Heat 2 Power
The New Stirling Engine Technology []

Instead of fluctuating temperature states like in classic Stirling engines, the thermal state remains constant throughout the entire system. The temperature gradient between the hot and cold sides is permanent, enabling high efficiency. Heating and cooling of the cylinders occurs via the cylinder walls themselves and along the entire stroke length, ensuring optimal heating and cooling of the gas. The working gas is additionally cooled in the low-pressure line before entering the cylinders before compression, making it particularly easy to achieve low temperatures here. The result: higher efficiency, lower material stresses, a longer service life – and significantly higher efficiencies with stable temperature control.

Unlike classic Stirling engines, the recuperator in the new technology is **no dead space**, as neither expansion nor compression from the cylinders continues as a cyclical gas movement. Instead, the gas flow is guided continuously and stationary by constantly switching between expansion and compression. This eliminates the typical oscillating flow with reversal points. The steady, uniform flow allows for targeted turbulent conditions in the tube bundle regenerator, which significantly improve heat transfer throughout the entire process. In classic engines, there were not only dead spaces but also dead times – during the reversal of the flow direction. With the New Stirling Engine Technology, heat transfer via the tube walls is significantly more efficient, as the gas velocity does not fluctuate cyclically and remains turbulent.

The recuperator size can be freely selected – without restrictions due to dead volumes. This leads to greater thermal energy recovery and reduces the required fuel input.

The entire Stirling engine installation is designed modularly: The cylinders are separate from the burner and cooler, allowing for flexible arrangement and assembly, e.g., on ships. Components such as heaters and coolers are not permanently attached to the cylinders and can be dimensioned to scale. Many parts are made of turned steel tube constructions, eliminating the need for complex milling or casting processes. The mechanics are designed to remain stable even at high temperatures, without active cooling or lubrication.
Control is entirely independent of external mechanics. Even the heat exchangers are easily replaceable. The modular design allows for flexible scaling depending on the desired performance – with minimal equipment effort.

Switching between thermal and chemical energy sources is also possible – for example, from high-temperature thermal storage to methane once the storage is exhausted. This enables uninterrupted operation, e.g., as a backup solution in grid operation.

Positioning the heater and cooler outside the cylinder enables flexible designs – for example, with integrated shell-and-tube heat exchangers and external heat pipes. Thanks to the stationary operation, no thermal cycling occurs.
The cold side can even drop below ambient temperature through recompression and intelligent cooling.
A thermodynamic advantage of the design lies in the ratio between the heated surface and the remaining gas volume in the cylinder. The internal piston rod reduces the effective expansion volume, while the entire cylinder wall is heated over the total stroke length. This results in a particularly favorable surface-to-volume ratio (S/V), which enables a high heat flux density and rapid, almost complete heating of the working gas. The heat pipes can heat the gas efficiently – supported by long contact time due to slow rpm's – and thus achieve smooth expansion without the need to actively heat the entire wall surface.

The moving components – piston and piston rod – are made of highly thermally conductive materials. This increases the heated surface area within the cylinder chamber. At the same time, a dynamic heat exchange occurs between the opposing both chambers of one cylinder – temperature-related deviations are compensated, and isothermal expansion is stabilized.

The work W gained per cycle in kJ is calculated using the formula:

$$W = n \cdot R \cdot \ln\left(\frac{V_\text{max}}{V_\text{min}}\right) \cdot \left(T_\text{max} - T_\text{min}\right)$$

Typical compression ratios: – Classic Stirling engine: approx. 2–3 – Gasoline engine: approx. 9 – Diesel engine: approx. 22 – New Stirling engine: up to ≥30 → significantly higher power density

Example values forln(Vmax/Vmin):
ln(30) ≈ 3.40  ln(22) ≈ 3.09  ln(9) ≈ 2.19  ln(3) ≈ 1.09

➡ With a feasible ratio of, for example, 30, the new Stirling engine achieves three times more useful work than classic Stirling engines. Double-acting cylinders further increase power density – a factor of six compared to single-acting engines.

