Gas Oil Engines

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Title:GasandOilEngines,SimplyExplained

AnElementaryInstructionBookforAmateursandEngineAttendants

Author:WalterC.Runciman

ReleaseDate:November17,2008[EBook#27286]

Language:English

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GAS AND O ILENGINES

SIMPLYEXPLAINEDAnElementaryInstructionBookforAmateurs

andEngineAttendants

BY

WALTERC.RUNCIMAN

FULLYILLUSTRATED

LONDON

ModelEngineerSeries.The"ModelEngineer"Series,no.26.

1905

CONTENTS

CHAP. PAGE

PREFACE 5I. INTRODUCTORY 7

II. THECOMPONENTPARTSOFANENGINE 13

III.HOWAGASENGINEWORKS 22IV. IGNITIONDEVICES 33V.MAGNETOIGNITION 47VI.GOVERNING 51VII. CAMSANDVALVESETTINGS 63VIII.OILENGINES 81

PREFACE

MY object in placing this handbook before the reader is to provide him with a simple andstraightforwardexplanationofhowandwhyagasengine,oranoilengine,works.Themainfeaturesandpeculiaritiesintheconstructionoftheseenginesaredescribed,whilethemethodsandprecautionsnecessarytoarriveatdesirableresultsaredetailedasfullyasthelimitedspacepermits.Ihaveaimedatsupplyingjustthatinformationwhichmyexperienceshowsismostneededbytheuserandbytheamateurbuilderofsmallpowerengines.Inplaceofgivingamerelistofcommonenginetroublesand their remedies, I have thought it better to endeavour to explain thoroughly the fundamentalprinciplesandessentialsofgoodrunning,sothatshouldanydifficultyarise,theengineattendantwillbeabletoreasonoutforhimselfthecauseofthetrouble,andwillthusknowtheproperremedytoapply. This will give him a command over his engine which should render him equal to anyemergency.

WALTERC.RUNCIMAN.

LONDON,E.C.

GASANDOILENGINESSIMPLYEXPLAINED

CHAPTERI

INTRODUCTORY

THEhistoryofthegasenginegoesbackalongway,andthehistoryoftheinternalcombustionengineproperfurtherstill.Itwillbeinterestingtorecountthemainpointsinthehistoryofthedevelopmentoftheclassofengineweshalldealwithinthefollowingpages,inordertoshowwhathugestridesweremadesoonafterthecorrectandmostworkabletheoryhadbeenformulated.

In1678AbbéHautefeuilleexplainedhowamachinecouldbeconstructedtoworkwithgunpowderasfuel.Hisarrangementwastoexplodethegunpowderinaclosedvesselprovidedwithvalves,andcool theproductsofcombustion,andsocauseapartialvacuumtobeformed.Bytheaidofsuchamachine, water could be raised. This inventor, however, does not seem to have carried out anyexperiments.

In 1685 Huyghens designed another powder machine; and Papin, in 1688, described a similarmachine,whichwasprovidedwith regularvalves,asdevisedbyhimself, in theProceedingsof theLeipsic Academy, 1688. From this time until 1791, when John Barber took out a patent for theproductionofforcebythecombustionofhydrocarboninair,practicallynoadvancementwasmade.The latter patent, curiously enough, comprised a very primitive form of rotary engine. Barberproposedtoturncoal,oil,orothercombustiblestuffintogasbymeansofexternalfiring,andthentomixthegasessoproducedwithairinavesselcalledtheexploder.Thismixturewasthenignitedasitissuedfromthevessel,andtheensuingflashcausedapaddle-wheeltorotate.Mentionisalsomadethat itwasanobject to injecta littlewater into theexploder, inorder tostrengthentheforceof theflash.

RobertStreet'spatentof1794mentionsapistonengine,inthecylinderofwhich,coaltar,spirit,orturpentinewasvaporised,thegasesbeingignitedbyalightburningoutsidethecylinder.Thepistoninthisenginewasthrownupwards,thisinturnforcingapumppistondownwhichdidworkinraisingwater.Thiswasthefirstrealgasengine,thoughitwascrudeandveryimperfectlyarranged.

In1801FranzoseLebondescribedamachinetobedrivenbymeansofcoal-gas.Twopumpswereused to compress air and gas, and themixturewas fired, as recommended by the inventor, by anelectricspark,anddroveapistoninadouble-workingcylinder.

TheatmosphericengineofSamuelBrown,1823,hadapistonworking inacylinder intowhichgaswas introduced,and the latter,being ignited,expanded theair incylinderwhilstburning likeaflame.The fly-wheel carried thepistonup to the topof its stroke, thenwaterwasused tocool theburntgases,whichalsoescapedthroughvalves,thelatterclosingwhenthepistonhadreachedthetopofitsstroke.Apartialvacuumwasformed,andtheatmosphericpressuredidworkonthepistononits down stroke. A number of cylinders were required in this engine, three being shown in thespecificationallconnectedtothesamecrank-shaft.AccordingtotheMechanic'sMagazine, suchan

enginewithacompletegasgeneratingplantwasfittedtoaboatwhichranasanexperimentupontheThames.

A two-cylinder engine working on to a beam was built in Paris, but no useful results wereobtained.

Wright'sengineof1833usedamixtureofcombustiblegasandair,whichoperatedlikesteaminasteam engine. This engine had a water-jacket, centrifugal governor, and flame ignition. In 1838Barnettappliedtheprincipleofcompressiontoasingle-actingengine.Healsoemployedagasandairpump,whichwereplacedrespectivelyoneithersideoftheenginecylinder,communicationbeingestablished between the receiver into which the pumps delivered and the working cylinder as thechargewasfired.Thedouble-actingengineswhichBarnettdevisedlaterwerenotsosuccessful.

Fromthistimetoabout1860veryfewpracticaldevelopmentsarerecorded.AnumberofFrenchandEnglishpatentsweretakenout,referringtohydrogenmotors,butarenotofmuchpracticalvalue.

