Lifted Partially Premixed Flames in Microgravity

2004·2.5 MB·English

by  Lock, Andrew J.

LIFTED PARTIALLY PREMIXED FLAMES IN
MICROGRAVITY
Aurew J, Tack, Ranjan Ganguly, shwar K. Puri Suresh I. Ayearwal,

University of Minais at Chicago
and

Uday Hegde, Nalonal Center for Microgravity Rerearch

Pataliy premixed flames are a elass of flames thul cm he established by dein ehewught
lacement of a fuclrich mixture im ventact with fuel-lean mixture, These Laenes ovcur
‘ibersise ia anany practical systems a8 well Ho instance, initially nonpremmxed vombustion may
inwotvesegioas of local extinction follavod by partial premixing and re-igntion [1]. Nonuriorm,
‘ewapocation ia spray Tams ean alsa oul i lnealfuo-rich regions in svhich burning occurs in
the putially premixed mode. The technique of lean direct injection. used to achieve stable
combustion and reducce pottuant levels, ul involves regions of purtialty premixed cur ustion.
1m addition, unviunted fies can originate in a artially premined wade when a pytolyzed oF
cevaporaced fuct forma an initial Fe-ricb mixture ith Ube wmbieat six. Purl prewixiug i so
‘important in nompremined fume Wfo[T pleuomens, sce le reaclaas ean mix to some extent
prior to ignition [2 3.

‘Under normal-jravity conditions, the flame heat release prnluces bulb Mow dilatation and
Sueyamey effets in purtully premixed Mares, Can expansion due Wu healing vanes duwaaeeact
‘motion sure w ibe lawefront. The Buoyant gases acueterate the flow ia an opposite direction
fe the anvity vec, cwsing air eulraiament thst enhances the fuel-air wixing and,
consequenlly, influedces the upstream region. While i is possible (0 minimize ecovitadonal
‘sffeuly in u premined Mane by isolating buuyaney effects (o he Iowar deusivy post flame region
‘or pluzns, iis not So straightforward to do so in doupromixed flames, Soveral investigations have
‘established that gautially premincd Macs cau contain two (even, thee) 1caction 2ouss [4,36 7,
8], one with a peemined-lke siueme and te other consisting of a tmnsport-liaited
‘noapremixed zone (in which mixing and eataiament afeots ave signiicaad, For these easons it
js important (@ Uadesstaad dhe infeaetion berween flew dilatation and buoyaney cffoss in
partially prewised flames.

Lifted. partally promised flames offer a dooper insight into the phonomsna of lifted
‘ayaguenised lames, Een st ho initial streams aro noupremised, partial promising oeeurs in
fhe rogion upstream of the wacting rogion and eventos» stable ase far ce diffusion Flame 19
“The flame romans anchored around a nares region of high local reaction (reaction ker! | 10)
“Thus anchor of the nonpremnd flames hus been atributed to upstrm tanspart of radical
rom tha seastion kernel. This radical flux increases the ghemieal reaction rates for imponant
saction sips near a stabilization point that ig located in a small premizing zane 10}.
simile between bumer sabilized and Wied ciple amos was suggested by Purl cy wl. [11 a8
|A means to relate burr stabilized flames and lifted flames, Our current papor socks to validate
thie idea farther hy elimination af buoyancy influence in the flame a0 thit the re af other mere
subtle characteristics affecting the flame ure alo idontfid,

Lifted Double and Triple flames are ortablished in tho UIC-NASA Parially Premixed
rwicrogravity rig. The flamon examined inthis paper are established ubove a svanmblar hunter
hocaue ite axisymmetric geometry allows for future inplementation of other non-inmasive

1: a prope ovat of aan eit for reat 2
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copiival diagnestio eachriques eusily. Boch butacranached stable fumes amd lied Qaunes are
Cetublished ae normal and mrieogaviy culos inte dnp cower ty

Dioet imaging of douhle und triple Que for a range of equivalence ratiy is recanted. The
sirucluss of the flames ix inferred viu Cs" cheuniluminesesnse messurements wing digital image
‘aipvlation 172] of the rovurded euloc iaagss. Informetion rogurding the Dame speed is also
Ubiaiod thrangh a cempurinun uf the aoamal and microgravity Filed Dase resis.

Figure 1 shows a llled double flame under normal and ricroumnvity. As van be eben fom
igure the Mane shifts down slighty in microgravity. This is a result of loss of buoyant
‘ocelcration of the hot pases allowing the Mame © scck cquibibrium betweea Naame spoed and
ow velocity ul a fewer aaial location, Another key paint of iterest dt can aot be observed
‘rom the figure, but is seta clearly i the video rooorded Uurimy Due diop is stsbiigy. The normal
gravity filed Muu ia dds contigursion was nbserved to oscillate with high amplivode, However
The micragruvily Dune was observed to he visually stible alert lata anslent ofthe drop.

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