1 Steam Cars : Phorum
General Steam Car topics
Valve timing
Posted by: Peter Heid (IP Logged)
Date: November 11, 2002 02:23PM
<HTML>It seems one of the keys to an efficient steam engine is getting the exact amount of steam in the cylinder needed to satisfy the conditions. The ability to change the valve timing is important to the conditions as faster engine speeds require enough time for the steam to get in and out of the cylinder. I speak of timing not lead because lead is the amount the valve is open at TDC and with poppet valves they are assumed to be fully open or closed. I hope to control the admission timing on a uniflow engine with electronic controls and this will allow any timing scheme I care to program into it. I have been wondering if there are any studies on engine speed and valve timing that I might use as a starting point ?
If the controls I have chosen do not provide a fast enough valve action for the shortest cutoff I desire, would changing the timing help limit the amount of steam introduced into the cylinder. If timed corectly, would the steam of admission fight that of compression and reduce that which is admitted to the cylinder ?
Peter Heid</HTML>
If the controls I have chosen do not provide a fast enough valve action for the shortest cutoff I desire, would changing the timing help limit the amount of steam introduced into the cylinder. If timed corectly, would the steam of admission fight that of compression and reduce that which is admitted to the cylinder ?
Peter Heid</HTML>
Re: Valve timing
Posted by: David K Nergaard (IP Logged)
Date: November 13, 2002 12:35AM
<HTML>In a uniflow engine, the compression should always be close to but less than the boiler pressure. This is set by cylinder design, i.e. "compression ratio" and valve timing has nothing to do with it.
The inlet valve should open at dead center and close when sufficient steam to carry the load has entered the cylinder.
Do not assume a poppet valve is either open or closed, any valve requires time to move. A major problem in automotive steam engine poppet valve design is getting them to move fast enough with forces that are reasonable, especially at very short cutoffs.</HTML>
The inlet valve should open at dead center and close when sufficient steam to carry the load has entered the cylinder.
Do not assume a poppet valve is either open or closed, any valve requires time to move. A major problem in automotive steam engine poppet valve design is getting them to move fast enough with forces that are reasonable, especially at very short cutoffs.</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Peter Brow (IP Logged)
Date: November 13, 2002 08:05AM
<HTML>Peter Pellandine once noted in an article in The Steam Automobile Bulletin that he spent considerable time tuning and refining cam profiles for his poppet valves. I'd expect to do a lot of cut & try with a cam grinder.
Despite the extra cost, complication, fabrication work and packaging challenges, I would prefer tandem poppet valves for short-cutoff engines. These can give extremely short cutoff with very mild cams & very low valve speeds/accelerations. Cam profiles could probably be copied directly from a production gas car engine. Tandem valves' much lower valve speeds & acceleration loads might actually give less friction loss than a highly-loaded single cam/poppet, despite the extra mass of two valves & their actuating means.
With tandem poppet valves for both inlet & exhaust, both cutoff & compression could be instantly, independently, & continuously varied to any combination of values, for absolutely optimum performance and efficiency with a given engine under all conditions. With electrical actuators for the valve timing controls, the valves could be completely controlled by a microprocessor & easily-retuned software (valve drive would still be mechanical). Or use a simple mechanical computer (with specially-profiled control cam, maybe a 2-axis cam correlating load & rpm) if desired. The downside would be the number of valves, 8 valves for each double-acting cylinder or 4 valves for each single-acting cylinder.
The lower loads & friction losses would also allow use of much larger valves if desired.
Peter</HTML>
Despite the extra cost, complication, fabrication work and packaging challenges, I would prefer tandem poppet valves for short-cutoff engines. These can give extremely short cutoff with very mild cams & very low valve speeds/accelerations. Cam profiles could probably be copied directly from a production gas car engine. Tandem valves' much lower valve speeds & acceleration loads might actually give less friction loss than a highly-loaded single cam/poppet, despite the extra mass of two valves & their actuating means.
With tandem poppet valves for both inlet & exhaust, both cutoff & compression could be instantly, independently, & continuously varied to any combination of values, for absolutely optimum performance and efficiency with a given engine under all conditions. With electrical actuators for the valve timing controls, the valves could be completely controlled by a microprocessor & easily-retuned software (valve drive would still be mechanical). Or use a simple mechanical computer (with specially-profiled control cam, maybe a 2-axis cam correlating load & rpm) if desired. The downside would be the number of valves, 8 valves for each double-acting cylinder or 4 valves for each single-acting cylinder.
The lower loads & friction losses would also allow use of much larger valves if desired.
Peter</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: C Benson (IP Logged)
Date: November 13, 2002 11:55AM
<HTML>Don't forget w/hi compression you'll need to keep a small distance between valve and piston,,,this is also a problem on alcohol engines [14:1] I have a piston as evidence,,which is polished where it touches the head when cold,,,before the cyl expands,,,,Mac said it was awful noisy when cold,,,,,Vellocette 1925 racer,,,105deg overlap,,,,Cheers Ben</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: David K Nergaard (IP Logged)
Date: November 13, 2002 01:12PM
<HTML>SES used tandom poppet valves and found the volume trapped between the two valves led to significant, and unexpected, efficiency losses. I don't think using dual valves conveys a significant advantages, the valves must still move rather quickly to achieve short cutoff at high revs.</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Jim Crank (IP Logged)
Date: November 13, 2002 02:25PM
<HTML>Peter,
Don't ignore the serious flow losses with tandem valves, and, as Dave said, the increase in clearance volume.
Read Dobles engine design notes for the Ultamax engine. He was thinking of 2,000 psi and 1800° F and was forced to consider poppet valves. Both hoped for criteria were totally hopeless.
Jim</HTML>
Don't ignore the serious flow losses with tandem valves, and, as Dave said, the increase in clearance volume.
Read Dobles engine design notes for the Ultamax engine. He was thinking of 2,000 psi and 1800° F and was forced to consider poppet valves. Both hoped for criteria were totally hopeless.
Jim</HTML>
Valve timing studies
Posted by: Peter Heid (IP Logged)
Date: November 13, 2002 05:42PM
<HTML>David,
Yes, the compression is determined by the volume ratios but I was wondering if the minimum cutoff was reached, could you change the timing to change the amount of steam admitted to the cylinder ? If the valve opens before TDC at low speeds will the compression limit the steam admitted to the cylinder ? Should not the inlet valve timing be advanced as the piston speed increases, at least for the highest performance ? Steam does have mass and it does take time to get it moving toward the cylinder and higher speeds require the admission to start sooner. If you start admission too soon, at the risk of being "lumpy" can you control the amount of steam admitted ?
Peter,
It sounds like doubles might have their troubles as Jim and David mention from a more informed side. My valve design is balanced when in motion and the only large load will be during the first 1 or 2 revolutions. A double poppet would surely increase the complexity and initial cost as well as the power consumption. For these reasons I have chosen a single poppet which will possibly require a more precise design parameters and tuning to function as required. I am starting on a design of somewhat slow engine speed but first and fore most the mass should be as low as possible, this is logical in any design but more critical as reaction times increase.
