Williams ws. Rankin
Posted by Howard Langdon
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Re: Williams ws. Rankin March 10, 2006 04:38PM |
Registered: 19 years ago Posts: 1,038 |
Hi Bill
I havn't did an analysis that has that much (+/1 100 PSI) variataion. A small variation of +/- 10 PSI of inlet pressure makes little differance. And of course it would make a differance how over compression is handled. Is allowed to just rise to whatever or shunted to some limit. My static analysis are all compression to inlet pressure or less. In an ideal cycle where compression is to whatever it works out to be from the volume change the compression work is returned upon expansion. However depending on the method you beleve is correct for the drop to exhaust pressure at the end of expansion the cycle calculations can be quite different. If you treate is an isoenthalip expansion. The up on recompression for any given pressure it will contain more heat then the expansion did. So when you mix the there is a heating effect from the mixxing making the expansion more efficient. In this case it less efficient to under compress. Over compression keeps gaining. But may soon run into the point of doing more compression work then expansion work.
Herry. Glad you got me looking the compound engine vs simple engine size. This is a great revolation for me. I had no idea the engine size could be reduce so drasticly by a compound. Modern high compression cycle type that is. Thanks.
Compound produces 3.67 times the power of a simple engine for a given displacement. I know this is counter intutitive. But it is true. It is simple really. It takes work to compress the steam in these engines. The copression work reduces the output work. It increases efficincy though you are getting less work out. The larger the clearance space the mor compression work it takes. The higher the clerance relative to cutoff the higher percentage of the expansion work work goes into the compresson.
I have worked up a MathCad work sheet to look at it in more detail. And I think I am right. With the MathCad work sheet I found the single engine would have to be over 3 times the size of a compound for the same output. Before some one takes this out of context, I am looking at high compression engines. Not the normal old antique hard were. Here is the deal. I compared simple engine running at 1000 PSIA. That about the highest pressure one can run in get close to a full expansion. Even that is questionable. It's input is 1000 PSIA at 950F. I set the end of expansion to 17 PSIA and exhaust 14.696. To get that I use a 3% clearance. Very low clearance. Hard to do. But wait the cutoff is at 1.024%.
Does anybody think such an engine could be built? I don't. Even if you could. It would be a throttled engine. There is simple no room to reduce clearance for longer cutoff for full expansion.
For comparson I chose 5% clearance in each stage of the compound engine. I used my MathCad cycle calculator and set up cycles for these two engines. The compound was a hard one here. I balanced it by hand. Adjusting the inter stage pressure and drops to get close to the same work producing over all expansion as the single expansion engine. I used inlet steam at 1480 PSIA And 800 F degrees. The efficiencies of the two engines came out close.
Here is the deal though. The simple engine with 3% clearance and 1.025% cutoff is a residual/inlet steam mix of 72.2%/27.8%. That is we have 27.8% inlet steam producing output work. On the other hand the compound having 3 stages of expansion runs a much higher of percentage of inlet steam through the cycle. The first stage residual/inlet relation of 11.4%/88.6%. The second is less at 14.6%/85.4%. The cycle is computed for a pound of steam in the cycle. The two part residual and inlet make up that steam. The first stage takes in 0.886 pounds of steam that mixes with 0.114 pounds to make that one pound in the cycle. So we have drasticly differents amounts of inlet steam going through the two engines. In the simple engine we have 27.8% inlet steam compared to the 88.6% in the compound. The compound has 3.19 times the mass of inlet steam going through the cycle. The reasion is the clearance limitation. These are both using compression to eliminate clearance loss. I also increased the inlet pressure on the compound. It has about the same over all expansion ration and efficiency. The increased pressure reduce engine size as the steam densith i greater. The compound has more head room and doesn't expand quite as low. These factor make for the compound producing 3.67 times the power for a given displacement. The compound could be 1/3 the phisical size of the simple engine for a given output.
Andy
I havn't did an analysis that has that much (+/1 100 PSI) variataion. A small variation of +/- 10 PSI of inlet pressure makes little differance. And of course it would make a differance how over compression is handled. Is allowed to just rise to whatever or shunted to some limit. My static analysis are all compression to inlet pressure or less. In an ideal cycle where compression is to whatever it works out to be from the volume change the compression work is returned upon expansion. However depending on the method you beleve is correct for the drop to exhaust pressure at the end of expansion the cycle calculations can be quite different. If you treate is an isoenthalip expansion. The up on recompression for any given pressure it will contain more heat then the expansion did. So when you mix the there is a heating effect from the mixxing making the expansion more efficient. In this case it less efficient to under compress. Over compression keeps gaining. But may soon run into the point of doing more compression work then expansion work.
Herry. Glad you got me looking the compound engine vs simple engine size. This is a great revolation for me. I had no idea the engine size could be reduce so drasticly by a compound. Modern high compression cycle type that is. Thanks.
Compound produces 3.67 times the power of a simple engine for a given displacement. I know this is counter intutitive. But it is true. It is simple really. It takes work to compress the steam in these engines. The copression work reduces the output work. It increases efficincy though you are getting less work out. The larger the clearance space the mor compression work it takes. The higher the clerance relative to cutoff the higher percentage of the expansion work work goes into the compresson.
I have worked up a MathCad work sheet to look at it in more detail. And I think I am right. With the MathCad work sheet I found the single engine would have to be over 3 times the size of a compound for the same output. Before some one takes this out of context, I am looking at high compression engines. Not the normal old antique hard were. Here is the deal. I compared simple engine running at 1000 PSIA. That about the highest pressure one can run in get close to a full expansion. Even that is questionable. It's input is 1000 PSIA at 950F. I set the end of expansion to 17 PSIA and exhaust 14.696. To get that I use a 3% clearance. Very low clearance. Hard to do. But wait the cutoff is at 1.024%.
Does anybody think such an engine could be built? I don't. Even if you could. It would be a throttled engine. There is simple no room to reduce clearance for longer cutoff for full expansion.
For comparson I chose 5% clearance in each stage of the compound engine. I used my MathCad cycle calculator and set up cycles for these two engines. The compound was a hard one here. I balanced it by hand. Adjusting the inter stage pressure and drops to get close to the same work producing over all expansion as the single expansion engine. I used inlet steam at 1480 PSIA And 800 F degrees. The efficiencies of the two engines came out close.
