Modified Gama cycle(cold hole/ambient scheme warning)
Posted: Fri Aug 11, 2023 7:19 pm
Ok guys I have another crackpot hot air scheme to prototype. Initial pressure gauge testing is encouraging to say the least! This is the culmination of my dive into the ambient/wind engine that is largely based on mass flow here viewtopic.php?f=1&t=5545 and testing on a fixed volume displacer cylinder to understand available pressure v. heat input here viewtopic.php?f=1&t=5539 and here viewtopic.php?f=1&t=5549. Links added for future reference.
The goal here is to make use of pressure AND mass flow, something pistons can't do.
I have to say I was largely inspired by Tom's take on self cooling cycles and especially his recent foray into air cycle machines, as well as Matt's deep dive on Gamma's. This modified cycle seems to be easy to construct and optimize. It should also work better at very large scale, and should benefit greatly from higher temperature input.
It also benefits from slow displacer cycle rates to improve heating and cooling times, while maintaining a constant utilization of energy flow.
Consider a STANDARD gamma type displacer cylinder(300k-600k) with the hot plate covered. Power piston at TDC and a 300k 1atm+compression ratio as a starting point, move displacer to cover cold plate and we heat air volume to 600k and drive piston toward BDC. Lets assume(for arguments sake) the work done on the piston drops gas temperature back down to 300k by BDC. (Back to ambient or colder and crank power is now being robbed from the engines output.)
So now atm pressure drives the piston back towards TDC, but only until internal pressure reaches 1atm, after that we have to put in the work of compressing the gas again.
I would argue that this is a relatively idealized cycle and would require careful balancing of compression ratio and displacer cylinder to power cylinder size, and varying load will affect the outcome as well.
Now, for the modified Gama cycle.
Again consider the starting point of displacer covering hot plate, only this time there is only 1atm at 300k and there is no piston.
Move displacer to cover cold plate. The volume of air is heated and allowed to leave the displacer cylinder via one-way check valve and flow to turbine or reciprocating free piston(think pneumatic air hammer). This air will dump to open atm so lets run it through multiple stages to extract all heat energy, anything left can go towards domestic hot water use. As far as I'm concerned, this is near 100% utilization of heat. Next, move displacer to cover hot plate. The effluent check valve has closed. What we are left with is a displacer chamber in a state of vacuum. The higher the Tmax, the less air will be left in the chamber, helping to make the next cycle even more efficient. The residual heat in the remaining volume of air is all that would be needed to be cooled externally. With intermittent heat input and a well designed hot sink, this could be reduced to a minimum.
With the hot plate covered and the chamber otherwise fully insulated, another one way check valve now allows ambient air to flow into the air cycle turbine that is connected to the same shaft as the hot turbine. The atmospheric air drives the cold turbine, adding power output and simultaneously lowering temperature to below ambient before it is allowed to expand into the displacer chamber and possibly further reduce in temperature. The influent check valve has now closed and we now have 1atm at a Tmin of BELOW AMBIENT air to start the cycle over again in a "supercharged" state, all while extracting power from ambient heat and pressure.
This cycle can easily benefit from tuned port ram air effect for both intake and exhaust scavenging. Also, the "atmosphere" can be replaced by a pressurized vessel of sufficient size(large enough to not be effected by operating volume of engine) and increase power further.
The goal here is to make use of pressure AND mass flow, something pistons can't do.
I have to say I was largely inspired by Tom's take on self cooling cycles and especially his recent foray into air cycle machines, as well as Matt's deep dive on Gamma's. This modified cycle seems to be easy to construct and optimize. It should also work better at very large scale, and should benefit greatly from higher temperature input.
It also benefits from slow displacer cycle rates to improve heating and cooling times, while maintaining a constant utilization of energy flow.
Consider a STANDARD gamma type displacer cylinder(300k-600k) with the hot plate covered. Power piston at TDC and a 300k 1atm+compression ratio as a starting point, move displacer to cover cold plate and we heat air volume to 600k and drive piston toward BDC. Lets assume(for arguments sake) the work done on the piston drops gas temperature back down to 300k by BDC. (Back to ambient or colder and crank power is now being robbed from the engines output.)
So now atm pressure drives the piston back towards TDC, but only until internal pressure reaches 1atm, after that we have to put in the work of compressing the gas again.
I would argue that this is a relatively idealized cycle and would require careful balancing of compression ratio and displacer cylinder to power cylinder size, and varying load will affect the outcome as well.
Now, for the modified Gama cycle.
Again consider the starting point of displacer covering hot plate, only this time there is only 1atm at 300k and there is no piston.
Move displacer to cover cold plate. The volume of air is heated and allowed to leave the displacer cylinder via one-way check valve and flow to turbine or reciprocating free piston(think pneumatic air hammer). This air will dump to open atm so lets run it through multiple stages to extract all heat energy, anything left can go towards domestic hot water use. As far as I'm concerned, this is near 100% utilization of heat. Next, move displacer to cover hot plate. The effluent check valve has closed. What we are left with is a displacer chamber in a state of vacuum. The higher the Tmax, the less air will be left in the chamber, helping to make the next cycle even more efficient. The residual heat in the remaining volume of air is all that would be needed to be cooled externally. With intermittent heat input and a well designed hot sink, this could be reduced to a minimum.
With the hot plate covered and the chamber otherwise fully insulated, another one way check valve now allows ambient air to flow into the air cycle turbine that is connected to the same shaft as the hot turbine. The atmospheric air drives the cold turbine, adding power output and simultaneously lowering temperature to below ambient before it is allowed to expand into the displacer chamber and possibly further reduce in temperature. The influent check valve has now closed and we now have 1atm at a Tmin of BELOW AMBIENT air to start the cycle over again in a "supercharged" state, all while extracting power from ambient heat and pressure.
This cycle can easily benefit from tuned port ram air effect for both intake and exhaust scavenging. Also, the "atmosphere" can be replaced by a pressurized vessel of sufficient size(large enough to not be effected by operating volume of engine) and increase power further.