Emerging Technologies in Reacting Flows Lecture 2

1
Emerging Technologies in Reacting Flows (Lecture
2)

• Applications of combustion (aka chemically
  reacting flow) knowledge to other fields
  (Lecture 1)
• Frontal polymerization
• Bacteria growth
• Inertial confinement fusion
• Astrophysical combustion
• New technologies (Lecture 2)
• Transient plasma ignition
• HCCI engines
• Microbial fuel cells
• Future needs in combustion research (Lecture 3)

2
Transient plasma ignition - motivation

• Multi-point ignition of flames has potential to
  increase burning rates in many types of
  combustion engines, e.g.
• Pulse Detonation Engines
• Reciprocating Internal Combustion Engines
• High altitude restart of gas turbines
• Lasers, multi-point sparks challenging
• Lasers energy efficiency, windows, fiber optics
• Multi-point sparks multiple intrusive electrodes
• How to obtain multi-point, energy efficient
  ignition? Transient Plasma Ignition (Wang et
  al., 2005)

3
Transient plasma discharges

• Also called pulsed corona discharges
• Not to be confused with plasma torch
• Initial phase of spark discharge (lt 100 ns) -
  highly conductive (arc) channel not yet formed
• Characteristics
• Multiple streamers of electrons
• High energy (10s of eV) electrons compared to
  sparks (1 eV)
• Low anode cathode drops, little radiation
  shock formation - more efficient use of energy
  deposited into gas

4
Characteristics of transient plasma discharges

• For short durations (1s to 100s of ns depending
  on pressure, geometry, gas, etc.) DC breakdown
  threshold of gas can be exceeded without
  breakdown if high voltage pulse can be created
  and stopped quickly enough

 
5
Characteristics of transient plasma discharges
Transient plasma only
Transient plasma arc

• If arc forms, current increases some but voltage
  drops more, thus higher consumption of capacitor
  energy with little increase in energy deposited
  in gas (still have corona, but followed by
  (relatively ineffective) arc)

 
6
Transient plamsa discharges are energy-efficient

• Discharge efficiency ?d 10x higher for
  transient plasma than for conventional sparks

7
Engines 101 - slow burn reduces efficiency

• Burn starts earlier in compression process, has
  to go to same v, result is higher s to get same
  heat addition (? Tds)
• Difference in work 2 triangular slivers vs.
  rectangle
• Burning BTDC or ATDC ALWAYS leads to lower
  efficiency since ALWAYS lower TH for same TL,
  thus ALWAYS lower efficiency Carnot strips

8
Engine experiments

• Theiss et al., 2005
• 2000 Ford Ranger I-4 engine with dual-plug head
  to test transient plasma spark at same time,
  same operating conditions
• National Instruments / Labview data acquisition
  control
• Horiba emissions bench
• Pressure / volume measurements
• Optical Encoder mounted to crankshaft
• Spark plug mounted Kistler piezoelectric pressure
  transducer

9
Electrode configuration

• Macor machinable ceramic insulator
• Coaxial shielded cable
• Point to plane geometry - by no means optimal

10
On-engine results

• Transient-plasma (corona) ignition shows increase
  in peak pressure under all conditions tested

Cylinder pressure (pounds/in2)
11
On-engine results

• Transient plasma ignition shows increase in
  Indicated Mean Effective Pressure (IMEP) under
  all conditions tested

Cylinder pressure (pounds/in2)
Vmax
Vmin
12
IMEP at various air / fuel ratios

• IMEP higher for transient plasma than spark,
  especially for lean mixtures (nearly 30)
• Coefficient of variance (COV) comparable

13
Burn rate

• Integrated heat release shows faster burning with
  transient plasma leads to greater effective heat
  release

2900 RPM, ? 0.7
14
Burn rates

• Transient plasma ignition shows substantially
  faster burn rates at same conditions compared to
  2-plug conventional ignition

2900 RPM, ? 0.7
15
Emissions data - NOx

• Improved NOx performance vs. indicated efficiency
  tradeoff compared to spark ignition by using
  leaner mixtures with sufficiently rapid burning
  (CO, UHC similar to spark ignition)

16
Transient plasma ignition for PDEs

• Significant limitation of Pulsed Detonation
  Engines is Deflagration to Detonation Transition
  (DDT) distance - if too long, cant get DDT
  within engine!
• Formation of initial pressure waves from
  deflagation is typically the slowest step, and is
  most amenable to acceleration by transient plasma
  ignition
• Pre-DDT region has lower pressure, less ISP
• Detonation tube experiments (Lieberman et al.,
  2005)

17
Transient plasma ignition for PDEs

• Stoichiometric C2H4-O2 with N2 dilution (air
  73.9 dilution)
• Spark plug (SP) vs Transient Plasma (PI)
• Much lower ignition delay times (time to first
  recorded pressure rise at Pcb1) with PI, with or
  without turbulence-generating obstacles
  (accelerates DDT but causes heat pressure
  losses)
• Note PI can reduce need for obstacles
  associated losses

