TWIN 32 x 38 mm - steam engine for small boats or canoes

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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fredrosse
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by fredrosse » Tue Feb 01, 2022 3:19 pm

".....It works with I.C. temps which are far higher than steam"

Actually not so! The main difference between IC engines and Steam Engines is that the cylinder temperatures in a steam engine are typically much higher. I am talking about the cylinder metal temperatures, not the working fluid temperature. This is because the heat transfer coefficient between the working fluid in an ICE (air intake, products of combustion) is very low, while the heat transfer coefficient for steam working fluid and the cylinder is fantastically high.

Internal Combustion Engines (ICE) have a cold air intake stroke, a relatively cold compression stroke, and hot power stroke (yes, hotter than steam), and finally a hot exhaust stroke, but all of this is with the low heat transfer coefficient of the gas fluids inside the cylinder. ICE practice keeps the cylinder metal well cooled, usually with a water cooled jacket at well under 212F (100C). Jacket water cooling in ICE engines enjoys a heat transfer coefficient which is generally quite high, about 70-100X the combustion gas heat transfer coefficient, and this holds cylinder temperature in ICE practice close to jacket water temperature. Air cooled ICE practice is somewhat higher, I have measured up to 260F (127C) on my motorcycle cylinders.

Steam engines on the other hand, with a heat transfer coefficient more than 500X the heat transfer coefficient found in ICE gas practice, results in the cylinder metal temperature closely held between steam inlet temperature and steam outet temperature, with the bias somewhat toward the main inlet steam saturation temperature, because this inlet steam gives the rapid cylinder condensation which is the main loss associated with steam engines. On the exhaust stroke the wet steam temperature has saturated "re-evaporation" removing heat from the cylinder, but not quite as well as the inlet steam, since at lower pressure/temperature the heat transfer here is not quite as fierce.

For a typical launch engine, 150 psig saturated steam 365F inlet ( 10 Barg, 185C) and atmospheric exhaust, 0 psig 212F ( 0 Barg/100C), the cylinder metal will run close to 300F, (149C), which is considerably hotter than typical ICE practice.
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by barts » Tue Feb 01, 2022 7:17 pm

Temperature limits for common aluminum alloys, esp. heat treated ones like 6061-T6 should be followed closely if strength or corrosion resistance is important. See http://www.matweb.com/search/datasheet_ ... 7d9e10be5b for details.

For saturated steam conditions, we can accurately predict the temperature of components and pick appropriate strength margins. For superheated conditions, we have to be much more careful since the temperature is much more variable. With 6061-T6 losing 75% of its strength going from 300F to 500F, we can see that we either need to pay close attention to both design and temperature in these conditions. In general, anyone considering using superheat in a small boat should stick to materials with ample high temperature performance - cast iron and steel.

In IC engines, peak temperatures are typically seen near the exhaust valve seat. In overhead valve engines, this is in the cylinder head of course. One of the typical failure modes of small L-head air-cooled lawnmower engines is localized yielding of the material around the exhaust valve seat, especially if the cooling fins are not kept free of grass clippings. Modern aluminum alloys have helped car engines become more resistant, but I remember back in the 1980s even a momentary loss of coolant would almost always result in a warped (yielded) aluminum cylinder head which would require remachining to seal again.

I seem to remember that the Semple steam engines ran aluminum pistons in aluminum cylinders w/ cast iron rings; this would be simpler construction and differential expansion would not be an issue. For saturated service, this should work pretty well.

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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by PeteThePen1 » Wed Feb 02, 2022 1:07 pm

Hi Dietrich and Friends

Sorry if I have dragged the thread off your original specification of which I am very supportive. It was me being curious again since my lack of engineering knowledge often has me wondering "how else could one do that?" That tendency probably comes from too many of my plans hitting problems (due to not spotting inherent problems) and then having to do a Plan B or even Plan C.

The engine is excellent and will be a veritable gem when finished. I am hoping that when my Alibre Atom 3D CAD skills are improved to try adding the engine drawing to the canoe that we discussed during Lock Down. My current assumption, possibly daft, is that the canoe would be built to split in two around the mid point. That is something the designers offer on some of their other canoes. Obviously like Fred and others the engine and boiler would be removable as seprate items. Thus each component would be no more than 20kg (ish) and be no longer than 6ft (1.8m) which would esily fit into the back of a car.

I think you idea of a boat that could be hung in the car port is excellent and probably represents the next size up, boating for two rather than for one. The difference is that such a boat would be more functional being larger, but woud not really meet the 'fit inside the car criterion'.

