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Modern Steam - Formula S Racecar

Posted by Rick.H 
Re: Modern Steam - Formula S Racecar
May 03, 2021 01:25PM
Better results can be achieved if the fuel is liquid hydrogen.


Due to very high steam temperature (over 2000F)
to turbine efficiency can exceed 50%.
Re: Modern Steam - Formula S Racecar
May 03, 2021 09:43PM
I'll agree that a steam engine needs higher rpm to be competitive -- despite assertions to the contrary, steam engines are not THAT different than internal combustion. Both engines obey the same basic mechanical rules and horsepower is going to be a product of torque and rpm. Torque is always going to be limited if reasonable efficiency is desired due to the need to reduce MEP. All this said, traditional direct drive is a losing proposition. Since horsepower is going to rise with rpm, a direct drive car won't reach peak power until reaching peak speed on the track. By contrast, gearboxes allow the engine to be spun up to peak power multiple times during an acceleration run, achieving higher average output. See attached drawing showing the conceptual differences between direct drive, a four speed transmission, and continuously variable transmission. Obviously, this is a simplified example and not representative of any actual system.

Feed water heaters are a non-issue in condensing cars. Condensers and feed heaters are both heat exchangers, each of them working with steam coming out of the engine, stacking heat exchangers to deal with the same working fluid should set off a few alarm bells. Steam leaving a cylinder is going to be saturated, in any realistic steam car design, since it would be wildly wasteful to have any but a small amount of superheat at release.. Assuming exhaust at atmospheric pressure (which is pretty likely given the limitations of air cooled condensers), the steam is going to enter the condenser at 212 degrees F. Operators of large, serious steam plants work to minimize condensate depression -- this is the temperature the condensate is cooled below saturation. Every fraction of a degree water is cooled below condensation temperature represents a loss of heat to the environment. (And a bigger, heavier radiator producing more aerodynamic drag.) A small amount of subcooling is necessary to prevent flashing in the condensate pumps and the condenser hotwell, especially if pressure changes rapidly -- but only a small condensate depression is maintained. This means that an efficient steam plant will be pumping feed water into the boiler at almost the same temperature as steam leaving the engine. Since heat exchangers require temperature differentials to operate, and since their effectiveness is proportional to the difference in temperatures, it is simple to see that feed water heaters can contribute little to a properly designed condensing system.

Likewise, radiant burners appear to possess little to no advantages. Arguing their superiority based on their use in cooking seems a false comparison. First of all, cookware is not a well designed heat exchanger. A pot or pan has a large surface against which a gas flame can impinge. This large surface allows a gasses to "pile up" before the surface without making contact -- we can get a booger of a boundry layer. Obviously, radiant heat is not affected by a boundary layer. This is not the situation with a boiler which is comprised of multiple tubes having small passages between them, the gas flow is broken up and forced into intimate contact with the tubes. Beyond this, there is the matter of temperatures. Let's say we want our race car to operate with steam at 1,000 degrees F. Radiant heat flows from hotter to cooler sources, just like convection or conductive heat transfer. This is a lot hotter than we cook some bacon. This means that the radiant heater has to be well above 1,000 ... let's say 1,500 in order to support a high rate of transfer. The radiant heater is bought up to temperature by combustion gasses and, since heat goes from hotter to cooler, these gasses must be hotter than the radiant emitter ... let's say the burner runs at 3,500 degrees with the gasses leaving the burner running about 1,800 degrees. Now that's a lot of hot gas, and the only way to avoid wasting that heat is to pass the gasses past cooler boiler tubes -- which means we are talking about convective heating. (Since radiant heating is line of sight, only the tubes neares the burner receive infrared, the others are convectively heated.)

Now, here's the rub. Conventional burners put out a LOT of radiant energy. Since the radiation can only heat the tubes in line of sight, the convective heat will by necessity largely heat the tubes further from the burner. in fact, the tubes closest to the burner often receive little but radiant heat because the tube temperature is approaching the temperature of the gas flowing past. Heck, it is possible for the backside of the radiantly heated tubes to emit infrared heat which will be absorbed by the nearest cooler tubes. Anyhow, from a practical standpoint, the radiant burner does almost exactly the same thing as a conventional burner, it pumps infrared radiation into the nearest tubes and hot gasses heat the tubes that follow. The only practical difference appears to be greater complexity.

Lest this seem like speculation, remember that steam car boilers run from around 75 to 90 percent efficient...with Abner Doble reporting 93 percent in one instance, but I am sure he fudged a bit by measuring efficiency while using room temperature feed water. In any case, at 90 percent efficiency, you are approaching the practical limit for a compact boiler -- once again because heat flows from hot to cold. As the cooling gasses interact with cooler tubes, the rate of heat transfer diminishes as the temperature differential drops. Improving efficiency much over 90 percent requires an impractically large boiler. This begs the question: "if some boilers are already about as efficient as is possible, what's the advantage of changing burners?" Honestly, I see no advantage.