With the New Stirling engine technology, the changes of state (expansion, compression, isochoric heating/cooling) occur at different locations in the system, one after the other. They occur sequentially and without overlap or mixing.

By closing the cylinders and maintaining minimal dead space, the heated/coolable gas volume exactly matches the expanded/compressed volume. In classic Stirling engines, however, a large portion of the enclosed gas mass remains thermally inactive – although it is compressed and expanded, it contributes little to power, as the expansion/compression propagates uselessly into the regenerator.

In the New Stirling engine, one crankshaft revolution already results in two power strokes. A single pair of cylinders therefore replaces a classic V8 gasoline, diesel, or marine engine with 4–8 cylinders, assuming the same number of cycles. ➡ Result: Significantly higher thermodynamic efficiency, approaching the ideal Stirling process.

The pipes are completely fluidically active – they do not represent any dead space and can therefore be designed with a large cross-section. This reduces flow resistance and minimizes the drive energy required to move the working gas. The system requires no conventional auxiliary units. This significantly reduces internal power losses – almost all of the supplied energy is converted into useful work. Unlike gasoline or diesel engines, there are hardly any losses due to charge cycles. The short path and targeted control inside the piston rod ensure efficient gas flow.

A large rod ratio leads to lower piston acceleration and a longer dwell time at dead centers, as well as a more uniform piston velocity profile, thus allowing more time for filling and emptying, more uniform heat transfer, and gas expansion = a more efficient thermodynamic process. Furthermore, vibrations and lateral forces on the connecting rods are reduced.

In conventional engines, heat flows from the hot to the cold part of the cylinder, especially when the piston cyclically moves between these areas. In the New Stirling Engine, the wall temperature is identical in both chambers – thus, there is no internal heat flow and no thermal displacement.

The working gas is not transported through heated pipes and then exits them again. Pipes and cylinders are designed so that no unused heat is lost to the environment.

Remaining heat losses due to radiation can be absorbed by an airtight enclosure: The air contained therein heats up and can be fed directly to the burner. This reduces the temperature difference that the burner must generate – thus saving fuel.

Heat losses at the wall surface are reduced by split cylinders (two chambers per block). The surface area per chamber is smaller than in single-acting engines – thus halving losses due to heat conduction.

Heat pipes enable a low-loss connection between the external heat source and the gas circuit. They require no moving parts and generate no airflow of their own, reducing heat loss to a minimum.

The design eliminates large engine blocks or metal casings, which typically radiate heat. Instead, the cylinders are insulated, and the directional design ensures heat loss only occurs on the hot side, not the cold side.

The pistons do not seal against the crankcase and do not require conventional oil routing. This largely eliminates the need for lubricants – especially in cold conditions.

Compression cylinders can be designed with durable polymer bearings such as Iglidur W300©. Air bearings for the control piston reduce friction and enable thermally robust operation.

Low speeds (approx. 200–600 rpm) and short, lightweight pistons minimize inertial forces. Hollow piston rods further reduce the moving mass. At the end of the power stroke, a gas buffer acts, which, together with the low speed, reduces the load from inertial forces.

The linear "boxer" configuration – i.e., the opposing cylinder arrangement – ensures mechanical balance: pressure peaks occur simultaneously and cancel each other out. This keeps the bearings and pistons mechanically unloaded.

In classic Stirling engines, adiabatic expansion and compression lead to steep pressure curves in the pV diagram. This results in high pressure differences and additional forces on the bearings and pistons – particularly problematic at high speeds.

The New Stirling Engine Technology, on the other hand, uses nearly isothermal expansion and compression – made possible by continuous wall heating and cooling. This makes the thermodynamic exponent n closer to 1 than κ (1.4 for air).

The graphic shows two curves:
– Adiabatic expansion (n = κ): steep pressure curve with a high pressure difference and thus increased mechanical stress.
– Isothermal expansion (n = 1): flat pressure curve, stable force distribution, ideal for efficient and low-wear continuous operation.

➡ This process not only reduces thermal peaks but also mechanical stress – and is a key element for the longevity of the entire drive system.

