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free piston
Posted by: Peter Heid (IP Logged)
Date: February 02, 2002 11:03PM
<HTML>Has anyone had any experience with or information on a free piston steam engine? It would seem like a good canadate for auxilery power such as pumping and electrical power generation.</HTML>
Re: free piston
Posted by: Mark Stacey (IP Logged)
Date: February 04, 2002 07:05PM
<HTML>I'm not sure what engine you are referring to.
A direct acting steam pump ie. weir type, is a free piston unit. The necessity to make the pump self starting and its slow speed tends to reduce efficency so these pumps have fallen out of favour. Could you expand on what you envisioned?
Cheers
Mark Stacey</HTML>
A direct acting steam pump ie. weir type, is a free piston unit. The necessity to make the pump self starting and its slow speed tends to reduce efficency so these pumps have fallen out of favour. Could you expand on what you envisioned?
Cheers
Mark Stacey</HTML>
Re: free piston
Posted by: Victor Snell (IP Logged)
Date: February 06, 2002 08:32AM
<HTML>
While in the Navy I visited a display at Treasure Island in the Submarine
training school. There was a free piston engine there that was taken from
a German U Boat. If memory is correct.
Diesel powered, it just compressed air for blowing tanks and whatever.
Started by the same air tank, it was a nice piece of engineering. There
were comments about the fact that it could be built as a electrical generator too, with an excitation coil - in the piston and DC Voltage.Then
have the alternator winding on the outside. Stainless non magnetic casing where the coil would be as steel would retard the magnitic flux.
The piston rebounded off each end by having a dead compression space beyond the valve position at each end. There the fuel was injected to
drive it back for the other end and its cycle was repeted. It ran quiet and
vibration was not seen.
So how did they balance it ? You tell me.
Vic</HTML>
While in the Navy I visited a display at Treasure Island in the Submarine
training school. There was a free piston engine there that was taken from
a German U Boat. If memory is correct.
Diesel powered, it just compressed air for blowing tanks and whatever.
Started by the same air tank, it was a nice piece of engineering. There
were comments about the fact that it could be built as a electrical generator too, with an excitation coil - in the piston and DC Voltage.Then
have the alternator winding on the outside. Stainless non magnetic casing where the coil would be as steel would retard the magnitic flux.
The piston rebounded off each end by having a dead compression space beyond the valve position at each end. There the fuel was injected to
drive it back for the other end and its cycle was repeted. It ran quiet and
vibration was not seen.
So how did they balance it ? You tell me.
Vic</HTML>
Re: free piston
Posted by: Peter Heid (IP Logged)
Date: February 06, 2002 09:08PM
<HTML>The free piston engine of which I am refering to is an engine with no crank shaft or connecting rods. The source of power and the application of the engine do not concern the definition. The piston or pistons use a gas compression spring to afford the return travel after the power stroke. the piston is normally a double ended afair with one end being the power piston and the other is the gas spring piston (bounce piston) or in some applications such as pumping, it is also called thework piston. There many designs of free piston engines but so far as I know the sterling engine is the only external combustion free piston engine. A company called sunpower out of Athens Ohio developed a 6 Kw single, free piston sterling engine-alternator combination for Cummins that uses a solar collector for the heat source and permanent magnets in the linear alternator.
The free piston engine seems to have been developed for gas generation in the gas turbine as shown in the 1857 brittish patent, number 1655, issued to F. Matteucci and E. Barsanti of florence Italy for a free piston atmospheric turbine. In 1864 Langen and Otto progressed with work on the same principal, followed by others but it was not until the efforts, started in 1922, by frenchman Pescara that the modern free piston engine took form. His first engine, an air compressor, was a gasoline engine completed in 1925. His second engine was operated on the diesel cycle and was completed in 1928. Pescara's original conception of the free piston engine is the basis for most engines built since then. Ford and GM have spent great sums of money on development programs involving the free piston turbine.
The Pescara design uses two power pistons each mated to a work piston, the power pistons share the same cylinder and compression is between them as in some two piston diesel engines. Compression is acheived by forcing the two pistons toward each other. The frequency or cycles per minute is a function of piston mass and gas spring math, which I will not bore you with here since there a couple of books that would do a better job of it than I could. The range of operation seems to be in the 360 to 3600 CPM for most engines produced. The sunpower sterling runs at 3600 CPM with a stroke less than 1 inch and a bore size around 5 inches to provide 60Hz power. The speed or frequency can be varied somewhat by varying the gas spring pressure. In the IC version, one piston would uncover the exhaust port and the other piston the inlet port near the end of the power stroke. The pressure in the bounce chambers must be equalized or a linkage must be used to provide for continueous synchronization of the pistons. With the diesel design, the linkage is used to operate the fuel injector. It is interesting to note that some free piston turbines were started in synchronous mode and after running breifly they were operated out of sync to even the pumping flow. Varying the fuel charge will effect the the outer dead point in the piston travel and compression including any pumping influences the inner dead point, TDC if you will. This allows a compression ratio that varies with output, the minimum with the shortest stroke and the maximum with the longest. As an IC engine, the free piston engine has exibited compression ratios from 10:1 to 50:1 at full output and thermal efficiencies in the range of 45 to 50%. The highest compression pressures at full out put run between 1000 and 1200 psi with initial combustion pressures around 2000 psi.
sorry it is draging out so long.
