Heat Engines

[vteco]

I'm going to make someover-generalizations, so forgive me, but it does approximate a topic I've thought a lot about, and in fact experimented with over the last 20 years.

Here goes the generalizations...

Internal combustion engines for transportation (as opposed to stationary uses) benefit from a couple of things not often discussed.

The first is that they like fluid fuels (gasses and liquids). Why? because they can be made to flow through pipes. And because they can be more easily mixed with the oxygen in air. And it can be metered.

The ability to flow through pipes is handy for locating fuel storage (a tank) separate from the engine in a convenient location on the vehicle.

Solid fuels, on the other hand, are more difficult to mix with air, more difficult to store, more difficult to convey from storage, and tough to get inside an engine quickly. A piece of wood bouncing around in a cylinder doesn't make a pretty picture.

The second is that they like fuels of the highest energy density possible. When thinking of liquids and gasses as fuels, you could make a continuum from the least dense, hydrogen, through other gasses like methane and gaseous state propane, through the liquids like gasoline, diesel fuel, home heating oil, and jet fuels.

In an ideal world you'd want the densest fuel possible, because they are the most compact, and compactness is an advantage in a vehicle. Not necessarily in a stationary engine, but in anything mobile, the less space a fuel takes up the better.

It would be great if we could use a solid for transportation. They have lots of density, many are also renewable, but there is no good way to use them in an internal combustion engine.

.....sorry time for dinner. But you probably see where I'm going with this....

[vteco]

It was pasta....

If you could make a transportation engine that ran on solid fuel in a convenient way, that would be cool. In general they would have to be external combustion types, so the fuel doesn't have to flow through pipes or bounce around in a cylinder, etc. etc.

Well it's been done before, actually, via the steam engine. Steam locomotives burned solid fuels. And there were even steam autos, though they tended to use liquid fuels.

A liquid fueled external combustion engine is by nature less efficient than a liquid fueled internal combustion engine because the energy contained in the fuel's heating power is more easily lost outside of an engine than inside it. If you heat a boiler much of the heat escapes as hot gasses up the chimney rather than manages to transfer through the boiler shell.

Those same hot gasses are all contained in an internal combustion engine until they do motive work, and are then released at a much lower energy content.

Energy efficiency aside, however there are other efficiencies that an external combustion engine might be able to capitalize on, which an internal combustion engine can't. One such efficiency is the ability to use unrefined solid bio-fuels.

While internal combustion engines can also use renewable biofuel fluids, like methane, and alcohol, both of those must be produced and refined from primary sources that are perfectly legitimate solid fuels to begin with.

In every fermentation, distillation, and refinement process to produce a fluid, you use lots of energy, and effort and infrastructure. You also create a waste stream that has to be disposed of. This actually can limit the production of liquid biofuels. Biodiesel produces a serious glycerine waste stream. Methane production can create excessive nitrogenous waste. Alcohol production similarly produces a waste streams which would be hard to deal with if the bulk of automotive fuel was made from it. Most of the liquid fuels we manufacture are also based upon monocultural food crops, which require farm quality land and massive amounts of fertilizers and pesticides.

External combustion engines are far less finicky. They can use basically anything that can be burned to produce heat. They are really heat engines. In fact a steam engine can use solar heat from a reflector. Or geothermal heat. The heat source can be from just about anything.

Steam isn't the only medium a heat engine can use. Hot air engines are heat engines that use air as a medium. In fact some don't even use that as the working fluid. Some more esoteric types use hydrogen, not as a fuel, but as a transfer medium.

bedtime....

[Piotrsko]

We did solid fuel back in the 1800-1900's. Wood, coal, whatever. Was however low density energy wise. I recall when they converted some of the loco's thay had to modify the fire box to make it smaller.

And there are periodic people making wood fired cars either by gassification or steam. Rather inefficient, however.

We also use solids as boosters strapped to the sides of rockets. Once lit, they are hard to un-light

I suspect that a solid fueled vehicle would be bigger and heavier than an equivalent gasser.

[vteco]

Well, I'm not a promoter of steam powered cars, but on the other hand I am very interested in seeing what can be done to advance heat engines, which include not only steam, but hot air and other fluid types.

I don't want to whitewash anything, but I also think that compact steam engine technology did not advance the way internal combustion engine technology did in the last hundred years. Mainly for lack of funding and market. Oil was cheap and available and relatively easy to utilize, so why would it?

Gassification, since it was mentioned, creates ash and tar problems for internal combustion engines, and if those are removed from the gas by filtration before the engine, become another waste disposal problem.

External combustion engines don't care about ash, and the combustion can be better controlled to eliminate tar than the slow oxygen-poor smoulder of a gassifier.

I think you're probably right about some weight difference for external combustion, but that may not be a prohibitive factor, when you consider the number of intentionally overpowered and overweight internal combustion vehicles on the road today. There's no definite weight minimum for steam. There are even steam powered motorcycles.

