US 2484544 A
Description (OCR text may contain errors)
Oct. 11, 1949. c. H. BENNETT ET AL 2,484,544
ELECTRICAL IGNITOR Filed Feb. 1, 1944 Jr 4a Patented Oct. 11, 1949 ELECTRICAL IGNTER Clarence Bennett, Philadl-pli'ii-tand Rihardi E.,iaWakeiieldliAldan, Pai, assignorstoi Selas Corporation of America, afcorpnration of-Penn'- sylvania f.
Application February 1, 1944, S'erial'jNr 520,640-` 1 Claim..
This invention"relates-toelectrical vign'itors; and more particularlyl to such` an ignitorI having` a high resistance wire heating element, which is operated momentarily and for short -intervals of timeA tofinstigate combustion of a combustible fuel; mixture'- and thereafter disconnected from a source of electrical supply when combustion of thefuel mixture is efected.y
Althoughlnot tobe limitedthereto, the improved1 electrical ignitor*A provided is especially useful in airplane' heaters for initially effecting combustion' therein. Airplane heaters now being provided:` operate'with acombustible fuell mixture of gasolineran'd air'inasmuch as gasolineis employed` for operating the airplane motors 'and suchifuelisavaable and readily lends itself fior heater operation.
In order toeffectignition oia'comlo'ustible mixtureroi gasoline-and air;v there ise-tlieinitial i ree quirement' thatari ignition temperature `of i about 160F. must-'be produced by the electrical ig' nitor. Further, the electrical ignitor must# be equally eiectivev to instigate combustion of the combustible fuel mixture at temperatures of 710? F; or as-low'as 60F. belowzero. In' addition?, they electrical ignitor `must/"be capable of J witlistanding` vibrations continuously produced` and developed-riot 'only by-thef-heaterfwitli whicl'iit is associatedtbutl'alsofbyfthe airplane-ifi whicnitie heater is installed.
They vibration problem' has been'- an especially troublesome one in an effort -t provide asatis-r factory electrical ignitorI for an4` airplane Y heater; Eachv time the ignitor is energized' the heating element maybe' heated to a temperature-'of 200 orl 300"rv` F. aboveA the requisite ignition i tempera#- ture of about 1600or F.; andf'it is at such times-5 when' the'wirehea-ting elementv is relatvelyvsoit and" at red heat; that the vibratonsiimpartedfto the-'ignitor' tend'to' shorten its -lifei Thisis particularly true whenl there is'noneuniformityin the heating ofthe wire Vheatingelementandso-called localized" overheating for' hot spots" develop.
Moreover,y when an f airplane 1 heater is"` started at'lrelativelyjlowternperatures; asat 60 F. belowv zero; forE example; the 'blast'V off air and kgasoline mixture" passing over ther ign-iter exercisesfa rela'- tlvel'yfz strong v cooling effect which' must be' over# comer'by the-Wire; heating element in orderJ to produce a source of heat at' aY sufil'ciently high' temperature to ignite the air and gasoline vm'ixturerat the ignition temperature ofi' about-1600ia-` Fi In addition,v the'electri'cal supplylusually pro; viddinan airplane lista-1241y to 28- volt system lin# steadiofftlieusual 1-10fto' `125 volt electrical supply 2; available.' in' l al dwelling and any' heavyv current drain on the system is objectionable.
In' accordancefwithlthis invention, `an .improved electricalignitori is providedl which is exception; allyruggedriandcapablefof withstanding constant andcontinuous vibration forflong periods ofuse. rIhisxis accornpliisl'ied:y bypr'ovidings' an lignitor!` in"1A cluding'- a core formed; of# refractory material which is externally thread'edi andabout which subst.initially` the; entire length-f ofi af resistance heatingwref is 1 helically 'Wound'. The individual tufrnsl/ are f evenly'spiat'cedl andy adjacent turns are shielded fronifonean'otlfierfbylfa Wf'allvof reiractory rriateri'al-v soYth-'at substrit lly uniform-heating ofi tliewire is" eiected'f and localized overheating or excessive spot heating is avoided.`
The-` portion-l of? tlief core externally' threaded and? woicin'd"withftlie'fwireiheating element is 1uncovered#aridicompletelyvexposed; so itliat` al-llpor; tons1iofithefheatlng element willbe subjected substantially toftl'lef same temperature* conditions produced'airiddeveloped -by thie'ignitori By. pro-` vidingla coref"01E-"refractorymaterialifor the heating==element;-sucli material Iis quickly heated ftof a red h'eat' byv the-fwireiv lieatingfrelement'funder the most adverse temperatura conditions; whereby rapid? and reliable ignition of thecombustible mixture isf eilected" witlr almlrliirnum current drain on theelectricalsupplyI-systemf.
