Portable Power From Miniature Combustion

Engines

Derek Dunn-RankinMechanical and Aerospace Engineering

University of California, Irvine

Keynote presentation – Taiwan Combustion Meeting, March 25, 2006

New power sources are needed to energize the next

generation technology for autonomy…

Portable Power

Systems

New power sources are needed to energize autonomous technologies

artificial organs

portable air reconnaissance

pervasive computing and communication

personal microclimates

personal robots

MEMS Power

Power and Energy Performance:Current Portable Devices

pager pacemaker > 87,600 hrs (10 years)

Stored Energy (Whr)1.0 10

0.1100 100001000

1

10

100

1000Po

wer

Nee

ded

(W)

1000 hr1 hr

100 hr

10 hr

6 min

36 sec

cell phone

artificial heart

small personal robot

minimal wearable computer

micro aircrafthonda humanoid robot

Bock C-Leg active knee

personal transport

exoskeleton

Desired Portable Device Performance

4G cell phone

UAV-Pointerpersonal microclimate

human endeavor

Power Scales

• 1000 W – microwave oven ~ horse

• 100 W – light bulb ~ human

• 10 W – small laptop ~ bat

• 1 W – cell phone ~ hummingbird

• 10 mW – pager ~ blowfly

• 10 µW – pacemaker ~ fruit fly

• 10000 W – riding lawnmower ~ elephant

PortablePower

images are not to scale

Portable Power Systems Scaling

•Simple Assumptions–15% fuel/energy conversion efficiency

–Fuel specific energy equivalent to liquid hydrocarbons (13kWhr/kg)

–Fuel occupies 66% of system

–Combustion can generate 100 W/cc chamber volume

• Compact Size and Low Mass– 60 g -- 6 kg power source weight– 0.01 -- 0.10 m system length scale– 60 cc -- 6 liter volume

• High Power and Energy – 10 W -- 1000 W power output – 1 hr -- 10 hr operation– 600 -- 6000 Whr/kg specific energy

Mass Specific Power and Energy

1 101

100 100001000

10

100

1000

10000

Stored Specific Energy (Whr/kg)

Sour

ce S

peci

fic P

ower

(W/k

g)

100 hr6 min

10 hr

1 hr

36 sec

3.6 sec

lead acid batterymini-diesel engine

Portable Power Target

Hydrocarbon fuel > 10000 Whr/kg

Solar--100 W/kg

Current technology fails to deliver sufficient energy and power density in the size needed for autonomy

primarylithium

rechargeablelithium

model airplaneengine

fuel cell

human legs

Hydrogen > 30000 Whr/kg

RTG --5 W/kg

high power lead acid

flywheelpneumatic

human metabolism

Elastic elements << 1 Whr/kg

automobileengines

hummingbird metabolism

Power Generation Science and Technology

electricalmechanical workpropulsion

heatmass

electrochemicalbiochemicalthermochemical

reformingrecharging

FuelProcessing

EnergyRelease

PowerExtraction

ExhaustManagement

High EnergyDensity Fuel Benign

Products

for Freedom Car

R.B. Peterson, Proc. IMechE, J. Power and Energy, vol. 219, pg. 371, 2005

Podolski, W. (2004) Fuel Cell Vehicles – Federal Perspective; Fuel Cell Vehicles

Fuel and Fuel Storage

Fuels with assumed 10% conversion efficiency

Energy Release & Power Extraction• Electrochemical

– batteries– supercapacitors– fuel cells

• Thermochemical– Stirling– rotary engine– turbine– pulse combustor– reciprocating engine– Swiss roll burner– film combustor

• Biochemical– biomolecular motor– biofuel cell– metabolic engine

• Electromechanical– compact generators– artificial muscle

• Thermomechanical– shape memory alloys– pressurized gas

• Thermoelectrics– nanowires– thermophotovoltaics

• Power Harvesting– solar– microwave reception– extraneous motion– vibration

• Chemomechanical– biomuscle

energy release power extraction

Fuel Cells• Rapid refueling• Low temperature• Direct conversion

to electricity• High theoretical

efficiency

Temperature C

Max

. The

rmod

ynam

ic E

ffic

ienc

y

AIR

FUEL e-

Typical fuel cell efficiency ~50%

Typical engine efficiency ~25%

LOADe

PRODUCT GASESRESIDUAL FUEL

FUEL OXIDANT

ANODE CATHODEELECTROLYTE(ION CONDUCTOR)

PRODUCT GASES RESIDUAL OXIDANT

ee

SOFCH2

H2OO O2

PAFCand

PEMFCH2

H2O

O2H+

MCFCH2

CO2

H2OCO3

CO2

O2

1000°C

200°C

90°C

650°C

AFC H2H2O

O2 80°COH-

Fuel Cell Types

Low temperature PEM has high power density and rapid response potential

Courtesy G.S. Samuelsen

Fuel Cell Operation

Load

Courtesy F. Prinz

PEM Membrane Electrode Assembly

Three phase zone-membrane-catalyst-gas

Hydrated H+

ions move freely as hydroniummolecule H3O+

Nafion by DuPont

Metabolic Processes

Bacteria may also provide a biologically-derived power model for heat generation

Cell functions, including electrochemical reaction, sensing and regulating power, and heat generation serve as personal power systems models