Maybe I have a myopic view. I live in 67 acres of woods surrounded by hundreds of thousands of tons of free fuel I cannot use to power more than a woodstove. It replenishes itself faster than I or even six more households could cut each winter. Yet we buy refined fossil fuels just to get down a mountain to town.

So when I think about terms like "efficiency" I guess it depends on what one means by it. Would an engine burning 40 pounds of wood to take me down the mountain to town, let me do errands and necessary shopping and then bring me back, while providing at most, say, a measly 36 horsepower be considered less efficient than 8 pounds of gasoline providing up to 150 horsepower for a short time, capable of doing the same thing?

Well, to most, obviously yes, gas is technically more "efficient" than a solid fuel. But maybe there are other measures of efficiency if you're looking at a 5 cord woodpile from the trees all around you and thinking about the benefit of a self renewing home grown resource.

I think both views are legitimate. So, I'll probably keep thinking about how such a possibility could be improved over what has come before re. heat engines.

[vteco]

This is a small high speed steam engine I designed and built several years ago as a challenge. I chose to build it entirely out of steel and cast iron scrap plumbing fittings and nails. It features a cam operated piston valve and uniflow exhaust.

It was great fun figuring out how to use those materials. The cylinder was a cast iron pipe union brazed to a base made out of a pipe cap. The head and crankshaft webs were made from flat steel stock, produced by flattening a piece of steel pipe. The crank and valve body were made from spikes. The piston was turned on my homemade metal lathe from a cast iron pipe cap. The marine engine type flywheel was brazed together from telescoping pipe sections and a pipe cap.

The engine test run sounded like an unmuffled two cycle engine of the same displacement. Much fun....

[vteco]

This was a rotary valved steam engine I made ten years ago from a junked Tecumseh horizontal utility IC as an experiment, driven with a timing belt. The head was replaced with a new one containing the rotary valve. Conversion was extremely simple, and valve events were easily controllable.

https://player.vimeo.com/video/65002574

[vteco]

This is a hot air engine I designed and built from all scrap materials for my father's 83rd birthday more than a decade ago. It was meant to look somewhat like an old mill engine.

I cast the aluminum frames. The displacer and power cylinders featured zero connection deadspace, since they overlapped from opposite directions inside the massive aluminum heatsink. It featured a graphite piston.

[freebeard]

Do you have a video or cut-away animation of this in operation? The crank journal looks skinny compared with the flywheel, if i'm reading this right.

What are your thoughts on my favorite internal/external hybrid engine, the Scuderi split-cycle?

https://en.wikipedia.org/wiki/Scuderi_engine

[vteco]

freebeard, I don't have a video of the engine. I worked until late the night before my father's birthday, trying to get it to run. It finally did and being unbalanced, and a surprisingly powerful runner, it practically jumped off the table, so I had to hold it down. I quickly cleaned it up, and packed it in a box with wrapping paper.

I ran it once with my father, who lived 3 hours away, and that was it. Before he passed away, my brother took control of his life, and when he died grabbed all he had, including the engine, which he claimed "didn't work anyway." Meaning he didn't know anything about timing a hot air engine to make it run.

My nephew told me my brother had left it out in his garage for years and that it had rusted pretty badly. When my brother became ill, my nephew a good kid, asked if I would like the engine back, as my brother was dispersing "his" assets. I was quietly given the engine back, in bad shape. My brother passed, and now the engine sits here just as it was found. Maybe some day I will fix it up to run again.

As far as an animation goes, here's one I found with a configuration somewhat like mine, except that in mine there is no connecting pipe between the two cylinders, they are opposed through the heat sink and offset enough to just allow a small overlap where they contact each other, which becomes the air passage. The pipe dead space is eliminated increasing compression.

https://www.youtube.com/watch?v=82xbhWiSOz4

re. the pin size, these engines develop relatively low power and reduction of friction is very helpful, so minimally sized pins and bearings are important, as long as they are adequate in strength and stiffness. The power piston is the only one that develops any force, and that one is closest to the flywheel. The displacer piston has little comparative loading.

The crankshaft on the far side of the flywheel is substantial and set in a skate ball bearing. This allowed me to cantilever it from a single bearing, and simplified the piston to displacer crank -- making it adjustable. A feature my brother failed to appreciate.

[freebeard]

Family. Can't live with 'em, can't live without 'em.

Pin size makes sense. What do you think of the Scuderi engine? The reason I think of it as a hybrid is that connection between the cylinders can be a compressed air tank. Which can be filled by the first cylinder or wind power ...or a Trombe:

Trompe
A trompe is a water-powered air compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse. Trompes were used to provide compressed air for bloomery furnaces in Catalonia and the USA. The presence of a trompe is a signature attribute of a Catalan forge, a type of bloomery furnace. Trompes can be enormous. Wikipedia