The Advantages of Non-Flow-Through Fuel Cell Power Systems for Aerospace Applications

NASA has been developing proton-exchange-membrane (PEM) fuel cell power systems for the past decade, as an upgraded technology to the alkaline fuel cells which presently provide power for the Shuttle Orbiter. All fuel cell power systems consist of one or more fuel cell stacks in combination with appropriate balance-of-plant hardware. Traditional PEM fuel cells are characterized as flow-through, in which recirculating reactant streams remove product water from the fuel cell stack. NASA recently embarked on the development of non-flow-through fuel cell systems, in which reactants are dead-ended into the fuel cell stack and product water is removed by internal wicks. This simplifies the fuel cell power system by eliminating the need for pumps to provide reactant circulation, and mechanical water separators to remove the product water from the recirculating reactant streams. By eliminating these mechanical components, the resulting fuel cell power system has lower mass, volume, and parasitic power requirements, along with higher reliability and longer life. These improved non-flow-through fuel cell power systems therefore offer significant advantages for many aerospace applications.

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The Advantages of Non-Flow-Through Fuel Cell Power Systems for Aerospace Applications

Mark Hoberecht & Kenneth Burke

National Aeronautics and Space AdministrationGlenn Research Center

Ian Jakupca

QinetiQ North America

March 1, 2011Next Generation Suborbital Researchers ConferenceOrlando, FL

NASA PEMFC Development History

• NASA initiated PEMFC studies during Shuttle upgrade program in late 1990’s at JSC• High DDT&E costs prevented switch from alkaline to PEM, in spite of several technical advantages

• RLV program funded initial development of PEMFC technology (2001)• A single vendor selected

• RLV transitioned into NGLT, SLI, and eventually ETDP programs (2001-2007)• Two vendors selected for Breadboard development• One vendor down-selected for Engineering Model development• Disadvantages of flow-through PEMFC systems became evident during testing of Engineering Model; balance-of-plant experienced multiple failures (rotating mechanical components)

• Began investigation of “passive” balance-of-plant concepts for flow-through technology (2005)

• Reactant pumps replaced with injectors/ejectors• Mechanical water separators replaced with membrane water separators

• In parallel, began investigation of non-flow-through technology through SBIR program (2005)

• Single vendor awarded contract

• Down-selected to non-flow-through technology over flow-through technology; initiated in-house development of balance-of-plant (2008)

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Fuel Cell Technology Development Mission Requirements Assessment

Lunar Architecture Studies identified regenerative fuel cells and rechargeable batteries as enabling technology, where enabling technologies are defined as having:

“overwhelming agreement that the program cannot proceed without them.”

Surface Systems

Surface Maintenance-free operation of regenerative fuel cells for >10,000 hours usingPower: ~2000 psi electrolyzers. Power level TBD (2 kW modules for current architecture)

Reliable, long-duration maintenance-free operation; human-safe operation; architecture compatibility; high specific-energy, high system efficiency.

Mobility Reliable, safe, secondary batteries and regenerative fuel cells in small mass andSystems: volume.

Human-safe operation; reliable, maintenance-free operation; architecture compatibility; high specific-energy.

Lander

Descent Functional primary fuel cell with 5.5 kW peak power.Stage: Human-safe reliable operation; high energy-density; architecture compatibility

(operate on residual propellants).

Shuttle “Active BOP”

Alkaline“Active BOP”

PEM

GlennResearch Center

JohnsonSpace Center

17 - 20 psia

PTTP

PTPT5

PT6

TPTP5

TP6TP PT

PT3TP3TP PT

M1RV1

COOLANT

OXYGEN PURGE 3/4" **AS4395-12 Male flarefitting

OXYGEN* Supply to 3/8" **AS4395-06 Male flare fitting

PR1

PR2

FC1

WT1

PTPT1

PT2

PRODUCT WATER 1/4"AS4395-04 Male flare fitting

19 psia +/- 3CATHODE

HYDROGEN* Supply to 1/4" **AS4395-04 Male flare fitting

TPTP1

TP2

SV1

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ANODE

FACILITYPOWERPLANTT1

Accumulatorwith bellows

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HYDROGEN PURGE 1/2" **AS4395-08 Male flare fitting

SV3

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100 - 275 psiaTemp > 10 C

21 psia +/- 2

19 psia +/- 3

19 psia +/- 3

21 psia +/- 3

17 psia

21 psia +/- 2 100 - 275 psiaTemp > 10 C

17 - 20 psia50 - 56 deg C

17 -20 psia44 - 50 deg C

3/4" Primary Coolant Loop

30 psia +/- 2

32 psia +/- 2

45 psia +/- 2

PT

PTPT7

PT8

M3

Secondary Coolant LoopHX1

PRIMARY COOLANT INLET 3/4"AS4395-12 Male flare fitting

PRIMARY COOLANT OUTLET 3/4"AS4395-12 Male flare fitting

25 +/- 10 deg C

50 - 56 deg C

44 - 56 deg C

17 - 20 psiaPRODUCT WATER 1/4"AS4395-04 Male flare fitting

44 - 56 deg C

Hydrogen pressure manifold

Oxygen pressure manifold

Flow-Through Flow-Through

GlennResearch Center

“Passive BOP”PEM

Flow-Through

“Passive BOP”PEM

GlennResearch Center

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injector/ejector

passive water separator

H2 O2

H2O H2O

O2

O2 / H2O

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H2O

injector/ejector

passive water separator

H2 O2

H2O H2O

O2

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Non-Flow-Through

Active Mechanical Component(pump, active water separator)= Passive Mechanical Component

