Heat 2 Power
The New Stirling Engine Technology []

Efficient Recuperator

• Since, in contrast to the classic machine, the amount of gas in the recuperator of a New Stirling Installation is independent of the size and number of cylinder pairs, it can be made much larger without creating a dead space. The recuperator is not lmited in its size and consequently its efficiency can be increased as desired, so that the fuel requirement decreases accordingly. The heat is trapped in the system and cannot be lost.
• Unlike conventional Stirling engines, the regenerator does not have a pendulous flow with a cyclically changing temperature. The heat transfer of a New Stirling Installation in the recuperator is more efficient with a quasi-continuous flow than with a pendulum flow (consistently high temperature difference).
• The regenerator does not only connect two cylinder chambers.
• With classic Stirling engines, the heat exchange in the regenerator is exhausted at the end of the cycle and the recovered energy corresponds to the mixed temperature between the initial and final situation when flowing through.
  With the New Stirling Engine only the hottest partial amount of the working gas in the tube space of the regenerator reaches the pipeline system in front of the working cylinders at high pressure permanently and continously and is fed to one of the working chambers as soon as its piston reaches dead center.
  Only the always coldest partial amount of the working gas is available on the other side in the regenerator and from there it is permanently and continously routed through the pipe system into the compression cylinder.

Stationary temperature conditions

Stationary temperature conditions throughout the New Stirling Installation with a permanent temperature gradient from the working to the compression cylinders maintain a high temperature difference between the expansion and compression cylinders.

Optimized expenditure on equipment:

• A single recuperator, heater and cooler for all cylinders means less complexity on equipment and higher efficiency than several sets of smaller heat exchangers for several pairs of cylinders, as is the case with conventional Stirling engines. The proposed construction and the planning of high performance makes sense in particular if several pairs of cylinders are used.
• The components of the system each have a simple basic design.
• The power density of the cylinders is 2 to 6 times higher than that of classic Stirling engines or combustion engines. A smaller installation is therefore sufficient for the same performance (for details see below: Power Density).
• A central burner simplifies flue gas routing and the use of a heat recovery system.
• Low development costs: Heat pipes, heat exchangers, piping, generator, measurement and control technology, crankshafts, etc. are state of the art and can be purchased from external sources as required. As a manufacturer, you can concentrate on the process, the plant layout and the performance-based design of the cylinders. Even small companies can realize systems with really large power output since the majority of the components are purchased parts.
• The system is primarily designed for large outputs with individual design, not for series production of smaller outputs. Therefore, each component can be optimized separately for each application.
• The use of industrial waste heat or excess power from renewable energy generation does not require any piping systems with water, steam or oil circuits, pumps or heat exchangers, but only a suitable design of the heat transfer elements for the Heat Pipes  or a simple air circulation system. It is a "plug-on" system.
• The Heater can be incorporated into the channel head of the regenerator (hot side), which is designed as an tube bundle heat exchanger.

  

  It is even conceivable that the entire burner unit is located in the head of the regenerator.

• There is no big, cast engine block. The cylinder-crankshaft unit consists of individual elements that are optimally held together in a yoke frame.
• Simple, optimal operation, without monitoring and setting operating temperatures in cooling circuits, lubricating oil temperature, mixture temperature, oil mist vapors in the combustion chamber, condensate removal, manual operation, etc..

No timing of cycles due to the cylinder angle:

Since there is always enough working gas in the recuperator and the subsequent pipelines in a suitable condition, a specific offset of the compression cylinders angle is not necessary as with typical Alfa-Stirling machines and the cylinders can be arranged at any angle to one another.

Versatility and variability:

• The entire system of the New Stirling Installation can be designed and scaled using a modular system.
• Dividing the system into separate devices is advantageous for installation and arrangement within an existing available space, for example on ships.
• Any suitable central heat source can be used (e.g. waste heat from industrial processes), which increases the range of possible uses of the system.
• Each element such as cooler, burner etc. can be exchanged, modified, repaired or relocated separately.
• The system can easily be converted to other fuel types at a later date. For example, a ship engine powered by heavy oil can be converted to diesel, Bio-LNG or H₂.
• A second regenerator can be connected in series to increase performance or to optimize it afterwards.
• The ability to use multiple heat sources makes the New Stirling Technology the optimal solution for the energy transition: You can use them as decentralized back-up power plants during dark lulls and operate with the heat from thermal storage systems, and when these are exhausted or not available, with LNG or methane.

