Air Independent Propulsion This is an ever moving technology These notes represent an overview but may not represent the latest parameters For non nuclear submarines submersibles and unmanned vehicles AUV UUV torpedoes Torpedo propulsion was originally stored high pressure air It evolved to heated air at the turn of the century using kerosene alcohol or Otto fuel Current torpedoes employ electrical storage or lithium sulphur hexafluoride systems Sulphur hexafloridegas is sprayed over a block of lithium which generates heat As is well known typical submarine propulsion uses a storage battery with engine recharging In all the stored systems the challenge is storage of the oxygen component The initiative behind the self propelled torpedo was provided by an Austrian frigate captain Giovanni Luppi After some unsuccesful attempts to propel a charge laden boat with a springdriven clockwork In 1864 he turned to Robert Whitehead 1823 1905 then technical manager in an Italian factory to design an improved version The result was a torpedo in October 1886 length 3 35 m diameter 25 5 cm weight 136 kg Propulsion was provided by 20 to 25 kg of compressed air driving a reciprocating engine with a high and low pressure cylinder Taken from Swedish Torpedo 100 Years 1876 1976 Secondary Batteries Lead acidsolid solid liquid discharges 2 1 8 V per cell charges 2 1 2 6 V per cell electrolyte H2 SO4 solid liquid Pb Pb O2 2 H2 S O4 2 Pb S O4 2H2 O 2 Pb 2 Pb 2 8 O 2 S 4 H energy density 67 lb kW hr check 67 lbf kW hr 30 391 kgf kW hr 8 2 O 2 S 4 H 1 67 Silver Zinc discharges 1 1 0 8 V per cell charges 1 6 2 0 V per cell electrolyte KOH energy density 20 lb kW hr 20 lbf kW hr 1 20 lbf lbf W hr lbf kW hr 9 072 50 14 925 kgf kW hr W hr lbf kW hr problem both cells hydrogen release in charging New developments NiCd Li rechargeable Fuel Cell originally developed by Roger Bacon H 2 and O2 are supplied to special electrodes with various electrolytes KOH in the alkaline cells proton exchange membranes PEM and high temperature carbonate in the molten carbonate cells solid oxides in other cells Energy conversion is relatively high 60 figure later overall reaction 1 H2 O2 H2 O 2 complete H2 2 O H 2 H2 O 2electons 1 theoretical voltage 1 23 V practical voltage 0 8 V 12 11 2006 1 2 O2 H2 O 2electrons 2 O H maximum power at constant T1 w dot max m dot h 1 T1 s1 h 2 T1 s2 G1 G2 G G Gibbs function h 1 h 2 heating value of fuel G hhv 0 825 to 0 95 depending on T 1 and state of H 2 O liquid or vapor with internal losses 60 conversion H2 consumption O2 consumption reactants 0 111 lbf kW hr 0 889 1 0 0 05 lbf kW hr lbf kW hr kgf kW hr kgf 0 403 0 454 kW hr kgf kW hr the volume is important and depends on the storage method as cryogenic liquids O2 sp gr 1 14 71 lbf ft H2 sp gr 0 064 4 0 3 3 kgf 1 137 10 lbf ft 3 m 3 64 074 kgf 3 m Other methods of storage include high pressure gas hydrides driven out by heat and pressure reduction or as liquid fuel which has to be reformed A summary of ypes of fuel cells from Fuel Cell Handbook Sixth Edition DOE NETL 2002 1179 By EG G Technical Services Inc Science Applications International Corporation Under Contract No DE AM26 99FT40575 U S Department of Energy Office of Fossil Energy National Energy Technology Laboratory P O Box 880 Morgantown West Virginia 26507 0880 November 2002 12 11 2006 2 A brief description of various electrolyte cells of interest follows A detailed description of these fuel cells may be found in Sections 3 through 7 Polymer Electrolyte Fuel Cell PEFC The electrolyte in this fuel cell is an ion exchange membrane fluorinated sulfonic acid polymer or other similar polymer that is an excellent proton conductor The only liquid in this fuel cell is water thus corrosion problems are minimal Water management in the membrane is critical for efficient performance the fuel cell must operate under conditions where the byproduct water does not evaporate faster than it is produced because the membrane must be hydrated Because of the limitation on the operating temperature imposed by the polymer usually less than 120 C and because of problems with water balance a H2 rich fuel is used Higher catalyst loading Pt in most cases than that used in PAFCs is required for both the anode and cathode Because CO poisons the catalyst the fuel may contain no CO Alkaline Fuel Cell AFC The electrolyte in this fuel cell is concentrated 85 wt KOH in fuel cells operated at high temperature 250 C or less concentrated 35 50 wt KOH for lower temperature 120 C operation The electrolyte is retained in a matrix usually asbestos and a wide range of electrocatalysts can be used e g Ni Ag metal oxides spinels and noble metals The fuel supply is limited to non reactive constituents except for hydrogen CO is a poison and CO2 will react with the KOH to form K2CO3 thus altering the electrolyte Even the small amount of CO2 in air is detrimental to the alkaline cell Phosphoric Acid Fuel Cell PAFC Phosphoric acid concentrated to 100 is used for the electrolyte in this fuel cell which operates at 150 to 220 C At lower temperatures phosphoric acid is a poor ionic conductor and CO poisoning of the Pt electrocatalyst in the anode becomes severe The relative stability of concentrated phosphoric acid is high compared to other common acids consequently the PAFC is capable of operating at the high end of the acid temperature range 100 to 220 C In addition the use of concentrated acid 100 minimizes the water vapor pressure so water management in the cell is not difficult The matrix universally used to retain the acid is silicon carbide 1 and the electrocatalyst in both the anode and cathode is Pt Molten Carbonate Fuel Cell MCFC The electrolyte in this fuel cell is usually a combination of alkali carbonates which is retained in a ceramic matrix of LiAlO2 The fuel cell operates at 600 to 700 C where the alkali carbonates form a highly conductive molten salt with carbonate ions providing ionic conduction At the high operating temperatures in MCFCs Ni anode and nickel oxide cathode are adequate to promote reaction Noble metals are not required Solid Oxide Fuel Cell SOFC The electrolyte in this fuel cell is a solid nonporous metal oxide usually Y2O3 stabilized ZrO2 The cell operates at 600 1000 C where ionic conduction by oxygen ions takes place Typically the anode is Co ZrO2 or Ni ZrO2 cermet and the cathode is Sr doped LaMnO3 12 11 2006 3 Table 1 1 Summary of Major Differences of the Fuel …