Classic Stirling engines suffer from low power densities – also due to the stretching of the original 90° piston arrangement, which leads to higher friction losses. Thanks to high compression ratios and the innovative cylinder design, the New Stirling Technology achieves the same power output with significantly less friction.

Friction losses can be drastically reduced by using a Hypocycloid linear guidance . A conventional crank mechanism generates three to five times more friction loss than a hypocycloid linear guide – depending on speed, lubrication, and size.

Unlike combustion engines, the heat generated by friction is not dissipated via the exhaust gas – it remains in the system and is largely transferred to the working gas. This creates a positive side effect: Frictional heat indirectly supports the heating process and increases efficiency.

For your information: In combustion engines, only about 27 percent of the total energy in the fuel is transferred to the engine as useful work via the crankshaft. Approximately 9 percent of the energy is lost as heat through friction in the engine.
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Hypocycloid straight guidance

A large piston rod ratio leads to more consistent piston speed, i.e., lower peak piston speeds and accelerations.

$$\dot{s}(\alpha) \approx \omega \cdot r \cdot \left( \sin(\alpha) + \frac{1}{2\lambda} \cdot \sin(2\alpha) \right)$$

ω = Angular velocity, resulting from the speed via ω = 2π · (n/60).
r = Crank radius. 2 x r = Piston stroke
α = Crank angle (current angular position of the crank)
λ is the rod ratio, the ratio of connecting rod length to crank radius: λ = l / r. A larger λ means that the piston movement is closer to an ideal sinusoidal curve, resulting in smoother running and lower lateral forces, hence, less friction.

The New Stirling Engine operates with only two cylinders – an expansion cylinder and a compression cylinder – which, however, are designed as double-acting cylinders. This results in four power strokes per two revolutions, whereas a four-stroke internal combustion engine, for example, only delivers one power stroke every two revolutions.

The friction points are optimized: Only two large piston rings are used for a pair of cylinders (instead of four to six), but the sealing occurs at the piston rod – with significantly smaller diameters there.

Furthermore, when using a Hypocycloid straight guidance instead of a crankshaft, the friction points of the crosshead axial guide are eliminated.

Conclusion: The New Stirling Engine generates more thermodynamically usable work with less friction – the friction loss per power stroke is only approximately 10% to 25% compared to conventional engines.

The new Stirling engine technology achieves particularly high efficiency because it eliminates many traditional sources of loss.
The thermodynamic efficiency approaches the Carnot efficiency, which is defined by the temperature difference between the hot and cold sides:
η = 1 – Tcold / Thot

Example: For T_hot = 1100K and T_cold = 300K, the result is:
η ≈ 1 – 300 / 1100 ≈ 0.727 → 72.7 %

Since there are no cyclic temperature changes, high-temperature-resistant materials can be used – without cracking or aging. Recirculated heat from the burner environment, piston friction, or radiation is either captured in the system and returned to the circuit, or can be used to preheat the combustion air – thus reducing the required burner energy consumption.

➡ The total energy yield is therefore significantly higher than with gasoline, diesel or classic Stirling engines.

The New Stirling Engine does not operate with explosive combustion like diesel engines, but with continuous heating via a central burner. This eliminates flashbacks and pressure peaks, and significantly reduces emissions.

Burner systems such as FLOX (flameless oxidation), porous, or jet burners can be installed – they operate with particularly low NO_x emissions and enable low pollutant emissions even without exhaust aftertreatment.

The New Stirling Engine Technology eliminates many costly components of traditional engines: no valve trains, no cylinder heads with complex control systems, and no lubricant circuits.

The components are mostly rotationally symmetrical and can be manufactured cost-effectively on CNC machines.
The modular design allows cylinder groups or control pistons to be easily replaced – ideal for maintenance or series production.
Since oil circuits are not required, not only are their purchase costs eliminated, but so are the operating costs for oil, filters, and regular replacement.

➡ Overall, the investment-to-performance ratio is significantly lower than that of conventional engines – while at the same time the running costs are lower.