NOVEL BURNER CONCEPT FOR PREMIXED SURFACE-STABILIZED COMBUSTION. S. Shakariyants Micro Turbine Technology MTT, b.v.

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1 Prceedings f ASME Turb Exp 212 GT212 June 11-15, 212, Cpenhagen, Denmark GT NOVEL BURNER CONCEPT FOR PREMIXED SURFACE-STABILIZED COMBUSTION V. N. Krnilv S. Shakariyants Micr Turbine Technlgy MTT, b.v. Micr Turbine Technlgy MTT, b.v. Eindhven, The Netherlands Eindhven, The Netherlands viktr@mtt-eu.cm savad@mtt-eu.cm L.P.H. de Gey Eindhven University f Technlgy Eindhven, The Netherlands l.p.h.d.gey@tue.nl ABSTRACT Surface-stabilized cmbustin is credited with high burning rates, extended lean flammability limits, wide mdulatin range and ther advantages. This makes it an attractive technlgy fr cmpact lw-emissin cmbustrs. The experimental gas turbine surface burners reprted t this date are prduced frm cmpressed and sintered Fe-Cr-Al fiber mats. The authrs have develped a new cncept f surface burner fabricated by braiding ceramic crds arund a ceramic frame. This simple methd prduces a basket-type surface suitable fr stabilizing lean premixed flames ver a brad range f perating cnditins. The use f ceramics extends pssibilities fr peratin at very high inlet temperatures with reduced risks f material sintering and xidatin. This paper presents test results with an experimental burner n a pressurized cmbustin rig with ptical access. The experiments were perfrmed under the fllwing cnditins: inlet temperatures f C, pressures f 1-3 bar, thermal pwer between 4 kwth and 32 kwth and equivalence ratis f Measurements f flue gas cmpsitin and pressure drp are als reprted in the paper. The perating windw fr lw-nox and lw-co cmbustin is analyzed. With the demnstrated perfrmance, the burner culd cver the perating envelpe f a 3 kwe recuperated micr turbine [1]-[2] with n pilt and n staging. This wuld als limit NOx t <4 % O 2 within the micr turbine lad range f 1% t 5%. NOMENCLATURE K Rati f mixture surface speed t laminar burning velcity, - p Pressure (abslute), bar S L Premixed laminar burning velcity, m/s T Temperature, C T ad Adiabatic flame temperature, C V surf Cmbustible mixture speed thrugh burner surface, m/s φ Fuel-t-air equivalence rati, - ω Mass flw rate, g/s Subscripts cmb Cmbustin in Inlet INTRODUCTION Premixing (typically, fuel-lean) is a widely accepted apprach fr clean and lw-nox gas-phase cmbustin. Premixed flames can be stabilized: 1) aerdynamically in either reverse, stagnant r divergent flws; 2) within prus media; and 3) n surface patterns. Gas turbine cmbustrs traditinally feature aerdynamically stabilized flames. Submerged cmbustin in bth inert and catalytic prus media is used fr infrared heating and gas cleaning. It has been als cnsidered fr gas turbines [3], yet s far remained primarily restricted t catalytic cmbustin: bth in R&D [4] and very limited cmmercial applicatin [5]. 1 Cpyright 212 by ASME

2 Surface-stabilized burners are widely used tday fr dmestic bilers, radiating heaters, dryers, etc. One can distinguish burners with surface cmbustin realized ver: 1) rigid prus plates (ceramic mnliths, perfrated metal plates, etc.); and 2) fiber decks cmpsed f cmpressed and sintered fibers, as well as prefabricated knitted and wven mats r clths. Anther distinctin can be made fr burners that cmbine surface cmbustin with Bunsen-type flames anchred by the adjacent surface cmbustin. Surface fiber burners have been cnsidered fr gas turbine cmbustin since, at least, 199s. Yet, the authrs are aware f nly very limited practical develpment in this respect: e.g., ALZETA Crp. has been reprting n prttype burners fr gas turbine cmbustrs based n perfrated fiber mats [6]-[7]. Ramadan, et al. presented the develpment f Fe-Cr-Al wiremesh burners at the Carltn University fr supplementary firing in the exhaust f micr-turbine based CHP systems [8]. The surface fiber burners knwn t this date, including thse prpsed fr gas turbines [6]-[8], are typically made frm Fe-Cr-Al based allys. This paper presents a nvel cncept f a braided ceramiccrd burner develped under the specific criteria f: - Design simplicity; - Ease f fabricatin; and - Suitability fr cmplete and lw NOx cmbustin at very high inlet temperatures. The primary applicatin f this cncept is freseen fr lw-cst recuperated micr gas turbines. The experimental burner presented in the fllwing sectins f this paper is scaled fr a 3 kwe micr turbine that is being develped by MTT [1]-[2]. Measurements and visual bservatins f the burner are reprted under the cnditins within the micr turbine s perating envelpe. The authrs als envisage ther applicatins in gas turbines in general and beynd. CONCEPT OF A BRAIDED BURNER FOR PREMIXED SURFACE-STABILIZED COMBUSTION Tday s aerdynamically stabilized lw-nox gas turbine burners incrprate achievements f decades-lng dedicated develpments in varius disciplines with the investment f large resurces. Cmmnly, very sphisticated flw systems with cmplex swirl generatin, fuel injectin, mixing and cling devices are featured. These als require intensive aerdynamic tuning (numerical and experimental), advanced materials and fabricatin methds. This is justified t ensure meeting the design and perating requirements. One f the particular challenges is t ensure cmplete, lw-nox and stable cmbustin with fuel-air premixing. The transfer f lw-nox cmbustin technlgies frm the mainstream large-scale gas turbines int micr turbines wuld typically translate int prhibiting csts related t bth develpment csts and cmbustr cst-price. This particularly hlds fr the emerging very small gas turbines rated belw 1 kwe. Herein, the challenges increase, at least, due t: - A range f factrs that may prmte flashback and burner verheating: High temperature f the air inlet and, cnsequently, cling flws in recuperated cycles; Higher surface-t-vlume ratis; Operatin withut a qualified peratr and under a high prbability f blunder in the very attractive cnsumer applicatins (e.g. micr CHP, autmtive, etc.); and Requirement fr prmpt mdulatin f the perating pint; - Lw allwable pressure lss; - The small scale that limits design chices by the applicability f cnventinal fabricatin methds; and - Lw cst-price requirements. Premixed surface burners present an interesting alternative t aerdynamic flame stabilizatin that can effectively address the challenges listed abve. Bth the ppularity f this burner type in varius appliances and the reprted gas turbine experience [6]-[7] cnfirms: relative simplicity f manufacturing; lw cst price ptential; ptential fr cmplete and very lw NOx cmbustin; durability; wide stability limits and resistance t flashback; wide range f mdulatin; lw pressure drp; high burning rates; and straightfrward scaling. The authrs have develped a new cncept f surface burner fabricated by braiding a high-temperature ceramic fiber crd acrss a ceramic frame (see Figure 1). The cmmnly accepted Fe-Cr-Al based fibers were nt selected n the grunds f thermal resistance in small micr turbines, wherein the cmbinatin f a lw cmpressr pressure rati and exhaust-heat recuperatin can translate int very high cmbustr inlet temperatures e.g. abve 7 C [1]-[2]. This leaves the margin f ~3 deg. with respect t the typical Fe- Cr-Al material limits f C. With the expected flame temperatures f C fr bth lw NOx and CO, this margin will be very difficult t maintain, especially during mdulatin and transients. Besides, the authrs are nt aware f Fe-Cr-Al applicatins in premixed cmbustin abve inlet temperatures f 455 C [7]. The methd f braiding was selected as an alternative t knitted and wven fiber clths. Braiding shapes the surface withut tailring any prefabricated material. Thereby, there are n material edges that require framing, fixing and ther types f handling. This is particularly advantageus in the case f ceramics. Furthermre, braided surfaces are very advantages fr flame stabilizatin at high burning rates: The flw f cmbustible mixture naturally divides very unifrmly ver the surface. The crd readily sustains surface burning. The vids between the crd braids issue flw jets that prduce Bunsentype flames. Their stabilizatin is greatly enhanced by the adjacent surface cmbustin. In rder t establish such a burning mde n sintered fiber burners, a surface perfratin is required. Besides, the vids can be seen thrugh braided surfaces as curved flw channels f a variable crss sectin. The narrw 2 Cpyright 212 by ASME