Cobern,
I have arranged a valve guide in the cylinder block and the valve seat in the head allowing the valve to open into the inlet port. The angle and position of the valve and guide allow a port under the valve that is shorter than the width of the valve head and with no piston clearance problems the valve can open to any extent desired.
My question is still: are there any studies of valve timing in relation to piston speed that one could use as a starting point by to build an engine of infinitely variable timing ? It would shorten the learning curve and reduce the wear on the "seat of the pants" dyno.
Peter Heid</HTML>
Yes, the compression is determined by the volume ratios but I was wondering if the minimum cutoff was reached, could you change the timing to change the amount of steam admitted to the cylinder ? If the valve opens before TDC at low speeds will the compression limit the steam admitted to the cylinder ? Should not the inlet valve timing be advanced as the piston speed increases, at least for the highest performance ? Steam does have mass and it does take time to get it moving toward the cylinder and higher speeds require the admission to start sooner. If you start admission too soon, at the risk of being "lumpy" can you control the amount of steam admitted ?
Peter,
It sounds like doubles might have their troubles as Jim and David mention from a more informed side. My valve design is balanced when in motion and the only large load will be during the first 1 or 2 revolutions. A double poppet would surely increase the complexity and initial cost as well as the power consumption. For these reasons I have chosen a single poppet which will possibly require a more precise design parameters and tuning to function as required. I am starting on a design of somewhat slow engine speed but first and fore most the mass should be as low as possible, this is logical in any design but more critical as reaction times increase.
Cobern,
I have arranged a valve guide in the cylinder block and the valve seat in the head allowing the valve to open into the inlet port. The angle and position of the valve and guide allow a port under the valve that is shorter than the width of the valve head and with no piston clearance problems the valve can open to any extent desired.
My question is still: are there any studies of valve timing in relation to piston speed that one could use as a starting point by to build an engine of infinitely variable timing ? It would shorten the learning curve and reduce the wear on the "seat of the pants" dyno.
Peter Heid</HTML>
Re: Valve timing studies
Posted by: John Winter (IP Logged)
Date: November 14, 2002 02:23AM
<HTML>Please keep this discussion going. I am at the point in my engine construction where I am settting up to mill, on a rotary table, a set of two three lobe cams. One lobe is 55% for starting then a 12% for running and at 180 deg. a 55% lobe for reverse starting and running. I plan to run a short trial with he finished cams and if correct then surface harden them. Any comment on this approach to cam building.
I have found this discusion very inlightening. Thanks
JOHN</HTML>
I have found this discusion very inlightening. Thanks
JOHN</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Peter Brow (IP Logged)
Date: November 14, 2002 08:03AM
<HTML>Peter, David and Jim,
I think that the extra clearance volume of tandem valves can be compensated for if the exhaust valves are of the tandem type too & properly controlled; SES's problem was probably a matter of control regime rather than the valve type/layout. I would only consider tandem valves if they were used on both inlet and exhaust, and with a mapped expansion/compression control regime similar to that advocated by Andy Patterson.
Flow resistance is higher with tandem poppet valves, and the valves still have to operate over twice as fast as valves in a 4-stroke IC engine at a given rpm. However, max steam engine rpm would necessarily be a fraction of max IC rpm, and with proper design/control the steam volume would theoretically be less -- less inlet due to higher expansion, and less exhaust due to higher compression. That is at max expansion/compression; with lower expansion/compression for overload conditions, flow resistance gets to be a problem, and that is what the flowpath has to be designed for. It wouldn't be a truly high-rpm engine, for this and other reasons.
I've tried unsuccessfully on several occasions to design acceptable tandem poppet valve systems. It is very difficult to package the things compactly, and to drive them, esp with DA cylinders. Their advantages are still purely theoretical, IMO, but worth considering for those seeking a more adventurous design approach.
Then again, I seem to recall reading of some experimental engine (Dutcher?) which used tandem poppet valves with good efficiency improvements, at least on the test bench. For whatever that's worth, which usually isn't much. Road efficiency (under mostly low- & variable-load conditions) is what counts, and that is usually far lower than theoretical & optimum test bench efficiencies.
A tandem poppet valve system is also more than twice as expensive as single poppets, and I'm not sure that the road efficiency improvements, if any, would justify the extra expense & design nightmares. For various reasons, Stephenson-driven piston valves are still hogging my drawing board.
I'll check out Doble's Ultramax notes; thanks for the tip. From what I've heard it was a pretty problematic concept. When you end up considering a cylinder cooling system for a steam engine, you've really gone off the deep end. I think Doble was a century or so ahead of materials & lubrication technologies with that concept. He sure knew how to keep himself challenged, though.
Peter</HTML>
I think that the extra clearance volume of tandem valves can be compensated for if the exhaust valves are of the tandem type too & properly controlled; SES's problem was probably a matter of control regime rather than the valve type/layout. I would only consider tandem valves if they were used on both inlet and exhaust, and with a mapped expansion/compression control regime similar to that advocated by Andy Patterson.
Flow resistance is higher with tandem poppet valves, and the valves still have to operate over twice as fast as valves in a 4-stroke IC engine at a given rpm. However, max steam engine rpm would necessarily be a fraction of max IC rpm, and with proper design/control the steam volume would theoretically be less -- less inlet due to higher expansion, and less exhaust due to higher compression. That is at max expansion/compression; with lower expansion/compression for overload conditions, flow resistance gets to be a problem, and that is what the flowpath has to be designed for. It wouldn't be a truly high-rpm engine, for this and other reasons.
I've tried unsuccessfully on several occasions to design acceptable tandem poppet valve systems. It is very difficult to package the things compactly, and to drive them, esp with DA cylinders. Their advantages are still purely theoretical, IMO, but worth considering for those seeking a more adventurous design approach.
Then again, I seem to recall reading of some experimental engine (Dutcher?) which used tandem poppet valves with good efficiency improvements, at least on the test bench. For whatever that's worth, which usually isn't much. Road efficiency (under mostly low- & variable-load conditions) is what counts, and that is usually far lower than theoretical & optimum test bench efficiencies.
A tandem poppet valve system is also more than twice as expensive as single poppets, and I'm not sure that the road efficiency improvements, if any, would justify the extra expense & design nightmares. For various reasons, Stephenson-driven piston valves are still hogging my drawing board.
I'll check out Doble's Ultramax notes; thanks for the tip. From what I've heard it was a pretty problematic concept. When you end up considering a cylinder cooling system for a steam engine, you've really gone off the deep end. I think Doble was a century or so ahead of materials & lubrication technologies with that concept. He sure knew how to keep himself challenged, though.