Here is the deal though. The simple engine with 3% clearance and 1.025% cutoff is a residual/inlet steam mix of 72.2%/27.8%. That is we have 27.8% inlet steam producing output work. On the other hand the compound having 3 stages of expansion runs a much higher of percentage of inlet steam through the cycle. The first stage residual/inlet relation of 11.4%/88.6%. The second is less at 14.6%/85.4%. The cycle is computed for a pound of steam in the cycle. The two part residual and inlet make up that steam. The first stage takes in 0.886 pounds of steam that mixes with 0.114 pounds to make that one pound in the cycle. So we have drasticly differents amounts of inlet steam going through the two engines. In the simple engine we have 27.8% inlet steam compared to the 88.6% in the compound. The compound has 3.19 times the mass of inlet steam going through the cycle. The reasion is the clearance limitation. These are both using compression to eliminate clearance loss. I also increased the inlet pressure on the compound. It has about the same over all expansion ration and efficiency. The increased pressure reduce engine size as the steam densith i greater. The compound has more head room and doesn't expand quite as low. These factor make for the compound producing 3.67 times the power for a given displacement. The compound could be 1/3 the phisical size of the simple engine for a given output.
Andy
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Re: Williams ws. Rankin March 10, 2006 06:34PM |
Registered: 19 years ago Posts: 1,268 |
Andy,
That is absolutely amazing!
I do have a question. It appeared that you used the displacement of the last stage as the comparative engine size. Final expansion. Did your results include also the sizes of the first and second stages?
What was interesting is that the single stage engine was using steam at 950 deg and the compound at 800 deg. yet the efficiencys were close. I expected that when the inlet temperatures are pushed up to the 1200 deg range the single can not do the expansions neccessary to keep up with the compound. Also noted that with the compound the temperatures of recompression were much more close to inlet.
Encouraging for the compounds indeed.
Go compounds -------- Bill G.
That is absolutely amazing!
I do have a question. It appeared that you used the displacement of the last stage as the comparative engine size. Final expansion. Did your results include also the sizes of the first and second stages?
What was interesting is that the single stage engine was using steam at 950 deg and the compound at 800 deg. yet the efficiencys were close. I expected that when the inlet temperatures are pushed up to the 1200 deg range the single can not do the expansions neccessary to keep up with the compound. Also noted that with the compound the temperatures of recompression were much more close to inlet.
Encouraging for the compounds indeed.
Go compounds -------- Bill G.
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Re: Williams ws. Rankin March 11, 2006 11:06AM |
Registered: 19 years ago Posts: 835 |
Hi Andy, Bill,
The 6cyl Cyclone engine only is only 90 lbs is 21" india. x 7" high. the crank is an adional 10" in heigth.This also includes the cam and heads and valves.
Max power at 6% cut is 92hp calc. howeveer best efficency is at about 25hp calc.
The total weight inc. gen.,cond. all pumps. blower complete all piping total gross is less than 340 lbs. Expanding to 1 asp. will make temp differental to difficult to drop the BTU without having a condencer the size of a doghouse.
Harry
The 6cyl Cyclone engine only is only 90 lbs is 21" india. x 7" high. the crank is an adional 10" in heigth.This also includes the cam and heads and valves.
Max power at 6% cut is 92hp calc. howeveer best efficency is at about 25hp calc.
The total weight inc. gen.,cond. all pumps. blower complete all piping total gross is less than 340 lbs. Expanding to 1 asp. will make temp differental to difficult to drop the BTU without having a condencer the size of a doghouse.
Harry
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Re: Williams ws. Rankin March 13, 2006 03:37PM |
Registered: 19 years ago Posts: 1,038 |
Hi Bill, Herry
Bill. On page three is the calculation of work/cuft. The sungle stage engine, Work(sub)1S and 3 stage compound, Work(sub)3S. Note in the the Work(sub)3S calculation I use the end of expansion volume of all three stages. The last two are scaled to use equal steam as is their work. I am amized it comes out that way. But is is basicly the relation of cutoff to clearance that does it. A single stage's clearance is mechanicly limited. I thinke 3% is pushing that limit.
I discovered an error in the calculation of the two work function. I doesn't effect the ratio. The sqin factor shouldn't have been used there. It a conversion of feet^2 to in^2 sqin = 144. It cancles out in figureing the ratio. The specific volumes are in ft^3/lb.
Herry there is no substitute for high pressure in getting high power densities. I did the analysis against a suppercitical engine as close to yours as I have info.
Using 3200 PSIA at 1200 F 6% cutoff. Used 8% clearance and exhaust pressure of 220 PSIA getting 3.26 HP/in^3 (3600 RPM) at 23.7% efficiency. Your cycle operatoring at high exhaust is wasting a lot of energy but could recover some form the exhaust. I set up a supper critical 3 stage compound. No were near the power density. The single stage has 2.86 the power density(work/in^3). While the compound has 2.1 times the efficiency. The comnpound would have to be 2.86 the size of the single stage to get the same power but it would use about half the fuel.
The high pressure doesn't increase the power density as much when expanding close to full expansion. In the other analysis the 3 stage compound had a power density of 0.91 HP/in^3 @3600 RPM. Operatoring from 1480 PSIA 800F The single stage at 1000 PSIA 800 F has a power density of 0.249 hp/in^3. The supper critical compound is at 1.14 HP/in^3. Going to supper critical/higher temperature doesn't help the compound as much on power density. The main gain there was efficiency.
But get an idea of a compound compared to a single stage at supper critical inlet I also did it with less expansion. The result is that by shifting the pressure and actully operatoring at a lower temp it is possable to get a lot better efficiency.
Bill. On page three is the calculation of work/cuft. The sungle stage engine, Work(sub)1S and 3 stage compound, Work(sub)3S. Note in the the Work(sub)3S calculation I use the end of expansion volume of all three stages. The last two are scaled to use equal steam as is their work. I am amized it comes out that way. But is is basicly the relation of cutoff to clearance that does it. A single stage's clearance is mechanicly limited. I thinke 3% is pushing that limit.
I discovered an error in the calculation of the two work function. I doesn't effect the ratio. The sqin factor shouldn't have been used there. It a conversion of feet^2 to in^2 sqin = 144. It cancles out in figureing the ratio. The specific volumes are in ft^3/lb.
Herry there is no substitute for high pressure in getting high power densities. I did the analysis against a suppercitical engine as close to yours as I have info.
Using 3200 PSIA at 1200 F 6% cutoff. Used 8% clearance and exhaust pressure of 220 PSIA getting 3.26 HP/in^3 (3600 RPM) at 23.7% efficiency. Your cycle operatoring at high exhaust is wasting a lot of energy but could recover some form the exhaust. I set up a supper critical 3 stage compound. No were near the power density. The single stage has 2.86 the power density(work/in^3). While the compound has 2.1 times the efficiency. The comnpound would have to be 2.86 the size of the single stage to get the same power but it would use about half the fuel.
The high pressure doesn't increase the power density as much when expanding close to full expansion. In the other analysis the 3 stage compound had a power density of 0.91 HP/in^3 @3600 RPM. Operatoring from 1480 PSIA 800F The single stage at 1000 PSIA 800 F has a power density of 0.249 hp/in^3. The supper critical compound is at 1.14 HP/in^3. Going to supper critical/higher temperature doesn't help the compound as much on power density. The main gain there was efficiency.
