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PowerMEMS2014 –Awaji, Japan

Development of Micro Cogeneration
System with a Porous Catalyst
Microcombustor
Shuhei Takahashi, Masateru Tanaka,
Naoya Ieda and Tadayoshi Ihara
Dept. Mechanical Engineering,
Faculty of Engineering, Gifu University, JAPANe-mail: shuhei@gifu-u.ac.jp
Nov. 21, 2014

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Outline1. Background & concept of micro-combustor
2. Characteristics of the combustor and thethermo-electric modules
3. Characteristics of the micro-blower
4. Design point of self-standing generation systemand its performance
5. Summary3/20

Background
Specific energy (Wh/kg)

10%efficiencyengine
Lithiumionbattery
The energy density of the hydrocarbon is muchhigher than those of the conventional batteries.

Quenching problemz

Combustion in a narrow tube is suppressed due to large heat loss tothe surroundings.

z

The quenching diameter of methane-air flame is about 3mm in thenormal condition.

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Concept of our microcombustor
 Catalyst assisted gas-phase reaction
A part of mixture occur surface reaction that sustain gas-phase reactionof the rest mixture.
1. Porous Pt catalyst: large surface area to obtain sufficient reaction heat
2. Ceramics wall: low thermal conductivity to suppress the heat loss
3. Low blockage: low pressure drop to achieve high-load gas-phase combustion

Porous thin catalytic layer on the inner wall of the ceramics tube
Catalytic layer

Mixture gas

Catalytic layer
Ceramics tube
Heat flow

Ceramics tube

1.2mm

Burnt gas

Catalytic reaction

0.8mm

Gas-phase reaction

5/20

Fabrication of the porous catalytic layer
Pt-water slurry

Catalyst powers (Pt)

Paint and Dry up(weak adhesion)

Diameter: 1m (Pt)

5mm
Catalyst slurry

Components
Pt black: 67wt%
Water : 33wt%

1. Paint the slurry by dipping

Sintering with CH4-air mixture(Sintered layer)

Weakly adhered catalyst(ER=1.6)

2. Dry up the paste
Porous catalyst
Mixture0.1mm

Hot Ni-Cr wire igniter
3. Sinter the catalyst with combustible mixture

Characteristics of the microcombustor

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Mass flow controller
Regulator
FilterValve

Mixture: methane-air
Flow rate: 20-200cm3/min@293K
Equivalence ratio: 0.6-8.0

CH4Combustor

Tube diameter: ID=0.8mm, OD=1.2mm
Material: mullite ceramics (3Al2O3/2SiO2)
Catalyst: platinum (Pt)
Sintering condition: ER=1.6

Air
CH4: 9.5cc/min, Air: 90cc/minFeatures
1. Very small output that allows human portability.

Output:~5W(min. 1.04W, max 10.4W) High turndown ratio

2. Very large energy release density

Output/Vol.:~5GW/m3(Tube i.d.~0.8mm, high temp. zone length~2mm)

Output/Area:~10MW/m2 (@ tube exit)
3. High exhaust gas temperature: >1100K
4. Wide flammability (Equivalence ratio: 0.8 ~ 8.0)
5. High durability (~1000 hours)
6. Low product cost ($2.00 per tube at lab. Level)7/20

Coupling with Bi-Te thermo-electric modules
TE modules are installed between the heat receiver and the heat sink.
High temperature source: Copper block heated wit the microcombustor
Low temperature source: Environment through the back plate
8 mm
7 mm

Heat receiver

Qloss
HburntHmixture2.2mm1.6 mm

8.5mm
9.0mm

Heat receiver

TE modules

Heat sink

Front view

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IR image of the co-generator
Side view
Heat sink block

338K
Thermoelectricmodules

461K
Microcombustor
Copper heat receiver303

523 (K)

Thermoelectric modules: Bi-Te 1MD04-017-12 (RMT Ltd)
Size: 3.8mm x 3.8mm x t2.3mm
Performance: Z=2.4 x 10-3/K (ZT=0.72@300K)
z Maximum allowed temperature of the above TE modules was 500K,
therefore, the size of the TE module was selected so that themaximum temperature does not exceed 500K.

9/20Electricity from the micro-cogenerator
Max. 3.00%

220

3200

250

Power (mW)Power (mW)

4.95W
5.73W
6.51W

200
150
100

2.5

180
160

2Ave. 2.87%

140

1.5
50

120

0123100100

Voltage (V)

110

120

Conversion efficiency (%)

Methane (ER=1.0)

Averaged efficiency: 2.87%
Champion record: 3.00%
Energy density: 417Wh/kg
Matching resistance: 10 
Mean voltage: 1.28V

1Flow rate (cc/min)Issues to set up self-standing cogeneration system

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 Compressed fuel, such as butane, can be supplied easily, but supply of
air to the combustor is hard when the dimension is small.
 Large pressure drop due to catalyst layer and high temperature areexpected.
 Control of air flow rate is difficult by entrainment method.
Example6cm
Fuel tank (Butane: 10cc)
15hours for 5W output
50hours for 1.5W output
Air intake and flow controller

4cmMobile

Micro-combustor
and generator

DisasterSports

Military

Forced air supply is preferable.
Micro-blower driven by the generated electricity

11/20Micro-blower (Murata Manufacturing Co., Ltd.)
20x20x1.85mm
Diaphragm is vibrated by piezoelectricelement
Large air flow rate for 5W class MC
High driving voltage for the TE modules
Find the design point.

