Soryu LABs vs LIBs, AIP and Indiscretion Ratios

According to the former Commander of the Japanese Navy Submarines Service, Vice Admiral (retired) Masao Kobayashi, in a lead-acid battery (LABs) submarine, one hour-ventilation by using a diesel generator (DG) is needed after battery charging to release hydrogen generated by the charging process. 

Based on this information, the indiscretion ratio of the five following submarine Cases/scenarios have been reviewed and very roughly estimated for Japanese submarine missions of 70 days. This is where the surveillance period is 50 days and transiting period is 10 days x 2 = 20 days) and the DG output (hotel load + propulsion) is 250kW:

Case I   (submarine length 84m, LABs, powered 100MW (or is that 100 kW?) - air independent

             propulsion (AIP), 2 x 2MW-generators, model SoryuMK I, IR =7%;

Case II  (length 84m, lithium-ion batteries (LIBs), 2 x 2MW-generators, model Soryu MK II)

              see Table below) IR=6%;

Case III  (long range Soryu proposed for Australian Future Submarine (AFS), length 90m, LIBs, 

               4 x 2MW-gnerators) IR=2.5%;

Case IV  (AFS, length 96m, 100MW-AIP, LIBs, 4 x 2MW-gnerators) IR=2%;

Case V   (AFS, length 96m, 100MW-AIP, LABs, 4 x 1MW-generators) IR=7%.

Comparison of Cases I and V shows that IR is determined by slow charge rate of LABs in a LAB-submarine. Comparison of Cases II, III an IV shows that output of the DG shows critical effects on IR for LIB submarines.

Performance at low speed means IR is Case IV>= Case III >>Case II >Case V = Case I.

Performance at high speed, which depends on batteries, is Case III>= Case IV >>Case II >Case V = Case I.

The facts that:

-  using up stored liquid oxygen (LOx) ends the usefulness of the Soryu’s Stirling AIP, and

-  LIBs are better than LABs

shows the flexibility of operation of each cases: Case III>= Case II >Case IV> Case V=Case I.

The superiority of AIP and LIBs, or simple LIBs, depends on a submarine’s mission. DGs play a critical role in both LIBs-submarines (Cases II and IV) within certain diesel power output ranges.

Anonymous thinks the future of LABs-submarines (Cases I, III and V) are limited with or without AIP and recent the tragedy of Argentina’s ARA San Juan shows LABs are not automatically safe.

Over 24 hours the balance of energy supplied [Es] to batteries and energy consumed [Ec] form batteries and AIP is described in equation (1)

(1)   Es = Ec

(2)   Es = Energy from diesel generator [Ed] + Energy from AIP [Ea]

(3)   Ec = Energy for propulsion [Ep] + Energy for hotel load [Eh]

The Indiscretion ratio (IR) which is the snorkeling period [ts] per day (=24h) is described in eq (4)

(4)   IR = ts/24 x 100 (%) = (tg + th)/24 x 100 (%)

(5)   ts = snorkeling period for diesel generation [tg] + snorkeling period for hydrogen release [th] 

        This is where, th =1h for LABs with hydrogen generation, and th = 0h for LIBs without 

        hydrogen generation.

Charge of batteries (capacity X (MWh)) with Y of C rate, Ed for ts is described in (6)

(6)   Ed = 1000XYtg  This where C daily energy from Z (MWh)-AIP for 50 days-opertion is 

        described in (7)

(7)   Ea =1000Z/50 =20Z

(8)   is derived from (2), (6) and (7), Es =1000XYtg + 20Z

(9)   If 250 kW of energy is consumed in an hour, then, Ec = 250 x {24-(tg + th)} ---

(10) is derived from (1), (8) and (9), 1000XY tg+ 20Z = 250 x {24-(tg + th)}

(11) is derived from (4) and (10), IR =[1-{(1000XY tg+ 20Z)/(250x24)}]x100=(tg + th)/24 x100 .  

       Where, tg = (250 x24-20Z-250 th)/(1000XY+250)  IR is from eq (11)

10MWh-LAB, non-AIP, 0.2 C rate, 2MW-diesel: X=10, Y=0.2, Z=0, th =1, IR=14.8%

10MWh-LAB, 100MWh-AIP, 0.2 C rate, 2MW-diesel: X=10, Y=0.2, Z=100, th =1, IR=11.1%

20MWh-LIB, non-AIP, 0.2 C rate, 4MW-diesel: X=20, Y=0.2, Z=0, th =0, IR=5.8%

20MWh-LIB, non-AIP, 0.4 C rate, 8MW-diesel: X=20, Y=0.4, Z=0, th =0, IR=3.0%

20MWh-LIB, 100MWh-AIP, 0.2 C rate, 4MW-diesel: X=20, Y=0.2, Z=100, th =0, IR=3.9%

20MWh-LIB, 100MWh-AIP, 0.4 C rate, 8MW-diesel: X=20, Y=0.4, Z=100, th =0, IR=2.0%

Though the estimates are based on many assumptions and are rough, the results clearly show the superiority of LIBs over LABs. Anonymous believes LIBs are indispensable to maintain the regional superiority of a conventional submarine.

By Anonymous