But get an idea of a compound compared to a single stage at supper critical inlet I also did it with less expansion. The result is that by shifting the pressure and actully operatoring at a lower temp it is possable to get a lot better efficiency.
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Re: Williams ws. Rankin March 13, 2006 06:38PM |
Registered: 19 years ago Posts: 1,268 |
Hi,
Just chimeing in here.
Mine works out to a power density for the rankine as 0.57 Hp/in3 @ 3600 rpm, the efficiency is around 29% but that is figuring in 5% losses for expansion and compression processes, which lowers the overall engine efficiency from roughly 32% . A greater expansion ratio accounts for the lower power density.
Anyway I think what it all means is that above a certain spot around 800 degrees the single starts loosing it's ability to expand enough for good efficiency at a decent power output without using tricks like a heat recovery exchanger. Of course there is nothing wrong with tricks as long as they work.
If I doubled the inlet pressure then only the first stage volume would change much, the overall engine size would be about the same as the last stage is the predominate determiner of size.
Best to All, Snowed in with a cold. ------------ Bill G.
Just chimeing in here.
Mine works out to a power density for the rankine as 0.57 Hp/in3 @ 3600 rpm, the efficiency is around 29% but that is figuring in 5% losses for expansion and compression processes, which lowers the overall engine efficiency from roughly 32% . A greater expansion ratio accounts for the lower power density.
Anyway I think what it all means is that above a certain spot around 800 degrees the single starts loosing it's ability to expand enough for good efficiency at a decent power output without using tricks like a heat recovery exchanger. Of course there is nothing wrong with tricks as long as they work.
If I doubled the inlet pressure then only the first stage volume would change much, the overall engine size would be about the same as the last stage is the predominate determiner of size.
Best to All, Snowed in with a cold. ------------ Bill G.
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Re: Williams ws. Rankin March 14, 2006 10:25AM |
Registered: 19 years ago Posts: 835 |
Andy Bill
The reason for super crital is for high heat exchanger (boiler) efficency. the condencer is the engine base and opperates at 20 psi abs and gives the compression a super charge effect as it is ballanced on the bottom of the piston and redusing clearance volume. Even a car radator operates with 2 atmos.for good heat exchange. I think you are missing a complete system.
Harry
The reason for super crital is for high heat exchanger (boiler) efficency. the condencer is the engine base and opperates at 20 psi abs and gives the compression a super charge effect as it is ballanced on the bottom of the piston and redusing clearance volume. Even a car radator operates with 2 atmos.for good heat exchange. I think you are missing a complete system.
Harry
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Re: Williams ws. Rankin March 14, 2006 01:55PM |
Registered: 19 years ago Posts: 1,268 |
Hello Harry,
At full power design exhaust pressure is around 23# abs and about 300 degrees. If the condenser can handle this it will handle the lower temps and pressures at partial power output. The idea is that the 'excess' expansions of the compound at partial output get absorbed in the wet steam region and the condenser can maintain a pressure slightly lower than engine exhaust.
Again there are a lot of work BTUs to get picked up under partial power conditions with the extra expansions and it doesn't take many to significantly increase efficiency.
Note that Andy set up the examples of the simple and the compound at about the same expansion ratios and the same efficiencys. At this the simple was about at its limit for expansions and efficiency at a very low cutoff while the compound was just getting started. The simple was using about a 1% cutoff and the compound 38%. The large difference in HP/in^3 was because at very low cutoffs the amount of residual steam in a simple is such a much higher percentage of the mix.
Andys example showed for the last stage a residual steam percentage of 14%. Since the last stage is the biggest part it is it's size which has the greatest effect. (mine has about 25% residual, two stages vs three)
The simple had 72% residual.
So for last stages only; if the simple were 100 in^3 mine would be 24 in^3 and Andys 21. This is, of course, a comparison of only one operating parameter where the simple has probably overreached it's limit. If we back off on the number of expansions and the theoretical efficiencys and the consequent little losses for the simple there is probably a little more overlap between the simple and the compound.
Good Day to All -------------- Bill G.
6
At full power design exhaust pressure is around 23# abs and about 300 degrees. If the condenser can handle this it will handle the lower temps and pressures at partial power output. The idea is that the 'excess' expansions of the compound at partial output get absorbed in the wet steam region and the condenser can maintain a pressure slightly lower than engine exhaust.
Again there are a lot of work BTUs to get picked up under partial power conditions with the extra expansions and it doesn't take many to significantly increase efficiency.
Note that Andy set up the examples of the simple and the compound at about the same expansion ratios and the same efficiencys. At this the simple was about at its limit for expansions and efficiency at a very low cutoff while the compound was just getting started. The simple was using about a 1% cutoff and the compound 38%. The large difference in HP/in^3 was because at very low cutoffs the amount of residual steam in a simple is such a much higher percentage of the mix.
Andys example showed for the last stage a residual steam percentage of 14%. Since the last stage is the biggest part it is it's size which has the greatest effect. (mine has about 25% residual, two stages vs three)
The simple had 72% residual.
So for last stages only; if the simple were 100 in^3 mine would be 24 in^3 and Andys 21. This is, of course, a comparison of only one operating parameter where the simple has probably overreached it's limit. If we back off on the number of expansions and the theoretical efficiencys and the consequent little losses for the simple there is probably a little more overlap between the simple and the compound.
Good Day to All -------------- Bill G.
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Re: Williams ws. Rankin March 14, 2006 03:00PM |
Registered: 19 years ago Posts: 835 |
Bill you have to also take into account the BTU loss through the entire system. every thing that has a loss is a condencer ie. the line from the boiler to to the engine , the engine, even the oil. Heat reclimed in the cyclone is calculated at 39% however in the real world it is probaly near 25%. It has no line loss or engine loss. A compound has large port heat losses that are not showing up on a paper engine.
Harry
Harry
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Re: Williams ws. Rankin March 14, 2006 04:17PM |
Registered: 19 years ago Posts: 1,268 |
Harry,
I hope that you were not thinking that in any way I was downing your engine. That is simply not the case as I believe it to be a magnificent piece of engineering and development. It's just that I see some possibilities with a compound that are worth pursueing.
It was with that in mind that I came up with a design that would alleviate some of the common disadvantages of the compound. Other than the line from the boiler to the engine many of the heat losses are contained, differently than with your engine but effectively. For its big size it s a very compact engine and should be easy to insulate.
As I mentioned not everything about it can be posted on the Phorum, wish it could. Sometimes the neccessity of holding back information makes it sound like, to misquote Dylan " Don't know what I'm tryin to hide to begin with". Hope thats not so.
Wishing You and your project well ---------- Bill G.
I hope that you were not thinking that in any way I was downing your engine. That is simply not the case as I believe it to be a magnificent piece of engineering and development. It's just that I see some possibilities with a compound that are worth pursueing.