Unit: mm

㻌㻌

400

1000

cold condition

350

400

20W
15W

200

1012

14200

5W

150
100

10W
5W
8250

㻌

㻌

600

010W

300

Power (mW)

Air flow rate (sccm)

800

2.0mm1.5mm
1.0mm
1.0mm with catalyst

500160246810121416182022Voltage (V)Voltage (V)Air flow rate in ceramics tube vs. driving voltage

Consumed power at micro-blower

2412/20

Pressure drop during combustion

Raised temperature due to combustion increases viscously.
Pressure drop in the tube increases 3 times during combustion
Air flow rate decreases 1/3 than that in cold condition
㻌I.D.=1.0mm

400

After combustion
Befoer combustion

300
250200㻌

Differential pressuer (Pa)350

Increased 3 times

150
100
5008.68.89.09.2

9.4

9.6

Voltage (V)Schematic of experimental setup

Pressure drop in the microcombustor

11/20Micro-blower (Murata Manufacturing Co., Ltd.)
20x20x1.85mm
Diaphragm is vibrated by piezoelectricelement
Large air flow rate for 5W class MC
High driving voltage for the TE modules
Optimize the design point.

Unit: mm

㻌㻌
1000

350

15W

10W

300

10W

400

5W
100
200

250
200

㻌

600
200

㻌

Air flow rate (sccm)

hot condition

Power (mW)

2.0mm
1.5mm
1.0mm
1.0mm with catalyst

300
800

4005W

150
100
50081012141600246Voltage (V)81012141618202224

Voltage (V)Air flow rate in ceramics tube vs. driving voltage

Consumed power at micro-blower

Optimizing the inner diameter

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Excess heat input causes erosion of the mesh structure.
MC with large diameter allows larger fuel input.
ID=0.8mm Æ 7W
ID=1.5mm Æ 15W
ID=2.0mm Æ 20W
Large diameter also decreases pressure drop
Æ low power consumption
Conflict!!
Large diameter results in low combustion efficiency.
900

Exhaust temperature (K)Butane-air
800
700
600

400

ID of 1.5mm ischoosen.

ID: 0.8mm
ID: 1.5mm
ID: 2.0mm

500

00.5

11.5

2

Equivalnce ratio

Exhaust gas temperature for different ID

SEM image of catalyst layer14/20Optimizing the input heat

The consumption power at the blower is estimated by multiplying theresult in cold condition by 1/3.
Assuming the conversion efficiency at 3.3%, the net output is calculated
by subtracting consumption power at the blower from the estimatedelectricity at TE modules.
㻌TE modules
OutputBlower,DC-DC

500

Input heat of 13.2W
is optimal.

300

㻌Power (mW)

400200100046810121416Input combustion heat (W)

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Design point of the self-standing system

The input heat was selected 13W to avoid excess power consumption at
the micro-blower.
The diameter was selected 1.5mm for its relatively low pressure drop anddurability for higher input heat.
The number of TE modules was 6 to avoid the temperature over 500K.
The output from TE modules were estimated as 430mW. (=3.3%)
The estimated driving voltage was from 14V to 17V.
400

800
ID: 1.5mm (Cold)
Comsumed power

600

300

400

200226sccm (13W)

100200Prediction

08101214

Driving voltage (V)160

Consumption power

Air flow rate (sccm)

Conversion efficiency: 4.1% (champion record)
Output : 533mW (matching resistance: 30)Schematic of the self-standing generation system

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The fuel, methane, is supplied by the mass flow controller.
The air is supplied by the micro-blower.
A part of electricity from the TE modules is supplied to DC-DC converter to pullup the voltage to 14-17V.
The rest electricity is consumed at the variable resistor and the net output ismeasured.

VAAVDC-DC=0.8~0.9

Determination of driving voltage of micro-blower

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The gloss output from TE modules are measured at the variable resistorof matching resistance (30).
The micro-blower with DC-DC converter is driven by the separated
power source of 4.0V, and the driving voltage for the blower is varied.

Driving voltage of 16V
Power supply (4.0V) is optimal.

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Performance at the design point
Matching resistance is 130, the driving voltage of the blower is 16V.
Input fuel enthalpy is 13.2W. The fuel and air flow rates are 23.8sccm
and 226sccm, respectively. The equivalence ratio is 1.0.
Input fuel enthalpy
Inner/outer diameters
Methane/air flow rate

Matching resistance of 130

Size and number of TE
modules (17 pairs)
Matching load resistance
Output voltage
Gross electricity from TE
modules
Efficiency of TE modules
Consumed power at
micro-blower
Consumed power at DCDC converter
Net output electricity
Final thermal efficiency

Performance at the design point
Matching resistance is 130.
The cold sides are cooled by ice.

The output voltage is 4.56V
160mW, =1.21%
Running more than 1 hour13.2W
1.5/2.5mm
23.8/226sccm
4mm x 4mm
6 (in series)
130
4.0V
403mW
3.35%
247mW
33mW
123mW
0.93%

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Comparison with conventional model engine

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The thermal efficiency of the world smallest internal combustion
engine is estimated about 1.5%.
The developed self-standing cogeneration system has efficiency ofthe same order although the thermal input is 1/20.

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Summary We developed a small self-standing generation system
in which the air supply system was driven by a part ofthe generated electricity. The thermal input was 13.2W
and the final output was 123mW; thus the final thermal
efficiency was 0.93%.
 The magnitude of the efficiency was close to the world
smallest conventional reciprocal engine Tee Dee 01
although the power size was less than its 1/20.

Future work To manufacture a portable power source including fuelsupplying device.
Acknowledgements
A part of this study was supported by Industrial Technology Research Grant Programfrom NEDO of Japan.

Recent conventional model engine
Recent model engines are incredibly small and their heat input arecomparable to that of our microcombustor.

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