Small engine dyno

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Bentwings

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Being a long time auto racer the first thing that usually comes up is how much power does the engine make.
So we are talking steamers down a ways. How much torque and rpm do thes little engines make ?

there have been a number of home small engine synod built over the years . So what’s involved. Usually the first is the brake dyno this I’d a measured length bar with some kind of braking agains a flywheel. The bar rests on a scale and measures pressure usually pounds against a scale. There is some means of forcing the flywheel to beare on the arm. Various means of causing the arme to try to slow the flywheel a brake shoe. I’m sure many of you have seen these at farm shows with big tractors huffing and puffing . We go to one every year and it’s surprising just how much those big old steam tractor can put out . There are a number of you tube links for small engine synod often directed at go kart engines. But thee are just to big for our little bench steamers . I saw one years ago at the farm show that was based on an old hyra magic transmission fluid coupling or fluid drive it was pretty primitive but it works well . I’ve given some thought to a model dyno but load cells re still pretty expensive so I’ve started lookin at reflux’s coupling . I think a small coupling could be made that you bleed water into or out of. That’s the principal that many really powerfull engine synod work on . Actually Pratt & Whitney used this type to test the big radial engine during the war years. Today car engine synod are electric but some do use the water idea. It’s measuring the torque that is the tech issues so anybody interested in a desk top dyno?
 

ruzzie

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Strictly IC Magazine

KIRK MINIATURE DYNAMOMETER,
by Bud Kirk & Bob Washburn.
A Hydraulic (Mechanical Water Brake) Dynamometer.
Issues # 62, 63, 64, 65, 66, 67, 69 & 70

Paul
 

lohring

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I've done dyno testing on RC boat engines since 2004. We tested gasoline engines from 2 hp to almost 12 hp over an rpm range that could reach 25,000 rpm. I bet we made over 1000 dyno runs. We used an inertial dyno. It is much simpler than a brake dyno and gives a full power curve with runs that take a few seconds. It also deals well with the peaky torque characteristics of piped two stroke engines.

An article on its construction is in Model Engine Builder issue 15. A general article on dyno building is here. An overview of inertial dynos is hosted by Performance Trends. One of the test series we ran was on a CMB 35. Others investigated fuel, tuned pipes, and various engines Tower Hobbies wanted to use for their RTR RC boat.

Prony brakes work fine for simple, low power and low rpm engines. However, if you want to do serious testing, an inertial dyno is the way to go. It's what all the serious small engine builders use, and chassis dynos, another form of inertial dyno, are often used by automobile engine builders.

Lohring Miller

CMB 35 on dyno.JPG
 

mrehmus

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IIRC there was a long description of a sophisticated of a model size dyno in SIC some years ago. Sorry cannot say what issue.

John
The dyno in SIC was faulty or so I was told by the author. SIC is unfortunately no longer available because Frances is now in a care home.
One that does work is the dyno published in Model Engine Builder magazine, Issue # 15 by Lohring Miller which is an inertial dynamometer that is good up to 25K RPM.
 

froudeg490

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In the near future I plan on building a small engine Dyno. It will most likely be a eddy current type very similar to a Froude EC38, but scaled down. I'll test it by spinning it up on my lathe bed.
 

lohring

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I also built an eddy current brake using computer disks and magnets. The inertial dyno is a lot less fiddly. I've also tested an electric outboard on a water brake dyno. It was much more time consuming.

Lohring Miller

P1010232.JPG P1010233.JPG P1010231.JPG electric motor dyno.jpg
 

froudeg490

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I also built an eddy current brake using computer disks and magnets. The inertial dyno is a lot less fiddly. I've also tested an electric outboard on a water brake dyno. It was much more time consuming.

Lohring Miller

View attachment 131893 View attachment 131894 View attachment 131895 View attachment 131896
Very nice. I agree that a inertia dyno is a lot simpler and less fiddly than a water or eddy current Dyno. I'm interested in seeing what design and operability challenges exist with a scaled down version of the large commercially available machines. I'm curious to see if I can close a speed loop on the Dyno. It may not be practical, but I'll give it a go.
 

lohring

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Look at the articles in my post above to get an idea of what's involved. Computers and software are the secret. I used Performance Trends data loggers and software, but there are others. I believe you can purchase kart engine size dynos completely ready built, but most are custom made. Chassis dynos are usually ready made.
The original work on inertial dynos was from Gordon Blair at Queens University in Belfast.

Lohring Miller
 

Bentwings

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I’m looking at small particle brakes I found some that aren’t too expensive basically it would mount on pivot the apply electrical load and read torque on small scale and rpm from digital meter calculation is relatively simple I don’t think small steam engine is going to set any records as rpm nd pressure are limited but it would b fun and good discussion topic . I have to look into item costs before I ge to serious about this. They are clean and not very big .

byron
 
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Hi Byron, simply: (please correct me if I am wrong? It's 45 years since I did this last...).
Max. Torque is max steam pressure x area of piston, x crank throw... per cylinder, and power is torque x stroke x rpm.
And for a double acting engine the steam is applied to push the piston in both directions.
Now in reality, there are losses when exhausting, and when steam is cut-off before end of stroke.... but that calculation should define some top limits for steam engine performance so you can size the dyno appropriately.
Does this make sense?
K2
 

