AME 436 Energy and Propulsion

AME 514

Applications of Combustion

Lecture 14: New Technologies#1

Emerging Technologies in Reacting Flows (Lecture 2)Applications of combustion (aka chemically reacting flow) knowledge to other fields (Lecture 1)Frontal polymerizationBacteria growthInertial confinement fusionAstrophysical combustionNew technologies (Lecture 2)Transient plasma ignitionHCCI enginesCombustion synthesis of photovoltaic cellsEnhanced oil recovery using in situ combustionMicrobial fuel cellsFuture needs in combustion research (Lecture 3)AME 514 - Spring 2015 - Lecture 15#2AME 514 - Spring 2015 - Lecture 15Transient plasma ignition - motivationMulti-point ignition of flames has potential to increase burning rates in many types of combustion engines, e.g.Pulse Detonation EnginesReciprocating Internal Combustion EnginesHigh altitude restart of gas turbinesLasers, multi-point sparks challengingLasers: energy efficiency, windows, fiber opticsMulti-point sparks: multiple intrusive electrodesHow to obtain multi-point, energy efficient ignition? Transient Plasma Ignition (Wang et al., 2005)#32Flame spread over solid fuels is a useful model for simple 2 phase spreading flames, like building fires. It has well defined properties which can easily be quantified, like the spread rate which relates to CO production. And it is highly dependant on the fuel and environment. Downward, opposed flow flame spread at 1g is generally well understood. However, opposed flow flame spread at microgravity is less understood but important in manned spacecraft.upward, concurrent flow flame spread, which is especially important in a building fire, is also less understood.AME 514 - Spring 2015 - Lecture 15Transient plasma dischargesAlso called pulsed corona dischargesNot to be confused with plasma torchInitial phase of spark discharge (< 100 ns) - highly conductive (arc) channel not yet formedCharacteristicsMultiple streamers of electronsHigh 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

#42Flame spread over solid fuels is a useful model for simple 2 phase spreading flames, like building fires. It has well defined properties which can easily be quantified, like the spread rate which relates to CO production. And it is highly dependant on the fuel and environment. Downward, opposed flow flame spread at 1g is generally well understood. However, opposed flow flame spread at microgravity is less understood but important in manned spacecraft.upward, concurrent flow flame spread, which is especially important in a building fire, is also less understood.AME 514 - Spring 2015 - Lecture 15

Characteristics of transient plasma dischargesFor short durations (1's to 100's 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

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Characteristics of transient plasma dischargesIf 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)Transient plasma onlyTransient plasma + arc

#6AME 514 - Spring 2015 - Lecture 15Transient plamsa discharges are energy-efficientDischarge efficiency d 10x higher for transient plasma than for conventional sparks

#7AME 514 - Spring 2015 - Lecture 15Engines 101 - slow burn reduces efficiencyBurn 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. rectangleBurning before or after piston/cylinder reaches its minimum volume ALWAYS leads to lower efficiency since it leads to lower TH for same TL, thus lower efficiency Carnot strips

#8AME 514 - Spring 2015 - Lecture 15Engine experimentsTheiss et al., 20072000 Ford Ranger I-4 engine with dual-plug head to test transient plasma & spark at same time, same operating conditionsNational Instruments / Labview data acquisition & controlHoriba emissions benchPressure / volume measurementsOptical Encoder mounted to crankshaftSpark plug mounted Kistler piezoelectric pressure transducer

#9AME 514 - Spring 2015 - Lecture 15Electrode configuration Macor machinable ceramic insulatorCoaxial shielded cablePoint to plane geometry - by no means optimal

#10AME 514 - Spring 2015 - Lecture 15On-engine resultsTransient-plasma (corona) ignition shows increase in peak pressure under all conditions tested

Cylinder pressure (pounds/in2)#11AME 514 - Spring 2015 - Lecture 15

On-engine resultsTransient plasma ignition shows increase in Indicated Mean Effective Pressure (IMEP) under all conditions testedCylinder pressure (pounds/in2)VminVmax

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IMEP at various air / fuel ratiosIMEP higher for transient plasma than spark, especially for lean mixtures (nearly 30%)Coefficient of variance (COV) comparable#13AME 514 - Spring 2015 - Lecture 15Burn ratesIntegrated heat release shows faster burning with transient plasma leads to greater effective heat release2900 RPM, = 0.7