Muscle Contraction

Up to 80% work/ATP conversion efficiency

Miniature Combustion Systems• Volumetric heat release from liquid fuel will

be necessary for highest power/mass ratios• Combustion is extremely fuel tolerant• Challenges include high surface-to-volume

ratios (thermal issues, flame quenching, short residence times)

• Three miniature combustion approaches– Catalytic JP-8 combustion with Stirling engine– Fuel film combustors– Miniature IC engines

Engine Efficiency with Size

0.1

1

10

100

0.001 0.1 10 1000 100000

Engine Mass (kg)

Est

imat

ed E

ffici

ency

(%)

Manufacturer's DataPower LawOS46 - MfrOS46- Meas.AP YellowJacket - Meas.AP Wasp - Meas.Cox Tee Dee - Meas

Courtesy of Chris Cadou, Univ. of Maryland

Powerplant Efficiency Viewpoint

1

10

100

10 100 1000 10000 100000 1000000

Storage Efficiency Qr (W-Hr/Kg)

Pow

erpl

ant E

ffici

ency

ηpw

r (%

)

JP10

Batteries

Model Aircraft Engine

DARPA DMFCObjective

Endurance = 0.1min 1.0 min

100 min10 min

1000 min

Courtesy of Chris Cadou, Univ. of Maryland

center for C ombustion StudiesYale

UCSD, February 14, 2005

• Electospray in multi-jet mode

• Whirled air injection to promote fuel/air mixing in smallest volume

• Design can be conformed to different geometries (e.g., planar, toroidal, cylindrical)

AdjustableLength

CatalyticLayers

Whirl(~4.5 L/min)

Axial(~0 L/min)

High-DensityCell Filter

TeflonFlange

PyrexChimney

HeatingTube AIR

(20 C)

GroundedRing

Swirl Mixer

FUEL

HV

COMBUSTION

Electrospray + Catalytic Combustion Concept

Courtesy of A. Gomez

center for C ombustion StudiesYale

UCSD, February 14, 2005

Free-Piston Stirling Engine Power Converter: from jet fuel to electric power

Courtesy of A. GomezApprox. 150 mm x 300 mm

Approx. 1 kg

Liquid-fuel Combustion in Small Volumes

Short Residence Time – fast vaporization and mixing are required

large liquid surface area should be exposed to hot gasesrapid transport of heat & mass in gas near liquid surface

Efficiency & Quenching Protectionminimize wall area / volume exposed to hot gases

Use wall film to maximize surface area and to minimize heat lossesUse swirlers and vortex generators to maximize transport rates

Film Combustor Configuration

Liquid Film

Liquid Film

FlameStreamlines

Swirling Air

Recirculation Caused by Strong Swirl

Sapphire Chamber

Chemiluminescence

Visible CH C2 OH

Top of sapphire tube

Base of sapphire tube

Flame Structure

• Four-stroke, compression ignition with resistively heated platinum catalyst glow plug

• Single cylinder, displacement = 4.89 cc

• Carburetor• Lubrication, oil premixed into fuel

• Weight, 279 g

O.S. Engine FS-30S

112 mm

86.5 mm

44 mm

Miniature IC Engine

Miniature Engine Dyno

FlywheelOptical Encoder

Motor

Pressure Transducer

Optical Fiber

PMT

PlenumAir rotameters

Fuel

Potentiometer

Scale

Dilution Tank

Exhaust Condensation and Collection

Buret

Thermocouple

Thermocouple

Engine

Small Engine Dyno

Optical fibre

Pressure transducer

Fuel tank

Valve pushrods

Exhaust line

Cylinder Head Instrumentation

Fiber optic alongside pressure transducer

Cylinder Pressure and Luminosity

Temperature = 143 C

-300

-200

-100

0

100

200

300

0 1 2 3 4 5 6 7 8 9 10 11 12

Shaft Rotations

Pres

sure

(psi

g)

-0.05

0.05

0.15

0.25

0.35

0.45

0.55

0.65

Lum

inos

ity (V

)

Pressure (psig)Luminosity

0

50

100

150

200

250

0 1 2 3 4 5 6Volume (cc)

Pres

sure

(psi

)

Intake

Compression

Expansion

Exhaust

Indicator Diagram

• The values of Da = 19.1 and Relo = 1048 are low, but consistent with those typical of full size IC engines.

• This engine lies on the boundary between the wrinkled laminar flame and the flamelets-in-eddies regimes.

• No turbulence effect of scaling down to the centimeter scale.

Figure from S.R. Turns, An Introduction to Combustion: Concepts and Applications, McGraw-Hill Inc., 1996.

Turbulence in the Centimeter Scale

Other Miniature Combustors

UCB Mini-Rotary Engine

USC Swiss Roll Burner

Summary• New portable power sources are critical for advancing

autonomous devices• Miniature combustion will be needed for highest

power/weight demands, such as micro air vehicles and mobile robots

• Short residence time and thermal control produce very poor efficiency performance currently

• Taking advantage of film combustion offers a possible solution

• Future and current work includes CFD modeling of the film combustor and new swirl enhancement strategies

• Acknowledgments – Taiwan hosts; Prof. W.A. Sirignano; J. Papac, T.K. Pham, J. Pompa, N. Amade Sarzi, Prof. Y.-C. Chao & Y.-H. Li, National Cheng-Kung University; NSF, UC Energy Institute

THANK YOU!