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.RC.
10-28-2009, 05:24 AM
What would be a rule of thumb for calculating approx engine hp for a given RPM..

I have a 15hp @ 2200 RPM Chinese horizontal diesel engine..

I want it to run a pump, but the pump only needs about 6hp to run...I was thinking of running the diesel engine at around 800rpm..
Does this sound feasible??

Evan
10-28-2009, 07:22 AM
How is it cooled? HP depends on the torque curve.

.RC.
10-28-2009, 07:29 AM
water cooled......Yes I know hp is a calculated figure...

Evan
10-28-2009, 08:25 AM
Diesels have a pretty narrow rpm range. Too slow and they don't get good mixing and will carbon up under load. You will probably have to change the fan pulley or whatever to get enough cooling. How fast the oil turns black will give an idea of how clean it is burning. 600 rpm is pretty slow for an engine rated at 2200. A lot depends on the engine though. An old steel wheel John Deere I drove many years ago ran slower than that all day. You could count the revs.

J Tiers
10-28-2009, 08:47 AM
You'd likely do better with some speed reduction via pulleys or whatever. Even though you do not need the HP, wear will be less running faster at light load than "lugging" the engine to get the power.

Yeah, yeah, it's a diesel. So what. It still needs more torque for a given power at low revs than at higher. That means more wear due to higher pressures on the wrist pins, big ends, and main bearings.

The available torque is AFTER compression, which takes quite a bit of energy, and at low revs, the flywheel energy is lower, in your case by something over 4x, limiting power 2 ways, since the lower speeds need MORE torque to give similar power. Then there is the curve due to engine characteristics.....

You start out at about 800/2200 x 15 or around 6 HP (at constant torque, not totally true), and then apply further reductions. Might be that you get half power at more nearly 1200-1400 rpm or so.

JCHannum
10-28-2009, 08:54 AM
What is the RPM requirement of the pump? That is as much of a factor as anything else. As Jerry suggests, belt it down to give the desired RPM at the pump input. The pump will only use 6HP at rated speed, presssure and volume. There will be some efficiency losses, but the engine won't be producing the full HP, and running at or near the design speed will not create other problems.

A.K. Boomer
10-28-2009, 09:38 AM
You don't want to lug it, and you don't want to wear it out either,
there is an optimal torque curve that you may be able to find specs on but if not and your just shooting from the hip I would say a place to start would be in the range of 1,200 to 1,600 rpm (im assuming when you state "horizontal diesel" you mean horizontally opposed twin)

But before building a pulley system I would run the engine in this range and find where its "happy place" is,
By happy place I mean where it feels like its settled into its harmonics VS trying to tear itself apart, try to do this under slight load if you can, (this is esp. important on diesels)
when you find this place and it falls into the acceptable running range then you have a starting point to do the math from.

You would be surprised just how much a couple hundred RPMs can make in either smoothness or terrible vibrations ----- and if this is the area where the engine is going to be living it can drastically either increase or reduce its service live, just the steel injector lines themselves are subject to failure more often if this is ignored.

Carld
10-28-2009, 09:41 AM
I'm with the others and I suspect the pumps rpm is around 1725 or more especially if it is intended for use with an electric motor. The pump has a performance rpm range just as the engine does and to operate them at reduced rpm would be a mistake but mostly for the engine.

While it is wasteful to use an engine twice the HP needed your still only going to use the fuel required to produce the HP needed to run the engine and pump. It's the same situation when farmers run generators and water pumps from the tractor PTO. The extra HP is just not used and the tractor only uses the fuel required to overcome friction and run the accessory.

One thing that hasn't been pointed out is your engines idle rpm is very likely real close to 800rpm or higher. At that point you may not generate much HP at all depending on the low rpm torque output.

Pherdie
10-28-2009, 10:03 AM
Specifications are frequently somewhat 'flexible'. Your 15 HP motor may be 15 'peak', or in actuality, 10-12 HP. Likewise, the efficiency of the pump may well be overstated.

It just may turn out you have a better match than you realize, HP wise.....

Fred

A.K. Boomer
10-28-2009, 10:16 AM
Absolutely --- you only want to use a percentage of the rating.

camdigger
10-28-2009, 11:04 AM
What would be a rule of thumb for calculating approx engine hp for a given RPM..

I have a 15hp @ 2200 RPM Chinese horizontal diesel engine..

I want it to run a pump, but the pump only needs about 6hp to run...I was thinking of running the diesel engine at around 800rpm..
Does this sound feasible??

