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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Fri Apr 03, 2015 12:25 pm 
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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Sun Apr 05, 2015 1:27 pm 
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To further expound on my ramblings..

This is how I've came to understand it:

No steam engine alone should have any "what will it do" horsepower rating applied to it. Other than suggested rate of work for the design.

Set a 5 hp I/C engine on the bench next to a rated 5 hp steam engine. One can point to the I/C engine and call it 5hp with certainty. Reason being simply connect a fuel source any size and it makes 5 hp er it's manufacturer says it does. The same cannot be said for the steam engine. Simply supplying a fuel source produces nothing (but burned paint). So it's actually zero horsepower.

Now connect it to a boiler, the other half of the plant- or it's other half, now it can do work that can be measured. The engine will produce what ever the boiler will put out.

It's really more correct to give the entire plant a horsepower rating. The engine is zero hp without the boiler.

My tug engine is sold as 10 hp. My boiler won't put out that much, I have it figured at somewhere between 4-6 hp. When people ask how many horsepower, I answer 4-6 horsepower. To answer 10 horsepower as I did early on and now realize was wrong, is meaningless. Matter of fact connecting it to a very large boiler would make it 20 hp? Which answer is correct? 4-6 horsepower depending on the wood, temperature of the lake etc. The output is as stable as the plant. That is the average it will yield on a steady run. Will it exceed that, of course. Build up a huge head of steam and crack the throttle fully open, maybe putting out over 10 hp. Will the 4-6 hp rating go lower than that? absolutely and does too often.

Engine design and that cut off and that valve design etc effects the output and will yield different levels of efficiency, that should be measured in percentage of engine efficiency, not horsepower.

-Ron


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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Sun Apr 05, 2015 4:52 pm 
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DetroiTug wrote:
My tug engine is sold as 10 hp. My boiler won't put out that much, .........

-Ron


Ron,

As I had mentioned in previous posts, the HP given can be derived through different methods and by including or excluding varying components of the system. The important thing to note that the HP rating is meant to show the maximum output that an engine or system is capable of producing. The calculation assumes that the engine does not have any constraint from outside factors, like inadequate steam supply. You can recalculate based on a lowered mean effective pressure (from the reduced boiler output) to get a result that shows what the engine is producing in that condition. Losses due to friction and other drive-train losses are often applied to the calculated rating to show what HP output for the a system is. Not knowing how or what the HP number represents makes it difficult to compare HP between engines and or systems. In any case, if a HP number is given for an engine alone the number is more than likely showing the maximum that the engine is capable of producing under ideal conditions. The user needs to apply the allowances necessary and de-rate the HP to reflect the output of the system (or measure the HP output as a system) if that is what he is looking for. The HP rating is always going to be number that represents the maximum engine output and the actual output at any given time is going to be different. In some cases the rated HP might be less than actual output if overdriven.

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Ken


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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Sun Apr 05, 2015 7:09 pm 
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It's interesting that we get so many questions about power, especially from dock bystanders. I honestly have no idea what power I'm getting at full snort. I would need to do an engine brake test to have any idea.

I have finally sorted out sufficient details around the boiler that, when the spirit moves me, I can run the engine at full throttle for an extended run and maintain the pressure at 100 psi or a bit higher. This happens at or not too far below the rated RPM of the engine (5 h.p. at 500 r.p.m.) so I delude myself that I am getting 5 h.p.

The down side is that this produces an almighty commotion, thrashing and vibration thus the whole performance is reserved for short sprints to prove a point. The stern wave alone is remarkable! The fuel consumption also. For what it's worth, such a sprint involves almost continuous hand firing with fist sized blocks of soft wood and the stack blower full open.

The drawback to burning liquid fuels is that when in a lazy cruising mode, a burner is still kicking up a fuss while my wood fire is almost silent. Since I currently spend the vast majority of my time drifting along at four knots or so watching wildlife and wool gathering, it will be a while before I change my fuel source.