Peter</HTML>
Re: Valve timing
Posted by: tom ward (IP Logged)
Date: November 14, 2002 08:05AM
<HTML>If we knew the maximum design speed for your engine it might be easier to calculate the ideal timing profile. We also need to know valve stroke length and the mass of the valve, rocker, and pushrod.
1200 rpm=20 rps or one revolution every 50 milliseconds. The downstroke would take 25 ms so 1% would be 0.25 ms. Since many IC engines run at 5 times that speed using vacuum pressure to draw the gases in the much higher relative pressures of steam almost make valve travel time seem trivial considering all the other factors effecting performance.
Have you considered the Corliss valve train?</HTML>
1200 rpm=20 rps or one revolution every 50 milliseconds. The downstroke would take 25 ms so 1% would be 0.25 ms. Since many IC engines run at 5 times that speed using vacuum pressure to draw the gases in the much higher relative pressures of steam almost make valve travel time seem trivial considering all the other factors effecting performance.
Have you considered the Corliss valve train?</HTML>
Re: Valve timing studies
Posted by: Peter Heid (IP Logged)
Date: November 14, 2002 04:39PM
<HTML>Tom,
The ideal profile is great for designing for that specific rpm but my "computer profile" will change with the conditions. I can not tell you the maximum speed the vehicle will achieve yet but it is geared for 13.7 rpm at 1 mph. When figuring mass of the valve train, don't forget they usually include half the mass of the spring also. In my valve system I will be excluding the rocker and pushrod to reduce the mass. The valve is about 32 grams complete with all moving parts and travels 0.25 to 0.30 inches. I have thought of Corliss valves but they have higher leakage, greater mass, and are less suited to a throttle by wire system. With the inlet valves acting as the throttle, valve leakage is very critical.
John,
It sounds like it would be nice to get the cam right the first try. Are your cams sliding ?
Peter Heid</HTML>
The ideal profile is great for designing for that specific rpm but my "computer profile" will change with the conditions. I can not tell you the maximum speed the vehicle will achieve yet but it is geared for 13.7 rpm at 1 mph. When figuring mass of the valve train, don't forget they usually include half the mass of the spring also. In my valve system I will be excluding the rocker and pushrod to reduce the mass. The valve is about 32 grams complete with all moving parts and travels 0.25 to 0.30 inches. I have thought of Corliss valves but they have higher leakage, greater mass, and are less suited to a throttle by wire system. With the inlet valves acting as the throttle, valve leakage is very critical.
John,
It sounds like it would be nice to get the cam right the first try. Are your cams sliding ?
Peter Heid</HTML>
Re: Valve timing studies
Posted by: David K Nergaard (IP Logged)
Date: November 14, 2002 08:45PM
<HTML>In Re: tandom valves; I believe SES found most of the additional losses were related to the trapped intervalve volume.
In Re: valve train stresses; acceleration loads are very serious at high engine speeds. Whether they become larger than steam loading on an unbalanced valve is moot. However, in a uniflow engine, compression pressure should be nearly boiler pressure at the time of valve opening so balancing valves is of little importance. I have considered using a "fat" valve stem so steam pressure can provide the force needed to close the valve rather than springs, but this is not even a paper study as yet.</HTML>
In Re: valve train stresses; acceleration loads are very serious at high engine speeds. Whether they become larger than steam loading on an unbalanced valve is moot. However, in a uniflow engine, compression pressure should be nearly boiler pressure at the time of valve opening so balancing valves is of little importance. I have considered using a "fat" valve stem so steam pressure can provide the force needed to close the valve rather than springs, but this is not even a paper study as yet.</HTML>
Re: Valve timing studies
Posted by: John Winter (IP Logged)
Date: November 14, 2002 11:28PM
<HTML>Yes Peter the cam assy. will slide to 3 positions. After the lobes are milled the setup will swing to allow the milling of 15 deg. slopes, where required, between each lobe. Slide travel is 1.5" on a 0.188 keyed 0.750 shaft. A space between the cams on the joining sleve will allow for a 5/8" sealed ball bearing to hold the cams in place and slide them on the shaft.
JOHN</HTML>
JOHN</HTML>
Re: Valve timing studies
Posted by: tom ward (IP Logged)
Date: November 15, 2002 07:59AM
<HTML>Peter,
I was thinking of using the spring action mechinism of the Corliss as a way to actuate poppet valves.</HTML>
I was thinking of using the spring action mechinism of the Corliss as a way to actuate poppet valves.</HTML>
Re: Valve timing studies
Posted by: tom ward (IP Logged)
Date: November 15, 2002 08:04AM
<HTML>At over 7000 rpm at highway speeds engine life could be measured with a stopwatch.</HTML>
Re: Valve timing studies
Posted by: Peter Heid (IP Logged)
Date: November 15, 2002 12:26PM
<HTML>David,
Try looking up the British-Caprotti rotary cam, double seated poppet valve. One of the distinguishing features is the lack of springs due to the use of steam pressure.
Tom,
There already are some "snap action" type poppet valves out there. I am sure I have seen them in my books. I believe they open and latch, release then close but there may be several other designs.
Peter Heid</HTML>
Try looking up the British-Caprotti rotary cam, double seated poppet valve. One of the distinguishing features is the lack of springs due to the use of steam pressure.
Tom,
There already are some "snap action" type poppet valves out there. I am sure I have seen them in my books. I believe they open and latch, release then close but there may be several other designs.
Peter Heid</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: William L. Petitjean, P.E. (IP Logged)
Date: December 02, 2002 02:39AM
<HTML>I have looked at most of the things talked about here.
Fundamentally, the main problem is that maximum efficiency is obtained at about 10% cutoff. This represents opening and closing the admission valve through about 20 degrees of crank angle instead of something like 180 degrees of crank angle for IC engines.
This means meaningful valve port areas create enormous inertia forces on the valve gears at high speeds as David Nergaard points out. Also, the small port areas relative to required cylinder volumes ensure that wiredrawing the inlet pressures to something significantly lower also occurs. This is a serious thermodynamic loss at high speeds.
Poppet valves are no panacea at high speeds and they add considerable complications and cost to any automotive steam engine. I abandoned research on different poppet valve arrangements a long time ago because of the inherent speed limitations of tradional steam engine designs.
This is why I am a champion of some type of water injection idea -- there are no inherent speed limitations and the injector and heat transfer ideas are wide open for development and expoitation. Poppet valves are an old and weary concept that have been beat to death (pardon the pun) over the years.
Incidentally, in my mind the Skinner dual camshaft poppet valve gear is the simplest and most efficient of the rotary cam valve gears. It worked very well and the stationary and marine gears were excellent down into cutoffs around 5% or 10%. These valve gears were limited to engine speeds around 400 or 500 rpm though. If you ran them too fast the valves would float.
Bill Petitjean</HTML>
Fundamentally, the main problem is that maximum efficiency is obtained at about 10% cutoff. This represents opening and closing the admission valve through about 20 degrees of crank angle instead of something like 180 degrees of crank angle for IC engines.