#14AME 514 - Spring 2015 - Lecture 15Burn ratesTransient plasma ignition shows substantially faster burn rates at same conditions compared to 2-plug conventional ignition2900 RPM, = 0.7

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Emissions data - NOxImproved NOx performance vs. indicated efficiency tradeoff compared to spark ignition by using leaner mixtures with sufficiently rapid burning (CO, UHC similar to spark ignition), though improvement isn't as impressive as one might hope because in general faster burning means high peak T, thus higher NO but maybe there's a more intelligent way to use the technology

#16AME 514 - Spring 2015 - Lecture 15Why do we have heat loss in IC engines? Because the cylinder wall is cold - typically just a little higher than the cooling water temperature, 120C (boiling point at 2 atm). This is much colder than the gases during combustion (2400K) and during expansion (down to 1200K). Why do we need to cool the cylinder? To keep the lubricating oil from getting too hot and breaking down. Also, with too large a temperature increase, thermal expansion will change the fit between the piston and cylinder and make it too tight or too loose.How significant is the loss?See Heywood (1988, Fig. 12-4): At low vehicle speed (meaning: low engine RPM, low Pintake) 50% of fuel energy is dissipated as cooling system losses; at higher speed, 30%; Heywood (p. 851) states that a 10% decrease in heat loss would mean about 3% increase efficiency Could we reduce the loss by using a ceramic (or whatever material) engine that could withstand high temperatures without oil lubrication? Analysis shows that raising the wall temperature doesn't help much, what is needed is a more nearly adiabatic engine (lower heat transfer coefficient). This is borne out by many experiments, peaking in the 1980's, using so-called "adiabatic" engines made of ceramics. This raised the wall temperature, but then you had more heat transfer during compression, thereby increasing compression work, so the efficiency didn't improve.Heat transfer in engines - catechism#17AME 514 - Spring 2015 - Lecture 15Heat transfer in engines - catechismHow can we decrease the heat transfer coefficient (h)? Heat transfer in engines is controlled by turbulence, so you'd need to decrease turbulenceHow can you do that? Engines are normally designed for high turbulence, so you could reverse-engineer the engine for lower turbulence (e.g. by avoiding swirl in the intake ports)Why don't we do that now? Because we need high turbulence (high u') to get fast burningIs there any way to burn fast without turbulence? Well DUH, TPI as we've just discussedDoesn't lower turbulence have a negative impact?Maybe, but actually it has at least one additionalsolid benefit; decreasing heat loss means that a smaller radiator can be used; the weight and cost of the radiator wouldn't be much less but the aerodynamic drag caused by radiators is significant and reducing the radiator frontal area could cause a noticeable increase in fuel economy just by reducing drag. Also there would be a slight increase in volumetric efficiency (the amount of air that can get into the engine; more air more fuel can be burned more heat release more power) because you're not forcing the air to follow a tumultuous path in order to get enough swirl to get high turbulence; with a more direct path there would be less pressure drop in the intake system and thus higher intake air density#18AME 514 - Spring 2015 - Lecture 15Transient plasma ignition for PDEsSignificant limitation of Pulsed Detonation Engines is Deflagration to Detonation Transition (DDT) distance - if too long, can't get DDT within engine!Formation of initial pressure waves from deflagration is typically slowest step & most easily accelerated by transient plasma ignitionPre-DDT region has lower pressureDetonation tube experiments (Lieberman et al., 2005) Stoichiometric C2H4-O2 with N2 dilution (air = 73.9% dilution)Spark plug (SP) vs Transient Plasma (PI)

#19AME 514 - Spring 2015 - Lecture 15Transient plasma ignition for PDEsMuch lower ignition delay times (time to first recorded pressure rise at Pcb1) with PI, with or without turbulence-generating obstacles (spiral insert) (accelerates DDT but causes heat & pressure losses), so can have higher repetition rates, thus more thrust but PI doesnt effect Specific Impulse (ISP) nearly as muchIn these plots ISP is defined as (Impulse / weight of mixture) not (Impulse / weight of fuel), so ISP values are very low

#20AME 514 - Spring 2015 - Lecture 15HCCI enginesBurning rapidly at minimum volume yields the best possible thermal efficiency, but damage due to knocking means we want to burn fast but not too fastHCCI - Homogeneous Charge Compression Ignition engines take advantages of this - controlled knockingBy using homogeneous reaction instead of flame propagation, conventional flammability/misfire limits absentCan burn very lean mixtures, low Tad, low peak temperature, low NOx formationLean mixtures - can obtain part-load operation without throttling and its lossesSince we're asking for knock, use high compression ratios, thus high th

