On-demand steam engine idea

[jsh111]

TL;DR Summary

This is a steam engine idea I am freely sharing. The idea is that large quantities of steam stored is dangerous, therefore generate it on demand for a piston engine. Please criticize/ tear it apart

Background: In my opinion the next decade has great potential for difficult circumstances for worldwide. I have been obsessed with coming up with a small electrical power generation system (minimum 500 watt, goal is 1kW) for charging batteries during disaster relief situations where refined fuels are scarce, but biomass is relatively abundant.

The attached block diagram is a rudimentary high level design for a steam engine that generates steam on demand for each power cycle, rather than storing steam in a boiler, which presents numerous safety concerns. It is inspired by the Brayton thermodynamic cycle, and indeed, I believe the above could be run on compressed air alone, if designed sufficiently efficient (minimizing dead volume in the burn chamber is critical).

Theory of operation: A fine water mist is generated by running compressed air through a carburetor filled with distilled water. The compressed air chamber is opened briefly by either a cam, or electronic sensor valve. compressed air mixes with a fine water mist via the carburetor, which is then pushed through a check valve into a burn chamber. This burn chamber is filled with numerous stainless steel grids to transfer heat to the small water droplets, and generate steam. The introduction of water (an already compressed fluid) to the air effectively increases the density of the working fluid (rather than just using compressed air alone). As the water mist and cool air contact the metallics grids, heat is transferred, causing the water to transition to steam and greatly expand. This expansion drives a power piston, which is mechanically linked to a compression piston that refills the compressed air chamber for the next cycle.

numerous improvements could be made:

1) Exhaust steam could be thermally recycled in a manner similar to the Ericcson cycle

2) rather than a carburetor/venturi, a fuel injection system could be employed to pre-vaporize the water, or perhaps an ultrasonic transducer to generate a water "fog" prior to the compressed air introduction

3) The flame chamber's volume is minimized by having a high density of metal grid/ volume

4) the flame could be external to the chamber in the case of unclean fuels, reducing efficiency, but allowing for much greater fuel flexibility and maintainability of the system

 

[osilmag]

Hello. How would you start the compressor piston when there is not any output to the power piston?

 

[Tom.G]

A Human-powered air pump to initially compress the air (e.g. bicycle air pump, etc).
Conceptually no different than starting your car.

Similiar concept used to start large Diesel engines:
https://en.wikipedia.org/wiki/Air-start_system

 

[Lnewqban]

The machine will still contain high pressure steam, requiring over-pressure safety devices.

Steam locomotives had a continuous process of converting thermal energy to reciprocating mechanical engine.
I believe that a steam micro-turbine, a mechanically simpler machine, could do it even better.

Please, see:
https://straction.wordpress.com/how-the-steam-engine-of-the-locomotive-works/

 

[sophiecentaur]

i thought that the favourite for quick start power sources was gas turbines. They are fast start and highly efficient.

But there are so many proposed systems and very few successful ones. To be successful you need to be (or own) a "very good Engineer" who can analyse the specific situation and choose a good optimal solution. You can pretty much guarantee any system that anyone fancies ('do it my way') will cost too much or deliver too little.

 

[russ_watters]

But there are so many proposed systems and very few successful ones. To be successful you need to be (or own) a "very good Engineer" who can analyse the specific situation and choose a good optimal solution.

Or to put it another way; they need to design the cycle. This diagram doesn't contain any numbers and leaves some gaps/things that are glossed over:

1. Is safety actually a big problem for modern steam engines? I don't think so. Does this idea actually do anything to improve safety? I doubt it.

2. OP doesn't know if this cycle is open or closed. That's pretty important, not something you can just handwave as a detail to be figured out later.

3. Combining closed steam cycles and open combustion cycles seems...might be hard to make work and the benefit is questionable.

4. Even a piston driven steam engine is pretty continuous at high rpm.

5. Atomizing isn't vaporizing.

Much of what's needed to understand how to analyze and design a cycle is learned in a 1st semester engineering thermodynamics class. I highly recommend taking one.

 

[Vanadium 50]

This diagram doesn't contain any numbers

It's much easier to revolutionize the world if you don't have to put numbers in.

Babcock and Wikcox have a wonderful book called Steam, now in its 43rd edition. Anyone who thinks they can make a better steam engine should either read it cover-to-cover or fess up to not being serious.

 

[jsh111]

The machine will still contain high pressure steam, requiring over-pressure safety devices.