It was with that in mind that I came up with a design that would alleviate some of the common disadvantages of the compound. Other than the line from the boiler to the engine many of the heat losses are contained, differently than with your engine but effectively. For its big size it s a very compact engine and should be easy to insulate.
As I mentioned not everything about it can be posted on the Phorum, wish it could. Sometimes the neccessity of holding back information makes it sound like, to misquote Dylan " Don't know what I'm tryin to hide to begin with". Hope thats not so.
Wishing You and your project well ---------- Bill G.
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Re: Williams ws. Rankin March 14, 2006 04:53PM |
Registered: 19 years ago Posts: 835 |
Bill
Like wise this is a foram for new ideas and I was just expressing some of the things that we had learned as I can learn from your ideas. Lively descusions bring out the best.
We all have our pet ideas. BMW, we can knock, they can afford it. At least Europe is looking at steam and that is to our benefit. It gives steam a new creditably. Whow! they just discovered a swash plate wheras this foram had debunked it a long time ago. see, they should have followed this foram. Keep banging away Bill
Harry
Like wise this is a foram for new ideas and I was just expressing some of the things that we had learned as I can learn from your ideas. Lively descusions bring out the best.
We all have our pet ideas. BMW, we can knock, they can afford it. At least Europe is looking at steam and that is to our benefit. It gives steam a new creditably. Whow! they just discovered a swash plate wheras this foram had debunked it a long time ago. see, they should have followed this foram. Keep banging away Bill
Harry
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Re: Williams ws. Rankin March 14, 2006 05:00PM |
Registered: 19 years ago Posts: 1,038 |
Hi Herry
Regarding losses. The typical loss appied to the Rankine cycle is 15% acording to all my engineering books. They are quite old. Were talking about 125 PSI to 300 PSI steam. These designs were based on no compression. From my calculations with compressions and with no compression I get that much and more differance between compression compared to non-cmpression. So if thoes old engin could operate at the low pressures with most of their losses acounted for by clearance loss I would expect a high compression engine to have very little loss at the same pressures. The Williams seams to prove this out. These were very large engines. Lots of surface area.
If your exhaust pressure is 20 PSIA then you sure have a lot of loss. I was using just slight lower pressure then the end of expansion pressure.
With that exhaust pressure (20 PSIA) the theortical HP/in^3 @3600 RPM is 6.36 HP/cuin. Thats twice what you clame to be getting. 180 PSIA exhaust pressure works out to 3.29 HP/cuin. I just revamped my cycle function to figure pump losses. These are the new figures with pump losses. Your engine figures higher efficiency 26.6% at 180 exhaust pressure. at 20 PSIA it drops to 23%.
Andy
Regarding losses. The typical loss appied to the Rankine cycle is 15% acording to all my engineering books. They are quite old. Were talking about 125 PSI to 300 PSI steam. These designs were based on no compression. From my calculations with compressions and with no compression I get that much and more differance between compression compared to non-cmpression. So if thoes old engin could operate at the low pressures with most of their losses acounted for by clearance loss I would expect a high compression engine to have very little loss at the same pressures. The Williams seams to prove this out. These were very large engines. Lots of surface area.
If your exhaust pressure is 20 PSIA then you sure have a lot of loss. I was using just slight lower pressure then the end of expansion pressure.
With that exhaust pressure (20 PSIA) the theortical HP/in^3 @3600 RPM is 6.36 HP/cuin. Thats twice what you clame to be getting. 180 PSIA exhaust pressure works out to 3.29 HP/cuin. I just revamped my cycle function to figure pump losses. These are the new figures with pump losses. Your engine figures higher efficiency 26.6% at 180 exhaust pressure. at 20 PSIA it drops to 23%.
Andy
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Re: Williams ws. Rankin March 14, 2006 05:11PM |
Registered: 19 years ago Posts: 1,038 |
Hi Bill
The engine I am working on is closest to the 1480 PSIA, 800F 3 stage compound. On paper the static cycles work to 30.5% efficiency with a power density of 0.91 HP/in^3. I do not like HP power densities calculated from static cycles. There lots of dynamic losses not included in static cycle calculation. What I mean by static cycle is basicly the text book like cycle that has no time factor. You can apply a percentage loss as you did. But really the static cycle doesn't tell us how RPM will effect output etc. Verious losses are time dependent. At higher RPM there is less heat losses and higher flow losses for example. I prefer work densities ft-lb/in^3 at this point. HP at 3600 RPM is meaningless on a paper engine. History shows power droping quickly above 1000 RPM on piston engines. It is unclear the cause of that drop. It apears to be flow resistance. The power curves I have match up will when flow restricton pressure drop is applied to inlet pressure. The S.E.S. papers have some HP plots of their engines and found some torque curves for Doble engine.
For comparsion I calculated HP density at Harry's staed RPM. So to sumerize the results.
Power . Power ................ Expansion ........ Inlet
density density ... eff stages ratio Quality Pressure temperature
HP/in^3 ftlb/in^3 ..... ....... x:1 .. .... .. .... ..
.249 .. 2.29 ... 30.6% . 1 .. 25.6 .. 95.4 .. 1000 ... 950
.914 .. 8.38 ... 30.5% . 3 .. 24.1 .. 89.2 .. 1480 ... 800 Andy
1.14 .. 10.5 ... 38.3% . 3 .. 60.0 .. 90.4 .. 4000 .. 1200
3.26 .. 29.9 ... 23.7% . 1 .. 7.71 .. 1.00 .. 3200 .. 1200 Harry??
3.45 .. 31.3 ... 30.3% . 3 .. 26.3 .. 87.6 .. 6000 .. 1150
Harry I figured the single stage supper critical engine to use what I could find on your engine. That was 3200 PSIA and 1200F inlet pressure, and 6% cutoff. No clearance spec - used 8%, No exhaust pressure spec - used 220 PSIA and full compression to back to inlet pressure. Pump work was not figured in efficiency calculatios but could easly be done. If you have thoes it would be of interest to see how close my compression cycle comes to a real engine.
What I see here is that to get high power densities we need high pressure. High RPM is also going to help increase HP power density. Harry, I can't comment on your efficiency. The exhaust pressure effects efficiency. With full compression, clearance has little effect on efficiency. Clearance does effects power density. I came up with thoes values from your 3 HP/in^3 at 3600 RPM power density clame.
I posted an analysis done with the 20 PSIA exhaust. Power density of 6.36 HP/cuin @ 3600.
Do you have a pressure sensor/gage in your exhaust line. Does the pressure vary much?
