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Home Built Engine Dyno

37K views 55 replies 10 participants last post by  dvnfarrell 
#1 ·
I'm starting this thread to continue the discussion from the "Engine Test Stand" thread we were hijacking.

I put water in the brake today. It's was leaking everywhere. Venting it helped most of it. I think a little Teflon and some hose clamps will fix the majority of the rest but it looks like the shaft seals are going to leak some. Completely full, it seems to be stalling my na SBC at around 2000rpm. Megatune kept locking up. I put 6 inlets and outlets for both sides. It has a double sided rotor and two stators. My intent for all the fittings is to be able to experiment with computer controlled load with multiple valves and to possibly recirculate the water through a cooling system. I think the way I have the hoses routed from one fitting to the other right now may be reducing the load by allowing to act more like a pump than a brake.


Watayahknow,
To answer your questions: I tried working on other people's stuff but wanted to work on my own and it's easier and more profitable to just get up and go to my day job. My intent was to make money to by tools to build and eventually sell my own parts. I just decided to go ahead and buy the tools. I've spent the past couple of years trying to learn how to maintain and operate the 5 axis machining center I stuffed in my garage. The Quad Turbo runs but I have some oil return issues with the lower turbos to sort out. My plan is to finish it when I have parts to show off.


Kevin
 
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#27 ·
Every commercial water brake has the vane count on the rotor and stator different by one vane. Most commonly 11/12 vanes, or 12/13 vanes.
This creates a very smooth torque absorption characteristic, as the vanes pass each other one at a time.

If you have the same identical number of vanes on both sides, the vanes will all line up and pass each other together, and there could be some significant torque pulsing every time the vanes simultaneously line up all the way around.

It will certainly work with the same number of vanes, but if you get some very strange noises or vibrations at certain speeds, you will know what needs to be done.
 
#28 ·
What stops axial movement of the rotor shaft? I guess that the rotor is keyed onto the main shaft but what stops the rotor from moving front to back and the rotor from hitting the stator?

I have started to draw something up and wondering about using thrust washers either side of the rotor to keep it central in the body.

For your materials am I right that the body and stators are aluminium and the rotor stainless? What did you use for the main shaft?

My main concern with mine is the data acquisiton - I'm happy with the mechanical and machining but will be a steep learning curve on the data side of things.

Cheers.
 
#29 ·
Here's a short video of the motor on the dyno. I had an issue logging RPM so there's no HP. Peak torque has only been 363 lbs. I'm going to try to find some more power before upping the limiter from 5k, switching to fuel injection, and adding boost. I may also put some headers on it and see what it does first. It has 1.94" Double Humps on it that seem to like a lot of timing. I started the day with timing at 36 degrees. I'm currently at 42 degrees and up 113 lb of torque. It's pig rich, but I figured I'd get the timing down first. On the second pull I flipped the wrong switch and caused all the steam. If I leave the water on it works better, but I'm going to have to add a pump and tank soon.

http://www.youtube.com/watch?v=JqEvsUcbPSY&context=C3277c64ADOEgsToPDskKjQA_wEd4J55Gml2s-Rvlh

mtrehy,
Sorry I missed your post earlier. This one is all steel. The rotor is welded to the shaft. All four bearings have eccentric collars.
 
#30 ·
Hey Kevin, many thanks for starting this thread :) . . . and to all others who have contributed. I have been thinking about this for quite a while. Have a few questions but no time at the moment. I need to re-read it a few times. Some pretty creative stuff here . . . :cool:
 
#31 ·
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.. :D
 
#33 ·
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 :)
 
#35 ·
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
 
#36 ·
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?
 
#38 ·
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.
 
#41 ·
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.
 
#43 ·
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.
 
#44 ·
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
 
#52 ·
Water brake of the size you are thinking about can run a total loss water system, so yes that part is pretty easy.

Eddy current machine just needs a big air blower to cool the brake disc.
The advantage is, it offers DIRECT and very fast electrical control of the dyno load, you don't need variable speed pumps or flow control valves which introduce a whole lot of extra control problems and are something extra to go wrong.

I am an electronics guy, and my own home rolling road dyno is eddy current, so my opinion is probably a bit biased.
But that is how I would tackle what you are trying to do if it was my project.
 
#54 · (Edited)
You are asking a great deal here ,in fact what you asking is what someone would expect to aquire in terms of knowledge over a period of several years at university,with at least 4 years of techincal training in the use of machine tools.
I have all of the above experience as it happens but even so it was still easier to hunt down an unused peice of gear.
Your basic need then is a device to hold a pair of round turbines in a housing,
One is engine driven,one is fixed to the rotor housing .

The housing has to be fed a constant,controllable flow of water .(allow the water to get hot and boil and you will not get a proper braking effect).
This housing must be free to rotate through an arc of 45 degrees.
An arm of 500 mm length must project off the housing so it pulls against a load cell. this cell sends it signal to your PC where you can read off the pressure being exerted on it by the engine.
Add more water,and you are increasing the amount of effort required to turn the engine driven turbine and thus more pressure on the load cell.
Thats what a dyno does.
So, to get around your first task...a turbine. The most effective is the Fluid coupler from a truck or bus which is not a torque convertor. OK,thats a hard one ,but they do exist especially in the UK where trucks such as Leylands,AEC,Foden etc used a preselector type trans and the huge diesel engines produced a lot of torque.Far more than you will ever see from a car engine. A car torque convertor will not work,they are too weak and you don't want a torque multiplier effect.
The actual size or design is not as important as keeping the water flow constant and the temperature down below boiling. And dynos will boil water quickly under load.
The only way to control water temoperature is to use a cooling tower,a Big one!. So start looking around slavage yards etc for air con cooling units which will fit where you want to operate. Pouring water down the drain is not a great idea ,it is expensive and wasteful.
OK ,you got this far and the thought of finding a turbine is too hard... I live where these parts are available and I didn't bother looking too hard...:D
here is the patent document for the DPX style of dyno. These are actualy very small but can handle huge horsepower,
All you need to do is down load the drawings and dimension the drawings yourself .
Hydraulic brake or dynamometer
The document goes into detail on how it works. Here is one depicted here. Not very big is it? it was sold at Auction in the UK for 95 pounds.

Now, an eddy dyno..if you do not have access to a lot of water , the next best option is get a Truck or Bus retarder. These are mounted on big rigs behind the trans and work on the principle of creating a magnetic flux which the truck attempts to turn .They turn the torque into heat energy but in the case of Dyno,the retarder is connected by an arm to a load test cell ,
Eddy current brake - Wikipedia, the free encyclopedia
Now,you need to be able use a few formulas for calculating just how much force is being transfered to the load test cell (look on ebay for plenty of examples for sale) so if you read this document,on page three are all the formlae you will need.
http://www.sussex.ac.uk/Users/tafb8/eti/eti_03_EngineTestingOverview.pdf
 
#56 ·
how should i determine how much debit of water will i use (Q)?
can i know ur email?

i get this formula, T = w * r^2 * p * Q
where T = torque of the shaft (engine)
w = angular velocity
r = impeller radius
p = density of water
Q = debit

i want to calculate the impeller radius, but i dont know the debit (Q)
 
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