Theinvention; togetlierwitn the objects y'and advantages thereof;A will become apparent from the-following descriptiontak'en in conjunction witl'rthe acc'ompafnyi'ngaI drawing forming Va`4 p'art of th specification; and? of which Fig lris" a? v'ew 'of anf electrical ignitor embodyirig tlie l invention` and alfragmentary sectional Viewf oi an airplane'fiheater into the combustion icl'amberiof 'which theignitor extends;
Fig: 2-`isa rienlargedlvertical sectional viewof the ignitor shown in Fig. 1 to illustrate the invention more clearly;
j Fig." 3"'is a: sectional.viewftak'enon line 3"-3" of Flg''Zfi' Fig, 4" isiariA end View of' the ignitor' Figs.y 1 'and l2); and
Fig...5l-is..a sectionalfviewsimilar to Fig. 2 illustrating. a .modication ,or the invention. f
Referringfto'the drawing, theY electrical-ignitor l 0 embodying Y the invention` comprises'. an outer shell' including two i tl'lreadedlyi` connected` parts 'IH Sand IZ-Which may-bie'r'eierred to' as a body and conneetorarespectivelyru body mi islpro'-Y vidediwitlitanf: externally threadedcout'erend I4 andi?whexagonalishapedinneriend l5', so :that it shown in 3 may be threaded tightly to the connector I 2 with the aid of a suitable tool.
The connector I2 intermediate its ends is formed with an internal shoulder I6 against which bears a plug I1 formed of a suitable refractory material. A core I8 also formed of refractory material is disposed within the outer shell and includes a collar or end portion I 9 which fits snugly against the plug II, a reduced neck portion 2D, a main body portion 2I, and a reduced end portion 22 projecting beyond the externally threaded end I4 of the body I I.
The plug II and core I8 .are formed with openings to receive a pin 23 having oneend projecting into the housing formed by connector I2, and the opposite end extending a short distance beyond the projecting end portion 22 of core I8. In order to anchor the pin 23 firmly in position, the annular plug I'I and collar I9 are recessed at their contacting faces to receive an enlarged head 24 formed intermediate the ends of pin 23. e
The outer projecting end 22 of core I8 is threaded, as indicated at 25 in Fig. 2, to form a yhelical groove about which is wound a wire or heating element 26. The wire 26 is tightly wound about the external portion 22 of core I8 and secured at its outer end at 2`I, as by brazing or welding, for example, to the pin 23. The
reduced end portion 22 extends a short distance Within the body II to form an annular space 2'I opposite the externally threaded portion I4, and the inner end of the Wire 26 is secured at 28 to the inner surface of the body I I, as by brazing or welding, for example, at the region of the annular space 21'.
In order to secure the plug I'I, core I8 and pin 23 in position within the outer shell without subjecting these parts to excessive force or strain when the body II and connector I2 are threadedly secured together, the inner wall of connector I 2 is formed with a longitudinally extending ridge or key 29 which terminates at one end at the shoulder I6 and at the opposite end at a circumferential groove or slot 30. The peripheral surfaces of the plug I'I and collar I9 of core I8 are provided with longitudinally extending keyways or slots formed to receive the ridge or key 29, thereby preventing rotating movement of the plug II andcore I8 within the outer shell formed by body I I and connector I2.
In order to prevent lengthwise movement of the plug I 'I and core I8, a ,ring 3I is snapped into position into the circumferential groove 3U. The ring SI is firmly held in position in the groove 3i) and overlies a shoulder 32 formed at the juncture of collar I9 and neck portion 2ll of core I8, so as to hold the collar I9 and plug I1 in position against the shoulder I6 formed within connector I2.