Andy
The engine I am working on is closest to the 1480 PSIA, 800F 3 stage compound. On paper the static cycles work to 30.5% efficiency with a power density of 0.91 HP/in^3. I do not like HP power densities calculated from static cycles. There lots of dynamic losses not included in static cycle calculation. What I mean by static cycle is basicly the text book like cycle that has no time factor. You can apply a percentage loss as you did. But really the static cycle doesn't tell us how RPM will effect output etc. Verious losses are time dependent. At higher RPM there is less heat losses and higher flow losses for example. I prefer work densities ft-lb/in^3 at this point. HP at 3600 RPM is meaningless on a paper engine. History shows power droping quickly above 1000 RPM on piston engines. It is unclear the cause of that drop. It apears to be flow resistance. The power curves I have match up will when flow restricton pressure drop is applied to inlet pressure. The S.E.S. papers have some HP plots of their engines and found some torque curves for Doble engine.
For comparsion I calculated HP density at Harry's staed RPM. So to sumerize the results.
Power . Power ................ Expansion ........ Inlet
density density ... eff stages ratio Quality Pressure temperature
HP/in^3 ftlb/in^3 ..... ....... x:1 .. .... .. .... ..
.249 .. 2.29 ... 30.6% . 1 .. 25.6 .. 95.4 .. 1000 ... 950
.914 .. 8.38 ... 30.5% . 3 .. 24.1 .. 89.2 .. 1480 ... 800 Andy
1.14 .. 10.5 ... 38.3% . 3 .. 60.0 .. 90.4 .. 4000 .. 1200
3.26 .. 29.9 ... 23.7% . 1 .. 7.71 .. 1.00 .. 3200 .. 1200 Harry??
3.45 .. 31.3 ... 30.3% . 3 .. 26.3 .. 87.6 .. 6000 .. 1150
Harry I figured the single stage supper critical engine to use what I could find on your engine. That was 3200 PSIA and 1200F inlet pressure, and 6% cutoff. No clearance spec - used 8%, No exhaust pressure spec - used 220 PSIA and full compression to back to inlet pressure. Pump work was not figured in efficiency calculatios but could easly be done. If you have thoes it would be of interest to see how close my compression cycle comes to a real engine.
What I see here is that to get high power densities we need high pressure. High RPM is also going to help increase HP power density. Harry, I can't comment on your efficiency. The exhaust pressure effects efficiency. With full compression, clearance has little effect on efficiency. Clearance does effects power density. I came up with thoes values from your 3 HP/in^3 at 3600 RPM power density clame.
I posted an analysis done with the 20 PSIA exhaust. Power density of 6.36 HP/cuin @ 3600.
Do you have a pressure sensor/gage in your exhaust line. Does the pressure vary much?
Andy
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Re: Williams ws. Rankin March 14, 2006 05:39PM |
Registered: 19 years ago Posts: 835 |
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Re: Williams ws. Rankin March 14, 2006 08:19PM |
Registered: 19 years ago Posts: 1,268 |
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Re: Williams ws. Rankin March 15, 2006 10:41AM |
Registered: 19 years ago Posts: 1,441 |
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Re: Williams ws. Rankin March 15, 2006 12:12PM |
Registered: 19 years ago Posts: 1,038 |
Herry
The exhaust pressure is the back pressure on the engine. That is the term used in the description of the Rankine cycle. An engine operates between inlet pressure and exhaust pressure. So we can understand each other. The points in the high compression static cycle are:
Inlet, Cutoff, end of expansion, exhaust, and compression.
Inlet, is just what it says. It is the stean properties of the fresh inlet steam entering the engine.
Cutoff, is the steam properties at the cutoff point. At this point we have a mixture of inlet steamm and residual steam. Between inlet and cutoff we have constant pressure. The residual steam is isentropicly changed to the inlet prssure and the cutoff state is figured as from the specific volume and enthalpy of the mixture. Specific volume being: cutoff volume divided by the sum of the inlet amd reidual mass and enyhalpy simply being the sume of the enthalpy of the two divided by the total mass to get specific enthalpy.
End of expansion is figured as an isentropic expansion to that point.
Exhaust is figured as an isoenthalip pressure change to the set exhaust(back pressure on the engine). Can use isentropic change as well or a combination depending on exhaust calk setting. I am using isenthalip as that seams to agree with the uniflow temperature charts that Peter H. posted on another thread.
Compression is an isentropic compression to the set compression pressure.
So is that 20 PSIA what I call exhaust pressure. I am doing static ideal cycles analysis to arive at the numbers I stated.
The cycle I used to get close to your supper critical engine cycle was inlet steam at 3200 PSIA and 1200F. 8% clearance, 6% cutoff, 20 PSIA exhaust (back pressure), and full compressio back to 3200 PSIA. Calculated out to 6.36466 HP/in^3 @ 3600 RPM. See the pdf on my last post. With pump work figured in the efficiency came out to 23%. If I use a exhaust back pressure of 180 PSIA the hp/in^3 comes out close to 3 Hp/in^3. Less clearance can also incrase hp/in^3.
If your exhaust back pressure is really 20 PSIA. Then you are lossing 50% of your power some were. That means you are operatoring closer to 11% efficiency then the 23% efficiency. On the other hand with an exhaust back pressure of 180 PSIA the cycle calculates out to 3.29 HP/in^3 at 26% efficiency. Pump work has been figured in to these numbers. In the 20 PSIA exhaust case you engine efficiency would be around 50% and at 180 PSIA it woulkd be closer to 100%. Note engine efficiency is not thermal efficiency. Engine efficiency is real engine performance against the ideal cycle.
The static cycle os only dealing with the engine processes. No other devices are involved. You may have heat recovery helping you efficiency that is ifigured in to an engine cycle.
The new function no longer figure feed water at atmospheric pressure 180 F. That ws the standard in my text books. I now figure feed water to be at exhaust pressure and it's temperature to be at 85% of the saturation temperature at the exhaust pressure. There wouldbe some pressure drop across the condenser. That is not figured in here. But it means your closed engine should calculater out closer. At the higher exhaust pressure there is around 12% less heat of vaporazation to remove to condense the steam. The pump work also a bit less.
I havn't noticed anyware you having made any efficiency clames.
Don't take offense. Just trying to make sense of what you have told us. I like the power density you are getting. But would also like to see good efficiency.
Atached is the analysis of single stage supper critical engine 3200 PSIA, 1200F.
Exhaust 12 20 PSIAand 180 PSIA. Cycle state point array shows inlet, cutoff, expansion, exhaust, and clearance points. First colum is cycle parameters. Also ataching Rankine.mcd that containes the cycle function used. I use Mr. Eds IFC-67 steamm library for the steamm property calculations.
Andy
The exhaust pressure is the back pressure on the engine. That is the term used in the description of the Rankine cycle. An engine operates between inlet pressure and exhaust pressure. So we can understand each other. The points in the high compression static cycle are:
Inlet, Cutoff, end of expansion, exhaust, and compression.
Inlet, is just what it says. It is the stean properties of the fresh inlet steam entering the engine.
