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Thread: Temperature diffrential methods and advise.

  1. #1

    Temperature diffrential methods and advise.

    OK here is my rough layout up to this point. The cylinder rides on bearings at the top and bottom with no rings it is within 2 and 5 microns from the cylinder wall held in place by the rod. The rod is pushed up by a oiled dead cylinder within a cylinder sleve pushed up by a rod turned by a crank. Everything not shown is oiled. Everything shown is not oiled.

    I have 1.44 gallons of liquid c02 heated to 600F for 600 bar or 4351 psig of which I am regulating at 4000psig.

    The 1.44 gallons are housed within two 2-1/2 sch160 pipes 30" long(1 gallon capacity each) at the top and bottom of the cylinders. The 2-1/2sch160 has a working pressure of 5039 at 600F.

    Now the cylinder design has a central exhaust and is a bump injection design. I have 6 of these double acting cylinders on a inline six block and this is a single stroke design. The size cylinders fire in groups at the same time. 1/6, 2/5, 3,4. Two cylinders fire at the same time.
    Each cylinder has two bumps injecting 1/16 flow over 2.5% of crank rotation. At my maximum rpm goal that is 16.67 injections(of .25 flow through 2 cylinders) per second.

    Now here is the tricky part that I am fighting with.
    Because the design is central exhaust.
    The cylinder reaches TDC and fires down towards the bottom exhausting halfway down and continues to drop before it is fired up on the other side of the cylinder expelling that spent gas more as it travels upward until it passes that halfway point then it begins to compress that gas.

    Now to offer more power I am trying to reduce the amount of that compression.

    Because the system is fully closed once c02 gas exits the cylinder I want to rapidly cool it and return it to liquid. I am doing this through a means of refrigerant/freezer. Basically a spiraling cooling tube surrounded with ice within a chamber that is -between -6 and 18 degrees. At the bottom of the chamber is a hydraulic pump that then injects the liquid c02 into the 600F chamber maintaining a constant 4000psig.

    Back to the compression issue.

    If I use a diaphragm(steel dome shaped valve) with a spring at say 800lbs. That should empty the cylinder to that point and that blast once cut off could be rapidly cooled as it drops through the spiral dropping in temp. That should leave 800 psig within the cylinder which I could deal with.

    But because I am dealing with just injecting 2.7% of the stroke and injecting that up to 16.7 times a second with that higher temperature radiating in the cylinder I am wondering if that spring will be overcome or if the temperatures will reach a higher psig then 800 using the diaphragm.

    Another option is to run no diaphragm(fewer parts yay). Cooling the piston to -6 at the central point. There would be radiate heat at the top and bottom and I feel that I can insulate in those areas.

    The plan here is to surround the cylinder with ice at with refrigerant at a constant -18 at the bottom and have the central exhaust run through a tube to the top of the ice chamber and spiral down the length of the cylinder on the outside before the CO2 liquid goes into the reservoir/pump/back into the heated chamber.

    I am no engineer, I know nothing about thermodynamics, This is not for school.
    I have loose ends pulled off of google sources at this point through pdf's and papers on the subject as well as tables and charts. This is just for a project/hobby I am trying to get parts around for and attempt to build. But I am trying to do a good portion of the math

    I am wondering if having the cylinder at the cooler temperature is going to drastically affect power in a negative way. I know it will cause less compression but am unsure if it will also take that brief 4000psig charge and reduce it.

    Or if I would be better off using the diaphragm keeping that cylinder at higher temperature and there by having a higher compression ratio working against the cylinder before it fires if that would affect power in a worse manner that way.

    Over the last year this has gone from steam(high pressure/weight/or low reserve), to compressed air(low recovery exhausting to ATM) to this sCO2(high pressure with respectable reserve) with very few changes to the cylinder design. The simplicity and ease of manufacturing has me wanting to use this central exhaust design. The full mechanical bump design with fewer moving parts(no valve rod/cam/metal on metal sliding requiring oil) is a reliable choice while being very low profile. I just need to find a way to get past this compression issue.

    Thank you for any help or advise.

  2. #2
    300 bar at 4351 psig^

  3. #3
    Important things I forgot to mention.

    The stroke of the working cylinder is 3.4" total.
    Piston diameter 2".
    Inside cylinder diameter is 2.125.
    Piston depth is .25".
    Rod diameter is .25".
    Valve angle 60 deg.
    Valve diameter .5".
    valve height off of face pushed up by piston 1/32 x2
    Valve spring pressure 200lbs adjustable via screw as valve wears/replaced/broken in. May eliminate this spring in future design.

    Head(top and bottom of cylinder) height 1".
    Head wall thickness 7/16"
    Port size into head 3/16"

    Diaphragm spring pressure 800psi adjusted via screw.
    Diaphragm diameter .4"
    Exhaust opening 3/8"
    Diaphragm cone recess .2"
    Diaphragm chamber diameter .6"

    Cooling chamber pipe Inside diameter .323"
    Cooling chamber pipe length 20'
    Cooling chamber height 6"
    Cooling chamber diameter 6"
    1 cooling chamber per cylinder into 2-1/2 sch160 x30" chamber to pump.

    Pump on 3200psig-3900
    Pump off 4000psig-4300(digital)
    Pump bypass 4400

    Safety valve 4700 psig
    Manual safety valve- Ball

    Throttle=ball valve x6

    Seals per piston 4
    Seals height .2
    Seal diameter .5
    Seal max operating temperature 1200F

    Bearings roller oiled sealed non serviceable
    Bearings per piston 2 rings
    Bearing height .3"
    Bearing od .5"
    Bearing id .25"

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