Efficient heat transfer:

• The heat can be fed in directly via circulating air circuits and thus saves the detour via secondary circuits or additional heat transfers which reduce efficiency and require complex equipment. These steps will be skipped.
• The heater and cooler are installed in the piping, not at the cylinder heads. Therefore their size is not limited to available space at the cylinder heads.
• In addition to the heater and cooler in the pipeline, there is permanent heat input resp. cooling, i.e. not only during filling / emptying, but during the entire stroke length.
• Heat transfer at the cylinder walls will be managed without heating / cooling dead areas (piston walls, connecting rod space) as in previous machines and without idle or dead times (between the strokes).
• There is only one heat transfer surface for two cylinder chambers.
• There are no burners on the cylinder head so the heat does not have to flow through thick material. Instead, the gas flows already heated into the expansion cylinder and cooled into the compression cylinder: The heat from the burner is conducted directly into the gas in the high-pressure line and also transferred to the gas within the static shell of the cylinder.
  

Enabling high temperature differences:

• The Carnot-Efficiency of previous machines is limited by their temperature range (highest: apr. 800K, lowest: apr. 400K). The New Stirling Machine allows the use of a higher temperature range even without using high sophisticated material. Since there is only one high-pressure line and one low-pressure line, it is easy to implement sufficiently dimensioned heater and cooler which ensure temperatures as desired in these lines (say 825K - 325K).
• The high efficiency of the regenerator means that the cooler and heater only have to transfer comparatively small amounts of heat. Since the temperature at the outlet of the cold side of the regenerator is already very low, the temperature of the working gas in the cooler can easily be brought closer to the cooling water temperature (ambient temperature). A lower temperature level of 300 K is within the realistically and economically feasible range.
• Application of advanced burner/vessel units like FLOX-burners , Pore-burners , COSTAIR-burner, Pre-evaporation burners etc. in combination with heat pipes  between vessel and gas, enable temperature ranges of apr. 1100K - 300K without a considerable temperature loss. The Carnot-Efficiency (calculated by temperature differences between heat source and cooler, not only between heater and cooler) increases from 0.5 to >0.7. Losses in the exhaust gas of such burners as mentioned above could be easily maintained below 10% if a heat recovery system is used. Since the advanced burner systems have internal recirculation, very low values can usually be achieved without a heat recovery system.
• Depending on the choice of the stainless steel, temperatures well over 900K are possible. Weldable steels such as 1.4401, 1.4301 and 1.4571 could be used, but also other alloys such as 1.4435, 1.4539, 1.4841, etc.
  A wide variety of high-temperature resistant ceramic materials and nickel and copper based alloys are available.
  
  For extremely high temperatures (e.g. for the piston rod), fiber-reinforced ceramics are recommended, which are also used as heat protection systems for spacecrafts that are exposed to high thermal stresses and vibrations.
  
  Nickel base alloys or bronzes like CuNi30Mn1Fe could be used for pipings and parts in the hot cylinder. These materials have been established in technology for quite some time and are used for many applications at 1000K.
• Since there are stationary temperature conditions in the plant, thermal shock loads do not occur.
• Heat pipes  can work considerably above 1000K (For example Ag, Li, Na, Hg, Cs). Heat pipes are designed for very long term operation with no maintenance.
• Many materials only have a low tensile strength at high temperatures. Large diameters of the piston rod reduce their mechanical stress and enable application of a heat resistant liner protection in the hot cylinders.
• Tensile stresses in the material due to the internal cylinder pressures are absorbed outside the cylinder (ring elements for radial forces, expansion bolts for axial forces) and are not directly exposed to the highest temperatures.
• The temperature difference between heater and cooler can be increased by integrating these devices into a heat pump and/or Rankine process.
• Classic machines were faced with the often unsolvable task of realizing a high temperature difference, since the material on the hot side of the system defined the upper temperature limit here. With the New Stirling Engine Technology, the focus is also on the cold side: post-compression in the cold cylinder after the exhaust process corresponds to the process of a pulse tube cooler. Overall, the temperature difference can easily be brought to a high level by easily cooling the cold side.

