutch, and rebuild parts are cheaply available).  I know of an old 2WD stake body one ton Ford that could be had for a song.  Medium duty trucks with dead engines are often reasonably priced - older Internationals, Top Kick/Kodiaks,, etc.  With any luck, am overkill twin countershaft transmission (RoadRanger or similar) will come in it.  For medium duties, bell housings are likely to be standard SAE, so making an adapter plate should be fairly simple.  This would allow for use of standard PTO equipment off the transmission or transfer case (wet kit, mechanical winch, what-have-you) from commodity/salvage yard parts.

Plenty of projects are in line ahead of this (e.g. a timber framed shop cum garage), but it seems like a good one to add to the queue.  A work truck that can be easily converted, once set up for steam, to run on most any fuel (wood chips/hog, coal, black oil, kerosene, used Stoddard solvent, even gasoline - and a Pons+Fleischman Mister Fusion, eventually!) by swapping or adjusting the burner assembly could be downright handy under exigent circumstances.  Obviously, the best time to do such a project is well before you actually need it...

One additional question (well, for now!):  how can engine braking be accomplished with a bump valve setup?  Just cut steam to the steam chest (manual ball valve or whatever)?

With standard reciprocation steam valve gear, the valve timing can be adjusted to effect this by way of the reversing gear  But, no timing adjustment is available with a basic bump valve arrangement.

So, if you have a load of saw logs or cement block pushing you down a hill, this could be like descending grades with diesels before Jacobs Clessie Cummins had his flash of insight, inspired by a descent of terror.  If at all possible, you'd like to stay out of the foundation brakes.  (Edit: Jacobs only manufactures these, but Clessie Cummins was the inventor, after a barely controlled descent down Cajon Pass - https://en.wikipedia.org/wiki/Jacobs_Vehicle_Systems#History ).

Maybe an auxiliary valve lift mechanism, so that steam can be admitted as the piston approaches TDC?  This might be accomplished if the check balls were tooling balls, with an attached stem.  Not sure what all this would require, but could be possible.  Starting to sound like a Jake brake for steam...

Kevin Olson wrote:

M Buenijo wrote:https://steamautomobile.com:8443/ForuM/file.php/1/2574/list.php?1

Looks like the document is available now. I think the forum where it was available was down for maintenance. Anyway, the main value of the document in my opinion are the few pics that illustrate the expander configuration.

Thank you.

Retrieved and saved.  Patience is indeed a virtue...

So, this expander/engine used 3 bump valves per cylinder, operated in parallel, with pretty typical looking ball bearing check valves.  Perhaps I should dig into the paper (I haven't yet, so I may be demonstrating my willful ignorance, now!), but was this a conscious choice on performance grounds, versus the Jay Carter "Chinese hat" style of valves?  Obviously, the ball style is easier to manufacture (assuming you can just buy carbide balls from McMaster Carr or wherever).  A quick internet search didn't turn up carbide countersunk washers to use as seats, but maybe hardened steel would be adequate.  I thought someone might have commodity kinematic ball supports with a conical contact available, but I didn't spot any on the quick - just Vs and flats.  I'm guessing that a bit more fine tuning of steam admission could be had be using differing pin lengths for each valve.  Maybe not usefully so, but possible, nonetheless.

Do you have direct experience with the ball style of valve, versus a conical lightweight Carter-style valve, especially as regards durability?  I'd seen some chatter indicating ball valves should be serviced every few hundred hours of operation (the exact figure varied from source to source, but this is the referenced order of magnitude).  For my current daily driver, that would be roughly twice per year.

I am now somewhat taken with this idea of using a high speed engine like the Carter setup to drive a conventional automobile through a manual transmission driveline.  Previously, I'd only considered low speed, high torque, direct drive for motive power, with all reversing in the valve gear, a la locomotive.  Of course, you could just select a gear appropriate for the immediate circumstance at hand, then drive, like with a tractor, with a low speed engine, but for a road vehicle, this isn't as convenient.  Mimicking the speed characteristics of the original IC engine (and making power by turns rather than brute force torque) seems more straightforward, and better suited to road use.

Work trucks with blown engines or smoked automatic trannies are readily available (e.g. my brother has a 4WD one ton with an automatic with bad dentition, just sitting, right now - an old Borg Warner 4-speed replacement could be had reasonably, is dump truck grade with the larger input shaft and beefier clutch, and rebuild parts are cheaply available).  I know of an old 2WD stake body one ton Ford that could be had for a song.  Medium duty trucks with dead engines are often reasonably priced - older Internationals, Top Kick/Kodiaks,, etc.  With any luck, am overkill twin countershaft transmission (RoadRanger or similar) will come in it.  For medium duties, bell housings are likely to be standard SAE, so making an adapter plate should be fairly simple.  This would allow for use of standard PTO equipment off the transmission or transfer case (wet kit, mechanical winch, what-have-you) from commodity/salvage yard parts.

Plenty of projects are in line ahead of this (e.g. a timber framed shop cum garage), but it seems like a good one to add to the queue.  A work truck that can be easily converted, once set up for steam, to run on most any fuel (wood chips/hog, coal, black oil, kerosene, used Stoddard solvent, even gasoline - and a Pons+Fleischman Mister Fusion, eventually!) by swapping or adjusting the burner assembly could be downright handy under exigent circumstances.  Obviously, the best time to do such a project is well before you actually need it...

I don't think steam power is a good alternative for automotive. But that would be an awesome project! Very challenging! Of course, I put a lot of thought into it previously only because it's interesting. But I don't see myself ever attempting it. I simply don't have the resources. I'm sticking with small scale CHP.