We also need to avoid the all-too-common trap of trying to wring every last BTU out of the steam by expanding as much as possible. I keep hearing arguments that piston engines can achieve the same large expansion ratios as turbines but it's easy to argue this is because the proponents don't fully understand some critical differences between piston expanders and properly designed turboexpanders. (A properly designed turbine stage causes a non-turbulent reversal in steam flow. Machines designed to be carried along by the steam flow suffer significant reductions in efficiency -- one example is the Tesla turbine. Likewise, the pressure drop between turbine stages converts pressure to velocity which the turbine rotor is designed to exploit, unlike piston engines.) One should be cautious trying to achieve lower MEP than internal combustion engines, no matter how many steam fans advocate very short cutoff. From the standpoint of raw theory, they are absolutely right, but practical application is being ignored. A few years ago, Art Gardiner (PhD in Mechanical Engineering) gave a lecture in which he discussed the concept of FMEP -- Friction Mean Effective Pressure. This is the MEP needed to overcome friction and it is pretty constant for any given engine speed. At some point, it is quite possible to expand steam to the point where power developed in the latter part of the stroke is less than the friction produced by the engine during that same portion of the stroke. This can be especially true for compound engines, given that the lower pressure pistons not only operate at lower MEP, they also have greater friction due to the greater piston and piston ring diameter and other loads due to heavier piston mass. This ignores the loss of power occassioned by the interstage pressure drop -- which is inherent to compound engines because you need a pressure differential to get steam to flow from one cylinder to another.

Anyhow, that's my two cents.

Edited 2 time(s). Last edit at 05/03/2021 09:56PM by frustrated.

Re: Modern Steam - Formula S Racecar
May 04, 2021 12:04PM
Novice - these guys are using Hydrogen.

Steam Dream
Re: Modern Steam - Formula S Racecar
February 03, 2022 10:18AM
Ken, you and rickh have both given me a lot to think about and also brought up a question or two at the least.
On FMEP the lower the friction the lower the MEP can be for expansion? Can you tell me what the coefficient of friction a typical steam engine will see compared to an IC engine? The reason I'm asking is that the coating I plan on using in my experimental engine has as a coefficient between .02 and .04.
The other question is the radiant vs convective heat transfer. I'm trying to figure how much radiant area for a boiler vs convective. I'm trying to build a boiler that will output around 200 hp. This is to be a recirculating/lamont boiler with a 800/800 pressure/temp.
And to all. What are the expected costs to make a steam generator with these specs? Just maybe a ballpark figure.
This will be used to power an experimental rotary engine design that my brother and Ihave been working on for over 10 years now. I'll put info on the engine in a separate thread sometime soon. I'll also take the boiler design talk to a thread I started years ago. I realized I needed a lot more studying before continuing that one.
Re: Modern Steam - Formula S Racecar
February 04, 2022 08:30AM
Hi Steve,

Your question is really impossible to answer because of the range of steam engines, the materials used in their construction, the degree of finish, and the lubrication methods employed. If we assume an engine built in a comparable manner to modern automotive engines, then the friction should be about equivalent.

FMEP was used because you could calculate horsepower using the PLAN method and simply exchange the MEP value for MEP - FMEP and calculate with the other values held constant. There are references citing various FMEP values for assorted components.

I am extremely skeptical of any coating having a coefficient between .02 and .04. Teflon on Teflon will only get down to 0.04 if you lubricate the surfaces -- while Teflon on steel is also only good for that value. Such plastics are undoubtedly fine for seals but were never intended for the kinds of pressure, temperature, and speeds that will be seen on a modern engine in such places as mains, crankpins, pistons and rings. Despite the push for electrification, auto companies are still spending sizable fortunes on work to improve internal combustion engines and they would be all over any material that could reduce friction to such a degree in a practical manner. This is to say nothing of the multitudinous number of bearing manufacturers.

Anyhow, all the rest of the pumps, blowers, alternators and the like also have to be factored in as losses before you can calculate for best efficiency. Then, probably assume about 80 percent boiler efficiency -- just to be on the safe side. Unfortunately, our ability to recover heat diminishes as differential temperature falls. I've been lectured before about condensing home furnaces and how applicable the technology is to steam cars. This is even true -- IF the car is non-condensing. Once you toss a condenser in, the boiler efficiency falls off dramatically simply because the feedwater temperature is going to be quite high.


Re: Modern Steam - Formula S Racecar
February 04, 2022 12:03PM
Hi Steve,
Hope all is well with you and staying warm.

Years ago I was an Engineer for Teledyne CAE and worked with gas turbine engines. I DD250 several F107 cruise-missal gas turbine engines to the Government. These rotating machines used labyrinth and shrouds that were sprayed with Nichole-Graphite plasma coating (Turbine nozzle/shroud). These seals are know as abrading seals. When they reach their maximum thermal growth, the abrading stops. At this point, they seal and have virtually no friction resistance. As Ken stated and evidence is that we did no calculation or figuring on friction. The engineering assumption is that it will be negligible after it wore in. With that said, I have no idea how your sealing method will if any effect MEP or FMEP. Sorry, can't help you on this one and offer the Teledyne experience as some reference to a rotation machine as opposed to a reciprocating machine.