Steam locomotives had a continuous process of converting thermal energy to reciprocating mechanical engine.
I believe that a steam micro-turbine, a mechanically simpler machine, could do it even better.

Please, see:
https://straction.wordpress.com/how-the-steam-engine-of-the-locomotive-works/

Yes, I agree, a pressure relief valve is an absolute necessity connected to the burn/ expansion chamber. I probably should have included that in the rough block diagram above.

A steam micro turbine is mechanically simple, but unless I am mistaken, micro steam turbines are not typically commercially available, and if they are, I'm sure the price is exorbitant. With the above concept, it is conceivable a small 4 stroke gasoline engine which is readily purchased for a low cost almost everywhere could be converted with some cam adjustments, and an additional valve.

I can go into more detail, but basically the idea would be to use the spark plug hole with a check valve to allow steam to enter the cylinder at TDC, doing work. The exhaust stroke would work in the normal fashion, and now instead of the intake valve opening, you delay it by half a cycle, so that there is another expansion stroke from the steam, since we're at TDC again, and once expansion is finished, open the intake valve to let out the used up steam. Another advantage of converting an already existing engine is that the oiling system is already in place (although admittedly not optimized for steam purposes).

TLDR: convert a gasoline engine to this purpose seems easier, cheaper, and simpler than machining a whole new engine

 

[jsh111]

It's much easier to revolutionize the world if you don't have to put numbers in.

Babcock and Wikcox have a wonderful book called Steam, now in its 43rd edition. Anyone who thinks they can make a better steam engine should either read it cover-to-cover or fess up to not being serious.

I apologize, this is just a rough idea I wanted to expose. I suppose I didn't make it clear enough, but I thought the "crayon" drawing would convey that implicitly. The goal is not to make a "better engine" but to make something cheaply that would run on a variety of unclean fuels during disaster scenarios. For this reason, it would not need to be terribly efficient. This is only a concept.

 

[jsh111]

i thought that the favourite for quick start power sources was gas turbines. They are fast start and highly efficient.

But there are so many proposed systems and very few successful ones. To be successful you need to be (or own) a "very good Engineer" who can analyse the specific situation and choose a good optimal solution. You can pretty much guarantee any system that anyone fancies ('do it my way') will cost too much or deliver too little.

I've discussed gas turbines in other posts here, and the concensus is that they are simply very inefficient at small scale, and the cost is very high. There ARE some commercially availble, but you get into the $10k USD range for something like 5KW of power

 

[jsh111]

Clarification: I don't think I made this clear in the original posting: The idea here is not that I've come up with something genius that will change the world. If I wrote this up as an engineering project requirement, it would be something like:

Design a simple electric generating system that can can operate on solid biomass or a variety of readily available liquid fuels, for use in disaster relief situations

system must:

Generate 1kW (objective) 500 W (minimum) DC power

10% thermal efficiency (objective) 5% (minimum)

Be very low cost to construct, maximizing commercial off the shelf components

In short, a cheap, easy to operate system made by converting an existing piston based engine. Not trying to revolutionize the world here, just make something that will work "in a pinch" and help others

 

[Flyboy]

A steam micro turbine is mechanically simple, but unless I am mistaken, micro steam turbines are not typically commercially available, and if they are, I'm sure the price is exorbitant.

Hmmm. That… might actually be a little more doable. Depending on how much you want to spend on custom parts, you could get a metal printed turbine like the one Integza got for this project:


Another option would be a Tesla Turbine, which, if optimized for it, can be used with steam.



Both are quite approachable and will be mechanically simpler and easier to DIY than a proposed steam piston engine conversion.

Personally, if you’re looking to do it yourself at low cost, I would suggest looking at the Tesla Turbine route.

 

[Lnewqban]

TLDR: convert a gasoline engine to this purpose seems easier, cheaper, and simpler than machining a whole new engine

I see.
The main problems regarding lubrication I see are:
1) Keeping the lubricant from getting contaminated with the condensate.
2) The lower temperature of operation, which allows greater leaks from combustion chamber into carter oil.
3) Rusting of internal passages in the engine block.

 

[sophiecentaur]

Be very low cost to construct, maximizing commercial off the shelf components

The ultimate here would be an 'off the shelf' petrol generator - even a second hand one. Reliable and easy to replace. This contrasts with a home built steam / stirling engine which has real aesthetic appeal but which requires a fair bit of workshop skill and equipment.
The latter seems to be the majority choice of amateur machinists and I suggest that fifty million flies can't be wrong. But the best fun project depends on what the individual regards as fun; that's the one to go for.