This means meaningful valve port areas create enormous inertia forces on the valve gears at high speeds as David Nergaard points out. Also, the small port areas relative to required cylinder volumes ensure that wiredrawing the inlet pressures to something significantly lower also occurs. This is a serious thermodynamic loss at high speeds.
Poppet valves are no panacea at high speeds and they add considerable complications and cost to any automotive steam engine. I abandoned research on different poppet valve arrangements a long time ago because of the inherent speed limitations of tradional steam engine designs.
This is why I am a champion of some type of water injection idea -- there are no inherent speed limitations and the injector and heat transfer ideas are wide open for development and expoitation. Poppet valves are an old and weary concept that have been beat to death (pardon the pun) over the years.
Incidentally, in my mind the Skinner dual camshaft poppet valve gear is the simplest and most efficient of the rotary cam valve gears. It worked very well and the stationary and marine gears were excellent down into cutoffs around 5% or 10%. These valve gears were limited to engine speeds around 400 or 500 rpm though. If you ran them too fast the valves would float.
Bill Petitjean</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Peter Heid (IP Logged)
Date: December 02, 2002 03:59AM
<HTML>William,
You say the Skinner valves would float at 400 or 500 rpm, what do they weigh ? On a small engine with reduced mass, it would seem the rpm would far exceed that available from a Skinner. I think you are compairing watermelons to peas. For example the high pressure piston valve on the 2500 Hp US Meritime triple expansion engine weighs 360 pounds. Port areas do not have to cause wire drawing to any noticable extent if the port is short, direct and of correct size, all achievable with proper design. Without a great outlay of time and money the development of a modern steam engine by an individual or small group effort is going to involve a conventional design employing valves. The poppet valve has the lowest leakage, fastest action, least power consumption (if balanced) and least cost in most steam applications. How could it add more to the cost of a steam engine than it does it's IC engine competitor. It can provide cutoffs needed for the most efficient of steam engine designs when operating at the speeds of F1 valve systems and remain very reliable. I see no need to trade this all in for an untested theroy.
Remember water is very destructive to most metals when impinged upon them at high surface temperatures.
Peter Heid</HTML>
You say the Skinner valves would float at 400 or 500 rpm, what do they weigh ? On a small engine with reduced mass, it would seem the rpm would far exceed that available from a Skinner. I think you are compairing watermelons to peas. For example the high pressure piston valve on the 2500 Hp US Meritime triple expansion engine weighs 360 pounds. Port areas do not have to cause wire drawing to any noticable extent if the port is short, direct and of correct size, all achievable with proper design. Without a great outlay of time and money the development of a modern steam engine by an individual or small group effort is going to involve a conventional design employing valves. The poppet valve has the lowest leakage, fastest action, least power consumption (if balanced) and least cost in most steam applications. How could it add more to the cost of a steam engine than it does it's IC engine competitor. It can provide cutoffs needed for the most efficient of steam engine designs when operating at the speeds of F1 valve systems and remain very reliable. I see no need to trade this all in for an untested theroy.
Remember water is very destructive to most metals when impinged upon them at high surface temperatures.
Peter Heid</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Ted Pritchard (IP Logged)
Date: December 02, 2002 04:31AM
<HTML>This is an interesting subject but I must say that it was just as well my engine designs did not hear what you doom and gloom people say about poppet valves! I did thousands of miles with the steam Ford Falcon and gave hundereds of demos. The engine never balked at all and always took off in the required direction!!
Cut-offs were 14%, 33% and 80% with reverse 80%. The three dimensional cams had smooth inclined ramps between the positions and you could change from anywhere to anywhere including reverse - but please dethrottle initially for the last one!
Regarding being limited to 1000 RPM.- This would have held us tob 22 MPH! In the early demos near LA we were running up to about 55 MPH at the top of out test hill which is 2500 RPM and later demos up to 67 MPH. = 3000 RPM.
I could suggest that if anyone is having trouble with baulking etc., first make sure you have a scale trap before the throttle. Way back my Stanley didnt want to stop. It had a lump of weld dirt in the throttle. I had to drop the boiler pressure and leap on the brake at the intersections where I had to stop!!! Dirt can also get under your poppet valves. If still having trouble, check the valves and seats. They are probably badly scored.
Complicated? My 2 cyl double acting uniflow had only four poppet valves. For the same no of impulses per rev you would need a V8 4 stroke engine with 16 or 32 valves!
Best wishes,
Ted Pritchard</HTML>
Cut-offs were 14%, 33% and 80% with reverse 80%. The three dimensional cams had smooth inclined ramps between the positions and you could change from anywhere to anywhere including reverse - but please dethrottle initially for the last one!
Regarding being limited to 1000 RPM.- This would have held us tob 22 MPH! In the early demos near LA we were running up to about 55 MPH at the top of out test hill which is 2500 RPM and later demos up to 67 MPH. = 3000 RPM.
I could suggest that if anyone is having trouble with baulking etc., first make sure you have a scale trap before the throttle. Way back my Stanley didnt want to stop. It had a lump of weld dirt in the throttle. I had to drop the boiler pressure and leap on the brake at the intersections where I had to stop!!! Dirt can also get under your poppet valves. If still having trouble, check the valves and seats. They are probably badly scored.
Complicated? My 2 cyl double acting uniflow had only four poppet valves. For the same no of impulses per rev you would need a V8 4 stroke engine with 16 or 32 valves!
Best wishes,
Ted Pritchard</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: George Nutz (IP Logged)
Date: December 02, 2002 11:13AM
<HTML> No doubt the poppet valve has great merit. Although the Skinner system has great merit it also has great mass as pointed out. Twenty years ago fiddled with a two cam single poppet valve infinitely variable cutoff but in it the two cams were in series, not parallel like the Skinner and of very little additional mass. Know its been mentioned before but Hal Fuller's(Skinner Engine Co) infinitely variable hydraulic poppet valve system worked very well up to 1800-2000rpm even in very short cutoffs. I believe the lift stayed constant until below 10% cut off, plus he regulated the engine speed totally thru valve duration and lift, not with a throttle and under greatly varying load conditions worked very well. Anyone know how well the balanced poppet valve system worked in the beautiful Bugatti steam railcar engine?
Best, George</HTML>
Best, George</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: William L. Petitjean, P.E. (IP Logged)
Date: December 03, 2002 04:30AM
<HTML>Thank you for your responses. While the poppet valve examples may all be well and good the primary limitation is the small degrees of crank angle that the valve must open and close within. this is something like 12% of the crank angle that an IC uses to operate its valves. It should be obvious the IC engine is a lot freer breathing than a poppet valve steam engine of any type or size!
Make no mistake, I am a machinery man and the examples given sound like beautiful pieces of machinery. Nonetheless, if you don't mass produce these mechanical contrivances they will always be so expensive they will never be anything but curious toys only the rich or obsessed will afford.