Your question on Radiant vs Convective is a good one. Unfortunately I can only give you a shot from the hip. My starting point would be 50% - 50% respectfully. You will need hot gas flow if your steam generator design includes economizer that may not receive radiant heat. Hope this helps.

As far as boiler making goes, you will need to divulge some of the concept to the point of what type of generating coils you would like to use. For example, Tom's website shows how he makes what we like to call the Ofeldt coil.

Ofeldt Coils, Tony Grzyb

Tom might be a good starting point. He makes pancake, coil and pyramid coils. I intend to get set up to make coils myself. I have secured a large 90* gearbox and motor that will easily wind almost any coil. My ETA is like 6 months from now, maybe longer, don't know until I get it in my hands. I may have it on my trailer at the spring mini-meet.

Best of luck,
Re: Modern Steam - Formula S Racecar
February 04, 2022 01:34PM
I can understand your skepticism on the coating which I originally came across here in the forums. In 2010 a study performed by the DOE came out concerning its properties and development by ames laboratories. I have been in contact with the company that did hold use of the patent, NewTech Ceramics and am now keeping up with the new company Elas LC . I can email you a copy of the old and a bit outdated DOE study and also will include a link to more current information.
The coating called B.A.M for boron-aluminum-magnesium, becomes part of the material to which it is applied somewhat like case hardening. The maximum hardness of the material is 34.55 Gpa and a .02 to .08 coefficient of friction depending on the exact formulation. I have actually inquired about its use for piston rings and was told that it doesn't hold up as well. Also it works better in a humid environment such as steam applications. It is being used in bearings and according to the DOE study significantly increases the useful lifespan of a bearing. I've talked with one of the current heads of Elas about the use of BAM in my engine design and he believes that it should work well as it has already been used in a similar application which he couldn't describe due to an NDA . Its easy to google B.A.M and find a lot of information but for a start this link is useful.

I agree that there are other losses to efficiency such as you mentioned and those as well will have to be taken into account. One advantage is that as the cylinder length of this engine will be quite long I am hoping that we will be able to expand the steam much more that would normally be possible. This of course is provided that the BAM coatings will cut the friction enough.
While we have done as much as we know how to do I don't claim that this design will work well enough as it is. Unless and until we have an actual prototype built and well tested I can't and won't make any guaranteed claims. I know better than that.
Please continue to point out possible problems and keep your skepticism going as well. Its always good to have help grounding oneself in reality.
Re: Modern Steam - Formula S Racecar
February 04, 2022 01:43PM
Rick, I plan on putting all information up on the forum and hope for a lot of good information and critique. I very much doubt that anything we will come up with would be patentable or worth trying to patent and would rather have any insights and plans available for the club even if it turns out to be what not to do. grinning smiley
Expect more information and drawings on the steam generator thread sometime tonight or tomorrow.
Re: Modern Steam - Formula S Racecar
February 04, 2022 01:46PM
Radiant vs. convective heat transfer

First you need an understanding of the two concepts, there more to it.
Heat radiate in all directions at the same speed as light unless something gets in the way. Hot gases flow through and around piping either in Turbulent flow of gases or laminar flow of gases.

In boiler designs most have banks of pipe or tubing. Pipe comes in standard pipe dimensions and tubing in tubing dimensions, the space between the tubes or pipe can be configured in two ways. Turbulent flow of gases or laminar flow of gases. Turbulent configuration generates more heat transfer then laminar flow of gases.

In a forced circulation design the combustion chamber should be lined with a coil of pipe that is the forced circulation coil for maximum heat transfer. The highest heat temperature of the burner against the coldest water for the most heat transfer. In most cases there in no steam bobbles generated in this coil as it is at a higher pressure then the boiler pressure. The rest of the generator the coils should be arranged so as to get maximum heat transfer, in my opinion in the turbulent flow design for most heat transfer.

Re: Modern Steam - Formula S Racecar
February 05, 2022 03:05AM
Rolly, that sounds like what my brother and I have planned. What he is working on is how much radiant heat coils we will need vs convective coils. We have rough ideas of how much from looking at similar steam generators. We are looking at using DOM tubing with a good safety factor for the pressure. I'm wanting to get around 200 hp out of this system which after unknown efficiencies of the engine might be good enough to drop in my old nissan someday. I'll hopefully have basic drawings to put up tomorrow sometime. I want to see how small and efficient we can make this without spending a fortune. And saying that I'm not sure how much this will roughly cost. I'm guessing at least in the thousands.
Thanks for your input and help!
Re: Modern Steam - Formula S Racecar
February 05, 2022 03:11AM
Rick, I'm going to take this over to the steam generator topic. I'll save talk about racing for if/when we get the engine up and running.
Re: Modern Steam - Formula S Racecar
February 07, 2022 12:25PM
Sounds good Steve...I'll chime in over there.

A quick aside, a scale prototype is a good idea at this point. See if you can get it to work. You know my steam powered scooter taught me so much. Your prototype will also.

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