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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Mon Apr 06, 2015 12:18 pm 
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"if a HP number is given for an engine alone the number is more than likely showing the maximum that the engine is capable of producing under ideal conditions."

The problem is; what are the ideal conditions? To my knowledge, there are no standardized parameters set by any sort of authoritative board or organization. Mike Browns ideal conditions are 250 psi and 700 RPM Many others are 150 psi and 500 RPM and then all over the map from there. Some steamcar folk and others are operating systems at well over 1000 psi. The steambike mentioned earlier operates at 700 psi (not with me near it of course). Scary bunch for sure :lol:

Any random numbers for an engine can be used in the PLAN formula with greatly varied results, until that engine is actually doing it, they're meaningless.

I read this forum and the steamcar forum daily and have for about seven years. No one that I know of is getting any unpredicted, surprising or unexplainable horsepower or performance out of any engine. ( I said "getting" lol, some claim to be achieving some unexplainable results, but have yet to be verified publicly and they have had ample opportunity for that) The reality is they are all about the same per bore and stroke for the system which they are a part of. The considerable contrasts in output come with boiler design, system design, operating pressure, RPM, fuel types and firing rates.

-Ron


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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Mon Apr 06, 2015 2:05 pm 
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DetroiTug wrote:

Any random numbers for an engine can be used in the PLAN formula with greatly varied results, until that engine is actually doing it, they're meaningless.

-Ron


Yes, I agree if one is pulling numbers out of a hat like it seems most are but as a designer I really want to know what I should expect before buying or building. It would be really embarrassing to build a boat and find that it won't go upstream under it's own power (it's happened). That's why the numbers do matter, but any good engineer knows that they must be based in reality as well. As always, one must be careful and understand what you are looking at, it's not like the HP rating are never inflated, especially when the marketers and alternative energy shills get involved. The HP rating is just a number that should be helpful in allowing caparison between engines and matching an engine to an application. As far as the numbers, the actual pressure doesn't matter, what does matter is what the HP will be at a given RPM and pressure. This gives some idea of the intended use and a baseline for comparison. 10 HP at 80 psi and 300 rpm is going to be used differently that 10 HP at 200 psi and 1000 rpm. In either case it's the same amount of work but it gives you an idea on how it can be applied. Like if you will need a transmission or other gearing.

The PLAN formula is a useful tool but the numbers input must be good. That is why the engine must be indicated or input data be taken from a reliable source, I believe there are steam tables that exist to allow the selection of MEP in a design context. If the MEP is just a guess the result will be suspect as well. The boiler pressure isn't what the PLAN formula uses and to do so will give a vastly inflated HP rating. The mean effective cylinder pressure (MEP) is the average pressure of the steam as it expands during the power stroke and is determined factors including; pressure at the steam port (different from boiler pressure) and the cutoff.

As far as ideal conditions, I just meant that the engine has to have enough steam to be able to run at full output for a reasonable period of time not a particular pressure. If your boiler isn't capable of supplying the pressure and volume needed you won't hit your HP rating, because you have another problem, not because of a incorrect HP rating.


Cheers

Ken


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 Post subject: Re: 1902 Steam Car Engine vs Mike Brown Engine - HP disparit
PostPosted: Mon Apr 06, 2015 3:40 pm 
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Edited, I misunderstood the comment I replied to.

Yes, in selecting an engine really all one needs to know is the bore and stroke. Most small 20ish footers a 3X4 single or equivalent compound will fit the bill.

My boiler is too small to make the 10hp that the engine can process. The reality is and I now know, I never needed that much. The boiler/engine will push the hull above hullspeed. So the boiler is ample. As Mike alluded to, pushing a displacement hull past it's calculated speed takes a substantial increase in power for each knot gained.

I was told by some that the tug would never be able to keep up with the narrow steam launches like the Elliot Bay, that wasn't accurate, I can run right with them as the video here shows. Note the boiler pressure.





-Ron


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