The key to the future is simplicity and expansions that drop nearly vertically down the Mollier Chart. The first is the unassailable strength of the steam engine and the second is only achievable at high speeds with a water injection type uniflow steam engine that uses no valves at all!
Bill (I am glad my name is not Fischer) Petitjean</HTML>
Make no mistake, I am a machinery man and the examples given sound like beautiful pieces of machinery. Nonetheless, if you don't mass produce these mechanical contrivances they will always be so expensive they will never be anything but curious toys only the rich or obsessed will afford.
The key to the future is simplicity and expansions that drop nearly vertically down the Mollier Chart. The first is the unassailable strength of the steam engine and the second is only achievable at high speeds with a water injection type uniflow steam engine that uses no valves at all!
Bill (I am glad my name is not Fischer) Petitjean</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Ted Pritchard (IP Logged)
Date: December 03, 2002 08:11AM
<HTML>Bill- Thank you for your further comments. You say you are a machinery man. Well I am a mechanical and automotive engineer. One definition of mechanical engineering is 'The PRODUCTION AND USE OF POWER."
Mechanical engineers learn Thermodynamics which is helpful in working out steam passage and valve sizes, pressure drops etc. and also Machine Design which includes cam design.
You tell me the relatively small crank angle that the valve is open for early cut-off. Thanks but I know that. My valve system was worked out for the correct valve opening for early cut-off and the proper procedure followed for the design:- Valves designed, [single beat type] estimates for weights worked out for the valve trains, for accelerations on valve opening, inertia forces checked for acceptable design stresses. Acceleration or rather retardation of the valve train while the follower goes over the cam nose worked out and the required spring forces estimated. This includes a small margin at the top design speed to prevent valve "bounce."
Regarding the statement that around 10% cut-off is most efficient- The "best" expansion ratio depends on more than one factor. For example, whether the engine is for stationary or automotive use is an important factor. Whether the engine can appreciate or make use of the high expansion ratio is another.
My Vee engine had its relatively short camshaft above the crankshaft. I thought the camshaft was not very complicated. After all I did some of the milling myself!! You can see on my web site how compact this 110 pound engine was. There are also accounts of some of the demos given.
Another point.- With the forward and reverse timings available, the engine is powerful on starting, and able to reverse. This saves a lot of complication ie.- in not needing a gearbox and clutch.
Best Wishes, Ted Pritchard</HTML>
Mechanical engineers learn Thermodynamics which is helpful in working out steam passage and valve sizes, pressure drops etc. and also Machine Design which includes cam design.
You tell me the relatively small crank angle that the valve is open for early cut-off. Thanks but I know that. My valve system was worked out for the correct valve opening for early cut-off and the proper procedure followed for the design:- Valves designed, [single beat type] estimates for weights worked out for the valve trains, for accelerations on valve opening, inertia forces checked for acceptable design stresses. Acceleration or rather retardation of the valve train while the follower goes over the cam nose worked out and the required spring forces estimated. This includes a small margin at the top design speed to prevent valve "bounce."
Regarding the statement that around 10% cut-off is most efficient- The "best" expansion ratio depends on more than one factor. For example, whether the engine is for stationary or automotive use is an important factor. Whether the engine can appreciate or make use of the high expansion ratio is another.
My Vee engine had its relatively short camshaft above the crankshaft. I thought the camshaft was not very complicated. After all I did some of the milling myself!! You can see on my web site how compact this 110 pound engine was. There are also accounts of some of the demos given.
Another point.- With the forward and reverse timings available, the engine is powerful on starting, and able to reverse. This saves a lot of complication ie.- in not needing a gearbox and clutch.
Best Wishes, Ted Pritchard</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Peter Heid (IP Logged)
Date: December 03, 2002 01:28PM
<HTML>Bill,
Though cam driven poppet valves have a proven track record, the valves of a steam engine do not have to be directly driven by the engine as per Hal Fuller's engine and those that have preceeded him. Continued development of this concept will surely evolve the steam engine beyond what any untested theroy can do without great cost. I would have to wonder of the complication and cost of a water injection system that varies the flow to meet power demands. What cylinder pressure do you expect to overcome as water tends to erode injectors at high pressure & temp. How will you drain the injectors, lines and pump if subjected to freezing weather ? Any home machinest can build the pnumatically sprung valve system used by todays F1 cars at over 19000 rpm. Would you like drawings and basic dimensions ?
Peter Heid</HTML>
Though cam driven poppet valves have a proven track record, the valves of a steam engine do not have to be directly driven by the engine as per Hal Fuller's engine and those that have preceeded him. Continued development of this concept will surely evolve the steam engine beyond what any untested theroy can do without great cost. I would have to wonder of the complication and cost of a water injection system that varies the flow to meet power demands. What cylinder pressure do you expect to overcome as water tends to erode injectors at high pressure & temp. How will you drain the injectors, lines and pump if subjected to freezing weather ? Any home machinest can build the pnumatically sprung valve system used by todays F1 cars at over 19000 rpm. Would you like drawings and basic dimensions ?
Peter Heid</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: William L. Petitjean, P.E. (IP Logged)
Date: December 04, 2002 06:11AM
<HTML>Hi Ted and Peter:
Thank you for your comments. There is no question in my mind that you and others on this forum have carried the reciprocating automobile engine farther than anyone else and I have no animosity toward this.
However, your arguments are mostly mechanical issues. The ultimate standard of measure is the shape of your indicator cards under normal operating conditions and how your expansion, exhaust and compression curves fit onto the Mollier chart.
It is an unfortunate historical fact that steam engine inefficiencies are simply overcome by building a little bigger boiler. This, in a nutshell, is why most powerplants don't use steam engines anymore. Another reason is steam engines cost more than other types of power plants for a given output. I tried selling steam engines for a living some years ago and these facts finally forced me to realize that something radical must be done before a steam engine becomes practical again in almost any application.
Efficiency, coupled with simplicity must be the foremost design criteria. In conclusion an inlet that only occurs over about 20 degrees of crank angle cannot be made to "breathe" very well unless the inlet pressure is excessive. If you start with a really high inlet pressure and apply that to the Mollier chart you will find the expansion ratio must be so large to convert most of the internal energy to work that 10% cutoff looks enormous. Sure, you can expand to some higher back pressure, but then you lose great gobs of potential energy in the lower absolute pressure ranges -- thus your efficiency is adversely and severely impacted. A water injection engine can operate at 0.01% cutoff if necessary to get the proper expansion ratio!
Additionally, and this is a point I didn't stress in earlier posts, It is impossible to expand to absolute pressures with anything but a uniflow cylinder utilizing the biggest exhaust ports possible. Exhaust loss is public enemy number one to any steam prime mover and it doesn't make any difference how you design the poppet valves. If they bottle up the exhaust steam so the exhaust line on your indicator card is elevated substantially above the condenser pressure you have lost a significant amount of potential energy to negative work that also throws more load on the condenser. The idea of using large cylinder exhaust ports and making the crankcase the condenser are really more important than the water injection idea because these features capture power most steam engines can't dream of developing.
