Torque versus speed for steam engine
Re: Torque versus speed for steam engine
The mentioned PLAN formula is hardly relevant here. There are some other factors to be considered.
In an ideal engine, a torque-rpm characteristic would be flat, and different for any given cutoff. That is to say, the power would proportionally increase with RPM, while the torque should remain constant. This is not actually the case, because of port throttling losses. Those increase with rpm in a non-linearly proportional fashion. They also depend on other factors, and can be evaluated from an equation given by Strahl many decades ago, which is fairly complicated to say the least. If anyone is interested, I can share some theoretical papers on the subject of engine thermodynamic analysis I have published some time ago by PM.
To illustrate what I am talking about, let me share a torque, power and RPM characteristic evaluated from theoretical analysis with all losses considered. This is is evaluated on a 1.2 kW uniflow engine, but the overall trend is valid for any steam engine. Nind is indicated power, M is torque. The different colored lines stand for cutoffs from 10 to 50%.
In an ideal engine, a torque-rpm characteristic would be flat, and different for any given cutoff. That is to say, the power would proportionally increase with RPM, while the torque should remain constant. This is not actually the case, because of port throttling losses. Those increase with rpm in a non-linearly proportional fashion. They also depend on other factors, and can be evaluated from an equation given by Strahl many decades ago, which is fairly complicated to say the least. If anyone is interested, I can share some theoretical papers on the subject of engine thermodynamic analysis I have published some time ago by PM.
To illustrate what I am talking about, let me share a torque, power and RPM characteristic evaluated from theoretical analysis with all losses considered. This is is evaluated on a 1.2 kW uniflow engine, but the overall trend is valid for any steam engine. Nind is indicated power, M is torque. The different colored lines stand for cutoffs from 10 to 50%.
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Re: Torque versus speed for steam engine
So, I'm confused about the PLAN formula and addiator's
I can tell you right now Nyitra is a my open experiment figuring this out for myself experimentally - Because I don't want a really fast running engine either . Right now my Toledo is geared heavy, I have two ratios between the two sprockets and the two pulley's. Both are trading torque for more rpm at the prop. I have tried this arrangement - and it is workable -but not optimum. I need more testing without seaweed... My current final ratio is 1:3.43. So if the Toledo was doing ~60rpm in my recent video the propeller is doing 205rpm.
The Toledo didn't want to go much faster than this, but I don't have enough data to say why because the seaweed was heavily influencing the results.
-CB
The original question in this thread:theoretical analysis with all losses considered.
It seems like the graph from addiator shows hp going up with rpm.wsmcycle wrote:Since the pressure of the steam is 100% at zero rpm, how does the Hp unfold as the rpm increases? I have a Navy K engine that "seems" to run too fast (rpm)
I can tell you right now Nyitra is a my open experiment figuring this out for myself experimentally - Because I don't want a really fast running engine either . Right now my Toledo is geared heavy, I have two ratios between the two sprockets and the two pulley's. Both are trading torque for more rpm at the prop. I have tried this arrangement - and it is workable -but not optimum. I need more testing without seaweed... My current final ratio is 1:3.43. So if the Toledo was doing ~60rpm in my recent video the propeller is doing 205rpm.
The Toledo didn't want to go much faster than this, but I don't have enough data to say why because the seaweed was heavily influencing the results.
-CB
Re: Torque versus speed for steam engine
Look at how power is defined as a physical quantity. It is the amount of work done in an amount of time. The unit itself (kW being a kJ/s) shows it clearly. At zero rpm power will always be zero, because you are doing zero rotations in a minute. In terms of rotating shafts, power can be described as N=M*omega or torque x angular velocity, angular velocity being just another way to note down the speed of the shaft (omega = PI*n/30).cyberbadger wrote:It seems like the graph from addiator shows hp going up with rpm.
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Re: Torque versus speed for steam engine
This makes sense but...addiator wrote:Look at how power is defined as a physical quantity. It is the amount of work done in an amount of time. The unit itself (kW being a kJ/s) shows it clearly. At zero rpm power will always be zero, because you are doing zero rotations in a minute. In terms of rotating shafts, power can be described as N=M*omega or torque x angular velocity, angular velocity being just another way to note down the speed of the shaft (omega = PI*n/30).cyberbadger wrote:It seems like the graph from addiator shows hp going up with rpm.
When is PLAN formula relevant vs your theoretical analysis and vice versa...
-CB
Re: Torque versus speed for steam engine
PLAN has little to do with torque, and all to do with power. It is always true, but it does not say much by itself, as mean indicted pressure which is one of the inputs is itself a product of many factors, and as I have written it actually depends on rpm due to the port throttling. If you look at the characteristics I have shown, you could actually very well replace the torque with MEP, the values would be different, but the trend identical. So, if torque is what you need and you have the MEP, then from aformentioned definitions, denoting torque by M and power by N=PLAn, M=N/omega=PLAn/(PI*n/30)=PLA*30/PI.cyberbadger wrote:This makes sense but...
When is PLAN formula relevant vs your theoretical analysis and vice versa...
-CB
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Re: Torque versus speed for steam engine
Ok, that makes sense. Is/how much is port throttling affected by valve design. D valve vs Piston valve. I'm assuming we are talking about the ports inside the engine?addiator wrote: PLAN has little to do with torque, and all to do with power. It is always true, but it does not say much by itself, as mean indicted pressure which is one of the inputs is itself a product of many factors, and as I have written it actually depends on rpm due to the port throttling. If you look at the characteristics I have shown, you could actually very well replace the torque with MEP, the values would be different, but the trend identical. So, if torque is what you need and you have the MEP, then from aformentioned definitions, denoting torque by M and power by N=PLAn, M=N/omega=PLAn/(PI*n/30)=PLA*30/PI.
-CB
Re: Torque versus speed for steam engine
The port area, opening, and design of the ports and valves, in the sense that the coefficient of discharge is always different. There is a semi-empirical formula for the pressure drop given by Strahl. Unfortunately not in SI units but the old kGf based system - thought conversion is trivial. I have pasted it as an image.
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Re: Torque versus speed for steam engine
So there!!
If you think you are too small to make a difference, try sleeping with a mosquito.
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Re: Torque versus speed for steam engine
I always love generic coefficients like mu in that equation.
You might as well throw out the whole equation because without experiment that equation is as useful as the spring equation until you experimentally find your spring constant.
-CB
You might as well throw out the whole equation because without experiment that equation is as useful as the spring equation until you experimentally find your spring constant.
-CB
Re: Torque versus speed for steam engine
It is actually quite easy to find mu for generic ports. This has been experimentally done thousands of times. I can refer you for example to Stumpfs 1922 book. This is only a simple approximation, and as all engineering formulas for flow losses it has a certain margin of error. This very equation was one of the basics in German locomotive design and was in excellent agreement with experimental results.cyberbadger wrote:I always love generic coefficients like mu in that equation.
You might as well throw out the whole equation because without experiment that equation is as useful as the spring equation until you experimentally find your spring constant.
-CB