18
HCCI engines

• Burning rapidly at minimum volume yields the best
  possible thermal efficiency, but damage due to
  knocking means we want to burn fast but not too
  fast
• HCCI - Homogeneous Charge Compression Ignition
  engines take advantages of this - controlled
  knocking
• By using homogeneous reaction instead of flame
  propagation, conventional flammability/misfire
  limits absent
• Can burn very lean mixtures, low Tad, low peak
  temperature, low NOx formation
• Lean mixtures - can obtain part-load operation
  without throttling and its losses
• Since were asking for knock, use high
  compression ratios, thus high ?th

19
Comparison of gasoline, diesel HCCI

• http//www.osti.gov/fcvt/deer2001/coleman.pdf

20
HCCI engines

• Much more difficult to control the rate and
  timing of homogenous reaction than a propagating
  spark-ignited flame various control schemes
  being studied
• Variable intake temperature
• Variable exhaust gas recirculation
• Variable compression ratio and valve timing
• Cycle-to-cycle control probably needed

http//www-cdr.stanford.edu/dynamic/hcci_control/h
cci.swf
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HCCI experiments in a single-cylinder engine

• http//www-cdr.stanford.edu/dynamic/hcci_control/M
  ODELING_talk.pdf

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HCCI experiments in 6 cyl. engine (1 cyl. HCCI)

• http//www.orau.gov/deer/DEER2002/Session9/dec.pdf

23
HCCI control using mixture ratio

• Shaver Gerdes, 2005
• Control peak pressure (minimize engine noise)
  using closed-loop mixture ratio control

24
HCCI control using mixture ratio

• Control peak pressure AND combustion timing (thus
  efficiency) using mixture ratio intake valve
  timing

25
HCCI - disadvantages (opportunities?)

• Difficult to control timing and rate of
  combustion
• If misfire occurs, gas mixture during the next
  cycle will be too cold for auto-ignition to
  occur (unless intake air heating is used), the
  engine will stop
• Cold starting?
• Operating window for HCCI operation (load and
  engine speed) is small - most HCCI concepts use
  conventional spark-ignited operation at higher
  loads (less lean mixtures)
• Additional components for control system -
  increased cost
• Relatively high friction losses due to low IMEP,
  thus friction loss is a higher of net work
  (indicated work - friction)

26
Microbial fuel cells

• Instead of combustion of fossil fuels to generate
  electricity, why not use biological processes
  that convert organic material into electron flow?
• Use any handy organic material instead of refined
  fossil fuel
• Bacteria (prokaryotes) differ from eukaryotes in
  the ability to use many different electron
  acceptors (oxidants) electron donors (fuels)
• Problem existing life forms are the result of a
  3 billion year single elimination tournament and
  did not evolve to serve at the pleasure of the
  upstart homo sapiens
• As a result, power attainable from existing
  organisms is low!
• Possible applications
• Sewage treatment - need to clean up organics
  anyway, why not make electricity in the process
• Autonomous micro air vehicles and ground sensors
  - live off the land rather than require supply
  chain

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Potential fuels and oxidants in nature
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Possible use of bacteria
Fuels (EDIBLES!!) SUNLIGHT
Glucose ORGANICS Ethanol
Formaldehyde
Methanol Hydrogen Ammonia Hydrogen
sulfide Sulfur Iron Manganese Carbon
monoxide Arsenite
Bugs eat and breathe anything!
Oxidants (BREATHABLES) ORGANICS fumarate,
DMSO TMAO Carbon dioxide Sulfur Sulfate Arsen
ate Selenite Iron Manganese Nitrate Oxygen
Asterisks indicate those that end up in rocks or
minerals (N does not, many others do!)
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Shewanella oneidensis

• Discovered in 1987 (Myers Nealson, 1988) in
  sediments in Lake Oneida (upstate New York)
• Energy source is lactic acid, hydrogen or
  formaldehyde
• Breathes rocks - manganese or iron oxides,
  doesnt need O2

30
Isolating Shewanella Oneidensis

• Shewanella have been shown to reduce solid oxides
  (Myers Nealson,1988) - counter-intuitive when
  discovered bacteria not known to reduced solid
  substrates
• Surface-related phenomenon catalysis of a new
  kind

Enrichment Culture Five
Days Incubation
Pure Culture on MnO2
Breathing MnO2
31
MFC with mediated electron transfer
e-
CH2O
O2 4 H 4 e- -? 2 H2O
EC
Bug
EC electron carrier methylene blue benzyl
viologen
CO2 H e-
H
Almost any bacterium can be made to generate
current this way
Cathode
Anode
Membrane
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Mediator-less MFC

• Shewanella strains and other metal reducers can
  use a carbon electrode as an electron acceptor
  (Kim, et al., 2002)

e-
CH2O
O2 4 H 4 e- ? 2 H2O
Direct e- flow
Bug
No EC added to anode
H
CO2 H e-
Very few bacteria can do this!
Cathode
Anode
Membrane
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Mediator-less MFC
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Testing organisms and mutants

• 0.002 moles of nutrient (lactate) added
• Time constant for consumption 15 hours
• Total current production of 8 coulombs
• 0.00022 moles of electrons
• Ratio lactate/electrons 101