Cutoff, is the steam properties at the cutoff point. At this point we have a mixture of inlet steamm and residual steam. Between inlet and cutoff we have constant pressure. The residual steam is isentropicly changed to the inlet prssure and the cutoff state is figured as from the specific volume and enthalpy of the mixture. Specific volume being: cutoff volume divided by the sum of the inlet amd reidual mass and enyhalpy simply being the sume of the enthalpy of the two divided by the total mass to get specific enthalpy.
End of expansion is figured as an isentropic expansion to that point.
Exhaust is figured as an isoenthalip pressure change to the set exhaust(back pressure on the engine). Can use isentropic change as well or a combination depending on exhaust calk setting. I am using isenthalip as that seams to agree with the uniflow temperature charts that Peter H. posted on another thread.
Compression is an isentropic compression to the set compression pressure.
So is that 20 PSIA what I call exhaust pressure. I am doing static ideal cycles analysis to arive at the numbers I stated.
The cycle I used to get close to your supper critical engine cycle was inlet steam at 3200 PSIA and 1200F. 8% clearance, 6% cutoff, 20 PSIA exhaust (back pressure), and full compressio back to 3200 PSIA. Calculated out to 6.36466 HP/in^3 @ 3600 RPM. See the pdf on my last post. With pump work figured in the efficiency came out to 23%. If I use a exhaust back pressure of 180 PSIA the hp/in^3 comes out close to 3 Hp/in^3. Less clearance can also incrase hp/in^3.
If your exhaust back pressure is really 20 PSIA. Then you are lossing 50% of your power some were. That means you are operatoring closer to 11% efficiency then the 23% efficiency. On the other hand with an exhaust back pressure of 180 PSIA the cycle calculates out to 3.29 HP/in^3 at 26% efficiency. Pump work has been figured in to these numbers. In the 20 PSIA exhaust case you engine efficiency would be around 50% and at 180 PSIA it woulkd be closer to 100%. Note engine efficiency is not thermal efficiency. Engine efficiency is real engine performance against the ideal cycle.
The static cycle os only dealing with the engine processes. No other devices are involved. You may have heat recovery helping you efficiency that is ifigured in to an engine cycle.
The new function no longer figure feed water at atmospheric pressure 180 F. That ws the standard in my text books. I now figure feed water to be at exhaust pressure and it's temperature to be at 85% of the saturation temperature at the exhaust pressure. There wouldbe some pressure drop across the condenser. That is not figured in here. But it means your closed engine should calculater out closer. At the higher exhaust pressure there is around 12% less heat of vaporazation to remove to condense the steam. The pump work also a bit less.
I havn't noticed anyware you having made any efficiency clames.
Don't take offense. Just trying to make sense of what you have told us. I like the power density you are getting. But would also like to see good efficiency.
Atached is the analysis of single stage supper critical engine 3200 PSIA, 1200F.
Exhaust 12 20 PSIAand 180 PSIA. Cycle state point array shows inlet, cutoff, expansion, exhaust, and clearance points. First colum is cycle parameters. Also ataching Rankine.mcd that containes the cycle function used. I use Mr. Eds IFC-67 steamm library for the steamm property calculations.
Andy
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Re: Williams ws. Rankin March 15, 2006 04:13PM |
Registered: 19 years ago Posts: 835 |
Andy You have complety missed it. clearance is 5% comp is 27 to 1 at 20 psi atmos. which lowers clearance volume. crankcase preasure is equel on the bottom of the piston. This engine is difficult to explane everything that is going on as it is all interrelated. the clearance volume also changes as rpm changes with the cutoff that varies 3% to overlap. and on and on.
Harry
Harry
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Re: Williams ws. Rankin March 15, 2006 05:09PM |
Registered: 19 years ago Posts: 1,038 |
Hi Herry
Wait a minut. 5% clearnce and 27:1 compression?? Can't buy that Herry. 1.05/0.05=21. Max if compressing full stroke is 21:1.
What are the parameters for the 3 HP/cuin? I might be able to do a cycle that matches it. Except for the 1472 F temperature limit of the IFC-67 formulations. I tried 5% clearance 20 PSIA and could only get 19.9:1 compression ratio. I have checks that limit compression to 1472 F to stay in the IFC-67 formulation temperature range.
Atached is cycles with 5% clearance. At 20PSIA exhaust I am limited to 19.9 compresion ratio by the 1472 temp limit. But with 5% clearance you could only reach 21:1 compressing full stroke any way.
Wait a minut. 5% clearnce and 27:1 compression?? Can't buy that Herry. 1.05/0.05=21. Max if compressing full stroke is 21:1.
What are the parameters for the 3 HP/cuin? I might be able to do a cycle that matches it. Except for the 1472 F temperature limit of the IFC-67 formulations. I tried 5% clearance 20 PSIA and could only get 19.9:1 compression ratio. I have checks that limit compression to 1472 F to stay in the IFC-67 formulation temperature range.
Atached is cycles with 5% clearance. At 20PSIA exhaust I am limited to 19.9 compresion ratio by the 1472 temp limit. But with 5% clearance you could only reach 21:1 compressing full stroke any way.
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Re: Williams ws. Rankin March 16, 2006 09:32AM |
Registered: 19 years ago Posts: 835 |
Andy sorry I mistyped clearance is 3%, should have read it but was in a rush have fun. It drops to4to 1 comp at 1rpm However this will not calculate correctly because of the reheat stage. 5% was the original cutoff and it stuck in my mind it was increased to 6% for an increase of max power However it did increse the water rate by a small amount. the best water rate is at 3% cutoff at 2000 rpm which is aprox 25hp where most cars would cruse.Again this is all varible and can be changed at will or a simple (computer)I know you like that, computer.It basicaly rpm dependent.
Harry
Harry
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Re: Williams ws. Rankin March 16, 2006 10:35AM |
Registered: 19 years ago Posts: 1,268 |
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Re: Williams ws. Rankin March 16, 2006 01:17PM |
Registered: 19 years ago Posts: 835 |
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Re: Williams ws. Rankin March 16, 2006 01:57PM |
Registered: 19 years ago Posts: 1,268 |
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Re: Williams ws. Rankin March 16, 2006 05:03PM |
Registered: 19 years ago Posts: 835 |
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Re: Williams ws. Rankin March 16, 2006 05:32PM |
Registered: 19 years ago Posts: 1,038 |
hi Harry
Is the 20 PSIA the exhaust pressure Does the cylander pressure drop anywars near 20 PSIA? The problmel I have with the 20 PSIA is that even 3% clearance is not near small enough to compress back up to 3200 PSIA. You would need >56:1 compression ratio.
Any compression helps efficiency. Full cmpression back to inlet pressure is not necessary for improvements.
A closed system could run the whole cycle at higher pressure. Say an exhaust pressure of 130 PSIA. The increassed pressure reduces output work, But on paper the efficiency increasses. Pump work is less and at the higher condenser pressure there is less heat to extract to condense to a liquid.
Would be interesting to varify this. How much pressure can your low pressure side take?