3 sectins help resist flashback. A braided burner als des nt require a substrate surface. EXPERIMENTAL BURNER Several burner cnfiguratins were hand-fabricated fr the experimental prf f cncept. These included flat and undulating surfaces, as well as burners with frames made f either crssing and nn-crssing arches. The latter burners featured the best surface pattern fr flame stabilizatin. Therefre, nly a burner f this cnfiguratin is described belw. The experimental burner is shwn in peratin in Figure 1. The burner frame is ceramic. It cnsists f an even number f U-arches and ne half-u arch. The surface crd is the Nextel TM 44 fibers (7% f Al 2 O 3, 28% f SiO 2, 2% f Ba 2 O 3 ) interwven tgether int as a sleeve. The crd is f ~2 mm in diameter in a nn-stretched state, while the fiber diameter is ~1-12µm. The recmmended material applicatin temperature is up t ~14C, while the melting temperature is ~18C. The diameter f the burner is 3 mm at the frame base. The flame stabilizatin surface area is ~35 cm 2. Figure 1: An experimental braided burner in peratin: a) at fuellean cnditin; b) at nearly stichimetric cnditin. This burner was scaled fr the perating cnditins f the MTT 3 kwe recuperated micr gas turbine [1]-[2]. The thermal input in the micr turbine is up t 3 kwth during thermal ramp-up, 18-2 kwth at base lad and 1-12 kwth at 5% lad. The inlet air temperature ranges between 72 C at the base lad and 2 C at cld-recuperatr start-up. The pressure range is between 3 bar at base lad and ~1.15 bar at start-up. EXPERIMENTAL SETUP MTT and TU Eindhven have jintly develped a micr turbine cmbustin test rig, which has been used in the MTT develpment prgram since 29. The braided burner in Figure 1 was tested n this test rig (see Figure 2). The burner was installed inside a quartz tube f 9 mm in diameter, which is representative f a can-type liner (Figure 2). This assembly was placed inside an versized pressurized cell. The cell has tw quartz-glass windws: fr a side view and a frnt view f the burner. The air supply was divided between the burner (cmbustin) and dilutin air. Pure methane was supplied as the fuel thrugh a custm-designed injectr. The injectr was succeeded by a mixing vlume f ~5cm 3. CH4 preheater dilutin/cling air cmbustin air Figure 2: Experimental setup. burner thermcuple Tin pressure cell quartz All flws n the test rig are cntrlled by Brnkhrst mass flw cntrllers with an accuracy f 1-2 %. The cmbustin air is preheated by a SUREHEAT MAX HT unit with a maximum temperature capability up t 9 C. The air temperature is measured within ±1K by a thermcuple clsely upstream the fuel injectr. The system pressure is measured in the pressurized cell by a transducer. The measurement signal is used t manually cntrl pressure via a thrttling valve in the exhaust duct. The exhaust flw cmpsitin is measured with an autmtive AREX analyzer. The mle fractins f CO, UHC, O 2, CO 2 and NOx, are measured. In testing at the lwest NOx and CO, the measurement limits f the AREX analyzer (~±1-2 actual O 2 ) were apprached. Due t this, the measurement accuracy f CO, UHC and NOx in these regimes is nt higher than 2-3%. The fllwing perating cnditins were established in the measurements: 1) cmbustin air temperatures between 22 C and 74 C; 2) pressures between 1.1 and 3 bar (abslute); 3) cmbustin air flws and equivalence ratis f 3-2 g/s and respectively. The latter crrespnds t thermal inputs between ~4 kwth and ~32 kwth. A snapsht f the experimental pints and cnditins is given in Figure 3: Each pint is marked by a red circle. It crrespnds t the inlet temperature and pressure n the T-p plane, as well as ranges f mass flw and equivalence rati indicated belw and t the right f the T-p plane respectively. Figure 3 als relates the experimental pints t the perating envelpe f the MTT micr turbine. The five and fur-pinted stars crrespnd t the base lad and 5% lad respectively. The dashed line shws the ramp-up f the micr turbine. t gas analyzer 3 Cpyright 212 by ASME