Lenoir's patent, dating from 24th January 1860, refers to a form of engine which receivedconsiderable commercial support, and consequently became very popular. Amanufacturer, namedMarinoni,builtseveraloftheseengines,whichweresettoworkinParisinashorttime.Then,duetosuddendemand, theLenoirCompanywas formed toundertake themanufactureof theseengines. Itwasclaimedthata4-horse-powerenginecouldberunatacostof3·4shillingsperday,orjustonehalf the cost of a steamengine using 9·9 pounds of coal per horse-power per hour.Many similarexaggerated accounts of their economy in consumption were circulated, and the public, on thestrengthofthesefigures,bought.

Itwasunderstood that 17·6 cubic ft. of gaswere requiredper horse-powerper hour, but itwasfoundthatasmuchas105cubicft.wereoftenconsumed.Thediscrepancybetweenthestatedfiguresandtheactualperformanceoftheenginewasadisappointmenttotheusingpublic,and,asaresult,theLenoirenginegotabadname.

Hugon, director of the Parisian gas-works, who, together with Reithmann, a watchmaker ofMünich,hotlycontestedLenoir'sprioritytothisinvention,broughtoutamodificationofthisengine.Hecooledthecylinderbyinjectingwateraswellasusingawater-jacket,andusedflameinsteadofelectricignition.Theconsumptionwasnowbroughtdownto87·5cubicft.

AtthesecondParisianInternationalExhibition,1867,anatmosphericengine,inventedbyOtto&Langenabout this time,wasshown. In thisenginea freepistonwasused inaverticalcylinder, theformerbeingthrownupbytheforceoftheexplosion.Theonlyworkdoneontheup-strokewasthattoovercometheweightofthepistonandpistonrod,andthelatterbeingmadeintheformofarack,engagedwithatoothedwheelontheaxleasthepistondescended,causingthefly-wheelandpulleytorotate.

BarsantiandMatteucciwereengagedindevisingandexperimentingwithanengineverysimilartothissomeyearsbefore,butOtto&Langen,nodoubt,workedquiteindependently.Barsanti'senginenever became a commercial article;whileOtto&Langen's firm, it is said, held their own for ten

years,andturnedoutabout4000engines.In1862theFrenchengineer,BeaudeRochas,laiddownthenecessaryconditionswhichmustprevailinordertoobtainmaximumefficiency.Hispatentsaystherearefourconditionsforperfectlyutilisingtheforceofexpansionofgasinanengine.

(1)Largestpossiblecylindervolumecontainedbyaminimumofsurface.

(2)Thehighestpossiblespeedofworking.

(3)Maximumexpansion.

(4)Maximumpressureatbeginningofexpansion.

Thesearetheconditionsandprinciples,brieflystated,thatcombinetoformthenowwell-knowncycleuponwhichmostgasenginesworkatthepresenttime.

Itwasnot until 1876, fifteenyears after theseprinciples hadbeen enumerated, thatOtto carriedthem into practical effect when he brought out a new type of engine, with compression beforeignition, higher piston speed,more rapid expansion, and a general reduction of dimensions for agivenpower.Duetothisachievement,thecycleabovereferredtohasalwaysbeentermedthe"Otto"cycle.

CHAPTERII

THECOMPONENTPARTSOFANENGINE

Having recounted very briefly the chief points in the development of the gas engine from itsbeginning,wemayproceedtodealwithmattersofperhapsmorepracticalinteresttothosewhoweare assuming have had little or no actual experience in making or working internal combustionengines.

Themoderngasenginecomprisescomparativelyfewparts.Apartfromthetwomaincastings—the bed and cylinder—a small engine, generally speaking, consists of four fundamentalmembers,viz.,thevalvesandtheiroperatingmechanism,thecamsandlevers;theignitiondeviceforfiringthecharge; and the governing mechanism for regulating the supply and admission of the explosivecharge.Thereare innumerabledesignsofeachoneof theseparts,andno twomakesarepreciselyalike in detail, as every maker employs his own method of achieving the same end, namely, theproductionofanenginewhichcomprisesmaximumefficiencywithaminimumofwearandtearandattention.

Therefore,beforedealingwitheachof theseprimaryparts inanarbitrarymanner,andwith thecycleofoperations indetail,wepropose tomakethereaderfamiliarwith thegeneralarrangementand method of working which usually obtains in the smaller power engines. In the followingillustrationsthesepartsareshown.A(fig.1)istheignitiondevicewhichcarriestheignitiontubetofirethecharge.HandI(fig.2)arethemainvalves,andGC(fig.1.)isthegas-cock.Thesideorcamshaft N (sometimes called the 2 to 1 shaft), the camswhichmove the leversM, the latter in turnoperatingthevalves,andcausingthemtoopenandcloseatthepropertime,areshowninfig.11.Abracketbolteduptothesideofcylinderformsabearingforoneendofthesideshaft,andalsocarriesaspindleatitslowerendonwhichtheleversoscillate,transmittingthemotionimpartedtothembythecamstothevalves.Themaincylindercastingandthebedneednodescription.Insomecasesthebedisintwoportions,thoughnowagreatmanymakersarediscardingthelowerportionaltogether,havingfoundthatitischeaper,andquiteassatisfactory,touseabuilt-upfoundationinstead,and,ifnecessary,tocutatroughforthefly-wheeltorunit.Thisarrangement,however,onlyobtainswherelarger engines are concerned. A half-compression handle by which the exhaust cam is movedlaterallyonthesideshaftasrequiredisnotneededonverysmallengines.

FIG.1.—GeneralArrangementofaGasEngineandAccessories.