While it is true mechanical engineering is about the "production and use of power", the thermodynamics and volumetrics must come first. Then the engine should be designed to operate the heat engine cycle as efficiently as economically possible. The best steam engine will have an indicator card that looks very much like a banana as this will best satisfy the PV and TS diagrams. This engine will have an expansion line that drops almost vertically on the Mollier chart and should have engine efficiencies between 80% and 90%. If you can achieve this your external combustion steam plant will approach diesel engine thermal efficiencies!
If multiple cylinders are used the engine is easily started and reversed directly. There is no reason cutoff cannot be extended to produce enormous overload outputs to start and accelerate automobiles. The temporary loss of efficiency is no worse than an engine that has poor efficency all the time. The only complication is multiple cylinders. There is no need for starters or transmissions.
I have worked around steam engines for nearly 40 years. I have few illusions about the double acting, inlet valve type, restricted exhaust port steam engine. It is a tired old beast. I have no resources at this time to build a hot head prototype engine. So I hoped a wild eyed, reckless steam car advocate might want to take up the banner. The posts on the fictitious Fischer steam engine are an indication of the steam car fraternity's opinion of the radical hot head engine concept. So I think I will let the whole idea go dormant again.
Bill Petitjean</HTML>
Thank you for your comments. There is no question in my mind that you and others on this forum have carried the reciprocating automobile engine farther than anyone else and I have no animosity toward this.
However, your arguments are mostly mechanical issues. The ultimate standard of measure is the shape of your indicator cards under normal operating conditions and how your expansion, exhaust and compression curves fit onto the Mollier chart.
It is an unfortunate historical fact that steam engine inefficiencies are simply overcome by building a little bigger boiler. This, in a nutshell, is why most powerplants don't use steam engines anymore. Another reason is steam engines cost more than other types of power plants for a given output. I tried selling steam engines for a living some years ago and these facts finally forced me to realize that something radical must be done before a steam engine becomes practical again in almost any application.
Efficiency, coupled with simplicity must be the foremost design criteria. In conclusion an inlet that only occurs over about 20 degrees of crank angle cannot be made to "breathe" very well unless the inlet pressure is excessive. If you start with a really high inlet pressure and apply that to the Mollier chart you will find the expansion ratio must be so large to convert most of the internal energy to work that 10% cutoff looks enormous. Sure, you can expand to some higher back pressure, but then you lose great gobs of potential energy in the lower absolute pressure ranges -- thus your efficiency is adversely and severely impacted. A water injection engine can operate at 0.01% cutoff if necessary to get the proper expansion ratio!
Additionally, and this is a point I didn't stress in earlier posts, It is impossible to expand to absolute pressures with anything but a uniflow cylinder utilizing the biggest exhaust ports possible. Exhaust loss is public enemy number one to any steam prime mover and it doesn't make any difference how you design the poppet valves. If they bottle up the exhaust steam so the exhaust line on your indicator card is elevated substantially above the condenser pressure you have lost a significant amount of potential energy to negative work that also throws more load on the condenser. The idea of using large cylinder exhaust ports and making the crankcase the condenser are really more important than the water injection idea because these features capture power most steam engines can't dream of developing.
While it is true mechanical engineering is about the "production and use of power", the thermodynamics and volumetrics must come first. Then the engine should be designed to operate the heat engine cycle as efficiently as economically possible. The best steam engine will have an indicator card that looks very much like a banana as this will best satisfy the PV and TS diagrams. This engine will have an expansion line that drops almost vertically on the Mollier chart and should have engine efficiencies between 80% and 90%. If you can achieve this your external combustion steam plant will approach diesel engine thermal efficiencies!
If multiple cylinders are used the engine is easily started and reversed directly. There is no reason cutoff cannot be extended to produce enormous overload outputs to start and accelerate automobiles. The temporary loss of efficiency is no worse than an engine that has poor efficency all the time. The only complication is multiple cylinders. There is no need for starters or transmissions.
I have worked around steam engines for nearly 40 years. I have few illusions about the double acting, inlet valve type, restricted exhaust port steam engine. It is a tired old beast. I have no resources at this time to build a hot head prototype engine. So I hoped a wild eyed, reckless steam car advocate might want to take up the banner. The posts on the fictitious Fischer steam engine are an indication of the steam car fraternity's opinion of the radical hot head engine concept. So I think I will let the whole idea go dormant again.
Bill Petitjean</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Peter Heid (IP Logged)
Date: December 04, 2002 12:43PM
<HTML>Bill,
My goal is to build a vehicle of super low exhaust emissions and my backyard budget doesn't allow for the most efficient engine design yet concieved. By applying today's existing technologies to existing designs, a very satisfactory vehicle can be produced that meets my goal and might achieve green recognition. If there is a demand for what I build maybe funding for research might lead me in directions such as yours but that would be quite a tall and expensive engineering mountain to climb. I appericate the unrestricted access to development along this line and I hope more people share there ideas as freely as you. I, as well as others would have to wonder of any untested therory, what gains it would produce in the real world and at what cost.
The first lesson I learned when entering the steam world, where experience has often shown: if it is not in papers, it's just vapors.
Peter Heid</HTML>
My goal is to build a vehicle of super low exhaust emissions and my backyard budget doesn't allow for the most efficient engine design yet concieved. By applying today's existing technologies to existing designs, a very satisfactory vehicle can be produced that meets my goal and might achieve green recognition. If there is a demand for what I build maybe funding for research might lead me in directions such as yours but that would be quite a tall and expensive engineering mountain to climb. I appericate the unrestricted access to development along this line and I hope more people share there ideas as freely as you. I, as well as others would have to wonder of any untested therory, what gains it would produce in the real world and at what cost.
The first lesson I learned when entering the steam world, where experience has often shown: if it is not in papers, it's just vapors.
Peter Heid</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: William L. Petitjean, P.E. (IP Logged)
Date: December 05, 2002 03:23AM
<HTML>Hi Peter:
You are exactly right. And, a green automobile is a worthy goal. Keep going. It will be interesting to see if your developments lead toward my concepts, or if they go in another direction. Thanks for the dialog.
Bill Petitjean</HTML>
You are exactly right. And, a green automobile is a worthy goal. Keep going. It will be interesting to see if your developments lead toward my concepts, or if they go in another direction. Thanks for the dialog.
Bill Petitjean</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: tom ward (IP Logged)
Date: December 05, 2002 04:42PM
<HTML>I question the wisdom of water injection because the triple critical point of water is only 705F. To achieve a liquid state near this temperature requires over 3200 psi. Secondly expansion from this pressure will quickly lower the temperature of the charge into the saturation range.