1.) Engine horsepower is calculated from two inputs, torque and speed. The rating of the engine is 15 HP at 2200 rpm. IF the torque were constant, theoretically your engine would put out about 5.75 HP at 800 rpm. BUT when reality kicks in and the torque curve is considered, the graph of torque vs rpm looks like a camels hump in profile. Generally, the engines are designed so the speed for the rated horsepower is somewhere near the top of the torque graph's hump. The Reader's Digest version is your engine won't put out 5.75 HP at 800 rpm more like 3.5 - 4 HP depending on the exact torque curve. You're still going to have to use some kind of mechanical reduction.
2.) hydraulic horse power is a function of GPM (determined by pump speed) and output pressure. This is, ignoring speed dependent losses, a direct mathematical relationship. What you haven't addressed, is how you're planning to get your pump to put out it's rated HP at the reduced engine speed?

Willy
10-28-2009, 11:29 AM
Ringer I've calculated HP based on BMEP and have come very close to what Camdigger has, I came up with 5.97 hp @ 8oo rpm.
I made a few assumptions in my calculations, such as a displacement of about 1100cc, with a bore and stroke of 115 mm, single cylinder, and a BMEP of 81 psi.
Even though these are theoretical figures they do represent maximum output achievable at that rpm. Probably not a wise operating parameter for engine longevity.

Here are some links to help in your calculations.

http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm

http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm

http://www.speedwaybids.com/calcs/bmephorsepower.html

lakeside53
10-28-2009, 11:36 AM
As others have said in various ways... Just run it at the pumps' rated speed, or, if that is significantly different from the engines rated speed, use a pulley or other reducer. Your POWER CONSUMPTION will be what the pump consumes... and the engine will be most happy close to its design speed.

Willy
10-28-2009, 11:46 AM
I think if you split the difference between a maximum speed of 2200 rpm and a low of 800 rpm you will achieve a balance of an engine which is not only running at a reduced rpm, but also will be running close to it's torque peak. Which is after all the most efficient rpm for an engine to operate at, both in terms of engine longevity and fuel efficiency.

.RC.
10-28-2009, 04:19 PM
Thanks everyone..The pump is a bare shaft version of what over here we call a firefighter pump.... A self priming pump coupled to a 5.5hp honda petrol engine.. It will be belt driven..

I have dug out the instruction manual for this diesel.. It is a big heavy (400lb) single cylinder 100X115mm boreXstroke and it says here it produces maximum torque (52Nm)at 1760rpm

camdigger
10-28-2009, 04:27 PM
Ahhh, so the HP rating is taken just "over the camel's hump of the torque curve"...

Carld
10-28-2009, 04:31 PM
Ringer, you need to match the pumps max load rpm to the engines high torque rpm. At that point you will have all the power you need to run the pump at it's full load.

Black_Moons
10-28-2009, 05:25 PM
Random other thought is just get a 6.5hp (gas) motor. Like the $100 ones at princess auto...

Unless you really are dead set on diesel.

Also, exhaust loudness, while louder at high rpms, will be lowered with less load on the engine.. and if noise is a consern, try investing in a better muffler for the exhaust, and/or body panels.

But yea, as everyone is saying, actual fuel usage for 6hp at 2200rpm is going to be close to that at 800rpm. It could even be less depending on how efficently the engine operates. (Of course, it could be more because of friction losses too)

Arcane
10-28-2009, 05:45 PM
Boomer's suggestion about finding a sweet spot in the RPM range makes the most sense. Try the engine at it's max torque speed of 1760 and see how it runs there and close on either side of that. The pump was probably designed to run very close to 3600 RPM originally so a 2:1 overdrive (roughly) would probably be just what the doctor ordered! :)

.RC.
10-28-2009, 06:14 PM
I will do some more investigating as to what speed I need to run the pump at... For interests sake here is the pump spec sheet, it is the single impellor model.

http://www.davey.com.au/site/DefaultSite/filesystem/documents/datasheets/D958-2%205150P%20&%205250P.pdf

Carld
10-28-2009, 11:01 PM
That link put a corrupted file on my 'puter. It kept telling me to run ckdsk so I did.

J Tiers
10-29-2009, 12:14 AM
Ahhh, so the HP rating is taken just "over the camel's hump of the torque curve"...

Makes sense, that way it slows down under load into a higher torque area, instead of sliding down the "backslope" and bucking to a halt!