Furtherreferencewillbemadetothisinanotherchapter,and,althoughthisisnotanecessityonasmallengine,itisalwaysemployedonenginesover2B.H.P.Infig.1,HWisthecoolingwateroutletandCWtheinlet.AsmalldraincockisshownatDC,throughwhichthewaterinthecylinderwater-jacketmaybedrawnoffwhenrequired.Thepipes leading to the inletandoutletof thissupplyareconnectedtothecoolingwatertankbymeansofacoupleofbroad,flatnutsandleadwashers,oneinsideandtheotheroutsidethetank,thelatter,whenclampedupwell,makingaperfectlywater-tightjoint.Theoutletpipemakinganacuteanglewiththesideof tank, thewashersusedthereshouldbewedge-shapeinsection.Itisalsodesirabletofitastop-cockSC,sothatthepipescanbedisconnectedfromtheengineentirely,orthewater-jacketemptiedwithoutrunningthewholeofthewateroutofthetank.TheexhaustpipeEPismadeupofgas-barrel.Itshouldleadfromtheenginetothesilencerorexhaustbox(ifoneisfoundtobenecessary)asdirectlyaspossible,i.e.,withnomorebendsthanareneeded,andwhatthereareshouldnotbeacute.Thesilencercanbeinsideoroutsidetheengine-room,whicheverismostconvenient;butbothitandtheexhaustpipingshouldbekeptfromalldirectcontactwithwood-work,andatthesametimeinareadilyaccessibleposition.

Beyondtheexhaust-pipeandboxandthewater-tank,thegasbagGBandgasmeter(wheresmallpowers are concerned, the ordinary house or workshop lighting meter may be used withoutinconvenience)aretheonlyotheraccessorieswhichareincludedinasmallinstallation.

FIG.2.—ASectionofaGasEngine.

Fig.2givesasectionalview,showingthecylinderandliner.Thelatterisaverydesirablefeatureinanytypeofgasengine,butespeciallyinthelargersizes;foratanyfuturetime,shoulditbefoundnecessary to re-bore the liner, it can be removed with comparative ease, and is, moreover, morereadilydealtwithinthelathethanthewholecylindercastingwouldbe.

Thelinerisvirtuallyacast-irontube,withaspeciallyshapedflangeateitherend.Atthebackendthe joint between it and the cylinder casting has to be very carefully made. This is a water andexplosionjoint;henceithasnotonlytopreventwaterenteringthecylinderfromthewater-jacket,butalsotobesufficientlystrongtowithstandthepressuregeneratedinthecylinderwhenthechargeisfired. For this purpose specially prepared coppered asbestos rings are used,whichwill stand bothwaterandintenseheat.Sometimesacopperringaloneisemployedtomakethejoint.Atthefrontendthelinerisjustagoodfit,andentersthebedeasily,andacoupleofboltsfittedincorrespondinglugsontheliner,passthroughthebackendofcylindercasting,sothatbytighteningupthesethejointatback end is made secure. A small groove is cut on a flange, and a rubber ring, of about 1⁄4-in.sectionaldiameter, is insertedherewhenthe liner is fitted into thecylindercasting.Thismakes thewater-jacketjointatthefrontend.

FIG.3.

FIG.5.

FIG.4.

Lugsareprovidedonthebedandcylindercastings,andareboredtoreceivesteelbolts—threearesufficient, provided themetal in and around these lugs is not pinched. In some cases a continuousflangeisprovidedonbothbedandcylinder,andanumberofboltsinsertedallthewayround.This,however,isunnecessary,andhasasomewhatclumsyappearance.Whentheseboltsaretightenedup,the cylinder and liner are clamped firmly to the bed; but the liner being free at the open end, canexpandlongitudinallywithoutcausingstressesinthecylindercasting.

ThecombustionchamberKisvirtuallypartofthecylinder,andhasapproximatelyequaltoone-fourththetotalvolumeofthecylinder.Theshapevariessomewhatindifferentmakesofengines;insomeitisrectangular,withallthecornerswellroundedoff;inothersitispracticallyacontinuationof thecylinder, i.e., it iscircular incross-section,with thebackendmoreor less spherical;while,again, it ismadeslightlyovalincross-section;butineverycasethecornersshouldbewellcurvedandroundedoff,sothatthereisnoonepartwhichisliabletobecomeheateddisproportionatelywiththerestofthecasting;infact,inthewholecylindercastingthereshouldbenosuddenchange,butauniformity in the thickness of the metal employed. This point should be carefully remembered,although it appliesmoreparticularly to thoseparts of the casting subjected tohigher temperaturesthantherest.

Themainbearings areusuallyofbrassorgun-metal, and are adjusted for running in the samemannerasanysteamorotherengineswouldbe.The"brasses"areinhalves,andarehelddownbythecast-ironcaps,asshowninfig.1.

Thesebearings require extremely little attention, anddonot show thewear and tearof runningnearlysosoonastheconnecting-rodbrasses.These,too,areusuallyofbrassorgun-metal;buttherearevariousformsofconstructionemployedinconnectionwiththebackendorpistonpinbearings.On very small engines the connecting rod is swollen at the back end in the forging, and thenmachinedupanddrilled,asshowninfig.3.Inthisholethebrassesareinsertedafterbeingscrapeduptoagoodfitonthepistonpin.

Aflatiscutononeofthebrasses,andasetscrewisfitted,asshown,topreventanymovementofthelatterafterthefinaladjustmenthasbeenmade.Alocknutshouldbeusedinconjunctionwiththissetscrew.Anothermethod,andonemoregenerallyusedonlargerengines,isshowninfig.4.Inthiscase thebrassesare larger than in the former,where theyarevirtuallyasplitbush;here theyhaveholesdrilledinthemtotakethebolts,thelatterusuallyandpreferablybeingturneduptotheshapeshowninfig.5.

CHAPTERIII

HOWAGASENGINEWORKS

Thegasengineofthepresentday,althoughfromastructuralpointofviewisverydifferenttotheearlyengine,oreventhatoffifteenyearsago,is,inrespecttotheprincipleuponwhichitworks,verysimilar.ThegreaternumberofsmallerpowerenginesinuseinthiscountryworkonwhatisknownastheOttoorfour-cycleprinciple;anditiswiththisclassofengineweproposetodeal.

Referencetothevariousdiagramsinthetextwillhelpconsiderably,andmakeitaneasymatterforanyreaderhithertototallyunacquaintedwithsuchenginestoseewhyandhowtheywork.

Coal-gas consists primarily of five other gases, mixed together in certain proportions, theseproportionsvaryingslightlyindifferentpartsofthecountry:—Hydrogen(H),50;marshgas(CH4),38;carbon-monoxide,4;olefines(C6H4),4;nitrogen(N),4.