4 One may see that the experimental pints were selected as t fully cver the perating envelpe f the micr gas turbine. T in, C p, bar cmb air, g/s Figure 3: Experimental pints (red circles) and cnditins: inlet temperature, pressure, mass flw and equivalence rati. Relatin t micr turbine perating pints: - base lad; - 5% lad; ramp-up. EXPERIMENTAL RESULTS Pressure drp ver the burner surface The burner pressure drp is a key design parameter and an imprtant perfrmance characteristic. At this stage, there are n methds t predict the pressure drp f the braided burner. Many factrs surface area, material and thickness f the frame and crd, braiding density pattern and patter, etc. etc. affect the resulting pressure drp. Pressure drp measurements were carried ut n a separate setup at the inlet temperature f 2 C nly, bth with and withut cmbustin. The effect f cmbustin was negligible. Results are shwn in Figure 4 versus the dynamic head evaluated n the basis f cld flw at the burner inner surface. pressure drp, mbar dynamic head = V 2 surf /2, Pa Figure 4: Nn-reacting flw pressure drp ver the burner surface versus dynamic head at T in =2 C. A virtually linear relatin was measured between the surface pressure drp and dynamic head. The relatin crrespnds t a hydraulic resistance cefficient f ~2 [mbar/mbar]. Thermal input Figure 5 prvides anther snapsht f experimental pints (differences in marker type and clr shuld be neglected related t the authrs pst-prcessing decisin). Each pint is characterized by the burner thermal input versus air flw rate, pressure and inlet temperature. thermal input, kw thermal input, kw cmbustin air flw rate, g/s (a) (b) abslute pressure, bar cmbustin air flw rate, nl/min (c) Figure 5: Burner thermal input versus: a) cmbustin air flw rate (ω); b) pressure (p); and c) inlet temperature (T in ). Relatin between ω, p, T in and φ is given in Figure 3. Relatin t micr turbine perating pints: - base lad; - 5% lad. Flame stabilizatin At lw mixture speeds thrugh the burner surface, the heat transfer frm the flame t the burner is significant and leads t the heating f the surface. This cmbustin mde is smetimes referred t as radiant. At high mixture speeds, the flame detaches frm the surface which can lead t a blw-ff. The ptimal perating mde lies between these tw extremities. Therein, the braided burner peratin is characterized by Bunsen-type flames stabilized n the crd braids. The stabilizatin is additinally facilitated by burning n the crd surface. It can be shwn that the mdes f burner peratin and flame stabilizatin can be best parameterized by the rati f the mixture surface speed t the laminar burning velcity (K=V surf /S L ). The K rati derived fr the experimental pints 4 Cpyright 212 by ASME

5 shwn in Figure 5 is pltted versus inlet temperature in Figure 6. Herein, S L is evaluated by the well knwn crrelatins in [9]. The exact K values crrespnding t varius burning mdes will always depend n the particular surface (braiding) pattern, surface cnfiguratin, crd type, etc. Fr the experimental burner cnsidered in this paper (Figure 1) the K rati culd be varied between 2 and 2. Visual bservatins shwed that the radiant mde was established at K ~ 2-3. The flames start t detach frm the surface at K>1-12. The ptimal range f K was fund between ~3 and ~1. rati V surf /S L Figure 6: Rati f mixture surface speed t laminar burning velcity versus inlet temperature. Experimental cnditins are given in Figure 3. Relatin t micr turbine perating pints: - base lad; - 5% lad. Emissins Figure 7 presents measured NOx and cmbined (CO+UHC) mle fractins versus adiabatic flame temperature. The measurements are scaled t % O 2 (as cmmn fr dmestic bilers and can be used fr micr turbines fr dmestic CHP). The emissin measurements shw a very strng flame temperature dependence. The rates f CO and UHC xidatin are generally strngly temperature-dependent. As per NOx: within the range f experimental cnditins, the likely dminant NOx frmatin pathway is the thermal (Zel dvich) mechanism. Variatins