Bentwings

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I think you are on the right track . I think multi cylinder models I’ll start from any osition of the crank but max torque comes at 90 degrees perpendicular to rotation so piston area time psi would equal max torque available just as air cylinder if the rod were connected directly to he piston as rocking piston compressors you would deduct the section area f the rod but in most of these steamers push on the bottom of the piston including pin bosses so. Just use piston area both ways. With slidepiston valves you migh have to advin are of thes to be technically correct. That kinda why I’d like a particle clutch so I could stop the crank in any position and measure torque at that point in automotive bench racing we use displacement time some value of cylinder pressure detonation is not easily measured except by observation when you see a hole in a piston or the torque caved in aluminum Dodd actually shear from detonation. I’ve seen not quite broken ones you can see the angle of over stressed metal . There is a guy on inter net that has a dyno.
JohnnyQ I think is his site. He has a really cool steam turbine too I just found ha site last night there has been lots of requests to purchase his stuff too he is missing a great opportunity here. Anyway thanks for the input. I’m a nut for calculations but far from math major . I’m working on design of aluminum boiler using 1/4” wall aluminum tube. There are some high strength materials available but I need more in-depth analysis. My solid works station does have fluid dynamics but it’s been many years since I was into that . I just need to sit down and study a bit . The particle clutch could be a very accurate measurement of torque at any crank position . Addin numbers to a spread sheet could produce a chart . Last night I ran internal expansion due to hat in the aluminum . I don’t think it serious but something to consider . I have to go for my daily walk we got more snow and 45 mph winds so some shoveling is in order too . So later
Byron
 
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Hi Byron,
  • 1/4" wall x 3" OD aluminium tube (Welded end plates??) should be OK for 100psi.
  • NWP, safety-valve full blow before 104psi.,
  • Hydraulic test at 200psi. (compensating for the change of permissible tensile stress between temperature of hydraulic test and temperature at Boiler steam pressure).
  • You must reinforce all tube wall penetrations with at least double the cross-sectional area of aluminium reinforcement. - Often standard bushes are way undersized to do this properly! Not sure how you do this on a welded boiler? - (Fillet?) Weld-section greater than tube wall-thickness? - Ask a man who makes ASME certified pressure vessels in aluminium...
  • End plate minimum thickness depends on flat or dished, joining method to the tube, what holes and where positioned, any fillets for reinforcement, any stays, or flue tubes connecting both ends, etc.
Enjoy the design work!
K2
 

Bentwings

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I’ve come up with an insertable end cap sealed with Teflon prongs it would be perimeter bolted like railroad engine. These would be machined dome shaped and 14” thick minimum. I haven’t done shear strength of stainless steel button head screws yet but I’ll do that interesting to note bung thickness . All fittings will be not inch. I’ve seen some pretty rediculous repaired fittings in race cars Uber some incredible stress. I don’t think I’ve ever seen a new pipe fitting install strip out from pressure. Even in motor explosions the lines go flying while the fitting stays put there are pressures in the 300 psi range in small to large fuel lines. It’s more likely leakage from not tightening the connection. I had a catch tank explode when it got filled with nitro fumes the aluminum sheet ruptured like it was torn paper but all the weld seams were intact as were the fittings it was only .040 aluminum sheet . Pretty spectacular as I was not far away the screw superchargers operate at about 60 psi boost and when they go off the magnesium manifolds shatter but fittings stay in with dangling hoses still on them . However I will reall look into how the fittings fit . I may even do a hydraulic test pipe just for the record since we have a portable hyd. Pump it would be interesting to see what gives first . It’s snowing again so some of this is going to have to wait we are supposed to have 50 mph winds today . 35 right now thinking back to the aero space R&d I remember hyd testing as and titanium battery containers. They were about model boiler size. They were laser welded in inert or high vacuum atmosphere . Usually the shell failed in the middle by essentially buckling due to exceeding metal yield strength . It did take a lot of pressure. Live testing involved direct shorting of extremely high power lithium batteries. It was said the batteries were as owerful as the ordinance they powered. Some of the most dangerous stuff I ever worked with. Several years before I started there a fire broke out and burned the whole building down . The fire dept just secured the area and said let it burn we will put out the ashes. Lithium fires are extremely dangerous an toxic . Thanks for the comments and alerts. Definitely will test before I commit to a build. I found o rings and have an easy way to install them there are other materials too. Parker is very helpful if you can get to tech help . I won’t weld anymore as I just don’t see we’ll enough. I could do stainless but unless I can find a nice immersion heater I’ll sheve that as external heating is just too inefficient .

now I’m looking for small gages or an electric panel . I just ordered a simple turbine that I’m thinking might be a good centrifuge to strip oil out of exhaust steam . Any thoughts ?
Byron
 
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Hi Byron, considering oily exhaust steam... this is the same as the mayonaise you will have seen in not very hot parts of regular town cars... (Not racing cars, they are stripped and cleaned too often and run too hot, and vent all their blow-by gases on the car behind!).
The mayonaise is formed from condensing steam to water vapour, each droplet forms around the tiny drop of vapourised oil that has condensed at a higher temperature than the water.... so the droplets making the emulsion are virtually molecular in size. Centrifigal separation with turbine blades may work, but the best way is post heating of the mayonaise droplets to evaporate the water - then centrifuging the oily steam, leaving oil. Simple hot cyclone separators do this as well, without the turbine.
(I think?).
K2
 

Bentwings

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I too also thought about after heater have not come up with something simple yet . I did chat with my son and they are getting a porta power hydraulic pump so testing the boiler won’t be hard they already have a water tank for testing tires so it could be submerged so internal water doesn’t spray all over if there is a leak. I just ordered a magnifying light for my work desk at home. I have a small assembly thing coming so I’ll get to try it out shortly .
I did find a steam oil supplier but it’s in the UK so I’ll still have to order it I did call my sons race car oil sponsor and they just laughed. The said they haven’t had steam oil for over 75 years. Then he asked how old I was that I even knew about it . Well I’m older than he is so I had the last laugh .
Byron
 
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