Keep up the good work.
Andy
Is the 20 PSIA the exhaust pressure Does the cylander pressure drop anywars near 20 PSIA? The problmel I have with the 20 PSIA is that even 3% clearance is not near small enough to compress back up to 3200 PSIA. You would need >56:1 compression ratio.
Any compression helps efficiency. Full cmpression back to inlet pressure is not necessary for improvements.
A closed system could run the whole cycle at higher pressure. Say an exhaust pressure of 130 PSIA. The increassed pressure reduces output work, But on paper the efficiency increasses. Pump work is less and at the higher condenser pressure there is less heat to extract to condense to a liquid.
Would be interesting to varify this. How much pressure can your low pressure side take?
Keep up the good work.
Andy
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Re: Williams ws. Rankin March 17, 2006 09:19AM |
Registered: 19 years ago Posts: 835 |
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Re: Williams ws. Rankin March 17, 2006 06:28PM |
Registered: 19 years ago Posts: 1,453 |
Andy, as I recall the Cyclone (regenerative) condenser acts as a centrifugal compressor, compressing the exhaust steam downline from exhaust ports to boost exhaust temp for better heat exchange. Look at the stated piston speeds, displacement, & target hps; this is not a full-expansion or full-compression (between cyl & heat exchanger pressures) engine. Emphasis on power/weight & multi-path heat regeneration. Interesting approach. Bill, 3% clearance with 2" stroke would be a 0.06" (a leprechaun hair under 1/16"
gap between piston crown & head (both dead-flat) at tdc. Tight, but sounds doable. Avg piston speed at cruise in the Stanley range (2"/2000rpm ~= 4"/1000). Not taking sides/debating here, just some notes to consider from what I've read. It's still a head-scratcher to me; corrections [and esp road tests] welcome.
Peter
gap between piston crown & head (both dead-flat) at tdc. Tight, but sounds doable. Avg piston speed at cruise in the Stanley range (2"/2000rpm ~= 4"/1000). Not taking sides/debating here, just some notes to consider from what I've read. It's still a head-scratcher to me; corrections [and esp road tests] welcome.
Peter
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Re: Williams ws. Rankin March 20, 2006 09:45AM |
Registered: 19 years ago Posts: 1,038 |
Hi Peter.
All that you say is correct. But the cycle calculation somewhat agrees with Harry's clame of 3 HP/cuin. The exhaust pressure makes a big differance in power density. If I use a pressure just below end of expansion pressure I do come up with a little better then 3 HP/cuin. If I use the 20 PSI then I come up with over 6 HP/cuin. I am not sure what anyone means by condenser pressure. Are we talking about the engine side or the output side? If it is the engine side. Then that is basicly the exhaust pressure. If it is the exhaust pressure then there is a lot of loss in that engine compared to the ideal cycle. I hadn't noticed but my cycle calculations were limiting compression to 1472 F temperature limit falling short of full compression when using 20 PSIA exhaust pressure. Compression is also limited by the clearance.
The main point is that the power density clamed by Harry is more then possable.
Andy
All that you say is correct. But the cycle calculation somewhat agrees with Harry's clame of 3 HP/cuin. The exhaust pressure makes a big differance in power density. If I use a pressure just below end of expansion pressure I do come up with a little better then 3 HP/cuin. If I use the 20 PSI then I come up with over 6 HP/cuin. I am not sure what anyone means by condenser pressure. Are we talking about the engine side or the output side? If it is the engine side. Then that is basicly the exhaust pressure. If it is the exhaust pressure then there is a lot of loss in that engine compared to the ideal cycle. I hadn't noticed but my cycle calculations were limiting compression to 1472 F temperature limit falling short of full compression when using 20 PSIA exhaust pressure. Compression is also limited by the clearance.
The main point is that the power density clamed by Harry is more then possable.
Andy
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Re: Williams ws. Rankin March 20, 2006 04:25PM |
Registered: 19 years ago Posts: 835 |
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Re: Williams ws. Rankin March 20, 2006 07:57PM |
Registered: 19 years ago Posts: 318 |
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Re: Williams ws. Rankin March 21, 2006 01:13PM |
Registered: 19 years ago Posts: 1,038 |
Hi Howard
The mathcad cycle function I have developed all use steam properties. Sorry havn't got any air cycles functions. They would be somewhat simpler.
The cycle calculater I have fugures 5 points plus pump work. The five points are inlet, cutoff, expansion, exhaust, and compression. Inlet is a set state given pressure and temperature. cutoff is figured as a mixture of the residual steam mass and inlet steam mass. The residual steam mass's properties is figured as an isentropic compression to up inlet pressure or as an isoenthalip expansion down to inlet pressure. Residules steam is either compressed by the inlet steam or an out flow occures when the inlet opens. The expansion is figured as an isentropic expasion. The expansion is figured given cutoff, expansion ratio, or ending pressure. The exhaust point is a set pressure. I am usen an isenthalip process for the pressure change from expansion to exhaust point. The compression point is figured as an isentropic compression. My MathCad steamm cycle functions return a cycle array having 6 columns and 7 rows.
The parameters in the first column:
Scale, Multi stage scaling factor. Scale factor to make a stage use same amount of inlet steam as the precious stage. 1.0 for singe expansion and first stage.
Clearance, Engine clearance as relitive to displacement.
Cutoff, Point inlet valve closes as a part of the stroke.
Exhaust close/compression, Point at which exhaust valve closes. Compression occures for this part of stoke. 0.98 means the compression occures over 98% of stroke.
Makeup steam part, Multi stage parameter. Part of inlet steam that is throttled down from first stage inlet. Used in power range analysis where relative stage size has been deturmned and fixed. Scale in this case is to make end of expansion volume match relative stage size. relative stage size is such that each stage uses as much or more steam as the previous. This make up parameter is the additional steam needed above that output from the previous stage.
Residual part, The mass of steam in the engine when the exhaust closes.
Inlet part. The mass of fress steam admitted thrugh the inlet port. The Residual part plus the inlet part make up 1 pound of steam.
Column 2 is the inlet steam properties.
Column 3 is the is the steam properties at the cutoff point. A mixture of residual and inlet steamm.
Comumn 4 is the expansion point. The steam properties at the end of expansion before the exhaust opens.
Column 5 is the residual steam properties after droping to the exhaust pressure.
Column 6 is the compressed steam properties. Compression is limited by IFC-67 1472 F temperature limit and by the maxum compression ration set by the clearance volume. Otherwise compression is to a given set pressure. It is computed as an isentropic compression from the exhaust point.
The state point columns 2 - 6 contain steam propertys. From top row to bottom:
Pressure, Temperature, Specific Volume, Specific internal energy, Specific enthalpy, Specific entropy, and Quality.
The following is an example of a cycle array having supper critical inlet at 3200 PSIA and 1200F.