#21AME 514 - Spring 2015 - Lecture 15HCCI enginesVideos courtesy Prof. Yuji Ikeda, Kobe University

StandardengineKnockingengineHCCIengine#22AME 514 - Spring 2015 - Lecture 15Comparison of gasoline, diesel & HCCI

#23AME 514 - Spring 2015 - Lecture 15Comparison of gasoline, diesel & HCCI

J. Dec., Proc. Combust. Inst., Vol. 32, p. 2727 (2009).

#24Much more difficult to control the rate and timing of homogenous reaction than a propagating spark-ignited flame; various control schemes being studied Variable intake temperatureVariable exhaust gas recirculationVariable compression ratio and valve timingCycle-to-cycle control probably neededAME 514 - Spring 2015 - Lecture 15HCCI engineshttp://www-cdr.stanford.edu/dynamic/hcci_control/MODELING_talk.pdf

HCCI experiments in a single-cylinder engine#25AME 514 - Spring 2015 - Lecture 15HCCI experiments in 6 cyl. engine (1 cyl. HCCI)Dec and Sjberg, 2002

#26AME 514 - Spring 2015 - Lecture 15HCCI control using mixture ratioShaver et al., 2009Control peak pressure (minimize engine noise) using closed-loop mixture ratio control

#27AME 514 - Spring 2015 - Lecture 15HCCI - disadvantages (opportunities?)Difficult to control timing and rate of combustionIf 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 stopCold 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)#28AME 514 - Spring 2015 - Lecture 15Combustion synthesis of materials for PV cellsCourtesy of Prof. Hai WangCurrent photovoltaic (solar) cells are reasonably efficient but very expensive to produce ( $10/watt vs. $1/watt for conventional electric power); net cost of solar 5x conventional powerDye-sensitized solar cells not as efficient but cheap to manufactureFirst proposed by ORegan and Grtzel (1991)Somewhat like fuel cellAnode: transparent, conductive glass, coated with TiO2 nanoparticles in turn coated with fluorescent dye to absorb incoming photonsElectrolyte: I- / I3- oxidation/reduction reaction basically a diode so current can only flow one directionCathode: Pt-coated transparent, conductive glass

#29Dye-Sensitized Solar CellSelectrolyteTransparent conducting glassdyeTiO2S*huox (I3-) red (I-)Redox mediatore-e-e--0.50.00.51.0E (V)maximumVoltage~0.75 V

Transparent conducting glass

AME 514 - Spring 2015 - Lecture 15I3- + 2e- 3 I-#Tradeoff: small particles have high surface area, so pick up more photons; large partlcies have fewer necks, so transport electrons less resistance optimal exists. TiO2 has a work function such that once an electron is in a conduction band it stays there and cannot jump to a valence band. (Unlike silicon). As long as the particle is truly crystaline, the electron wont fall. (Performance is limited by regularlity of the crystal.30TiO2 particle considerationsTiO2 has advantages over silicon - TiO2 work function such that once an electron jumps to conduction band it stays; cannot fall back down to valence band (if particle truly crystalline)Ideal particle size < 10 nmToo large: low surface/volume ratio, dont get good electron collectionToo small: too many contacts between particles, causes high resistance to electron flowCurrent technique for anode fabricationCommercial TiO2 powder (> 20 nm)Making a paste/paint & screen printingSinter at 450 C (glass substrate only)Stain with dyeWang methodParticle synthesis and film deposition in one stepNo need to sinterAME 514 - Spring 2015 - Lecture 15#TubularburnerShielding ArC2H4/O2/ArSynthesis method stagnation flameFlame StabilizerTTIPCarrier gas ArTTIP/ArElectric mantleParticle properties controlled by Flame temperature (argon dilution) Reaction time (flow rate) Ti precursor concentration TTIP, (Titanium Isopropoxide)vOvOTmaxburner-stabilized flameStagnation flameAME 514 - Spring 2015 - Lecture 15

#Flame Structure (C2H4-O2-Ar, f = 0.4)

