Comparison of Submarines

New Stirlingmotor Technology vs. Combustion Engine + AIP

1. Submarine concept with combustion engine + AIP:

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2. Submarine concept with New Stirling Engine:

Size proportions adapted as far as possible to realistic proportions of the U-216
X= space gained compared to the AIP version

Typical features and characteristics:

1. Submarine concept with combustion engine + AIP

• The propeller is powered electrically. There are three sources of electrical energy that can be used alternatively or in combination:

  - Main engine, designed as a Diesel GenSet
  - Batteries
  - AIP (Air independent propulsion), designed as an H₂ fuel cell system

• An additional hull section wth an AIP drive is installed. AIP is using fuel cells and require tanks for liquid oxygen and storage for H₂ (such like Magnesium borohydride with 15 % by weight of H₂)
• The main engine (MTU 396 series) is used for surfaced travelling. AIP of apr. 360 kW is used for submerged stay or submerged slow travel.
• AIP normally allows submerged travelling speeds up to apr. 4 knots for apr. 15...20 days.
• The generation of 1000 kWh by the AIP requires apr. 55 kg H₂, storage capacity of metal-hydride of apr. 380 kg as well as apr. 460 kg O₂.
• Cryo-Oxygen is stored in the outer section. Since H₂-storage is limited due to weight and space, the onboard-production of H₂ by reformer plants is considered.

2. Submarine concept with New Stirling Installation

• The propulsor is electric driven and will be fed with power by the main engine or the batteries.
• One engine for all purposes, an additional hull section wth an AIP drive is not required. The New Stirling GenSet generates electric power at surfaced and submerged travelling.
• Compressed oxygen for burning the fuel at submerged travel is stored in the outer section. The decompression will be used to generate additional electric power by an turbine and deep temperatures for cooling the engine (reduced cooling water temperature and heat signature).
• The generation of 1000 kWh by the New Stirling Engine requires apr. 145 kg Diesel fuel as well as apr. 83 kg O₂. In total, this is only a quarter of the weight of the substances carried compared to the use of H₂ fuel cells.
  Large battery capacities are not required, since only 8300 kg O₂ at 335 bar ( 19,5 m³ Calculation of real gas factor of 1.0335531 and density of 425.52 kg/m³ based on the corrected Van der Waals-formula acc. to Redlich-Kwong-Soave. ) are required to generate enormous 100,000 kWh when submerged. Li-ion batteries would need 200 m³ for this energy. The O₂ tanks in the sketch above (approx. 2x45m³) would be sufficient to generate 500,000 kWh, i.e. about as much energy as the fuel for surface travel up to now is carried along.
  
  Conclusion: It is more efficient to use space for O₂ than for batteries or H₂. Then there is no longer a difference between submerged or surfaced range.
• Two or three mid-sized New Stirling GenSets share a common regenerator. If only few power is required, only one New Stirling GenSet is in operation. However, it uses the entire size and capacity of the regenerator and its performance. Efficiency and heat signature are optimized.
• In total, a New Stirling Engine provides better performance (submerged range, fuel consumption, drive power), considerably less complexity and requires less space. As a result, a New Stirling Drive is obviously significantly less expensive.
  
  The space gained (see illustration above) is sufficient, for example, to install a Mk 41 vertical launch system with eight cells for missiles .