When the ignitor I is inserted into a combustion space, it is highly desirableto provide an air-tight seal within the outer shell of the ignitor, so that ilow of air from within the housing' of the connector I2 past the refractory plug I'I, lcollar I8 and pin 23 into the combustion space, is avoided. In order to insure such an air-tight seal, the portion of the pin 23 extending into core I8 is coated with a suitable high temperature cement, such as, for example, sodium silicate or the like, before being inserted into the core I8. Likewise, the recessed portions of the plug I'l and the collar I 9, which receive vthe enlarged head 24 of pin 23, are coated with such a high temperature cement beforethese. parts are assembled.
' extending combustion chamber 36 of annular shape having side walls 3`I. At the bottom of combustion chamber 36 is provided a burner screen 38 which may be formed of thin plates of refractory material stacked together and having slots or recesses formed therein to provide a plurality of burner ports 39. A mixture of air and atomized gasoline is introduced through the ports 39 into the combustion chamber 36, and the upper ends of the ports 39 constitute the regions at Awhich a plurality of flames are produced and maintained. I l
rIhe heat liberated in combustion chamber V3,5 by the burning of the air and gas mixture is given up to air passing through annular spaces 40 formed by the side walls 3l of combustion chamber 36 and outer and inner walls 4I and 42, respectively. Although the side walls 3'I are shown as being smooth, these walls may be provided with fins (not shown) which may extend therefrom into the combustion chamber 36 and also into the spaces 40, so as to provide a relatively extensive heat transfer surface for taking up heat in combustion chamber 3S and giving up such heat to air passing through the annular spaces 40. The products of combustion are discharged from the combustion chamber 36 in any suitable manner, and the air heated in spaces 40 may be utilized to effect heating of one or several spaces in an airplane in which the heater 35 is adapted to be installed.
Since the airplane heater 35 forms no part of the invention and is merely illustrative, further description thereof will not be made here. If desired, reference may be made to the aforementioned Hess and Townsend patent for a detailed description of the airplane heater, the disclosure of which may be considered to be incorporated in this application.
To accommodate the ignitor I0, the airplane heater 35 is provided with a hollow sleeve 43 at the region of an opening formed in the outer side wall 31 of combustion chamber 36. The sleeve 43 extends outwardly from the combustion chamber 36 at such an angle that the inner end ofthe ignitor I0 is disposed above the burner screen 38 and extends lengthwise thereof for a short distance. The outer wall 4I of the heater 35 is formed with a suitably shapedopening in alignment with the sleeve 43, so that the ignitor I0 may be inserted into the heater and threadedly secured to the outer. end of the sleeve.
A suitable electrical fitting (not shown) is adapted to be connected within the housing formed in connector I2 to connect the pin 23 to a source of electrical supply.v The circuit for the ignitor is completed from the pin 23 through the wire heating element 26 and body I I to the sleeve 43 which serves as a ground connection. The ignitor I0 is of a type which is only operated momentarily and at short intervals of time to instigate combustion of the combustible fuel mixture, and, after combustion has been effected, isdi'sconnected from the source of electrical supply,
encima Whenrthefignitor: IIJ is'fenergi'zed; thaw-ire heat'- ying element? 261instantly-becomes Aheatedftoa-red heat:A and'. immediatelyfthereafter. and in a: rela'- tively shortintervar of time, viz-a matter'of a fewseconds; the'thread'ed projecting portion 22 off the refractory` core ISI-beginsfto-glow and also reachesredheat aty a-` temperaturel of at least 116009'F. toieffect ignition of the mixtureiof air and gasoline introduced into the-1 combustion chamber 36. While it is imperative.- to produce this ignition temperature initheishortest interval of ftime possible, it mustbe accomplished without raising'the wire heatingelement 26 to such a high temperature approachingv its critical. destruction point.`
. Ithas been found that by providing a Iwirev2l Whichuis fully exposedthroughout its entirelength andi-wound. aboutA the threaded refractoryy part 22; anignitor islobtainedwhich is extremelyreliable and effective to instigate` combustion of a fuel.mixture of air and gasoline. The wire 26 is ofisuchsize and lengththat itsresistance will develop the desired high temperature of at least 1600MB. when connected to a 24- to 28 volt source of` electricalsup-ply usually available in an airplaner. The threaded refractory part 22 is pref erably formed of a ceramic which will withstand y high thermal shock,y and'mayibe formed of any tendingto rupture the wire, the helical-groove 25.5is of suflicientdepth so. that theladjacent-turns offthe wirefare .effectively shielded from ione another by a wall of refractory material. In this Way heat is always radiated and conducted from the wire toward a refractory wall surface rather than directly between two adjacent turns of wire openly exposed to one another.
