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Valve area to cylinder volume ratios for various engines
Posted by: Caleb Ramsby (IP Logged)
Date: February 28, 2003 06:42PM
<HTML>Hi all,
I have been trying to figure out the valve area to the cylinder volume of various engine. I havn't been to find out much from looking in my various literature. The books go into detail about valve design, actuation and various other aspects, but not as much on valve size. Especially the car information.
I am wondering if any of you could either let me know where I could find a graph or table of various valve area to cylinder volume ratios of various valve designs and engine types or if some of you could enlighten me with your vast literature.
For comparision my latest engine deisgn has a 1 sq." of valve area to 4.588 cubic "s of expander volume or .22 sq.":1ci. ratio. I am just wondering how this ratio compares to the piston engines and their various valve types.
I know that the various valve designs have different flow patterns that can negate the larger valve area and there are other problems that arise with the various designs and I will keep this in mind.
I am aware that valve area is one of the biggest limitations in steam engine speed and the loses in pressure of the intake and increase in pressure in exhaust steam are to blame. With minimal pressure loss and steam velocity I would think that reciprocating steam engines could reach a piston speed of 3,000 fpm. and rotary expanders a much higher speed because of the lessened loads on engine parts. I know that locomotives got to some high speeds(around 1,500 fpm. and higher) but I believe they had to run at a low cutoff at higher speeds because of the pressure loss and steam velocity, thus their peak hp was limited.
Of course one must keep in consideration the expansion and flow of the steam at these high speed, because this causes some pecular results on it's own, as the steam tries to keep up and then get ahead of the expander when it is moving fast.
Well thanks for any help.
Caleb Ramsby</HTML>
I have been trying to figure out the valve area to the cylinder volume of various engine. I havn't been to find out much from looking in my various literature. The books go into detail about valve design, actuation and various other aspects, but not as much on valve size. Especially the car information.
I am wondering if any of you could either let me know where I could find a graph or table of various valve area to cylinder volume ratios of various valve designs and engine types or if some of you could enlighten me with your vast literature.
For comparision my latest engine deisgn has a 1 sq." of valve area to 4.588 cubic "s of expander volume or .22 sq.":1ci. ratio. I am just wondering how this ratio compares to the piston engines and their various valve types.
I know that the various valve designs have different flow patterns that can negate the larger valve area and there are other problems that arise with the various designs and I will keep this in mind.
I am aware that valve area is one of the biggest limitations in steam engine speed and the loses in pressure of the intake and increase in pressure in exhaust steam are to blame. With minimal pressure loss and steam velocity I would think that reciprocating steam engines could reach a piston speed of 3,000 fpm. and rotary expanders a much higher speed because of the lessened loads on engine parts. I know that locomotives got to some high speeds(around 1,500 fpm. and higher) but I believe they had to run at a low cutoff at higher speeds because of the pressure loss and steam velocity, thus their peak hp was limited.
Of course one must keep in consideration the expansion and flow of the steam at these high speed, because this causes some pecular results on it's own, as the steam tries to keep up and then get ahead of the expander when it is moving fast.
Well thanks for any help.
Caleb Ramsby</HTML>
Re: Valve area to cylinder volume ratios for various engines
Posted by: Roland Evans (IP Logged)
Date: February 28, 2003 10:35PM
<HTML>Caleb
I have never seen a list or known of a published ratio. The only way I have been able to calculate this is to study a given design. If it is an eccentric operated valve, the port area is never completely opened on the intake side. In most cases the exhaust side is always fully opened. The thing is it’s the time it is opened. Advance lead will give a valve fully opened at TDC. Up stroke is always different then the down stroke. A longer valve travel will create a longer time and less wire drawing as the speed of the valve is faster. Other valve gear can do other things. I still believe large valve area and straight ports with piston valves straight to the cylinder with almost no clearance volume, eccentric driven will make for a very nice engine as good as any other design on a piston operated engine. I think you have to calculate from the start of a design the max RPM you will need and figure the port area you will need to get rid of the exhaust steam.
Rolly</HTML>
I have never seen a list or known of a published ratio. The only way I have been able to calculate this is to study a given design. If it is an eccentric operated valve, the port area is never completely opened on the intake side. In most cases the exhaust side is always fully opened. The thing is it’s the time it is opened. Advance lead will give a valve fully opened at TDC. Up stroke is always different then the down stroke. A longer valve travel will create a longer time and less wire drawing as the speed of the valve is faster. Other valve gear can do other things. I still believe large valve area and straight ports with piston valves straight to the cylinder with almost no clearance volume, eccentric driven will make for a very nice engine as good as any other design on a piston operated engine. I think you have to calculate from the start of a design the max RPM you will need and figure the port area you will need to get rid of the exhaust steam.
Rolly</HTML>
Re: Valve area to cylinder volume ratios for various engines
Posted by: Caleb Ramsby (IP Logged)
Date: March 01, 2003 04:17PM
<HTML>Rolly,
I had a fealing that was the case. I had looked through my Kent and
Mark books and although they have siginificant data tables about the various specifics of steam engines I hadn't seen any valve area to cylinder volume ratios. Oh well, I guese I will just have to get some more engine drawings and study them.