(injector/ejector, passive water separator)=

Fuel Cell Technology Progression to Simpler Balance-of-Plant

Active coolant pump (coolant loop not shown)

Active coolant pump

(coolant loop not shown)

Flow-Through

Fuel Cell Technical Approach: “Non-Flow-Through” Water Management

Non-Flow-Through PEMFC technology characterized by dead-ended reactants and internal product water removal• Tank pressure drives reactant feed; no recirculation • Water separation occurs through internal cell wicking

Develop “non-flow-through” proton exchange membrane fuel cell technology to improve system-level mass, volume, reliability, and parasitic power

Flow-Through components eliminated in Non-Flow-Through system include:• Pumps or injectors/ejectors for recirculation • Motorized or passive external water separators

anod

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gas recirculation pump

active water separator

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Non-Flow-Through

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System-Level Comparison of Flow-Through vs. Non-Flow-Through PEMFC Technology

Design Parameter Flow-Through Non-Flow-Through

Efficiency − −Mass

Volume

Parasitic Power

Reliability

Reactant Utilization

EquivalentReactant Storage

“Depth-of-Discharge”

Life

Cost

TRL

1-kW Flow-Through PEMFC System

3-kW Non-Flow-Through PEMFC System

(mock-up)

Non-flow-through PEMFC system has a substantially simplerbalance-of-plant than conventional flow-through PEMFC system.

This offers significant advantages.

Non-Flow-Through PEMFC Technology Vendor Comparison

• Infinity selected as “baseline” non-flow-through PEMFC vendor very early in program

• Awarded very first non-flow-through Phase I SBIR (2005)• Demonstrated development success led to Phase II and Phase III contract awards• Very advanced and robust cell technology• Excellent cell performance• Superior water removal• Knowledgeable team with extensive flight hardware development experience (Shuttle, Apollo, Gemini)

• Other subsequent SBIR and IPP vendors competed for “alternate” role

• ElectroChem, Proton, and Teledyne stacks all experienced water management issues• ElectroChem & Teledyne most promising “alternate” technologies

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Non-Flow-Through PEMFC System

External System

Reactant Supply

Mechanicals

Fuel Cell Stack

ElectronicsModule

PowerConditioningand Battery

Hydrogen GasOxygen Gas

Balance of Plant (BoP)

Communication BusSensor/ActuatorPower

HeatWater/Coolant

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FuelCell Stack

H2 Vent

S

S

S

P

T

PP

T

PP

S

P

P

S

S

H2O Fill

O2 Vent

O2 Supply

H2O Drain

H2 Supply

Non-Flow-Through PEMFC System Schematic

P

P

P

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Small Fuel Cell System Balance-of-PlantComponents for Fuel Cells

• Integrated balance-of-plant demonstrated in conjunction with the laboratory scale fuel cell stacks

• During this testing, the balance-of-plant ran on a battery source consuming only 10 watts of parasitic power to operate the fuel cell system

• A full-scale (3-kw fuel cell system) balance-of-plant will likely operate on only 50 watts or less of parasitic power (same number of components, but some components larger)

Solenoid Valves Pressure

Transducers

PressureRegulator

Pressure Transducers

PressureRegulator

Pressure Accumulator

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FUEL CELL STACK

Actuators• Solenoids

• Pump(s) (TBD)

Sensors• Pressure

• Temperature

• Voltage

• Current

Control, Monitor & Communications

• Micro Processor

• Data Acquisition and Control Signals

• Multiplexers

• Amplification

• A/D D/A Conversion

• Communication Port(s)

ExternalComputer

Power Management (includes battery for startup)

• DC / DC Converters (3V,5V, 6V,12V)

• Power MOSFETs for switching of internal loads

• Battery Power at start-up

• Transition of power from battery to fuel cell for internal loads

• Battery Recharging

• Constant current source for optional electrolytic startup of fuel cell

• Circuit Over-Current Protection

External Power Interface

Unregulated Power

Regulated Power

Digital CommunicationSensor Outputs

Ext. Spacecraft Subsystems

Balance - of – Plant Electronics

Non-Flow-Through PEMFC Electronic Interface

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Future Activities – Flight Hardware

• Passive Water Control• Advanced Thermal Control Systems• Non-Flow-Through Reactants• Integrated Fluidics

– Endplate manifold houses all process fluid plumbing and fluidic measurement and control components

• Thermally compensated bolts eliminating Belleville washer stack-up

• Power – Nominal output power: 3 kWe

– Peak output power: 6 kWe

– Parasitic Power: 15 W to 35 W• Envelope

– Length: 60 cm (24 inches)– Width: 39.4 cm (15.5 inches)– Height: 25 cm (9.8 inches)– Weight: TBD (estimated 75 kg)