The threaded refractory part also facilitates ignition of the combustible fuel mixture at abnormally low temperatures, such as, for example, 60 F. below zero. Under such conditions the the cool blast of air and gas mixture introduced into the combustion chamber 36 exercises a considerable cooling effect when passing over the ignitor ID. However, heat is both radiated and conducted from the lwire 26 to the threaded refractory part 22 at a suiciently rapid rate to bring the projecting part 22 to a red heat in a relatively short interval of time. Hence, the refractory part 22 serves as a heat reservoir and soon reaches a temperature which is sufficiently high to effect ignition of the combustible fuel mixture even under the most adverse operating conditions. In order to bring the refractory lpart 22 to a red heat quickly, this outwardly projecting part of core I8 is of reduced cross section and considerably smaller in diameter than the main body portion 2 I.
One of the important features of the ignitor I0 contributing to its reliability, is that the wire heating element 26 is fully exposed and uncovered throughout its entire length. In this way no heat The threaded refractory par't 22 about 6 pockets:- ar'effU formed `which tenth to;` rupture:V the wire` heating? element; and. the;` wire.: is-f'heated substantially uniformlyf over. the. entire portion which is wound! about` the.y threaded refractory part 22. It will be seen-.in Fig..2zthat.1.the,fwire 2-I'isfnot1 wound about; the athreadedrportion with: in space 2.1 at thelend of body! II; andithatfLthe rstaturniofwire =is formed aboutathef` refractory partL 225: a shortadistance outwardly:fromr` thexetremefen'diof: the 'bodyL Ill..
It? has: been. found. that in@ an, airplanei heater 325% like. thatcdescribed', the ignitorl I Il: preferably should be locatedi abouttS/t abovez the.I burner screen; 38.12 inf. order to effect?v reliableY ignition; of the combustible .fuel mixturezund'er. all operating conditions; encountered.. After' ignition hasbeen effected and. theignitor;lisvfdeeenergized; the outer projecting: endlv 22 of.'core1l8lis'then subjected to the heated productsf off combustion lat'. at tempera:- turefof'atleastl2360or The outer refractory part should be,y sufficiently massive so thats heat may befdissipat'ed therefromatiazsufiicientlyrapid ratetolthev` mainsfbody portion 211 rof corel-'I8iand tozother parts oithe ignitor to prevent overheatiing: of'. the wire heating element 2fwhen.tl-refair-l plane heater 3 Slis being; operated;-
Thewire heating .elementi 26 mayf. betformed'iof anyi suitable highV resistance metal,.suchf as. Nichrome orA platinum',.for=exampl'e:.. By Wayfoffex.- ample..A only. and'. without` limitation; arry ignitor like ithatidescribed :andliillustrat'edi hasbeenlsuee cessfully used inwhicha 271'"length oflNo.l 25 B. & Sgauge YlSli'chrome.;wire is wound for; au dis:- tance of :about 7/g about ai threaded refractoryv partlapproximatel-y:% in diameter. When corr-A nectedito. azsourceLof'electrical supply varying be tween 24ito28 volts, without'V any external resist'- ance;A thecurrent :drainis about' 5i amperesr Whenzthefelectricallsupply is atabout 24 volts; a temperature. of.4 about. 160.0"."F is' producediat aboutdwatts perlinearffootrofwire; and whenthc electrical supply is at abouti 28 :volts,f alltempera'- turer of; about 19609' is' produced at about 7 watts@peri-linear?.` foot. of? wire. Since the 1 fusion pointtof NichromeswireI-is about 2200i itw-ill be evident that 7 watts per linear foot represents about the maximum capacity of the wire in the example just given. However, even under the most adverse operating conditions and while being subjected to vibrations developed by the airplane heater, the ignitor has been exceptionally reliable and ignition of the combustible fuel mixture has always been effected in a relatively short interval of time.
