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  #31 (permalink)  
Old 05-03-2012, 01:41 AM
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After thinking about building an engine dyno myself ,using the fluid coupler from something like a AEC ,Leyland or other British bus,or Alvis amoured car i was looking through a local parts advertizing mag and found a complete Froude Dyno for sale ...so I will use that instead. it worked out cheaper buying this old girl than to build my own..

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  #32 (permalink)  
Old 07-30-2013, 08:09 AM
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hi Kevin. i want to know how u build that water brake dyno
i want to design a water brake using water pump, but i dont know where to start designing
what the first step that i must do or i must calculate...

i want to use that for motorcycle with 23,5 kW (32 PS) power...
thanks

my email: dvn.farrell@hotmail.com
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  #33 (permalink)  
Old 07-30-2013, 03:16 PM
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Well, if you are going to use a water pump then the first step would be to find one that can take the forces you are going to apply. I’m not going to design the thing for you but I will point out a few steps. You mentioned 23,5kw but fail to specify an RPM of interest. I assume, since it is a motorcycle, you will not be interested in anything less than 5,000 rpm. I will “guess” you will want to test in the range of 5,000-10,000RPM or higher? See how this works . . . you need to precisely define what you are going to test before you can define an apparatus to collect the data. So using the horsepower formula you will find the torque needed to produce the KW you want at the RPM you are interested in. Now you have Torque, RPM, and KW. Select a water pump that will live under those conditions. Since motorcycle RPM is quite high it is doubtful there will be a water pump in that RPM range so you may have to reduce rpm to the pump using gears, belts, or chains. All of those have their individual merits. And of course, as soon as you introduce speed reduction you have now changed load (torque) by some ratio factor. While this can be a tedious, iterative approach, the reason you are doing this is because it is fun! ENJOY :-)
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  #34 (permalink)  
Old 07-30-2013, 04:34 PM
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Here is a link to the PTS flow bench Forum which also has a home made dyno section. Quite a few ideas there....
PTS Flowbench Forum - Login
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  #35 (permalink)  
Old 07-31-2013, 05:00 PM
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DVN,
If you want to use a water pump I agree with SaltFever about finding one in your RPM Torque range. If you just want to tune the motor you could probably just use the rear brake to load it and tune on a stand. You could even loosely calculate from the compression of the suspension or use a load cell. Data acquisition is the next step. Load cells require quiet circuits and lots of amplification. If you want egt's, thermocouples only output millivolts and require a bit of math or look up tables.

Kevin
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Old 07-31-2013, 11:25 PM
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thx for the help

i gonna use the water brake dyno for testing the motorcycle until 3 days or more, so i want to design a water brake dyno because water can dissipate heat very well

the motorcycle is Kawasaki Ninja 250R
max Power: 23,5 kW / 11000 rpm
max torque: 21 Nm / 10 000 rpm

what should i do, i just have that information?
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  #37 (permalink)  
Old 08-01-2013, 05:36 AM
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oya, beside using water pump is nearly impossible because of the rpm..
i want to design them with a usual water brake dyno which has stator and rotor..but i dont know how to design the stator and rotor for the water brake dyno, i dont have much knowledge..
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  #38 (permalink)  
Old 08-01-2013, 06:48 AM
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I suggest you go to the link I provided to the Flow Bench and dyno Forum, and register there as a new member. The dyno section is a members only part of the Forum.

There are nine pages on that particular thread alone, about home construction of a water brake dyno power absorber, including a lot of pictures, many ideas, and links to other threads on building home water brake dynos.

Go over there and post in that thread, members there will be able to help you.
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  #39 (permalink)  
Old 08-01-2013, 10:27 AM
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i have join the forum that u gave to me..i search "water brake dyno" and some stuff like that, but the search result didn't show the threads that i am searching for...
maybe u can help me where is the discussion in that forum that discussing water brake dyno..

thanks
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  #40 (permalink)  
Old 08-01-2013, 10:42 AM
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hi, i have found that...thanks..

but if anyone can help me how to design and calculating the stator and the rotor, i really really appreciate that, really thanks for that..
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  #41 (permalink)  
Old 08-01-2013, 04:29 PM
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Rotor and stator cannot be made too large, the whole thing can be run almost dry where the torque loading would then be just about zero.
What determines the overall size would be the maximum torque at very low revs, as your bike develops only 21Nm at 10,000 rpm, something only a very few inches in diameter should hold that just fine.