That noted, if you ever decide to actually try this, then you should contact me before you get started as I have some good ideas on steam generator, furnace, and condenser. The expander part is relatively easy - especially when you're considering a system with a highly variable output.

Kevin Olson wrote:One additional question (well, for now!):  how can engine braking be accomplished with a bump valve setup?  Just cut steam to the steam chest (manual ball valve or whatever)?

With standard reciprocation steam valve gear, the valve timing can be adjusted to effect this by way of the reversing gear  But, no timing adjustment is available with a basic bump valve arrangement.

So, if you have a load of saw logs or cement block pushing you down a hill, this could be like descending grades with diesels before Jacobs had his flash of insight, inspired by a descent of terror.  If at all possible, you'd like to stay out of the foundation brakes.

Maybe an auxiliary valve lift mechanism, so that steam can be admitted as the piston approaches TDC?  This might be accomplished if the check balls were tooling balls, with an attached stem.  Not sure what all this would require, but could be possible.  Starting to sound like a Jake brake for steam...

I haven't considered this. Just off the cuff, one possibility is to place something akin to a blast damper (i.e. fast-acting valve) in the steam exhaust line before the condenser. A steam relief in the system can made to lift at a fairly high pressure like say 100 psi. This would fairly quickly increase the exhaust pressure on the steam expanders leading to very high cylinder compression. Additional lines installed in the cylinder heads might include steam relief valves that connect back to the steam exhaust. Again, this is just off the cuff. The idea is the high pressure settings would be significantly less than peak steam operating pressure - so they would not normally lift during normal operation (only braking).

I just completed an extended test run of my steam generator. I operated for two hours with steam temperature maintained at approximately 600F and pressure roughly 500 psig (these are the steam conditions I plan for the first expander test). I measured the condensate mass flow rate to determine the feedwater absorbed almost exactly 40,000 BTU/hr. I measured the steam generator furnace exhaust temperature at 250F. The peak temperature on the steam generator casing near the top was approximately 300F. The top center of the casing where I install a removable plug was approximately 350F. These figures suggest the steam generator is highly efficient. Of course, I'm just ballparking, but these number suggest on the order of 85% efficiency (lhv basis). Assuming this is reality, then a recuperator + additional thermal insulation I have planned for a later prototype could take the efficiency to 90%+. The thermal losses in the steam generator/boiler is the first loss in a steam power plant - so optimizing efficiency there goes a LONG way to increasing overall efficiency.

I suppose I'm tooting my own horn here, but this is quite good - especially considering how simple is the system and how quickly I am able to assemble it.

M Buenijo wrote:I don't think steam power is a good alternative for automotive. But that would be an awesome project! Very challenging! Of course, I put a lot of thought into it previously only because it's interesting. But I don't see myself ever attempting it. I simply don't have the resources. I'm sticking with small scale CHP.

Fixed power, with fairly consistent loads, is a lot easier to do well, for certain.

You've clearly considered this more than have I.  For what reasons do you think that reciprocating steam is a poor choice for an automotive prime mover?  Is it mostly the difficulty of coping with the widely variable load (and the turn down ratio of the burner that entails, though I might have a useful idea on that count, too), on grounds of achievable thermal efficiency, or due to something else (perhaps in addition to these) which I haven't yet properly considered?

Prior to this, for something suitable for a Mad Max, get the serum through to the settlement, EOTWAWKI type of scenario, I had mostly been considering something which could be (or was already) powered by an International DT360 (compact wet linered inline 6, parts commonly available, tunable injection with the Bosch P-pump, and a very stout bottom end) or a Detroit 53 series (acoustic assault, but demonstrably tough, good parts availability, fairly simple and reasonably fuel efficient for a mechanically injected diesel).  The 53 series does have factory Jakes available, but they seem to be upwards of $1,000 USD per hole, a little steep.  The DT360 would need an exhaust valve as no factory Jakes are available.  Both of these could be run on centrifuged/filtered black oil or biodiesel.  A gasifier, with pilot injection, could stretch a limited supply of diesel-ish fuel, with a decrease in rated output (patience!).  The long term maintainability mainly relies on laying in a goodly supply of normal wear parts before disruptions come.

But, reciprocating steam is much simpler mechanically, so it might likely be more maintainable under difficult circumstances.  What has made me leery of steam as a viable option is boiler safety (but this is mostly addressed with a monotube) and the need for everything to be built super stout for a direct drive, high torque setup (fine for locomotives or ships perhaps, where the weight penalty is negligible, but less good for a work truck).  Being able to run at high crankshaft speeds allows for re-use of standard automotive components, which opens up a world of possibilities.  Choose proven stout stuff, with ubiquitous and cheap rebuild components, for the rest of the drive line, and away you go.  Obviously, this is a lot easier to do with a well-chosen body on frame truck (my current GMT 400 cab and chassis isn't ideal for this for a whole host of reasons, despite having been a bargain) and thoughtfully select discrete driveline components, than it is with any modern unibody passenger car.

M Buenijo wrote:That noted, if you ever decide to actually try this, then you should contact me before you get started as I have some good ideas on steam generator, furnace, and condenser. The expander part is relatively easy - especially when you're considering a system with a highly variable output.

This may never come to fruition (as I said, lots of stuff is in line ahead of any such project), but thank you for the offer.

I think I've sufficiently derailed your CHP thread for now!  Thanks for your indulgence of my ignorance.

And now, back to our regularly scheduled programming...