Gasaloneisnotexplosive;andbeforeanypracticalusecanbemadeofit,aconsiderablequantityofairhastobeadded,dilutingitdowntoapproximatelytenpartsairtooneofpuregas.Thismixtureisnowhighlyexplosive.

The readerwill dowell to bear these facts constantly inmind, especiallywhenhe is repairing,adjusting, or experimentingwith a gas engine.Wewish to emphasise this at the outset, because aconsiderationof thesefactswillkeepcroppingup throughoutallourdealingswith thegasengine,and ifoncea fairlyclearconception isobtainedofhowgaswillbehaveundercertainandvariousconditions,half,orevenmorethanhalf,our"troubles"willdisappear;thecrythatthegasenginehas"gonewrong"willbeheardlessoften,anduserswouldsoonlearnthatthegasengineisinrealityasworthyoftheirconfidenceasanyotherformofpowergeneratorincommonuse.

Buttoreverttotheexplanationofthecycleofoperations.Thecycleiscompletedinfourstrokesofthepiston,i.e.,tworevolutionsofthecrankshaft.

At the commencement of the first out-stroke (the charging or suction stroke) gas and air areadmitted to thecylinder through therespectivevalves(fig.6),andcontinue tobedrawninbywhatmay be termed the sucking action of the piston, until the completion of this stroke (the precisepositionoftheclosingandopeningofthevalveswillbereferredtolateron).Thenextstroke(fig.7)isthecompressionstroke.Allthevalvesareclosedwhilstthepistonmovesinwards,compressingthegases,untilattheendofthisstroke,andattheinstantofmaximumcompression,thehighlyexplosivechargeisfiredbymeansofthehottubeoranelectricspark,asthecasemaybe.Theensuingstroke—the second out-stroke of the cycle—is the result of the explosion, the expanding gases driving thepistonrapidlybeforethem;this,then,istheexpansion,orworkingstroke(fig.8.)

FIG.7.—Compressionstroke,duringwhichallvalvesremainclosed.

FIG.8.—Secondoutstroke,showingpositionofvalvesduringworkingstroke.

FIG.6.—Commencementoffirstout-strokesuctionorchargingstroke.Gasandairvalveabouttoopen.

During the last—the second inward—stroke (fig. 9) the exhaust valve is opened,andthereturningpistonsweepsalltheburntgases (the product of combustion) out intotheexhaustpipeandsointotheatmosphere.This completes the cycle, and the piston,crank, and valves are in the same relativepositions as formerly, and the same seriesof operations is repeated again and again.Ofcourse,itisnotalwaysthecasethatbothairand gas valve are opened on the charging stroke; that depends upon the method employed togovern the speed of the engine. Supposing it were governed on the hit andmiss principle (to beexplainedhereafter),thegasvalvewouldbeallowedtoremainclosedduringthechargingstroke,andairalonewouldbedrawnintothecylinder,thencompressed,butnotbeingexplosivewouldsimplyexpand again on the working stroke, giving back nearly all the energy which was absorbed incompressingit,andfinallybeexhaustedinthesamemannerastheburntgasesare.

FIG.9.—Secondinwardstroke,showingpositionofvalvesduringtheexhauststroke.

FIG.10.—Firstout-stroke,showingpositionofvalvesduringthechargingstroke.

Fig. 10 shows diagrammatically the position of crank, piston, and valves during the chargingstroke.

FIG.11.—CrossSectionofCylinder.

In figs. 1 and 2we gave drawings of two gas engines, which are typical examples ofmodernpractice. Huge strides have been made in recent years in gas-engine work, as regards bothworkmanshipandefficiency,sothat to-daywehaveinthegasengineamachinewhosemechanicalefficiencycomparesfavourablywiththatofanyotherpowergenerator,andwhosethermalefficiencyisverymuchgreater.

FIG.12.—LongitudinalSectionofCylinder.

Figs.11and12showrespectivelyasectionalendandsideelevationofthecylinder,fromwhichitwillnotbedifficultforthereader,howeverunacquaintedhemaybewithgas-enginework,toseehowthevariousrequirementsandpeculiaritiesoftheengineshouldbeconsideredandprovidedfor.

Amostimportantdesideratuminanymachineorengineisthatitshallbeassimpleinconstructionas ever possible; complicated mechanism should only be introduced when such addition orcomplication compensates adequately for what must necessarily be a higher first cost, andincidentallythegreaterwearandtearandattentioninvolved.Figs.11and12showwhathasbeendonetosimplifytheconstructionofthegasengineinrecentyears.Themainfeatureinthiscaseistheveryget-at-ablepositionofthetwomainvalves—theairvalveFandtheexhaustE.Thesevalves,asmaybeseenfromthedrawing,arecapableofwithdrawalafterthecoverofthecombustionchamberhasbeenremoved.Thelatterisanironcasting,shapedandfaceduptomakeanabsolutelytightjoint;noasbestosoranypackingisusedtomakethisjoint—andisheldinplacebyfourstuds,asshown.Thus,

allthatisnecessaryistoremovethefournuts,liftthecoveroff,thenpulloutthepinswhichkeepthespiralspringsinposition,andwithdrawthevalves.Thelatterareseateddirectontothemetalofthecylindercasting,thegun-metalbushesAandBactingasguides.FurtherreferencetoA(themixer),whichservesatwofoldpurpose,willbemadelateron.

Thegasvalveandcockaremountedinaseparatecasting,whichiscarriedbyacoupleofstuds,thejointbetweenthisandcylinderbeingmadewithapieceofrubberinsertion.Thegasentersatthegas-cock,passesthroughthevalveandportG,androundtheannularspaceinthebushor"mixer"A,previouslymentioned,andthencethroughanumberofsmallholesinsame,immediatelybelowtheseatoftheairvalveF.Atthesametime,pureairisdrawninviatheairbox(asexplainedhereafter),throughportL(fig.11),andthenceupthecentreofbushAandoverthesmallholesthroughwhichthegasisflowing.Thetwothenthoroughlymixandenterthecombustionchambertogetherastheairvalve F is opened. This device produces a perfectly homogeneousmixture,which conduces in nosmallmeasuretoperfectcombustionwhentheexplosiontakesplace,anduponwhich,toaverygreatextent,dependstheefficiencyoftheengine.Besidespossiblelossinthisdirection,however,thereisanothersourceofwastewhichcannotbeeliminated,and that is theheat takenawayby thecoolingwaterwhichsurroundsthecylinder.Asthislossisinevitable,thebestthingwecandoistomakeitassmall as possible. Theoretically, it would be no small advantage if we could work at very muchhighertemperaturesthanwedoatthepresenttime,anditisonlycertainmechanicaldifficultieswhichbarthewayandsoeffectuallypreventthealreadyhighthermalefficiencyoftheenginebeinggreatlyincreased.

