Heat 2 Power-Engine []

Unlike classic Stirling engines with constantly changing temperature conditions, the entire Heat2Power system operates with a stable thermal profile. The temperature gradient between the hot and cold sides remains constant, enabling a highly efficient design. Instead of theoretical isotherms, the concept relies on realistic adiabatic processes, allowing for an approach to physical limits.
The working gas is additionally cooled in the low-pressure line before entering the cylinders, making it particularly easy to achieve low temperatures here.
The result: maximum internal heat recovery, high efficiency, lower material stresses and a significantly extended service life with stable process control.

The recuperator is designed as a tube bundle, with the high-pressure flow passing through the tube side – this keeps pressure losses low and the mechanical design easily manageable.
The low-pressure flow passes through the shell; the shell therefore only needs to be designed for the low-pressure flow, reducing material and manufacturing costs.
The flow is consistently counterflow; turbulent conditions are deliberately created via geometry and flow velocity, without cyclic reversals.
The tube side can be made of smooth or structured tubes (e.g., internally ribbed) to optimize heat transfer, while the shell is baffle-guided (segmented) for defined cross-sectional velocities.
Material selection follows the temperature side: high-temperature-resistant steels on the hot tube side; cost-effective grades on the cool shell side. This ensures that critical components remain thermally and mechanically decoupled.
Scaling is achieved via the number of tubes, tube length, and shell diameter; the overall size is not limited by dead volumes. Design criteria include pressure loss budgets, target NTU, and permissible temperature approximation.
The continuous gas flow keeps the turbulence constant over time, preventing cyclical drops in the effective heat transfer coefficient and maximizing internal heat recovery.

The Heat2Power engine utilizes a hypocycloid gear that replaces the conventional crankshaft, enabling linear piston guidance with minimal lateral forces. This significantly reduces friction losses, allowing for a particularly flat piston geometry.
The internal mechanics are deliberately kept simple – without complex valve trains or external control elements.
All assemblies are modular and can be dimensioned or replaced independently.
Even at high temperatures, the mechanics remain stable, as no active cooling or lubrication is required.
These design simplifications result in high reliability and facilitate scaling up to power outputs exceeding 10 MW.

Fuel and source neutrality: The heat source only feeds the hot circuit; the internal process remains unchanged.
Load control: Efficiency remains high even at partial load, as the adiabatic process and steady gas flow prevent cyclical dips in heat transfer.
Storage integration: Coupling with high-temperature storage systems enables medium storage durations and stable continuous load provision.
Peripheral options: The recuperator and cooler are freely scalable (number of tubes, length, shell diameter) without dead volume limitations.
Installation flexibility: Separate modules facilitate placement in existing systems, including separate media paths and maintenance zones.

Positioning the heater and cooler outside the cylinder allows for flexible designs – for example, with integrated shell-and-tube heat exchangers and external heat pipes. Thanks to the steady-state operation, no thermal fluctuations occur.
The cold side can even be cooled below ambient temperature through recompression and intelligent cooling.

The work W gained per cycle depends significantly on the compression ratio and temperature difference.

For context: The following approximation formula results for an idealized isothermal process:

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

Typical compression ratios:
– Classic Stirling engine: approx. 2–3
– Gasoline engine: approx. 9
– Diesel engine: approx. 22
– Heat2Power-Engine: up to ≥30 → significantly higher power density

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

➡ With a achievable ratio of, for example, 30, the Heat2Power engine achieves three times the useful work compared to classic Stirling engines. Double-acting cylinders further increase the power density – by a factor of 6 compared to single-acting engines.

In the Heat2Power-Engine technology, the state changes (expansion, compression, isochoric heating/cooling) occur sequentially at different locations within the system. They happen sequentially and without overlap or mixing.

By sealing the cylinders and minimizing dead spaces, the amount of gas heated/cooled corresponds exactly to the amount expanded/compressed. In contrast, in conventional Stirling engines, a large portion of the enclosed gas mass remains thermally inactive – although it is compressed and expanded, it contributes very little to the power output, as the expansion/compression propagates uselessly into the regenerator.

One crankshaft revolution in the Heat2Power-Engine already results in two power strokes. Therefore, a single pair of cylinders replaces a conventional V8 gasoline, diesel, or marine engine with 4–8 cylinders for the same number of cycles. ➡ Result: Significantly higher thermodynamic efficiency.

Example of a calculation for a system with approximately 4400 kW (8 cylinder pairs with a total displacement of 550 liters, 500 rpm). The calculation already includes pressure losses in the pipelines and friction losses. It is based on a detailed, segmented calculation of expansion and compression, taking into account realistic pipe lengths, internal components, bends, etc., in conjunction with a thermal storage tank with 8x12 modules, a convection cooler and an absorption cooler between the thermal storage tank and the compression cylinder.