Steam near 3200 psi is nearly as dense as water anyway so why not superheat it several hundred more degrees and achieve better thermal efficiency? The same small valve can be used (more like a fuel injector) with a piezoelectric actuator to cut cycle times to the microsecond range.
What is the wall thickness needed to use 3200 psi safely?</HTML>
Steam near 3200 psi is nearly as dense as water anyway so why not superheat it several hundred more degrees and achieve better thermal efficiency? The same small valve can be used (more like a fuel injector) with a piezoelectric actuator to cut cycle times to the microsecond range.
What is the wall thickness needed to use 3200 psi safely?</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Mike Bennett (IP Logged)
Date: December 05, 2002 05:31PM
<HTML>Peter,
Would you please sent me any diagrams of the F1 valve train. I would like to use this technology to make a balanced poppet retrofit on a 71 series 2 stroke diesel/steam engine. Any ideas on isolating the steam to convert to gas pressure?
On your quest for cylinoid controls, there was some research on pulse cylinoid control of nitrous systems, maybe could be adapted?
If you have dwgs. in a dfx. format (autocad 2000 or earlier) it would help.
Thanks,
Mike
mbennett@royaltycarpetmills.com</HTML>
Would you please sent me any diagrams of the F1 valve train. I would like to use this technology to make a balanced poppet retrofit on a 71 series 2 stroke diesel/steam engine. Any ideas on isolating the steam to convert to gas pressure?
On your quest for cylinoid controls, there was some research on pulse cylinoid control of nitrous systems, maybe could be adapted?
If you have dwgs. in a dfx. format (autocad 2000 or earlier) it would help.
Thanks,
Mike
mbennett@royaltycarpetmills.com</HTML>
Re: Valve timing v/s gasket
Posted by: C Benson (IP Logged)
Date: December 05, 2002 06:27PM
<HTML>Timing advanced,,,,headbolts stretch, an' a bit bl'ws past head gasket,,,Timing retarded,,,piston goes down, no high pressure,,,I wonder if the boys will try to start this one w/ either too OOOps , cheers Ben</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Peter Heid (IP Logged)
Date: December 05, 2002 06:33PM
<HTML>Mike,
What I have are the drawings of the Renault system from 1993 when these systems were first introduced and they have changed little. I found it in a copy of race car engineering magazine. The exact dimensions are built to match the pressures you have to work with. It really is a very simple system and anyone could copy the design. As soon as I get a chance to dig out the magazine I will bring it to work and make you a copy. I will also make a copy of the Caprotti valve gear using a steam spring. Sorry the drawings would only be jpeg or the like, you can't have it too easy.
Peter Heid</HTML>
What I have are the drawings of the Renault system from 1993 when these systems were first introduced and they have changed little. I found it in a copy of race car engineering magazine. The exact dimensions are built to match the pressures you have to work with. It really is a very simple system and anyone could copy the design. As soon as I get a chance to dig out the magazine I will bring it to work and make you a copy. I will also make a copy of the Caprotti valve gear using a steam spring. Sorry the drawings would only be jpeg or the like, you can't have it too easy.
Peter Heid</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Terry Williams (IP Logged)
Date: December 16, 2002 10:18PM
<HTML>I will second Ted's recommendation as to poppet valves. I have well over 1300 hours on my steam outboard motor with poppet inlet and exhaust valves. Originally the engine ran up to 3000 RPM or above, but max engine speed was reduced to 2000-2200 when gearing in the lower end was changed. If you guys really want machinery that runs rather than talking about it endlessly, try something that has been proven to work. When you have experience with something that works, then you can get exotic.</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: mitesh (IP Logged)
Date: March 18, 2004 02:43PM
<HTML>hi sir i am doing a project on the topic valve timing poppet timing . please u can give me some information . i am in need of it .</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Andy Patterson (IP Logged)
Date: April 15, 2004 02:33PM
<HTML>HI Benson
I think that you wour high compression piston was just not shaped right if ti hit the head when the engine was cold. My brothers and I ran Honda's on methanol at 18.5:1 compression. We spent a lot of time getting the piston crown shape just right. The engine didn't get very hot. You could put your hand on the head any time. It inly got worm to the touch. The carb manafold tube was a different story. You could get your finger froze to it. We did away with the paper gasket and used a heat conductive sealent to try and keep the carb from freezing.
Andy</HTML>
I think that you wour high compression piston was just not shaped right if ti hit the head when the engine was cold. My brothers and I ran Honda's on methanol at 18.5:1 compression. We spent a lot of time getting the piston crown shape just right. The engine didn't get very hot. You could put your hand on the head any time. It inly got worm to the touch. The carb manafold tube was a different story. You could get your finger froze to it. We did away with the paper gasket and used a heat conductive sealent to try and keep the carb from freezing.
Andy</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Andy Patterson (IP Logged)
Date: April 15, 2004 04:53PM
<HTML>Hi Bill
You idea of the most efficient engine has some big holes in it's explanation. How are you going to vary the power? Pressure, Cutoff or a combination.
The most efficient cycle would run at boiler pressure(No throttle) expand down very close to exhaust pressure and recompress back to inlet pressure. Power would be varied by the amount of steam. The only way to vary the amount of steam with out changing the expansion ratio and/or pressure is by varing the cutoff and clearance together to maintain a constant expansion ratio. The exhaust close must also be varied to maintain compression back to inlet pressure. The rules out a uniflow type of engine as it's compression ratio is generally fixed. Though varying the clarance also varies the compression ratio of a uniflow. It does track to the compression ratio needes to compress back to inlet pressure. An engine operatoring is nothing like any every built. It would have continuious variable clearance and valve timmings. The amount of power is basicly a function of the cutoff. Cutoff would need to vary from almost 0 at max clearance to what ever produces the expansion ratio at min or 0 clearance. The expansion ratio id of course dependent on the inlet steam pressure and temperature. But at 1000 PSIA we are talking about around 3.5% max cutoff and clearance. Around a 27:1 expansion/compression ratio.
To get around the valve timming and small clearance problems I have been working on a high compression compound design. A tripple expansion compound can get the desired over all expansion ratio of 27:1 in 3 steps of 3:1. This works out very well for valve timming. At low power we are at low RPM using very short(almost 0) cutoff and lots of clearance. At high RPM we are close to 38% cutoff with almost 0 clearance. But time wise(seconds) the valves are operatoring at almost the same rate. Makes for a doable electric driven valve. This type of engine gets an almost constant efficiency over a decient power range. Trying to achieve better then a 32:1 torque varation with constant efficiency.
With complete valve timming control this engine can go to longer even over lapping cutoff for self starting or more torque. It can run at almost zero clearance with no compression to 50% clearance with almost full stroke compression.
My current design is an opposed pistons arange ment. Two pistons to a cylande on seperate cranks. By varing the phase relation of the two cranks you get continious variable clearance. As a side effect the engine displacement also varies. The displacement helps increase the power range. As the clearance is increased the effective engine displacement is decreassing. So at high clearance and short cutoff the steam usage is not onle reduced by the short cutoff it is also reduced by engine displacement.