.RC.
10-29-2009, 04:18 AM
That link put a corrupted file on my 'puter. It kept telling me to run ckdsk so I did.

Worked OK for me...

---------------------------------------------

I have done some more working out... I believe I need 5kW at the pump to get it to do what I want...If I add about 15% for losses in the belts it would bring it up to about 5.75kW..

I will work on 8hp as the required power..

I worked out thanks to Willy's links that as 1760 rpm the engine puts out 12hp...

I think it I run it at 1500rpm and run the pump at 3200rpm it should run it easily...

My next problem is how to cool the engine...It did not come with a radiator and the previous owner just used a 1000 litre tank for cooling...The engine has a pump attached to it, and I was thinking of a radiator and fan..

It is actually not a bad motor for a chinese one...It has been sitting for a couple of years yet it started up straight away today...Oh yea, it runs backwards as well ;)

http://img.photobucket.com/albums/v606/OzRinger/chinadiesel001.jpg

A.K. Boomer
10-29-2009, 08:34 AM
I would still search for the sweet spot in the acceptable RPM range but its not as critical as I first mentioned due to the shear mass of that beast, when you stated Chinese I was thinking the newer stuff, they actually have some diesel alloy blocks that are sleeved and those babies rattle if their not happy at certain RPM's.

That unit must have lived in a "hut" of some kind? surely never left outside with that exhaust...

Carld
10-29-2009, 09:04 AM
The pump data page never did open and I am not trying to do it again.

That looks like a sturdy engine and may last centuries. I think the radiator and fan will work but be sure to keep the engine temp at 190 deg F because diesels like to run at that temp. They don't like running cold.

wierdscience
10-29-2009, 01:54 PM
4250 max pump rpm means you will be belting up anyway.If it were me I would let the engine fall on it's governor @2200 and belt it to spin the pump @4,000.

Comparing torque and rpm usually works out better than HP and rpm IMHO.

Carld
10-29-2009, 03:14 PM
That's what I was looking for, thanks wierd. Your right, he should run the engine at high idle and set the pulleys so the pump runs at 4000 rpm. It will probably use almost all the available HP with the pump under a full load anyway.

.RC.
10-29-2009, 04:52 PM
4250 max pump rpm means you will be belting up anyway.If it were me I would let the engine fall on it's governor @2200 and belt it to spin the pump @4,000.

Comparing torque and rpm usually works out better than HP and rpm IMHO.

I don't have enough water to run it at 4200 rpm..

Black_Moons
10-29-2009, 05:07 PM
Awww thats an awsome looking diesel engine :) I allmost want one just to play with.. and maybe make a generator out of..

.RC.
10-29-2009, 06:38 PM
That looks like a sturdy engine and may last centuries. I think the radiator and fan will work but be sure to keep the engine temp at 190 deg F because diesels like to run at that temp. They don't like running cold.

The amusing thing is when you buy these engines they supply a full rebuild kit as well....

I bought it second hand for $100, it has been shedded it's entire life...

Carld
10-29-2009, 09:14 PM
Maybe they think the engine will last so long the company will be out of business and that's the only way your going to have parts to rebuild it.

MrSleepy
10-30-2009, 06:32 AM
We used to have a few 3 cylinder diesel kubota engined mowers that had around 3000 hrs on them...when the revs were lowered the oil pressure used to drop off aswell..

Running this engine at low revs could affect the oil pressure and cause premature ageing or failure..

Rob

.RC.
11-22-2009, 01:31 AM
Progress has been slow due a badly injured finger, but I have got the pulleys sorted out and made up a shaft to fit on the engine..

I had to repair the 180mm pulley, it was originally a double sheave but one of the sides had been badly broken...I made up a new side for it and bolted it on with six, 6mm cap screws..

The engine shaft is made out of three pieces of steel welded together...

http://img.photobucket.com/albums/v606/OzRinger/shaft001.jpg

http://img.photobucket.com/albums/v606/OzRinger/shaft002-1.jpg

http://img.photobucket.com/albums/v606/OzRinger/shaft003.jpg

http://img.photobucket.com/albums/v606/OzRinger/shaft004.jpg

dp
11-22-2009, 01:51 AM
What would be a rule of thumb for calculating approx engine hp for a given RPM..

I have a 15hp @ 2200 RPM Chinese horizontal diesel engine..

I want it to run a pump, but the pump only needs about 6hp to run...I was thinking of running the diesel engine at around 800rpm..
Does this sound feasible??