The pipelines are fully flow-active – they have no dead space and can therefore be designed with a large cross-section. This reduces flow resistance.
Unlike gasoline or diesel engines, there are no charge exchange losses. Due to the short path and precise control inside the piston rod, the working gas is efficiently guided and cannot be lost.

In conventional engines, heat flows from the hot to the cold part of the cylinder, especially when the piston moves cyclically between these areas. In the Heat2Power-Engine, both chambers have identical wall temperatures – thus eliminating internal heat flow and thermal displacement.

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, also due to the flat piston – this halves heat conduction losses.

Heat pipes enable a low-loss connection between the external heat source and the gas circuit. They require no moving parts and do not generate their own flow – this reduces heat loss to a minimum.

The pistons do not seal against the crankcase and do not require a conventional oil passage. This means that lubricants can be largely dispensed with – especially in cold conditions.

Compression cylinders can be equipped with durable polymer bearings such as Iglidur W300©.

Low rotational 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, combined with the low rotational speed, reduces the load from inertial forces.

The linear "boxer" configuration (an opposing cylinder arrangement) ensures mechanical balance: pressure peaks occur simultaneously and cancel each other out. This keeps the bearings and pistons mechanically relieved of stress.

The Heat2Power-Engine technology utilizes near-adiabatic expansion and compression.
– Adiabatic Expansion (n = κ): steep pressure curve with a high pressure difference.
– Isothermal Expansion (n = 1): flatter pressure curve.

Conventional Stirling engines suffer from low power densities – partly due to the extension of the original 90° piston arrangement, which leads to higher friction losses. Heat2Power technology achieves the same power output with a significantly shorter stroke thanks to high compression ratios.

Since lateral forces are completely eliminated from the pistons, they can be designed with a flat profile – guide seals or longitudinal supports are unnecessary. A single piston ring with a small gap is sufficient for each double-acting cylinder – for thermal separation, not for external sealing.

Sealing against gas loss occurs exclusively in the area of ​​the piston rod – with a significantly smaller diameter than the piston itself. This results in only minimal friction losses over a small area.

Furthermore, any potential leaks occur exclusively on the side facing the crankshaft – meaning a maximum of two potential leak points for four cylinder chambers.

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: The frictional heat indirectly supports the heating process and increases efficiency.

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

For your information: In combustion engines, only about 27 percent of the total energy in the fuel is delivered as useful work via the crankshaft. Approximately 9 percent of the energy is lost as heat through friction within the engine.
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If a crankshaft is used instead of a Hypocycloid straight-line guidance system, the mechanics can be positively influenced by a large connecting rod ratio λ. The ratio between the length of the connecting rod and the stroke of the engine (connecting rod ratio) significantly affects the dynamics of the piston, i.e., the velocity profile over the stroke. A large connecting rod ratio results in a more uniform piston speed, and thus 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, derived from the rotational speed using 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 motion is closer to an ideal sinusoidal curve, resulting in smoother running, lower lateral forces, and therefore less friction.

The Heat2Power-Engine operates with only two cylinders – an expansion cylinder and a compression cylinder – which are, however, designed to be double-acting. This results in four power strokes every two engine revolutions, whereas, for example, a four-stroke combustion engine 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 takes place at the piston rod – there with significantly smaller diameters.

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

Conclusion: The Heat2Power-Engine generates more thermodynamically usable work with less friction – the friction loss per work cycle is only about 10% to 25% compared to classic machines.

The Heat2Power engine achieves exceptionally 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: With T_hot = 1100K and T_cold = 300K, the following results:
η ≈ 1 – 300 / 1100 ≈ 0.727 → 72.7 %

Since no cyclic temperature changes occur, high-temperature resistant materials can be used – without cracking or aging.
Recovered heat from the burner environment, piston friction, or radiation is either trapped in the system and fed back into the cycle, or can be used to preheat the combustion air – thus reducing the required burner energy input.

➡ The overall energy yield is therefore significantly higher than with Otto, Diesel or classic Stirling engines.

The Heat2Power-Engine does not operate with explosive combustion like diesel engines, but with continuous heating via a central burner. As a result, depending on the system, there are no flame fronts or pressure peaks, and emissions are significantly reduced.

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

The Heat2Power-Engine does away with many cost-driving components of classic machines: no valve trains, no cylinder heads with complex controls, no lubrication circuits.

The components are mostly rotationally symmetrical and can be manufactured cost-effectively on CNC machines.

Thanks to their modular design, cylinder assemblies can be easily replaced – ideal for maintenance or series production.

Heat exchangers, piping, sensors, etc. are standard purchased parts.

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