One of the disadvantages with my engine is that there is a 90 deg. curve just as the steam enters the intake area of the engine and when leaving the exhaust. After it turns it goes straight into the expander. To make it other wise would make it very difficult to machine.
Sometimes I wish that I didn't understand that when one is designing an aparatus, it doesn't matter how well it works on paper if it can't be built or would take a substantial effort on the machinists side of things.
This is where one of my other obsessions comes into play, blacksmithing. After making two forges and many other contrivences that are needed to practice the art, then actually making things from just chunks of steel one gets a much more acute understanding of what it actually takes to bring something from a design to a working object, it also helps that when I was a little kid I was helping my father in his secondary job as an independant constructor. Making porches, sidewalks, walls and such.
When I calculate things I try to do a perfect theoretical calculation first, just to see what the engine could do if all things were perfect. Then I add in things like friction losses, loss of steam pressure through tubing, resistance of flow at valves and ect. After doing this it gives one a better understanding of what is lost in the various real world processes that the engine must do.
Caleb Ramsby</HTML>
I had a fealing that was the case. I had looked through my Kent and
Mark books and although they have siginificant data tables about the various specifics of steam engines I hadn't seen any valve area to cylinder volume ratios. Oh well, I guese I will just have to get some more engine drawings and study them.
One of the disadvantages with my engine is that there is a 90 deg. curve just as the steam enters the intake area of the engine and when leaving the exhaust. After it turns it goes straight into the expander. To make it other wise would make it very difficult to machine.
Sometimes I wish that I didn't understand that when one is designing an aparatus, it doesn't matter how well it works on paper if it can't be built or would take a substantial effort on the machinists side of things.
This is where one of my other obsessions comes into play, blacksmithing. After making two forges and many other contrivences that are needed to practice the art, then actually making things from just chunks of steel one gets a much more acute understanding of what it actually takes to bring something from a design to a working object, it also helps that when I was a little kid I was helping my father in his secondary job as an independant constructor. Making porches, sidewalks, walls and such.
When I calculate things I try to do a perfect theoretical calculation first, just to see what the engine could do if all things were perfect. Then I add in things like friction losses, loss of steam pressure through tubing, resistance of flow at valves and ect. After doing this it gives one a better understanding of what is lost in the various real world processes that the engine must do.
Caleb Ramsby</HTML>
Re: Valve area to cylinder volume ratios for various engines
Posted by: Jerry Peoples (IP Logged)
Date: March 01, 2003 08:37PM
<HTML>Caleb
"Admission Port Analyses", TM No. 133 is available from the SACA Storeroom for $8.00. Adequate port sizing depends upon cylinder volume, cutoff and engine speed.
Jerry</HTML>
"Admission Port Analyses", TM No. 133 is available from the SACA Storeroom for $8.00. Adequate port sizing depends upon cylinder volume, cutoff and engine speed.
Jerry</HTML>
Re: Valve area to cylinder volume ratios for various engines
Posted by: Roland Evans (IP Logged)
Date: March 02, 2003 10:13AM
<HTML>Port area
Doble used the formula Port area = Piston area times piston speed divided by 10,000
Herreshoff used on D valves engines the height of the port = the bore diameter divided by 10
And the width = diameter times .75 to .88
Rolly</HTML>
Doble used the formula Port area = Piston area times piston speed divided by 10,000
Herreshoff used on D valves engines the height of the port = the bore diameter divided by 10
And the width = diameter times .75 to .88
Rolly</HTML>
Re: Valve area to cylinder volume ratios for various engines
Posted by: Caleb Ramsby (IP Logged)
Date: March 03, 2003 11:23PM
<HTML>Jerry,
Thanks I will order that and take a look!
Rolly,
Thanks for the formulas, they will be very usefull.
Just this past weekend I visited my local used book store and found "Elements of Heat-Power Engineering" by, Hirshfeld and Barnard, 1913.
They state "For the rate at which the steam is supplied to the cylinder to ba always equal to the rate at which volume is made available by the piston, the following expression must be satisfied:
a times v = A times V
in which :
a = area of passage
A = area of piston
v = velocity of steam
V = velocity of piston
Then
a = A times V divided v
I think this will be a usefull one also.
Thanks all!
Caleb Ramsby</HTML>
Thanks I will order that and take a look!
Rolly,
Thanks for the formulas, they will be very usefull.
Just this past weekend I visited my local used book store and found "Elements of Heat-Power Engineering" by, Hirshfeld and Barnard, 1913.
They state "For the rate at which the steam is supplied to the cylinder to ba always equal to the rate at which volume is made available by the piston, the following expression must be satisfied:
a times v = A times V
in which :
a = area of passage
A = area of piston
v = velocity of steam
V = velocity of piston
Then
a = A times V divided v
I think this will be a usefull one also.
Thanks all!
Caleb Ramsby</HTML>
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