Itisnoeasymattertoovercomethesedifficultiescompletely,butimprovementsinthisdirectionarecontinuallybeingmade,sothattroubleswhichattendedthegas-engineuseryearsagonolongerexist.

Allthatwerequireofthecoolingwateristhatitshallkeepcertainworkingpartsoftheengineatareasonabletemperature;forinstance,thecylindermustnotbesohotastodeprivethelubricatingoilofitspropertytolubricate,neithermusttheexhaustvalvebecomesohotastocauseittoseizeinthebush and stick up; but, beyond such considerations as these, the higher the temperature is at thecommencementofeachexplosionthemoreefficientwilltheenginebe.Theobject,then,istodoaslittle coolingaspossible, and to apply thecoolingeffect at the rightparts; hence thepassages andchambersthroughwhichthecoolingwatercirculatesshouldbesoarrangedthatthosewhichrequiretobekeptatalowtemperatureareincloseproximitytothecoolingwater.Onsomeoftheenginesofdaysgoneby, theexhaustvalvewascarried ina large ironcasting, this in turnbeingbolted to thecylinder casting and communicating with the combustion chamber by means of a port. Such anarrangement was found to be not only clumsy but inefficient; the water passages were small anddifficulttogetat;theyreadilyfurredup;andmoreover,thejointbetweenthiscastingandthecylinderwasnecessarilyawaterandexplosionjoint,andthefewerwehaveofthesethebetter.

The method—if it may be called a method—of overcoming or preventing the exhaust valvebecomingtoohotis,inthecaseoffigs.11and12,simplyoneofjudiciousarrangementanddesign.ThecoolingwaterentersbytheinletK(fig.11),andcirculatesroundtheexhaustvalveportXand

valveE immediately, beforebecomingheated, thuskeeping thehottest of theworkingparts of theengineatasuitabletemperature;andthevalveseat,beingindirectmetalliccommunicationwiththecoldwater,doesnotbecomeburntorpitted.Ontheothersideof theexhaustvalvewehave theairvalveanditspassages,throughwhichcoolairiscontinuallybeingdrawn;thisalsohelpstokeeptheexhaustvalvecool.

From this, then,wemayconclude that overheatingof the cylinderwill notoccurundernormalconditions,givenanengineofgooddesign;but,ifthistroubledoesarise,wemaysafelylookfirstofall for some defect in the cooling water circulation. Some waters contain a greater amount ofimpuritiesthanothers,andconsequentlythewaterspacemayfurrupmorerapidlyinonedistrictthanin another. But this deposit, even under the worst conditions, accumulates very slowly, and theoperationofcleaningoutthewater-jacketisaveryinfrequentnecessity.Theexhaustvalve,however,maybecomeoverheatedif it isallowedtoget intobadcondition, i.e., leaky.Itsseatshouldbewelllooked after, or the hot gaseswill blow pastwhen it is presumably shut; and if this defect, slightthoughitmaybetobeginwith, isallowedtodevelop,boththeseat, thevalvehead,andthespindlewillbecomeburntawayandpitted,perhapsbadly,duetotheexcessiveheat.

CHAPTERIV

IGNITIONDEVICES

Theignitiondevicescommonlyemployedmaybedividedintothreemainclasses—themetaltube,theporcelain tube, and the electric ignition.These againmaybe subdivided:The first being eitherironornickel (hecknumas theyare sometimescalled); thesecondareof twokinds—single-endedand double-ended; and the third takes many forms which many of my readers are possibly wellacquaintedwith,suchasthemagneto,theinductioncoilandtrembler,andthehigh-tensionmagnetoignition, the latter device having been used successfully on various occasions, though not yetuniversallyadopted.

Thefirst-namedhaveoneortwoadvantagesoverthenickeltube.Theyareveryinexpensive,andareeasilyheatedtotherequiredtemperature;moreover,theycanbemadeathome,shouldoccasiondemand.Ontheotherhand,theyarenotsodurable,haveaveryuncertainlife,andconsequentlyneedrenewing frequently—their average life being not more than 60 working hours. Fig. 13 gives anoutline drawing of an iron tube, with its burner and chimney fixed in position. The tube is verysimilartoapieceof1⁄4-in.gas-barrel,closedupatoneendandataperthread(1⁄4-in.gas)cutontheother;infact,gas-barrelmaybeusedformakingthesetubesathome—andmeasureabout7or8in.overallItisscrewedintoafiringblock,whichinturnisscrewedintothecombustionchamberend,sothatwhenrighthomeitisinsuchpositionthatthetubestandsquitevertical.Thesectionofthetube,fig.13,showstheconditionitgetsintoafterhavingbeeninusesometime.Thebore,itwillbeseen,hasbecomealmostcompletelyclosedup,sothatthereispracticallynocommunicationbetweenthehotpartofthetubeandthecombustionchamber.Thisclosingupoftheboreisverygradual,anditisintheearlystagesofthisprocessthaterraticfiringislikelytooccur;sometimesthechargewillbesuccessfully firedandsometimesnot. Itmaybeaswell tomentionhere that the lengthof the tube,althoughtoacertainextentimmaterial,shouldneitherbeexcessivelylongnorabnormallyshort,thepreciselengthvaryingwiththesizeoftheengine.A1⁄4-in.tube,8ins.long,maybeusedsuccessfullyonenginesrangingfrom1⁄2to6horse-power,providedasuitableburnerisfittedenablingthetubetobe heated at any required spot. After the first charge has been fired, and the exhaust takes place,practically all the burnt gases are cleared out of the cylinder, but a small amount of these willgenerally remain in the tube and the bore of the firing block.On the ensuing compression stroketheseinertgasesarecompressedtothefarendofthetube,thusmakingwayfortheexplosivemixturetoreachthehotportion,andexplode,thussendingajetofflameintothemainvolumeofthemixturewhich is immediately ignited.Hence there isnoadvantage inhavinga tube too long,while,on theotherhand,itmustnotbetooshort.