Thermodynamic efficiency:

• Classic Stirling engines do not even come close to achieving the idealized process as shown in the pV-diagram. The isotherms cannot be implemented technically because they only affect a partial volume, namely that of the heated / cooled volume. However, the total expanded / compressed volume is larger and concerns the total amount of gas, some of which is also in the other cylinder. The maximum mixing temperature over the entire amount of gas is lower, the minimum mixing temperature is higher.
  The New Stirling Technology, however, provides that the amount of gas heated / cooled during a cycle is identical to the amount of expanded / compressed gas.
• The heating / cooling of the cylinder walls brings the expansion and compression cycle even closer to the theoretical isothermal state, which results in a higher degree of efficiency compared to the adiabatic process. Isothermal expansion and compression is also favored by the fact that heat does not flow away between the two chambers of a cylinder. The continuous piston rod in the cylinder chambers, which has a large surface compared to other machines, also takes on the temperature of the gas and increases the contact surface between gas and material.
• The closing of the cylinders during the strokes causes an almost perfect isochoric change in the state of the cycles ② ③ and ④ ① in accordance with the theoretical, ideal process. For the classic machine, a discontinuous cylinder movement would be required.
• No overlapping of the work cycles: the changes in state (isothermal or adiabatic expansion - isochoric cooling - isothermal or adiabatic compression - isochoric heating) are clearly separated from each other by the switching device for filling / emptying the cylinders. The corners of the pV diagram are better extended.
• Maintaining the compression ratio: Since there are practically no dead spaces, there is almost no loss of pressure or heat due to the gas escaping in pipelines during the expansion and compression of the gas, as is the case with the classic machine.
  
  The gained used work in kJ calculates to
  
  W = n·R·ln (V_max/V_min) (T_max - T_min)
  
  Changings in the part "ln (V_max/V_min)" (=compression ratio) of this formula will affect the result considerably:
  
  ln (compression ratio=50) = 3.91
  ln (compression ratio=40) = 3.69
  ln (compression ratio=30) = 3.40
  ln (compression ratio=22) = 3.09
  ln (compression ratio=15) = 2.71
  ln (compression ratio= 9) = 2.19
  ln (compression ratio= 5) = 1.61
  ln (compression ratio= 3) = 1.09
  
  
  While the compression ratio of gasoline and diesel engines results from the volumes in the extreme positions of the pistons, the compression ratio of classic Stirling engines (of the α type) depends essentially on the phase shift angle of the pistons.
  The necessary heat exchangers and the regenerator result in considerable dead volumes, so that classic Stirling engines usually only achieve a compression ratio in the order of magnitude of 2 to 3, while Otto and Diesel engines have typical values of 9 and 22.
  
  With other words: A New Stirling Engine with a realized compression ratio of 30 outperforms classic Stirling engines in terms of power output by a factor of 3. Diesel engines are exceeded by 10% ... 25%, Otto-engines by apr. 50%. Furthermore: The simple but rigid design of of the cylinders of the New Stirling Machine allows considerably higher compression ratios as mentioned with the corresponding higher efficiencies.

Low internal losses:

• Since the pipelines no longer represent a dead space, their cross-section can be enlarged, which reduces the flow resistance.
• Flushing losses or charge cycle losses, such as those that occur in valve controls in internal combustion engines, occur only to a very small extent.
• Filling / emptying of the cylinder chambers over short distances and large flow cross-sections.
• Unlike other machines, considerable power is not diverted for the operation of ancillary units (turbo charger, water pumps, camshaft/valve train etc.).

Reduction of heat losses:

• Since both chambers of a cylinder have the same temperature, the typical disadvantage of conventional machines is eliminated, that heat flows from the hot to the cold part and the piston moves from the hot to the cold area.
• As with the classic Stirling machine, the working gas does not lead uselessly away from the working cylinder through heated lines during the expansion cycle, there is no mutual heating / cooling on shared pipes.
• Unlike internal combustion engines, a significant proportion of the heat is not discharged through the exhaust gas. Unused heat remains in the cycle and is fed back into the process. The energy is trapped in the system.
• Since two cylinders share a cylinder for each chamber, the wall heat losses are halved compared to single-acting machines.
• When using heat pipes , there is no great temperature loss between heat source and gas
• Piping, regenerator and cylinder can be easily insulated against heat loss, which in any case only occurs on one side of the plant. There is no cast engine block with a large surface area that could radiate heat or through which heat could be dissipated.
• The remaining heat radiation losses via the surfaces of the system can be recovered: The entire system can be enclosed in an airtight housing, the interior of this shell is heated up by the heat losses from the system. The air required to burn the fuel can be taken from this room, in which fresh, cold air from the surroundings constantly flows in at the same time.