In Fig. l5 is illustrated an ignitor |011, which is a modification of the embodiment described above and in which parts similar to those illustrated in Figs. 1 to 4 inclusive are referred to by the same reference numerals.
In Fig. 5 the pin 23a, only includes the portion projecting into the housing formed by connector I2 and terminates at the enlarged head portion 26a. Since the pin 23a does not extend through the core I8, the bore 45 in the core remains open throughout its length from the recessed collar end I9 to the extreme end of the threaded projecting portion 22. As in the embodiment illustrated in Figs. l to 4 inclusive, the wire 26 is tightly wound ina helical groove in the outer projecting portion 22 and secured at its inner end at 28 to the body II. The annular space formed by the reduced end portion 22 within the outer end of body II may be filled with a suitable high temperature cement 46.
The wire or heating element 26 includes an outer end portion 41 which, from the outer end of the coiled part on the reduced end portion 22-, extends through the opening 45 in core I8 and a small opening 48 in pin 23a. The end of the Wire passing through the opening 48 in pin 23a is secured at 49, as by brazing or welding, for example, to the extreme tip of the pin. The opening 43 is relatively small so that, after securing the end of the wire to the pin at 49, the opening 48 is closed and sealed without increasing the size of the pin 23a, wherefore the usual electrical tting (not shown) may be readily positioned within the housing formed in connector I2.
The embodiment of Fig. 5 possesses the advantage that, when positioned in an airplane heater like that shown in Fig. l, no brazed region at the outer threaded projecting portion 22 is subject to the high temperature heat products of combustion in combustion chamber 36.
It has been found that the ignitors I0 and Illa illustrated and described are exceptionally reliable under the most adverse operating conditions encountered in practice. The disposition of the wire heating element 26 about the reduced threaded projecting portion of the refractory core about which adjacent turns are uniformly spaced and shielded from each other, and having the coil 26 uncovered and exposed throughout its entire length on the refractory portion 22, have contributed considerably to the reliability of the ignitor. Even when the igntors l0 and lila are not disconnected from the source of electrical supply after ignition of the combustible fuel mixture has been effected, the ignitors have not failed and have stood up remarkably although the ignitors are positioned only a short distance from the burner screen 38. This has been accomplished, it is believed, by the complete exposure of the heating element 25 on the threaded projecting portion 22 in the combustion chamber 36 and the effective dissipation of heat from the latter to other parts of the ignitor.
While several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various modifications and 'changes may be made without departing from the spirit and scope of the invention. 4Thus, the annular space 2T' at the outer end of body l l in Fig. 2, for example, may also be lled with a suitable high temperature cement. It is therefore contemplated to cover all modlcations and changes which come Within the spirit of the invention, as pointed out in the Iollowing claim.
What is claimed is:
In an ignitor. the combination of an outer metallic shell, an inner refractory core snugly received in said shell, said core having a cylindrical portion projecting beyond said shell, said projecting portion being of a reduced diameter and having a helical groove formed on its outer surface and extending from the end thereof toward said shell, a resistance wire wound in said groove from a point adjacent to the end of said projecting portion toa point near the end of said shell, said wire and groove being of such relative sizes that the Wire is entirely received in said groove whereby adjacent turns thereof are not exposed to each other, a terminal extending through said core, one end of said Wire being attached to said shell and the other end thereof being attached to said terminal.
CLARENCE H. BENNETT. RICHARD E. B. WAKEFIELD.
REFERENCES CITED The following references are of record in the le of this patent:
UNITED STATES PATENTS Number Name Date 2,024,387 Rabezzana Dec. 17, 1935 2,129,962 Rabezzana Sept. 13, 1938 2,404,841 Hess et al July 30, 1946 FOREIGN PATENTS Number Country Date 571,909 France Nov. l, 1923 764,956 France Mar. 12, 1934