FIG.13.

FIG.14.

FIG.15.

Theasbestoslining,showninfig.13,maybeofvariousthicknesses,accordingtothesizeofthechimneyandthetube;thereasonforthiswillbeapparenttomany;butbeingamostimportantfactor

intheheatingofthetube,andconsequentlytheworkingoftheengine,itwillbeadvisabletodealwiththispointmorefully.

Duemainlytothepeculiarbehaviourofirontubesunderheatandinternalpressure, it isalwaysadvisable to look to them first of allwhen the engine shows signs ofmissing fire; and to alwaysexamine the bore of a fresh one, and ascertain that it is perfectly clear before putting it in. Theadjustmentoftheignitiontube,althoughoneofthemostimportantandnecessarytobemadeonthewholeengine,isinitselfaperfectlysimplematter.Itmustbeunderstoodthattheignitiontubecannot,withtheordinarymeansatourdisposal,bekeptattoohighatemperature;butitmustnotbeassumedthateitherthesizeoftheflame,orthetimetheflamehasbeenalight,isconclusiveevidencethatthetubeis,oroughttobe,sufficientlyhottofirethechargesuccessfully.Itisanuncommonthingtohearamanexclaim—afterithasbeenpointedoutthathistubeispracticallycold—"Why,it'sbeenalightforhours!"

Ifsuchisthecasewithyou,reader,youmayveryrightlyassumethattheburnerisnotproperlyadjusted,andsodoesnotgivetherightkindofflame.

Inorder toget thehottestpossible flame, thequantityofgasandairmustbemixed in the rightproportions. A common fault is that there is too much gas allowed to flow through the nipple,comparedwith theamountofairbeingdrawninat theairaperture, fig.13.Theresult is,wegetaflameofgreatlength,butonewhichisnotatallsuitedtoourrequirements;andinsteadofgivingupitsheattothetubeandtheasbestosliningofthechimney,alargeamountofgaswearepresumablyburninginthechimneyisnotbeingburntthereatall,for,onapplyingalightjustabovethechimneytop,aquantityofthisgaswearewastingwillbeseentoburnwithaflickeringblueflame.

Toputmattersright,itisnecessarytodooneoftwothings—eithercutdownthesupplyofgasorincreasetheair-supply.Providingtheairapertureisnormal,i.e.,thesamesizeasitwasoriginally,itisbettertoadjustthegas,whichmaybedonebytappingupthenippleN,asindicatedintheenlargedsketch,fig.14,untiljusttherightamountofgascanflow.

Asarule,ifthereistoomuchair,theflamewillburnwithaloudroaringnoise,andisliabletofireback.Thenippleshouldthenbeopenedoutwithasmallreamer—thetangofasmallfile,groundtoalongtaperpoint,makesanadmirabletoolforthispurpose.Whethertheburnerisoftheordinarybunsentype,ortheringorstovetype, theaboveremarksapply,asineverycasetheflowofgasisgovernedbythesizeoftheorificethroughwhichitflows.

There isnoneed touseanythingbeyonda touchofoilwhenputting inanew tube, inorder tomake a perfectly tight joint; white or red lead are quite unnecessary, and are liable to make it atroublesomematter to remove the tubeon futureoccasions.Neither shouldundue forcebeappliedwhenputtinginnewtubes;itisliabletowearthethreadinthefiringblock,whichresultsinapartialstoppageof theignitionhole,as indicatedinfig.15.Thisisespeciallythecaseifwehappentogetholdofatubewithitsscrewedpartslightlysmallerthanusual.

Theasbestoswithwhichthechimneyislinedshouldbeabout1⁄8in.thick,and,whenrenewing,the

samethicknessshouldbeusedasoriginally.Athickerboardwillreducetheannularspaceroundthetube,andwillhaveachokingeffectontheflame—muchthesameasreferredtoabove,whenthereistoomuchgasandnotenoughair.Asimplemethodofliningthechimneyistocutablockofwoodtothe inside dimensions of the chimney, less 1⁄4 in. in width and thickness, then soften the asbestoscardboardbyimmersinginwater,andbenditroundthewood,cuttingofftotherequiredsize,i.e.,tillthetwoedgesformaneatbuttjoint.Itcanbeallowedtoremainonthemoulduntildry—whenitwillretainitsshape—orcanbeputintothechimneystraightaway,ifitiswantedforuseimmediately.Inthelattercase,however,itwillbesomefifteenminutesorsobeforethetubewillattainitsworkingtemperature.Asbestosliningsgraduallybecomewornandragged,andsmallflakesareapttodetachthemselvesandfalldowninto theburner,which,ofcourse,prevents theflameplayingas it shouldaroundthetube.Insuchcasesitisnotalwaysnecessarytofitanewlining;ifthechimneyisremoved,the loose flakes shaken out and the asbestoswell damped and patted downwith awoodenor steelfoot-ruleorothersuitablyshapedtool,itwillbefitforanotherlongspellofwork.

The nickel or hecknum tubes are treated in the samemanner as the iron, but, aswementionedbefore,aremoredurable,butrequiremoreheatingtogetthemuptoaworkabletemperature.Theirgreaterfirstcostiscompensatedtosomeextentbymakersinsomecasesguaranteeingthemforsixmonths.