  If the warm air of the housing is used for combustion, the burner has to generate a smaller temperature difference and saves fuel accordingly.

Wear

• Little or no lubrication required. For example, by using plastic plain bearings, oil-free operation of the compression cylinders can be guaranteed. Both the axial bearing and the sliding linings of the piston can be made from the material Iglidur W300^©. On seals can therefore be completely omitted.
• Gaps between the control piston and piston rod serve as air bearings.
• Short pistons, hollow piston rods and low speeds lead to low inertia forces.
• Gas buffers in the cylinders at the end of the work cycle in combination with a low speed reduce the inertial forces significantly. The effect of pressure peaks due to adiabatic rather than isothermal expansion / compression are also reduced by approximating the theoretical isothermal process by continuously heating the cylinder walls.

  

  For isothermal expansion, n=1. With adiabatic expansion, n=κ, so that the curve is steeper and there is a higher pressure difference, which leads to additional forces on the crankshaft bearings. This was a typical problem with classic Stirling engines.

  With a linear arrangement of expansion and compression cylinders ("boxer engine"), the pressure peaks that occur simultaneously in the cylinders at the dead centers compensate each other.

Power density:

• Compared to classic Stirling engines, not only part of the enclosed gas mass changes from one temperature level to another during operation. The other part is only compressed and expanded in classic machines without participating in the thermodynamic cycle and contributing to the engine performance. With the New Stirling Engine, on the other hand, the entire amount of gas that is expanded or compressed takes part in the thermodynamic process. Therefore, same cylinder sizes deliver more power output. As explained above, the New Stirling Technology requires apr. a third of cylinder size compared to a classsic engine to achieve the same power output. And since the New Stirling Engine Technology has double-acting cylinders, the advantage over classic Stirling engines with single-acting cylinders increases by a factor of 6.
• An eight-cylinder Diesel or Otto engine or a four cylinder ship engine (two-stroke Diesel) has the same number of work cycles per crankshaft revolution as the New Stirling Installation proposed here with only one working cylinder and one compression cylinder. Since the machine should be operated optimally at low speed, it is advisable to increase the number of cylinder pairs instead of the projected speed in order to achieve high system performance.

Little friction losses:

• The New Stirling Motor avoids the disadvantage of classic machines that their lower power density and low compression ratio results in an unnecessarily long piston stroke and thus unnecessarily high friction losses.
• There are no lateral forces acting on the pistons, so that the pistons are not used for longitudinal guidance or for sealing in the direction of the crankshaft chamber. They can be made very flat so that only one piston ring is required.
  Therefore, only two piston rings are required for 4 cylinder chambers (1 double-acting hot cylinder and 1 double-acting cold cylinder).
• Since minimal overflow losses between the two chambers of a cylinder are acceptable during the working cycles and the rings are not used for sealing to the outside or to the crankshaft space, the friction here can be drastically reduced compared to conventional machines with a suitable design and defined gap dimensions.
• The friction losses due to the required sealing against gas loss, on the other hand, concentrate on the small diameters on the piston rods. Possible gas and friction losses can only occur at an annular gap that is small compared to the overall diameter of the piston. The gas losses (leakage flows) can also only occur on the side facing the crankshaft, i.e. a maximum of two small possible leaks for four cylinder chambers.

Comparison of a 2-cylinder machine with other machines per 2 crankshaft revolutions (each eight friction pathes):

• New Stirling Machine (1 hot + 1 cold cylinder): Four work cycles, friction paths with low contact pressure of only two piston rings = 0.5 work cycles / friction path. Friction concentrated at piston rod diameters.
• 2-cylinder Ship enginge (2-stroke Diesel): Two work cycles, friction paths with high contact pressure of several piston rings = 0.25 work cycles / friction path. Friction appears at piston diameters.
• Stirling standard machine (1 hot + 1 cold cylinder): two work cycles, friction paths with high contact pressure of several piston rings= 0.25 work cycles / friction path. Friction appears at piston diameters.
• 2-Cylinder Otto or Diesel engine (4-stroke): One work cycle, friction paths with high contact pressure of several piston rings = 0.125 work cycles / friction path. Friction appears at piston diameters.