Making something that is well balanced and that will not fly apart at those high rpm (and is safe) would be a much more important issue than size.
Rotor and stator just have straight radial vanes that pass each other with some small mechanical clearance between.
There must be a different number of vanes on rotor and stator, usually one more vane on one than the other.
The reason why, is that only one moving and one stationary vane will pass each other at any instant, and this gives a much smoother torque absorption.

There will be a water outlet right at the outside periphery of the outer casing, and this needs to be fitted with a restrictor orifice to control the volume of water flow.
You just need enough water flow to prevent boiling at maximum horsepower.
The water pressure developed by an 11,000 rpm spinning rotor will be enormous, so the orifice size will be a quite small drilled hole.
That, plus the water flow and water temperature rise at full power needs some experimentation.
Think about how long it takes for a 2.5Kw electric kettle to boil a couple of quarts of water. Your 25 Kw engine will boil the same volume of water in 1/10 the time.
That will give you a rough idea of how much water flow you need without going into a bunch of thermodynamic calculations. Its not a lot of water.

The water flows into the centre of the casing, and how much water you feed into the casing determines the dyno loading. Water flow needs to be controlled either with a variable speed pump, or some kind of flow valve in such a way that it can AUTOMATICALLY control and hold a constant dyno speed.
If the engine tries to speed up, feed in more water. If the engine starts to bog, reduce the water flow into the casing.

That is basically all there is to it.
The rotor tries to pump itself dry through the outlet orifice, and you need to keep feeding enough water into it to hold down the engine rpm to the required amount.
At low rpm the casing would be almost full of water and offers a certain torque resistance as the water shears between the moving and stationary vanes.
At very high rpm (with the same inlet flow) the casing will be almost dry, with the rotor working in only a very thin skin of water glued to the circumference of the casing by extremely high centrifugal force. Interestingly, the torque resistance stays almost the same right through the whole rpm range, but the volume of water held inside the casing rises as rpm drops, and falls as rpm rises.
That is the magic of the water brake dyno, almost constant torque resistance with rpm.

There is a danger with that !!!
With something like a turbo engine, or a highly tuned bike engine, the torque can suddenly dramatically increase with rpm at some point, and the engine speed can then run away.
That is why you really need an automatic speed control system to adjust water flow with very highly tuned engines.
With ordinary low performance engines you can very often get away with manual control of dyno load.
But with a highly tuned engine with a very peaky torque curve it starts to become more difficult to hold the engine at a constant speed, and even dangerous with a high risk of sudden engine runaway to destructive rpm.

So be careful.
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  #42 (permalink)  
Old 08-01-2013, 10:25 PM
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oo..okay, thanks to u...
if i reduce the rpm from 11000 to 5500, is it okay?
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  #43 (permalink)  
Old 08-01-2013, 10:58 PM
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Should be.
What happens is the speed drops to half, and the rotor becomes a less efficient pump with less ability to pump itself dry through the outlet orifice restriction.
Because you have not changed the incoming water flow, the drum fills up more, and the torque resistance stays the same.

If you keep reducing the rpm and not altering the incoming water flow, the drum fills even more. Once the drum is entirely full of water it cannot fill any more.
At that point the water brake is at its fullest mechanical resistance, and any further reduction in speed would reduce the torque holding ability.

So a small water brake will work fine with high power high rpm engines.
For big torque low rpm engines you need a bigger diameter water brake.
Bike engines are easy to hold, big capacity high boost turbo diesels very difficult.
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  #44 (permalink)  
Old 08-02-2013, 08:00 AM
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Well,after considering building my own,and doing a ship load of research( i even read a pile of Phd thesis on the subject) I found the easist way out was to hunt down a used item. i found a Heenan and froude G series withless than 100 hours of use on it. Mine for the princely sum of $2000. If you want to find a lot of info check out the Heenan and froude patent documents. They invented the principle of the water brake for use on the first steam ships...!
heenan-froude dynamometer | casing | rotor | 1921 | 0065 | Flight Archive
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  #45 (permalink)  
Old 08-03-2013, 12:15 AM
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Quote:
Originally Posted by mercmad63 View Post
Well,after considering building my own,and doing a ship load of research( i even read a pile of Phd thesis on the subject) I found the easist way out was to hunt down a used item. i found a Heenan and froude G series withless than 100 hours of use on it. Mine for the princely sum of $2000. If you want to find a lot of info check out the Heenan and froude patent documents. They invented the principle of the water brake for use on the first steam ships...!
heenan-froude dynamometer | casing | rotor | 1921 | 0065 | Flight Archive
do u know how to calculate and step-step to design a water brake dyno? for stator n rotor design...thx
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