In theory this is the most efficient variable power positive displacement steam engine possable.
Andy Patterson</HTML>
You idea of the most efficient engine has some big holes in it's explanation. How are you going to vary the power? Pressure, Cutoff or a combination.
The most efficient cycle would run at boiler pressure(No throttle) expand down very close to exhaust pressure and recompress back to inlet pressure. Power would be varied by the amount of steam. The only way to vary the amount of steam with out changing the expansion ratio and/or pressure is by varing the cutoff and clearance together to maintain a constant expansion ratio. The exhaust close must also be varied to maintain compression back to inlet pressure. The rules out a uniflow type of engine as it's compression ratio is generally fixed. Though varying the clarance also varies the compression ratio of a uniflow. It does track to the compression ratio needes to compress back to inlet pressure. An engine operatoring is nothing like any every built. It would have continuious variable clearance and valve timmings. The amount of power is basicly a function of the cutoff. Cutoff would need to vary from almost 0 at max clearance to what ever produces the expansion ratio at min or 0 clearance. The expansion ratio id of course dependent on the inlet steam pressure and temperature. But at 1000 PSIA we are talking about around 3.5% max cutoff and clearance. Around a 27:1 expansion/compression ratio.
To get around the valve timming and small clearance problems I have been working on a high compression compound design. A tripple expansion compound can get the desired over all expansion ratio of 27:1 in 3 steps of 3:1. This works out very well for valve timming. At low power we are at low RPM using very short(almost 0) cutoff and lots of clearance. At high RPM we are close to 38% cutoff with almost 0 clearance. But time wise(seconds) the valves are operatoring at almost the same rate. Makes for a doable electric driven valve. This type of engine gets an almost constant efficiency over a decient power range. Trying to achieve better then a 32:1 torque varation with constant efficiency.
With complete valve timming control this engine can go to longer even over lapping cutoff for self starting or more torque. It can run at almost zero clearance with no compression to 50% clearance with almost full stroke compression.
My current design is an opposed pistons arange ment. Two pistons to a cylande on seperate cranks. By varing the phase relation of the two cranks you get continious variable clearance. As a side effect the engine displacement also varies. The displacement helps increase the power range. As the clearance is increased the effective engine displacement is decreassing. So at high clearance and short cutoff the steam usage is not onle reduced by the short cutoff it is also reduced by engine displacement.
In theory this is the most efficient variable power positive displacement steam engine possable.
Andy Patterson</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 02, 2004 12:17AM
<HTML>One thing that occurs to this illiterate is that tandem, or even triple, EXHAUST poppet valves are a good notion, in that the area of each being SUB one square inch... a decent compression spring could close them against a reasonable PSIG...and the good old bash valve idea ( Sydney Clement "SPUDS" ) could actuate them. On a locomotive the inlet poppet valve is then actuated by the say "Allen" straight link motion alone, the two systems being independent. I have put this to our Bob Carr, State Premier, in a development of the NSWGR D57 or 58 freight engines, 3 cyls. with 2 valve gears and levers for the 3rd. internal cylinder....little modification needed and higher pressure as well I seem to remember.</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 02, 2004 05:38AM
<HTML>and more....we'll get steam on rail before road...agreed? Let's try 4 poppet bash valves in unison, spring loaded against 19 bar or 275.5 PSIG, exhaust valve area two square inches say, loading 551 PSIG over 4 valves, its 137.75 PSIG on each compression spring.
Each valve has a core for bashing of say one eigth inch diam... area that... and an area of half a square inch... plus that... giving a diam. of a whisker over 8 tenths of an inch , YES? Its all under a steam tight manifold??!!??
We could have a rocker and 2 stems and 2 glands....BORING!!!!
Allen straight link worked well, BUT with slide valves, lets get it onto poppets AND use say ten per cent cut-off with decent superheat for the design speed...110 km/hour?
Drawback:- valve seats outside cyl. head instead of inside...anathema from god???</HTML>
Each valve has a core for bashing of say one eigth inch diam... area that... and an area of half a square inch... plus that... giving a diam. of a whisker over 8 tenths of an inch , YES? Its all under a steam tight manifold??!!??
We could have a rocker and 2 stems and 2 glands....BORING!!!!
Allen straight link worked well, BUT with slide valves, lets get it onto poppets AND use say ten per cent cut-off with decent superheat for the design speed...110 km/hour?
Drawback:- valve seats outside cyl. head instead of inside...anathema from god???</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 02, 2004 09:55AM
<HTML>Decapod 4-10-0, 2 driver sets unflanged, 58 inch drivers @ 110 km/hr, 21T per axle, F of A is 4.55, 51744lbs. tractive force, BP</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 02, 2004 10:11AM
<HTML>19 BAR , bore 18.3 inches 4 cylinders, stroke 32 inches, 9.86CF S.V. 3338 IHP at 10% cut-off, 1600 CF of heating surface, 50 SQ. FT. grate, 480 SQ. FT. superheater, piston speed is 1065 FPM.</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 02, 2004 10:49AM
<HTML>YES, O.K. 18.3 INCH BORE cyls. is too big... so its three 21.2 inch cyls. for about 9.8 CF swept volume...Stanier used 16.5 inch cylinders on the "Scots".</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 03, 2004 02:07AM
<HTML>Mountain 4-8-2 41395 lbs tractive force @10% valve timing BMEP is 49 PSIA four 16.4 inch bore cylinders</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: July 03, 2004 10:33PM
<HTML>Is a Challenger the answer ? Reverse order the cylinders...HP to the front with REsuperheated compounding. What for? To be fully ARTICULATED, yes? The drive is divided , everything outside the frames to please the Yanks, and this is essential! Malaysia and Austria, with decent service regimes have had great success with the poppet valve, the former on metre gauge. I have put such a proposal to Martin Ferguson our shadow Minister for Transport</HTML>
Re: Valve timing -- Tandem Poppets
Posted by: Stuart J. McIntosh (IP Logged)
Date: August 17, 2005 10:37AM
<HTML>WOW, this black stuff is becoming costly, even in REAL terms, yes, no ?
What is the reaction of a free market; pass the cost to the consumer......... INFLATION, then the good old credit squeeze and a crash ?!?
BUT, pioneers seem to get "done" in various ways and the plagiarist wins by building on their experience.
Does the Government, heresy heresy, have to take a role, as the pioneer ?
THIS is clear, building on EXPERIENCE WORKS !!!</HTML>
What is the reaction of a free market; pass the cost to the consumer......... INFLATION, then the good old credit squeeze and a crash ?!?
BUT, pioneers seem to get "done" in various ways and the plagiarist wins by building on their experience.
Does the Government, heresy heresy, have to take a role, as the pioneer ?
THIS is clear, building on EXPERIENCE WORKS !!!</HTML>
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