1 _____ 3200 _____ 3200 _______ 138.909 ___ 130 _______ 3200
0.03 __ 1200 ______ 1208.594 __ 355.586 ___ 352.345 ___ 1226.225
0.06 __ 0.282746111 0.284833305 3.260364978 3.483409237 0.28908362
0.33149 1402.905 __ 1407.269 __ 1110.961 __ 1110.971 __ 1416.202
0 _____ 1570.335 __ 1575.936 __ 1194.769 __ 1194.769 __ 1587.386
0.32849 1.5748535 _ 1.5782195 _ 1.5782195 _ 1.5850467 _ 1.5850467
0.67151 1 _________ 1 _________ 1 _________ 1 _________ 1
The parameter colume shows a 3% clearance, 6% cutoff with compression for 33.149% of the stroke. This is not a uniflow engine. The exhaust is open for almost 66% of the stroke. There is 0.67151 pounds of steam going through the engine while 0.32849 pounds is residual steam recycled in the engine. This cycle predicts 3.78167 HP/cuin at 3600 RPM. The inlet columes shows the steam state at 3200 PSIA and 1200 F. At cutoff the compressed residual steam has mixed with the inlet steam and brings the mixture temp up to 1208.594F. With 3% clearance and 6% cutoff the steam expands to 138.909 PSIA a long a constant entropy line of 1.5782195. It drops to 130 PSIA exhaust pressure retaining it's enthalpy of 1194.769 and is then compressed back up to 3200 PSIA were it atains a temperature of 1226.2F. This is a stable compression cycle. It is calculated by an iteration method until the cutoff enthalpy remains stable.
It isn't Harry's cycle. I havn't developed any uniflow cycle functions. The process of the pressure drop at exhaust is debatable. Using constant enthalpy process doesn't work out wih conservation of energy laws. But I can not get an isentropic process as sugested by Ted to work out either. On another topic a UniFlow temperature chart was posted. It shows clearly that the presure drop of the residual steam can not be isentropic as the compression temperature is clearly above the inlet temperature.
Andy sorry Howard. I don't have siftware to do that. Can do for steam. Would take some time to develop thoes function.
Andy
The mathcad cycle function I have developed all use steam properties. Sorry havn't got any air cycles functions. They would be somewhat simpler.
The cycle calculater I have fugures 5 points plus pump work. The five points are inlet, cutoff, expansion, exhaust, and compression. Inlet is a set state given pressure and temperature. cutoff is figured as a mixture of the residual steam mass and inlet steam mass. The residual steam mass's properties is figured as an isentropic compression to up inlet pressure or as an isoenthalip expansion down to inlet pressure. Residules steam is either compressed by the inlet steam or an out flow occures when the inlet opens. The expansion is figured as an isentropic expasion. The expansion is figured given cutoff, expansion ratio, or ending pressure. The exhaust point is a set pressure. I am usen an isenthalip process for the pressure change from expansion to exhaust point. The compression point is figured as an isentropic compression. My MathCad steamm cycle functions return a cycle array having 6 columns and 7 rows.
The parameters in the first column:
Scale, Multi stage scaling factor. Scale factor to make a stage use same amount of inlet steam as the precious stage. 1.0 for singe expansion and first stage.
Clearance, Engine clearance as relitive to displacement.
Cutoff, Point inlet valve closes as a part of the stroke.
Exhaust close/compression, Point at which exhaust valve closes. Compression occures for this part of stoke. 0.98 means the compression occures over 98% of stroke.
Makeup steam part, Multi stage parameter. Part of inlet steam that is throttled down from first stage inlet. Used in power range analysis where relative stage size has been deturmned and fixed. Scale in this case is to make end of expansion volume match relative stage size. relative stage size is such that each stage uses as much or more steam as the previous. This make up parameter is the additional steam needed above that output from the previous stage.
Residual part, The mass of steam in the engine when the exhaust closes.
Inlet part. The mass of fress steam admitted thrugh the inlet port. The Residual part plus the inlet part make up 1 pound of steam.
Column 2 is the inlet steam properties.
Column 3 is the is the steam properties at the cutoff point. A mixture of residual and inlet steamm.
Comumn 4 is the expansion point. The steam properties at the end of expansion before the exhaust opens.
Column 5 is the residual steam properties after droping to the exhaust pressure.
Column 6 is the compressed steam properties. Compression is limited by IFC-67 1472 F temperature limit and by the maxum compression ration set by the clearance volume. Otherwise compression is to a given set pressure. It is computed as an isentropic compression from the exhaust point.
The state point columns 2 - 6 contain steam propertys. From top row to bottom:
Pressure, Temperature, Specific Volume, Specific internal energy, Specific enthalpy, Specific entropy, and Quality.
The following is an example of a cycle array having supper critical inlet at 3200 PSIA and 1200F.
1 _____ 3200 _____ 3200 _______ 138.909 ___ 130 _______ 3200
0.03 __ 1200 ______ 1208.594 __ 355.586 ___ 352.345 ___ 1226.225
0.06 __ 0.282746111 0.284833305 3.260364978 3.483409237 0.28908362
0.33149 1402.905 __ 1407.269 __ 1110.961 __ 1110.971 __ 1416.202
0 _____ 1570.335 __ 1575.936 __ 1194.769 __ 1194.769 __ 1587.386
0.32849 1.5748535 _ 1.5782195 _ 1.5782195 _ 1.5850467 _ 1.5850467
0.67151 1 _________ 1 _________ 1 _________ 1 _________ 1
The parameter colume shows a 3% clearance, 6% cutoff with compression for 33.149% of the stroke. This is not a uniflow engine. The exhaust is open for almost 66% of the stroke. There is 0.67151 pounds of steam going through the engine while 0.32849 pounds is residual steam recycled in the engine. This cycle predicts 3.78167 HP/cuin at 3600 RPM. The inlet columes shows the steam state at 3200 PSIA and 1200 F. At cutoff the compressed residual steam has mixed with the inlet steam and brings the mixture temp up to 1208.594F. With 3% clearance and 6% cutoff the steam expands to 138.909 PSIA a long a constant entropy line of 1.5782195. It drops to 130 PSIA exhaust pressure retaining it's enthalpy of 1194.769 and is then compressed back up to 3200 PSIA were it atains a temperature of 1226.2F. This is a stable compression cycle. It is calculated by an iteration method until the cutoff enthalpy remains stable.
It isn't Harry's cycle. I havn't developed any uniflow cycle functions. The process of the pressure drop at exhaust is debatable. Using constant enthalpy process doesn't work out wih conservation of energy laws. But I can not get an isentropic process as sugested by Ted to work out either. On another topic a UniFlow temperature chart was posted. It shows clearly that the presure drop of the residual steam can not be isentropic as the compression temperature is clearly above the inlet temperature.
Andy sorry Howard. I don't have siftware to do that. Can do for steam. Would take some time to develop thoes function.
Andy
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