in the measurement results at each given flame temperature can be related t variatins in the residence time (via varying pressure and flw rates), as the next significant gverning factr. Other factrs are O 2 and OH availability at varying equivalent rati and ther secndary effects. If ne wuld adpt emissin limits depending n the applicatin f the burner, Figure 7 will help selecting the flame temperature range fr bth lw NOx and prducts f incmplete cmbustin (CO+UHC). Fr example, the T ad range between 1425 C and 1625 C crrespnds t NOx between ~ ppm and 4 ppm and (CO+UHC) between 1 ppm and ~ ppm respectively. O 2, [ppm] O 2, [ppm] NOx p1.2t22 NOx p1.2t3 NOx p1.2t4 NOx p1.5t2 NOx p1.5t5 NOx p2t3 NOx p2t6 NOx p2t65 NOx p2t7 NOx p2t incmplete cmbustin and quenching NOx p2.5t53 NOx p3t54 NOx p3t6 NOx p3t65 NOx p3t7 NOx p3t perating range NO >4ppm@ O x 2 18 IU p2.5t53 IU p3t54 IU p3t6 IU p3t65 IU p3t7 IU p3t risk f burner verheating 185T, C ad IU p1.2t22 IU p1.2t3 IU p1.2t4 IU p1.5t2 IU p1.5t5 IU p2t3 IU p2t6 IU p2t65 IU p2t7 IU p2t74 ad 185 T, C Figure 7: NO x and cmbined (CO+UHC) mle fractins versus adiabatic flame temperature. T in and p are given in the legends: p1-p3 1-3 bar; and T22-T C. Relatin between ω, p, T in and φ is given in Figure 3. At lwer flame temperatures, cmbustin cmpleteness starts t reduce rapidly. Higher flame temperatures can still be accepted, shuld the NOx limit be relaxed. Yet, the risk f burner verheating increases with an increase in T ad, particularly when accmpanied by an increase in T in. In the experiments, T ad > 19 C were als allwed at lw inlet temperatures, as shwn in Figure 8. Figure 8 als explicitly shws that NOx < 4 ppm and (CO+UHC) > 1 ppm culd be maintained within a very brad range f inlet temperatures: frm 22 C up t 74 C. The crrespnding equivalence ratis are shwn in Figure 9. adiabatic flame temperature, C NO x >4ppm@ O2 perating range incmplete cmbustin and quenching risk f burner verheating Figure 8: Experimental pints n the plane f adiabatic flame temperature inlet temperature. Relatin between ω, p, T in and φ is given in Figure 3. Relatin t micr turbine perating pints: - base lad; - 5% lad. 5 Cpyright 212 by ASME

6 equivalence rati NO O x 2 perating range incmplete cmbustin and quenching risk f burner verheating Figure 9: Experimental pints n the plane f equivalence rati inlet temperature. Relatin between ω, p, T in and φ is given in Figure 3. Relatin t micr turbine perating pints: - base lad; - 5% lad. MICRO TURBINE APPLICATION POTENTIAL The experimental burner has permitted a very brad mdulatin f perating parameters. Cmplete and stable cmbustin withut hardware verheating was maintained within (Figure 5-Figure 9): - The pressure range f 1 bar t 3 bar; - Inlet temperature range f 22 C t 74 C; - Adiabatic flame temperatures between 1425 C and 18 C; and - Thermal pwer range between 4 kwth and 32 kwth. Apart frm the prf f cncept, this demnstrates a high applicatin ptential fr recuperated micr turbines. With the demnstrated perfrmance, the burner culd cver the perating envelpe f the MTT 3 kwe micr turbine [1]-[2] with n pilt and n staging, including (Figure 3, Figure 5): - Cld light-ff at nearly atmspheric pressures and inlet temperatures; - Ramp-up with: A reductin in the equivalence rati and increase in the inlet temperature crrespnding t the recuperatr heat-up; and Increase in the air flw rate and pressure crrespnding t the turbmachinery characteristics; - Base-lad at T in ~ 725 C, p ~ 3 bar; and - 5% lad at T in > 7 C, p > 2 bar, which crrespnds t mdulatin at cnstant recuperatr gas-side inlet temperature. In additin t this, such a single burner wuld limit NOx t <4 % O 2 within the micr turbine lad range f 1% t 5% (Figure 7-Figure 9). This is a cmmn limit fr dmestic bilers, which is relevant fr micr CHP applicatins. At 15% O 2, as cmmnly expressed in the gas turbine cmmunity, this crrespnds t ~ 11 ppm. N specific pressure lss requirement was taken int accunt in the fabricatin f the experimental burner. Extraplatin f the cld-inlet pressure lss measurements (Figure 4) nt the MTT base