Added 2mM lactate
Added MR-1 (no lactate)
Electrolyte (no MR-1)
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Comparison of different species in MFCs
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Results Current production
MR-1 mutant ?mtrA
MR-1 double mutant ?mtrC/ ?omcA
MR-1 mutant ?mtrB
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(No Transcript)
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Summary of MFC results

• Almost a perfect 11 correlation with the ability
  to reduce iron MFC activity
• All negative current cases share the absence of
  MtrA MtrB
• MtrE deletion results in 50 increase in current
  production as well as rate of iron reduction
• Formation of nanowires (!!!) (Gorby et al., 2005)
  required for current production - electrical
  conductivity of these wires has been proven,
  though it hasnt been proven that they actually
  conduct in MFCs

39
MFC engineering at USC
Max. power density
200 mW/m2
0.2 mW/m2
0.2 mW/m2
22 mW/m2
FUN Science Physiology
Engineering
Date

• 30 mL volume
• Repeatable
• Air oxidant
• Aerobically grown MR-1, new media

• 30 mL volume
• Repeatable
• Air oxidant
• Anaerobically grown MR-1

MFC design

• 10 mL volume
• Unrepeatable
• Potassium ferricyanide oxidant

• 50 mL volume
• Real fuel cell design

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Possible design paradigm shift?

• O2 permeability of Nafion-117 at 25C
• 10-14 Mole/m-s-Pa
• Air cathode, 100 µm membrane
• ? 0.82 A/m2 current loss
• Trivial for PEM fuel cells using hydrogen,
  methanol or formic acid (can get 1 A/cm2) but
  critical for MFCs (1 A/m2)
• Proton conductance of Nafion-117 at 25C
• 0.08 S/cm
• Results in 12 µV drop for 1 A/m2 - trivial for
  MFCs (0.3 Volts OCV)
• Results in 0.12 V drop for 1 A/cm2 - dominant for
  CFCs
• Conclusion CFCs have very different membrane
  requirements than MFCs

Kocha et al. 2006
Siu et al. 2006
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Possible design exploiting MFC characteristics

• Resistive losses in Nafion not an issue for MFCs,
  but O2 crossover is!
• Could use different material with lower O2
  permeability at the expense of lower proton
  conductivity OR
• Fin design using laminated Nafion
• Inner layers thicker than outer layers - protons
  must be conducted farther
• Greater anode than cathode area since anode
  surface reaction rate is much smaller
• Practically eliminate O2 crossover without
  incurring significant voltage loss due to proton
  resistance

42
Summary - MFCs

• Microbes are highly adapted for electron transfer
• Strain MR-1 is very versatile metal reducer
• mtr genes are present in almost all metal
  reducers tested thus far
• Interaction with solid metal oxides requires
  outer membrane enzymes
• Microbial Fuel Cell activity is a good proxy for
  metal ion reduction
• Nanowires are apparently intimately connected
  with the ability to reduce solid substrates
• Engineers wanted

43
References

• Gorby, Y., et al. (2005). Electrically
  conductive bacterial nanowires produced by
  Shewanella oneidensis strain MR-1 and other
  microorganisms. Proc. Nat. Acad. Sci. U.S.A.,
  10311358 11363.
• Kim, B-H., et al. (2002). A mediator-less
  microbial fuel cell using a metal reducing
  bacterium, Shewanella putrefaciens Enzyme and
  Microbial Technology 30, 145-152
• Kocha, S. S. Yang, J. D., Yi, J. S. (2006).
  Characterization of Gas Crossover and Its
  Implications in PEM Fuel Cells. AIChE J. 521916
  1925.
• D. Lieberman, J. Shepherd, F. Wang and M.
  Gundersen (2005). Characterization of a Corona
  Discharge Initiator Using Detonation Tube Impulse
  Measurements, 43rd AIAA Aerospace Sciences
  Meeting and Exhibit, Reno, NV, Jan. 10-13, 2005
  (AIAA Paper 2005-1344).
• Myers, C.R. Nealson, K.H. (1988) Bacterial
  Manganese Reduction and Growth with Manganese
  Oxide as the Sole Electron Receptor. Science
  240, 1319-1321.
• Siu, A., Schmeisser, J., Holdcroft, S. (2006).
  Effect of Water on the Low Temperature
  Conductivity of Polymer Electrolytes. J. Phys.
  Chem. B. 6072 6080.
• Theiss, N., Levin, J., Liu, J. B., Zhao, J.,
  Wang, F., Ronney, P. D., Gundersen, M. A. (2005).
  Transient Plasma Discharge Ignition for Internal
  Combustion Engines. 4th Joint U.S. Sections
  Meeting, Combustion Institute, Philadelphia, PA,
  March 2005.
• Wang, F., Liu, J. B., Sinibaldi, J., Brophy, C.,
  Kuthi, A., Jiang, C., Ronney, P. D., Gundersen,
  M. A. (2005). "Transient Plasma Ignition of
  Quiescent and Flowing Fuel Mixtures, " IEEE
  Transactions on Plasma Science, 33844-849.