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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by Mike Rometer » Tue Feb 08, 2022 10:14 am

(quote) "For a typical launch engine, 150 psig saturated steam 365F inlet ( 10 Barg, 185C) and atmospheric exhaust, 0 psig 212F ( 0 Barg/100C), the cylinder metal will run close to 300F, (149C), which is considerably hotter than typical ICE practice."

I think the difference here is theoretical as opposed to practical. I don't see many water-cooled steam engines around. The bore will be clamped between TWO cylinder heads it cannot move. It is even debatable that the ali block is needed at all, apart from attaching things to.
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by TahoeSteam » Wed Feb 09, 2022 2:03 am

I'd be more concerned with unnecessary heat loss with aluminium being better at heat transfer.
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by fredrosse » Fri Feb 11, 2022 12:20 am

".....I think the difference here is theoretical as opposed to practical."

With respect to the cylinder metal temperature conditions of ICE practice vs our steam engines, the numbers I generated are quite accurate, and indeed the theoretical does represent truth, IFF the engineer doing the calculations applies fundamentals correctly. All engineering calculations involve tolerances that have some level of uncertainty, and addressing how the uncertainty of measurements & other parameters impact the accuracy of answers is a branch of engineering that is well understood and reliable. We know that steam/water, boiling or condensing, has a fantastically high heat transfer coefficient when compared to ordinary gasses such as air or the products of combustion in engines. We also know, very accurately, the temperatures at which steam boils, or condenses, according to the local saturation pressures. These facts dominate the conclusion reached about cylinder metal temperatures.
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by dampfspieler » Fri Feb 11, 2022 5:25 am

Hello,

in this threat i want to show, how i built a small steam engine for different purposes, especially canoes and small boats because there is no one on the market and there are no drawings available.

I am interested in finishing it and if it is tested successfully i will optimise it.

This moment i am not interested in discussions about materials and its specifications.

Be so kind and friendly and open an different treat if you are interested in discussion about optimising steam engines. You are hijacking my build report.

Thank you for considering my request in the future. If I have questions, I will ask them and ask for advice.

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Dietrich
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by TahoeSteam » Mon Feb 14, 2022 5:54 pm

Dietrich,

How do you intend on mounting the engine and connecting it to the propeller? Is the geared drive for pumps or connection to the propeller?
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Re: TWIN 32 x 38 mm - steam engine for small boats or canoes

Post by dampfspieler » Thu Feb 24, 2022 7:31 pm

Wesley,

the engine will be mounted on two longitudinal beams with eight bolts.

Twin3238_305kl.jpg
the base plate of the engine with the eight borings for the bolts
Twin3238_305kl.jpg (47.01 KiB) Viewed 12981 times

To achieve a universal design, the base plate can be rotated about the longitudinal axis to build a clockwise or counter-clockwise rotating engine, depending on which direction of rotation the propeller requires. I will build the engine for a clockwise rotating propeller.

Twin3238_282kl.jpg
Twin3238_282kl.jpg (74.27 KiB) Viewed 12981 times

I would like to connect to the propeller shaft with a metal bellows coupling at the end of the flywheel. The gearing for the pumps is similar to Kelly's VIVIDUS engine.


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Re: TWIN 32 x 38 mm - oil pump eccentric with adjustable stroke

Post by dampfspieler » Sun Mar 06, 2022 9:00 am

Hi,

because I've been having trouble sleeping lately, I found the time to draw my idea of an eccentric with an adjustable stroke, here's the result.

Ölpumpenexzenter_kplt_Explosion_20220306.jpg
Ölpumpenexzenter_kplt_Explosion_20220306.jpg (64.26 KiB) Viewed 12811 times

The eccentric consists of a fixed disc, which is attached to the shaft with two set screws, a movable disc, on which the ball bearing sits, on which the outer ring with the fastening lug for the drive rod is clamped, and a clamping plate, which the movable disc on of the fixed disc in the desired position.

The movable disc. A stroke of 0 to 6 mm is adjustable.

Ölpumpenexzenter_beweglich_20220306.jpg
Ölpumpenexzenter_beweglich_20220306.jpg (43.65 KiB) Viewed 12811 times

I came up with this solution because on all steam engines with mechanical oil pumps that I know of, the amount of oil pumped was clearly too large and reducing it was hardly possible or very difficult.

Wasserpumpenexzenter_beweglich_20220306.jpg
Wasserpumpenexzenter_beweglich_20220306.jpg (57.58 KiB) Viewed 12807 times

The moving disc for a water pump could look like this. Its stroke can be precisely adjusted using a screw so that the water pump only delivers the amount of water that is really required to maintain the water level in the boiler.

The drawings are unmeasured because they are intended as ideas for readers' own work.

Hope it enjoys.
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