Computations used the Sandia counterflow flame code and USC Mech II5001000150020002500Stagnation surface (x = 3.4 cm)T (K)Particle nucleation/growth region0100200300400500Axial Velocityv (cm/s)Laminar flame speedParticle nucleation/growth region10-410-310-210-11002.72.82.93.03.13.23.3Mole FractionO2C2H4HH2COH2OCO2Distance from nozzle, x (cm) AME 514 - Spring 2015 - Lecture 15#33Growth time limited to 2 ms because of thermophoresis. On increasing T side of flame, convection is rapid and TP cant hold particles, but as particle approaches stagnation plane, U decreases and TP force pushes particle along faster (about 1 m/s), limiting growth time and thus particle size. Also very uniform residence time for on-axis and off-axis particles.Aspects of particle growthGrowth time limited to 2 ms because of thermophoresis (TP) moves particles to from high T to low T in gas; for particles much smaller than mean free path

(Good website on thermophoresis: http://aerosol.ees.ufl.edu/Thermophoresis/section01.html)On increasing T side of flame, convection is rapid and TP cant hold particles in place against convectionAs particle approaches stagnation plane, V decreases and TP force pushes particle along faster ( SL), limiting growth time and thus particle sizeVery uniform residence time for on-axis and off-axis particles characteristic of stagnation flow

AME 514 - Spring 2015 - Lecture 15

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Increase Ti Precursor ConcentrationParticle size distributionsParticle size can be well controlledSize distribution widens as median size increases but the size variation still small compared to other methods

AME 514 - Spring 2015 - Lecture 15#

Flame Stabilized on Rotating SurfaceWant boundary layer thickness d ~ (n/wrad)1/2 < distance from flame to stagnation surface, so rotation doesnt affect particle formation & growth

~0.3 cmAME 514 - Spring 2015 - Lecture 15#36Stationary vs. Rotating Stagnation Plate

Rotating the stagnation surface results in smaller particles and narrower distributionsAME 514 - Spring 2015 - Lecture 15#37

Comparison with commercial TiO2Tested under the standard AM1.5 solar lightUse Solaronix purple dye, comparisons made under comparable conditionsFSTS films (largely unoptimized) outperform Degussa powder with screening printingMethod allows continuous, reel-to-reel fabrication of DSSC photoanodes in one step

AME 514 - Spring 2015 - Lecture 15#AME 514 - Spring 2013 - Lecture 15In situ enhanced oil recoverySee review by Mahinpey (2007)Heavy-oil reservoirs containing high-viscosity oil are impossible to produce via conventional pumpingViscosity decrease via steam injection expensive & of limited effectivenessCan inject air and combust a portion of oilHas seen limited field use but can be effectiveLimited laboratory experiments, in small diameter tubesReal situation: large cross-section instabilitiesSimilar to filtration combustion of porous solidVery similar to flames in Hele-Shaw cell (see lecture 8)Flow described by Darcys LawBuoyancy (RT), thermal expansion (DL), viscosity change (ST) instabilities. But a non-premixed, 3-phase (air, oil, inert porous solid) system!Practical limitation emissions!How to conduct laboratory experiments that are relevant to oil field production?

#39AME 514 - Spring 2015 - Lecture 15In situ enhanced oil recoveryhttp://www.netl.doe.gov/technologies/oil-gas/publications/eordrawings/BW/bwinsitu_comb.PDF

#40AME 514 - Spring 2015 - Lecture 15In situ enhanced oil recovery

Kk, et al. (2008)

#41AME 514 - Spring 2015 - Lecture 15ReferencesDec, J. E., Sjberg, M. (2002). HCCI Combustion: The Sources of Emissions at Low Loads and the Effects of GDI Fuel Injection. 2002 Diesel Engine Emissions Reductions (DEER) Conference, San Diego, CA, August 2002. (http://energy.gov/sites/prod/files/2014/03/f9/2002_deer_dec.pdf)Heywood, J. B., Internal Combustion Engine Fundamentals, McGraw-Hill, 1988M. V. Kk, G. Guner, S. Bagci, Oil Shale, Vol. 25, No. 2, pp. 217225 (2008)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).Mahinpey, N., Ambalae, A., Asghari,K., In situ combustion in enhanced oil recovery (EOR): A review, Chem. Eng. Commun. Vol. 194, pp. 995-1021 (2007)B. ORegan and M. Grtzel, Nature 343, 737-740, 1991.Shaver, G. M., Gerdes, J. C., Roelle, M. J. (2009). Physics-Based Modeling and Control of Residual-Affected HCCI Engines, J. Dyn. Sys., Meas., Control 131(2), 021002.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, 33:844-849.

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