High efficiency and energy yield:

• The design enables very high levels of efficiency to be achieved by maintaining high temperature and compression ratios, by reducing friction and temperature loss, approaching the theoretical isothermal and isochoric work cycles without their overlapping. Thus, approaching close to the Carnot-Efficiency, which is even higher than with other types of machines.
• Further fuel saving can be achieved by simply integrating a heat recovery system of the burner. The overall efficiency obviously outperforms all known "Power to Heat" systems.
• The compression ratio is not limited by the specific properties of the fuel (e.g. Diesel: self-ignition with apr. 21 bar compression) as is the case with explosion engines.

Simple structure, low complexity:

• The New Stirling Engine Installation is an impressively simple construction. In principle, only one regenerator or recuperator, one heater and one cooler, each of a simple design, are required for any number of cylinders. There are no turbochargers, pumps, complex cooling systems, complex lubrication systems, complex fuel systems or exhaust gas cleaning systems. As an external system, only a system to provide the working gas is required .
• If the recuperator has a sufficiently high degree of efficiency and the heating / cooling on the cylinder walls is optimally designed, an additional heater or an additional cooler can be designed to be relatively small. However, it is always advisable to keep an efficient cooler in the low pressure line as cooling the working gas is the easiest way to achieve a high high / low temperature ratio.
• Control of the discontinuous filling / emptying without camshaft, springs, belts, linkage, gears or similar, no auxiliary energy or auxiliary units required. All elements of the switching device are located inside the piston rods and are not exposed to a burner flame and do not require any mechanics for external control devices.
• All elements are exchangeable. Cylinders are easy to repair because the heat transfer elements, the liners, the heat insulation rings, the outer casing rings, etc. are easily exchangeable too.
• Even with a high number of cylinders, for example, the number of heat pipes remains below 100.
• Many components can be made modular in a simple manner as sheet steel constructions without a casting process. There are almost only turned parts, hardly any milled or cast parts. For the most part, components with a comparatively simple geometry are used.
• No electrical control pumps required when using heat pipes.
• The machine is easy to dismantle. Short downtime phases, fewer staff required, fewer spare parts required.

Overall, very few individual parts are required.

Environmental friendliness:

• The constellation with a central burner (continuous heating, no explosion) facilitates the implementation of a heat recovery system.
• The expected high efficiency of the machine means little energy requirement.
• The use of a single heat source allows application of combustion processes with extremely low pollutant emissions and the use of advanced burners e.g. for flameless oxidation (FLOX) , Pore-burners , COSTAIR-burners  etc. The use of advanced burners with heat guidance by heat pipes  into the gas alone enables fuel savings of 20-50%.
• The installation is capable to use carbon-free or bio-fuels. Lean gases (low calorific gas) from various sources (e.g. landfill sites, biogas, biomass gasification or natural gas extraction from low-quality storage facilities) can be used which formerly only have been flared uselessly.
  
  LBM (Liquefied Biomethane), Bio-LNG or Renewable LNG, is ideal as a climate-neutral fuel for ships. It is not only space-saving to store, but the use of the burner technologies mentioned also avoids the disadvantageous "methane slip" that occurs with other types of engines.
• Due to the low nitrogen oxide emissions, the relevant emission limit values can often be complied with without any additional denitrification system.

Costs

• Investment costs: As described above, the system has a relatively simple structure compared to conventional large engines and gets rid of numerous ancillary units that are particularly customary on ships (e.g. HT and LT cooling water system, preheating pump, boiler, starting air system and compressed air system, auxiliary diesel, scavenging air pumps, filling rods, decompression valves, scavenging air blowers, fuel booster pumps, valve systems, turbochargers, intercoolers, and and and ...).
  
  Without attempting a direct comparison to other types of systems, common sense alone dictates that the New Stirling Technology leads to drastic savings in production, assembly, spares, space requirements and commissioning.
• Operating costs: In addition to low maintenance and repair costs, it is primarily energy consumption that has to be considered here. Heavy oil costs around USD 300 per ton, while marine diesel is at least USD 200 higher. A ship with an output of 12 MW needs almost 10,000 tons per year. Overall, this results in fuel costs of 5,000,000 USD p.a. If you could save 10% of this and invest this in a New Stirling Engine with high-temperature heat exchanger, you would have compensated for the expenses quickly.
• The high efficiency can easily compete with that of fuel cells, even with SOFC cells. However, their lifespan is only 10 years, so it makes sense to convert H₂ into electricity in a New Stirling Engine instead of in a fuel cell.

Examples