Oftheporcelainignitiondevices,wewilldealwiththedouble-endedtubefirst,itbeingthemorecommonly used of the two in this country. This form of tube is usually about 3 in. long, 1⁄2 in.diameter,andopenatbothends.Itmaybemountedinametalcasting,informnotunlikethesmallgasstovesforheatingsolderingirons.Itisheatedthegreaterpartofitslengthbyacoupleofrowsofgasjets,andisfrequentlysurroundedbyanasbestoslining.Thewholearrangementisinrealityatinyfurnace.Wheninpositionforworking,oneendofthetubeisopentotheignitionpassageleadingandcommunicating with the combustion chamber, while the other end is sealed, through butting upagainstametalcaporplate.Anasbestoswasher is interposedbetween the tubeateachendand themetal it bears against, thusmakingamoreor less flexible joint.A thumbscrew is arrangedat theoutsideendofthetube,bymeansofwhichpressurecanbeappliedtoclampitupbetweenthewasherstothedesiredextent.Somecarehastobeexercisedinadjustingthisformoftubeforrunning.Whenheatedtotheworkingtemperatureit,ofcourse,expands,sothat,iftighteneduptoomuchwhencold,itisunderafairlyhighcompression;andwhentheengineisstarted,andtheexplosiontakesplace,itnotinfrequentlybursts,ifthereisnotsufficient"give"inthewasherstoallowfortheexpansion.Ontheotherhand,ifnotclampedupsufficientlytighttostartwith,whentheexplosionoccurs,thewasheratoneoreachendisblownout.Thisadjustmenthastobemadetoanicety,and,althoughasomewhatdifficultmatter,successmaybeattainedafteroneor twotrials. It isadvisable,afteranewtubehasbeenputin,tostartuptheenginegently,i.e.,withlessthanthenormalsupplyofgas,andincreasetothe full amount gradually whilst running. This may be done by simply opening the gas-cock onenginepartiallyinthefirstplace.

Thesingle-endedporcelaintubeisnotsowellknownhereasonthecontinent;why,wecannotsay;certainlyitispreferableineveryway.Wegiveafewillustrations,showingthemethodofusingthis

FIG.16.

tube.

Figs.16and17showthegeneralarrangementoftubeandchimneyandthemannerinwhichtheyare fixed to thecylinder.Thedeviceconsistsprimarilyof threeparts—thebodyorchimneyB, thecoverC,andthetubeitselfT.Thebodyisalightironcasting,carriedbyacoupleofstudsSS,whichareeitherscrewedintothefiringblockF,ordirectintothemetalofthecylindercastingifnofiring-blockisused;thelattermayverywellbedispensedwithinthesmaller-sizedengines.

Thetubeismadeofthinporcelain,slightlybell-mouthedatitsopenend,andismountedinathickmetal washerW, as shown in fig. 18 in section, the joint beingmadewith a little asbestos paper,moistened.

TheblockFandthefaceofthebodyB(fig.16)arerecessedtotakethewasherWeasily,butthedepthofbothrecessestakentogethermustbeabout1⁄16 in. lessthanthethicknessof thewasherW;thus,whenthetubeisplacedinpositionbetweenthebodyBandtheblockF,andtheformerscrewedupbymeansofthetwonuts,asshowninthefigure16,theeffectistoclampthewasherwhichcarriesthetube,butnottheporcelaintubeitself.

FIG.17.

FIG.18.

Thelatterisleftperfectlyfreetoexpand;andyet,owingtoitsparticularshape,thepressureinthecylinderduringthecompressionandexplosionstrokeonlytendstomakethejointbetweenthetubeandwashermoresecure.TheactionofthisignitiondevicedependsuponthetubeheaterH,whichismerelyasmallbunsenburner,theflameofwhichimpingesonthetubeatoneparticularspot,raisingittoaveryhightemperature—almostwhiteheat.Mostofmyreaderswillknowtheformationofthebunsenflame.Itincomposedoftwodistinctzones.Theinnerone,markedAinfig.18,isaperfectlycoldpartoftheflame,andappearstobeapale-bluecolouredcone.

Itistheouterzonewhichisthehotportionoftheflame,hencethispartonlymustbeallowedtoplayonthetube.ThetipoftheblueconeAmustbekeptabout1⁄4in.belowthetube,inordertoensurethehottestpartoftheflameimpingingpreciselywheretheheatisrequired.

Thetotallengthofthewholeflameis, toacertainextent, immaterial;but,generallyspeaking,itshouldbeadjustedsothatthelengthoftheinnerconeAisabout1in.or1-1⁄4in.Thesamemethodswhichwedescribedintheearlypartofthischaptercanbeemployedintheadjustmentofthisburner,butsomecareshouldbeexercisedtogetthecorrectflamelength.

Theresultofallowingthecoldpartoftheflametoimpingeonthetubeisobservableinfig.18.Theblackspotindicatedonthedrawingactuallyappearsasablackorsootyspotwhenlookingatthetubeundertheseconditions;butinrealitynodiscolorationwhatevertakesplace,thespotdisappearingimmediatelytheconeAismadeshorter,ortheburnerHloweredinthechimneyB,sothatthetipofAisjustbelow,anddoesnottouchthetubeatall.

The adjustment of the length of coneAmaybe accomplished in twoways—(1) bykeeping thesupplyofgasconstant,andvaryingtheamountofairadmittedatapertureK,fig.18;(2)bykeepingthesupplyofairconstant,andvaryingtheamountofgasadmittedthroughnippleN.Thefirstmethodis to be preferred when it is necessary tomake any slight adjustment due to the variation of gaspressureduringtheday,andmaybeaccomplishedbyfittingasmallslidingshieldG,asshowninthefigs.16and17,andmovingitroundsothatitcovers,moreorless,theapertureK.ThusthelengthofconeAmaybeadjustedtoanicetyinaveryfewseconds.Thisshieldkeepsalldraughtsandpuffsofwindfromthefly-wheelawayfromtheaperture,andhelpstheflametoburnverysteadily.Inthefirstplace,ofcourse,theflamewillberegulatedbyopeningoutortappingupthenippleN(anenlargedsketchofwhichisgiveninfig.14),sothatconeAisjustabout1-1⁄4in.longwhenairapertureisfullopen;butoncethisisdone,anyfutureadjustmentcanbemadebythrottlingtheair-supply,orraisingorloweringtheburnerbodily,thesetscrewkeepingitinanydesiredposition(seefig.17).