I must finish tomarrow.
Peter heid</HTML>
The free piston engine seems to have been developed for gas generation in the gas turbine as shown in the 1857 brittish patent, number 1655, issued to F. Matteucci and E. Barsanti of florence Italy for a free piston atmospheric turbine. In 1864 Langen and Otto progressed with work on the same principal, followed by others but it was not until the efforts, started in 1922, by frenchman Pescara that the modern free piston engine took form. His first engine, an air compressor, was a gasoline engine completed in 1925. His second engine was operated on the diesel cycle and was completed in 1928. Pescara's original conception of the free piston engine is the basis for most engines built since then. Ford and GM have spent great sums of money on development programs involving the free piston turbine.
The Pescara design uses two power pistons each mated to a work piston, the power pistons share the same cylinder and compression is between them as in some two piston diesel engines. Compression is acheived by forcing the two pistons toward each other. The frequency or cycles per minute is a function of piston mass and gas spring math, which I will not bore you with here since there a couple of books that would do a better job of it than I could. The range of operation seems to be in the 360 to 3600 CPM for most engines produced. The sunpower sterling runs at 3600 CPM with a stroke less than 1 inch and a bore size around 5 inches to provide 60Hz power. The speed or frequency can be varied somewhat by varying the gas spring pressure. In the IC version, one piston would uncover the exhaust port and the other piston the inlet port near the end of the power stroke. The pressure in the bounce chambers must be equalized or a linkage must be used to provide for continueous synchronization of the pistons. With the diesel design, the linkage is used to operate the fuel injector. It is interesting to note that some free piston turbines were started in synchronous mode and after running breifly they were operated out of sync to even the pumping flow. Varying the fuel charge will effect the the outer dead point in the piston travel and compression including any pumping influences the inner dead point, TDC if you will. This allows a compression ratio that varies with output, the minimum with the shortest stroke and the maximum with the longest. As an IC engine, the free piston engine has exibited compression ratios from 10:1 to 50:1 at full output and thermal efficiencies in the range of 45 to 50%. The highest compression pressures at full out put run between 1000 and 1200 psi with initial combustion pressures around 2000 psi.
sorry it is draging out so long.
I must finish tomarrow.
Peter heid</HTML>
Re: free piston
Posted by: David K. Nergaard (IP Logged)
Date: February 07, 2002 01:07PM
<HTML>I have seen several free piston engines doing external mechanical work; Diesel pile drivers. The cylinder head is loose in the cylinder and rests on the pile. The other end of the cylinder is closed and forms an air compression spring. Air and exhaust valving was done with ports in the cylinder wall, as in any other two stroke design.
In operation, the compression stroke ended when the piston hit the head, starting the pile moving. Oil injection and combustion produced thrust on both the piston and the pile. Near the top of the piston stroke, a huge black smoke ring emerged from the exhaust port. A truly earth shaking machine!</HTML>
In operation, the compression stroke ended when the piston hit the head, starting the pile moving. Oil injection and combustion produced thrust on both the piston and the pile. Near the top of the piston stroke, a huge black smoke ring emerged from the exhaust port. A truly earth shaking machine!</HTML>
Re: free piston
Posted by: Peter Heid (IP Logged)
Date: February 07, 2002 05:54PM
<HTML>They say haste makes waste, I found it makes typos also.
With 2 piston assemblies operating as exact opposites of each other, the engines running balance and smoothness is almost perfect. The IC engines have been run on in the diesel various fuels such as gasoline, kerosene, vegetable oils, peanut oils, and even whale oil with the horsepower output increasing with the caloric value of the fuel used. The velocity of the piston(s) is greater during the power stroke or out bound portion of the cycle than it is in the return or bounce stroke allowing less time for loss of heat to the cylinder walls and more time for the intake and exhaust flows. This allows the engine to exibit very good thermal and volumemetric efficiencies.
As with any mechanical device we wish to use for our purposes, there are a few disadvantages present in the free piston engine. Starting can be a tricky afair and variations on this theme include compressed air in the bounce chambers or in the work cylinder and even the explosive force of a bullet-less 22 caliber rim fire cartridge has been used. the thermal efficiency is best at full output and drops with the power curve.
My thoughts about steam use in the free piston engine include the use of two pistons, both uncovering exhaust valves before their return created by the bounce cylinder. A unaflow, with an inlet valve tripped by the return of one or both of the pistons. Bounce pressure can be controlled by regulated steam pressure in the bounce chambers and may also be used for starting.
