Do I need valve springs?

[dn24210r]

I am sorry to keep bothering you all and thank you for all the help up to this point.


I am looking at spring types and rates looking at pneumatic springs recently for this bump design and I am wondering if I have enough pressure to push the head of the valve down closing it without the need for springs at all.




Basically I have a bump design where as the piston rises it comes in contact with the valves allowing the pressure to be injected forcing the piston down where the thing then exhaust before hitting the bottom valves forcing it back up.

In my little crude drawing you can see where I have provisions for a spring of types and passage way for screw to adjust spring rate as well as a passage way to and replace the valves as the bump area wears out.

But, the more I think about it the more I believe that the pressure of around 4400psig within the 3/16 passage way pressing against the head of that valve will be enough to seat that valve tight against the valve seat holding it in place after the piston drops no longer pressing that valve upwards.

I am not sure where to look at this as I am not just looking at the valve head area I am looking at the compression forces that will be pressing up against that valve which I believe will be in the 300psig range multiplied by the remaining area which ends up being around 1200 psig pushing up against underside these valves before the piston reaches the top and that pressure is balanced momentary as the piston reaches TDC then injects the 4400 into the open passage around the valves forcing that piston down.

With this crude math I believe I have essentially created a pneumatic spring of sorts with no real spring in effect.

Less moving parts yay.

I think there is no need valve springs at all. The pressure within the system would remain the same throughout it's range only the flow would be restricted. This could create a pressure drop and the pressure at the top of the valves could become overcome with the compression. As long as I stay above this compression pressure the valves should remain closed completely until acted upon my the piston.

Right?





The cylinder is a 2 1/2 sch 160 pipe heated to 500F degrees for a max working limit of 5505 psig.
The Cylinder is 2.875 OD and 2.125 ID with a central 3/16" exhaust port
The piston is 2" diameter and .25" thick with no rings riding on a .25" rod held in place with bearings and seals not allowing the cylinder to touch the walls.
The intake passage way containing 1600-4300 psig is 3/16 tall and 1.5" wide
The valves are 1" diameter at the head face and neck down at a 60 degree angle 1/4" to a orifice that is 3/8" diameter.
The valve bump neck is 1/4" diameter.
This allows each of the valves to inject through a 1/8" opening around the bump neck for a total injection port of .25.
The bump length controls the duration
The valves should fire a maximum of 16.67 per second
A seated valve at the central exhaust port with 300psig on the backside should allow the higher pressures within the cylinder press against it forcing it open then closing the seated valve off once the pressure reaches 300psig within the cylinder.

The pressure is being obtained by heating co2 to super critical temperatures then cooling it on the exhaust side to -15F through differential passage ways and one way valves to keep the pressure against the valve face as low as possible reducing compression within the cylinder allowing for greater efficiency.



Am I way off on this?
Am I close?

I have looked over the formulas for area and pressure differential and think I am close in my crude understanding. But, I could use a few nudges and recommendations.

I am not a engineer and not in any classes to become one. I am just trying to get as close as I can with this before I start building it and finding flaws I can hopefully overcome.

Any help through criticism or just recommendations would be more then appreciated.

[dn24210r]

One thing I forgot to mention is when the engine is at rest with no heat applied the co2 will be at atmospheric temperature which should keep between 400 and 800psig pressing against the valve head. The valve head being larger at the top then at the valve neck should keep the valve seated against the valve seat even when the engine is off.
I will need to make sure that I have both proper cooling on the exhaust side and proper heating established on the intake side before firing the engine to make sure I do not have the compression forces overcome the pressure withing the 3/16 passage ways sending the cylinder firing upwards 3/4 of the ways through the down stroke kind of deal.

Voltage at 110 sources could be used to maintain the proper temperatures at all times for quicker startup times.

[dn24210r]

The top and bottom of the cylinder will be hotter causing the cylinder and piston to expand in those areas more then the center. This being said I do not feel the expansion will be substantial enough to perform a tight seal.

An amount of compression should be leaked down.

The use of high pressure injection at short pulses(2.7% before and 2.7% after TDC) should overcome the leaks while reducing the counter acting compression before injection.

In my head the leak down between the piston and cylinder wall will reduce the counter active compression to a manageable level where no valve springs will be needed.

Through the use of 300psig of pressure pushing against the backside of the exhaust valve holding the valve closed against the exhaust port due to the temperature being kept at a constant -15 degrees F while being maintained through the use of temperature differential valve sizing.
The amount of " Base" cylinder pressure should remain constant at 300psig As run time is increased keeping that -15 will become an issue. But one I feel I can overcome through the use of refrigerant and spooling the hot gasses away from the exhaust port.

Being constant compression at the top of the cylinder should leak down and be shared equalizing to a degree.
There will be compression at the top of the cylinder. But it should be lessened through the use of leaking around the top of the cylinder and thus raising the pressure within the bottom end of the cylinder.

To a degree that I can not even start to properly estimate.

There will be compression and there will be pressure lost when injection occurs through the leak down.
But, I feel it is manageable and simplifies the design.


At this point I feel I have moved from paper drawings and working tolerances of the materials.
To something I can begin getting material around for construction.


Any advise or recommendations would be appreciated.