Does the pump require 6hp at 800 rpm? The engine can put out 20hp at 2200 but doesn't necessarily have to. If the pump only requires 6hp at 2200 then that is what the engine will produce. 2000 - 2200 rpm is a sweet spot for a lot of engines. My Harley lugs badly below 1900, frinstance. And even with the heavy flywheels it has, you can still feel the rods whipping on the power stroke. I think a Diesel would not be happy running slow - especially an engine designed for stationary work. And a Diesel running slow with a low mass load on it will probably be even less happy.

.RC.
11-22-2009, 03:06 AM
Does the pump require 6hp at 800 rpm? The engine can put out 20hp at 2200 but doesn't necessarily have to. If the pump only requires 6hp at 2200 then that is what the engine will produce. 2000 - 2200 rpm is a sweet spot for a lot of engines. My Harley lugs badly below 1900, frinstance. And even with the heavy flywheels it has, you can still feel the rods whipping on the power stroke. I think a Diesel would not be happy running slow - especially an engine designed for stationary work. And a Diesel running slow with a low mass load on it will probably be even less happy.

I am going to run it at 1400rpm now.. which should give me 8hp...The pump requires 6hp at 3200rpm taking into account belt losses..

oldtiffie
11-22-2009, 05:26 AM
In all of the discussion so far, I have yet to see what sort of pressure heads are required to be driven with any line valve/s open and closed or restrictors applied.

Is the inlet pressure head positive (non-vaccuum) or negative (vaccuum) and what sort of inlet flow is there?

I presume that the pump is an impellor (non-positive displacement type).

A.K. Boomer
11-22-2009, 07:45 AM
Ringer don't get me wrong your work looks stellar, im just questioning one thing in design and that's just how far you have that add on shaft hanging out from the main flywheel ----- doesn't look like its a good machined mating surface either and also looks like it lacks fastening (but I think those are dowels and you must have the bolt heads on the other side) --- if there's going to be any belt tension (and power transfer) at all on that I see fret-city till it works itself loose,,,
Personally I would have kept it much more tighter in --- maybe even skipped the shaft and key and just went with the 6 bolt hole pattern and appropriate sized spacers and mounted belt drive directly to flywheel...

Again, not to offend and just an observation.

.RC.
11-22-2009, 04:07 PM
AK the shaft is held on by three studs which go through the flywheel and have nuts on the other side...It rests against a machined section of the flywheel...

I had to make it long as the flywheel is held on by a large ~3" AF nut which sticks out from the flywheel..

darryl
11-22-2009, 07:37 PM
The unknown quantity- the load on the pump in actual operation- that's what's going to determine the hp requirement and the rpm it needs to turn to get the job done. The engine itself will want to run at a sweet speed so when it's loaded down, the rpm won't drop too much. Maybe it would be ok under load at 1800 rpm, but I have a gut feeling that you'd be better keeping it above 2000 rpm. Also by abdominal sensing, I think you can pretty much direct couple the pump to the motor, then if your flow rate is too high you could use an adjustable water bypass valve so you wouldn't have to experiment with pulley ratios. If your flow rate is just a little high, you'd still have the option to reduce the engine speed, but I wouldn't drop it much from the specified rpm.

If your flow rate is too low and the engine is lightly loaded, then you need to overdrive the pump via the pulley ratio.

I have to agree with everyone who has alluded to the idea that you want to keep the engine operating within a fairly narrow rpm range where it is most efficient. Lots of reasons why that is a good idea, and only one of which is that it will probably burn the least amount of fuel at that spec, even if it is only lightly loaded. Ok, that's my .02c

.RC.
11-22-2009, 10:17 PM
I have the performance chart for the pump, it needs 5kw at 3200rpm at the pressure I need....1400rpm is not slow for a single cylinder large diesel engine...Look at the listeroid, it runs at 650rpm, and to get more hp out of them they increse the RPM's to 1000...

Increasing RPM's to increase power output is a trick used by all the major engine manufacturers...

.RC.
01-20-2010, 04:42 AM
A bit of an update, progress has been slow due to injury and drought and other stuff, but I have finally put a radiator on the engine and test run it... It seems to be a goer at this stage.. I have some tidying up to do and some guards to make but I now think I am on the homeward stretch..

http://img.photobucket.com/albums/v606/OzRinger/engine2.jpg

http://img.photobucket.com/albums/v606/OzRinger/engine3.jpg

http://img.photobucket.com/albums/v606/OzRinger/engine1.jpg