If it is so great, what do we use it for ? like the sunpower sterling, electrical power generation is a very good use when setup as a linear alternator. The engine also shows great abilities as an air pump and pressures around 60 psi were supplied to free piston gas turbines with great volume. The output to the turbine included the hot exhaust gasses mixed with the pumped air. Fuel consumption is directly related to the output pressure and of course the higher the pressures, the greater the fuel demand. I find no record of the FPE being used to pump vacuum but low pressures and high volume are the trademarks of efficiency. Maybe with the free piston engine the cost of auxiliries to the steam system can be reduced to a point where operating with an exhaust vacuum is of greater overall benefit.
Peter Heid</HTML>
With 2 piston assemblies operating as exact opposites of each other, the engines running balance and smoothness is almost perfect. The IC engines have been run on in the diesel various fuels such as gasoline, kerosene, vegetable oils, peanut oils, and even whale oil with the horsepower output increasing with the caloric value of the fuel used. The velocity of the piston(s) is greater during the power stroke or out bound portion of the cycle than it is in the return or bounce stroke allowing less time for loss of heat to the cylinder walls and more time for the intake and exhaust flows. This allows the engine to exibit very good thermal and volumemetric efficiencies.
As with any mechanical device we wish to use for our purposes, there are a few disadvantages present in the free piston engine. Starting can be a tricky afair and variations on this theme include compressed air in the bounce chambers or in the work cylinder and even the explosive force of a bullet-less 22 caliber rim fire cartridge has been used. the thermal efficiency is best at full output and drops with the power curve.
My thoughts about steam use in the free piston engine include the use of two pistons, both uncovering exhaust valves before their return created by the bounce cylinder. A unaflow, with an inlet valve tripped by the return of one or both of the pistons. Bounce pressure can be controlled by regulated steam pressure in the bounce chambers and may also be used for starting.
If it is so great, what do we use it for ? like the sunpower sterling, electrical power generation is a very good use when setup as a linear alternator. The engine also shows great abilities as an air pump and pressures around 60 psi were supplied to free piston gas turbines with great volume. The output to the turbine included the hot exhaust gasses mixed with the pumped air. Fuel consumption is directly related to the output pressure and of course the higher the pressures, the greater the fuel demand. I find no record of the FPE being used to pump vacuum but low pressures and high volume are the trademarks of efficiency. Maybe with the free piston engine the cost of auxiliries to the steam system can be reduced to a point where operating with an exhaust vacuum is of greater overall benefit.
Peter Heid</HTML>
Re: free piston
Posted by: Mark Stacey (IP Logged)
Date: February 08, 2002 09:32PM
<HTML>Thanks everyone for the extra information.
I had only read about free piston engines in L J K Setright's book Some Unusual Engines. The free piston engines described were all compression ignition with the combustion gases feeding an exhaust gas turbine from whose shaft power was extracted.
Setright mentions the difficulties operating with a varying load.
Cheers
Mark Stacey</HTML>
I had only read about free piston engines in L J K Setright's book Some Unusual Engines. The free piston engines described were all compression ignition with the combustion gases feeding an exhaust gas turbine from whose shaft power was extracted.
Setright mentions the difficulties operating with a varying load.
Cheers
Mark Stacey</HTML>
Re: free piston
Posted by: Peter Heid (IP Logged)
Date: August 27, 2002 07:37PM
<HTML>A direct relative of the free piston engine is the opposed piston design and it has popped up for me again, in issue number 12, Jan/Feb 1991 of Old Glory magazine I happened across a Commer truck from 1960 with a Rootes opposed piston 3 cylinder 6 piston engine. It displaces 3.25 litres and produces 105 bhp at 2400 rpm and 270 foot pounds of torque at 1200 rpm using the 2 stroke cycle uniflow diesel principal. This is a very compact engine and makes great power for it's size. I have often wondered if any opposed piston engine, free or linked, has been tried in a steam version. You can't argue with compression ratios from 10:1 to 50:1, low parts count and uniflow design.
Peter Heid</HTML>
Peter Heid</HTML>
Re: free piston
Posted by: Carl Helsing (IP Logged)
Date: June 08, 2006 06:10AM
<HTML> Try any early steam railway site. Those locomotives used free pistons in air and water pumps.I have a 1946 Audel's manual,entitled Pumps,Hydraulics And Air Compressors with complete diagrams and explanations of their operation,as also used in industry.You might be able to dig up a copy of the text or similar.
<a href="mailto:hihobmw@netheaven.com?subject=free piston">Peter Heid</a> wrote:
>
> Has anyone had any experience with or information on a
> free piston steam engine? It would seem like a good
> canadate for auxilery power such as pumping and electrical
> power generation.</HTML>
<a href="mailto:hihobmw@netheaven.com?subject=free piston">Peter Heid</a> wrote:
>
> Has anyone had any experience with or information on a
> free piston steam engine? It would seem like a good
> canadate for auxilery power such as pumping and electrical
> power generation.</HTML>
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