lad perating pint, translates int a burner pressure lss f ~6 mbar r ~ 2%. Fr such a lw pressure-rati micr turbine, this is high. Therefre, the burner particularly the surface and braiding pattern requires further ptimizatin. Such issues as structural mechanics and life f the braided burner have nt yet been investigated. In general, the use f a flexible crd is advantages fr managing thermal stresses. By nw, several braided burners were tested withut failures. The burner presented in the paper has clcked few tens f hurs, including peratin in the radiant mde and frequent startsstps. The burner surface did nt shw any visible indicatins f deteriratin. Yet, this time is surely very shrt t draw any cnclusins n life. Besides, the authrs acknwledge that the nvel cncept prpses new structural slutins and materials fr gas turbine cmbustrs. The authrs are als aware that the use f ceramics in gas turbines has been lng assciated with uncertainties, lack f experience and a requirement fr mre R&D [1]. CONCLUSIONS - A new cncept was develped fr a surface burner fabricated by braiding ceramic crds arund a ceramic frame. - An experimental burner has clcked few tens f hurs n a cmbustin test rig. It has demnstrated cmplete and stable cmbustin withut hardware verheating within a brad range f perating cnditins: a) 1-3 bar; b) T in = C; c) φ = ; d) T ad = C; and e) 4-32 kwth. - Cmbustin was stabilized within the range f mixture surface speed t laminar burning velcity rati (K) f 2-2. A cmbinatin f attached Bunsen-type flames and surface burning was established at K = When crrected t % O 2, NOx f -4 ppm and (CO+UHC) f 1- ppm were prduced in the range f T ad = C at 1-3 bar. - The braided cncept is an interesting technlgy candidate fr lw-emissin, lw-cst gas turbine cmbustrs. - The experimental burner has been tested at pints cvering the perating envelpe f a 3 kwe recuperated micr turbine [1]-[2]. - The single burner withut a pilt and staging culd cver the pints crrespnding t cld light-ff, rampup, base lad and 5% lad. Cmplete and stable cmbustin was maintained. - The same single burner wuld als limit NOx prductin t <4 % O 2 at cnditins similar t the micr turbine base lad and 5% lad. 6 Cpyright 212 by ASME

7 REFERENCES [1] Visser, W. P. J., Shakariyants, S. A. and Ostveen, M., 21, Develpment f a 3 kw micr turbine fr CHP applicatins. In ASME Turb Exp 21: Pwer fr Land, Sea and Air, Glasgw, ASME Paper GT [2] Visser, W. P. J., Shakariyants, S. A. and Ostveen, M., de Later, M. T. L., Ayed, A. H. and Kusterer, K., 212, Perfrmance ptimizatin f a 3 kw micr turbine fr CHP applicatins. In ASME Turb Exp 212: Cpenhagen, ASME Paper GT [3] Ellzey, J. L., Barra, A.B., and Diepvens, G., 26, Simulatin f a prus burner fr a gas turbine. in G. D. Ry (editr), Cmbustin prcesses in prpulsin: cntrl, nise and pulse detnatin. Oxfrd: Elsevier Butterwrth-Heinemann. [4] Fant, D. B., et al., 2, Status f catalytic cmbustin R&D fr the Department f Energy Advanced Turbine Systems Prgram, Jurnal f Engineering fr Gas turbines and Pwer, 122, pp [5] Kajita, S., and Dalla Betta, R., 23, Achieving ultra lw emissins in a cmmercial 1.4 MW gas turbine utilizing catalytic cmbustin. Catalysis Tday, 83, pp [6] Weakley, C. K., et al., 22, Develpment f surfacestabilized fuel injectrs with sub-three ppm NOx emissins. In Prceedings f IJPGC 22: IJPGC [7] Greenberg, S. J. and McDugald, N. K., 24, Fullscale demnstratin f surface-stabilized fuel injectrs fr sub-three ppm NOx emissins. In ASME Turb Exp 24: Pwer fr Land, Sea, and Air, Vienna, Austria, ASME Paper GT [8] Ramadan, O. B. et al., 27, Experimental investigatin and evaluatin f a lw NOx natural gasfired mesh duct burner. In ASME Turb Exp 27: Pwer fr Land, Sea and Air, Mntreal, ASME Paper GT [9] Muller, U. C., Bllig, M. and Peters, N., 1997, Apprximatins fr Burning Velcity and Markstein Number fr Lean Hydrcarbn and Methanl Flames, Cmb. Flame, 18, pp [1] Richersn, D. W., 26, Histrical review f addressing the challenges f use f ceramic cmpnents in gas turbine engines. In ASME Turb Exp 26: Pwer fr Land, Sea and Air, Barcelna, ASME Paper GT Cpyright 212 by ASME