From the foregoing remarks it will be seen that themost noteworthy features of this form ofignitionaretheeaseandcertaintywithwhichthetubecanbefixedinafewmoments;thatwhenthetwonutsonthestudsSShavebeentightenedupthereisnolikelihoodofthejointsbeing"blown,"for,aswe said before, only themetalwasher is clamped up, the porcelain tube itself being as free toexpandas itwasbefore. It is also at onceobviouswhen any adjustmentof the flame is necessary;thereneedbenouncertaintyastowhetherthetubeishotenoughornot.

CHAPTERV

MAGNETOIGNITION

Thethirdformofignitionwehavetodealwithistheelectric.

Thereareagreatnumberofdifferent typesmadeandused,but forgas-engineuseperhaps thatknown as themagneto ignition is themost satisfactory.With this form, neither accumulators, drybatteries,orsparkcoilsarerequired,andconsequentlyagreatersimplicityisarrivedatthanwouldotherwisebethecase.

Infig.19weshowdiagrammaticallytheordinaryformofmagnetomachine.Virtuallyitisasmalldynamowhich is fixed to the sideof cylinder casting, and is operated in themanner shortly tobedescribed.Aswe do not propose to enter intomore than a brief explanation ofwhy and how thisapparatus generates current to produce the required spark, perhaps a simple analogy will makemattersmostintelligibletoanyreadernotwellacquaintedwithelectricalphenomena.Weknowthatwhenacurrentofelectricityisflowinginawire,andthewirebesuddenlybroken,asparkwilloccuratthepointofbreakage.Thisfactmaybeobservedinanordinaryelectricbellwhenringing;atthetipof thecontactbreakeranumberof tinysparksmaybeseentooccur,duetotherapidmakeandbreak of the current flowing in the circuit. Precisely the same action takes place in ourmagneto-igniter,but,insteadofamultitudeoftinysparks,weproduceoneatatime,atdefiniteintervals,viz.,atthecommencementofeachexplosionstroke.

FIG.19.

Inthelaterformofmagnetomachinesthereisasoftironsleevebetweenthemagnetpolesandthearmature.Theformerisconnectedtoasystemofleversbywhichareciprocatingmotionisimpartedto itbymeansofasuitablyarrangedcamonthesideshaft. Ithasbeenfoundthatbetterresultsareobtainedby causing themagnetic field tomove relative to the armaturewinding than tomove thelatterthroughastationaryfield.Referencetothediagrams,figs.20and21,willmakethisclear.

Infig.19thecamCisshownjustonthepointofallowingtheleverLtoflybackintoitsnormalposition,due to theactionof the springscomprisingadashpotS.As thecamrotates, itpushes thelever L to the left, the sleeve (or virtually the armatureA) is also rotated through a portion of arevolution comparatively slowly; but as soon as L is released, the sleeve (or armature) flies backagainalmostinstantaneouslyandforthemomentisgeneratingacurrentinthesamemanneraswouldanyordinarycontinuouscurrentdynamo.

FIG.20.

FIG.21.

At the instant the maximum current is being generated, the circuit is broken by means of thecontactbreakerD,fig.19,whichweshowindetailinfig.22.Thelatterismountedontheendofthecombustionchamber,andconsistsoftwoparts,DandP.

FIG.22.

D is an easy fit in theholebored to receive it, andhas amushroomvalveheadand seating, asshown,sothatitmovesreadilywhenstruckbytheprojectionEontherodR(fig.19);butyet,actinginthemannerofanon-returnvalve,itallowsnogastoescapewhentheexplosiontakesplaceinthecylinder.Disthereforeindirectmetalliccommunicationwiththeengineframeandearth.

Pisafixedmetalpin,carefullyinsulatedfromallcontactwiththeengineframeandearth.Tothispin one end of the armaturewinding is connected,whilst the other end is connected to the engineframe.

Thusaclosedcircuitisformed,andwhenthecurrentisgenerateditflowsfromoneterminalofmagnetothroughwiretopinP,ontoD,throughDtoearth(i.e.,engineframe),andsobacktootherterminalonmagneto.

Andas thecircuit isbrokenbetweenDandP,weobtainaspark,aspreviouslyexplained,whichmaybetimedtotakeplacebyadjustingthepositionofcamConsideshaftrelativelytothepositionofpiston.

Itmaybesaid that thepositionof themagneto-igniter is immaterial; itwillbefixedindifferent

positions on different types of engines, and so long as the operating mechanism is simple andeffective,i.e.,asdirectasispracticable,itworkswell,andrequireslittleattention.ThetimingofthesparkwillbedealtwithinthechapteronCamsandValveSettings.

CHAPTERVI

GOVERNING

The devices for governing the speed of the enginemay be divided, broadly speaking, into twoclasses—theinertiaorhitandmissgovernor,andthecentrifugal.Ofthelattertypewewillgiveaninstancefirst.Infigs.23and24thegovernorgearisshowndiagrammatically,consistingofacoupleofweightsWWsuspended from a vertical spindle.These fly apartwhen caused to revolve by thebevelwheel gearingBB, and raise the sleeveS to a greater or lesser extent.A recess in the latterengages a lever arm L, through which the vertical movement of the sleeve S is converted into ahorizontalmovementofthesleeveT.ThelatteriscarriedbythevalveleverP,andisvirtuallyarollerwhichengageswithoneorotherofthestepsofthecamC,accordingtothespeedoftheengine.Theobjectofthisarrangementistokeeptheratioofairtogasuniformthroughoutallvariationsofload.ThegasandairvalveareshownasbothbeingoperatedbythesameleverP,theaccuratetimingofthelatterbeingobtainedbymeansofsetscrews.

FIG.23.

FIG.24.

MessrsDougill&Co.'senginesare fittedwithastepdowncamandgovernorsuchas this.Thecentrifugalgovernorisoftenarrangedsothatinsteadofthechargebeingmerelyreducedinvolume,thewholechargeiscutout,andnoexplosionwhatevertakesplace.(Inthisrespectthesameresultsareobtainedaswhenahitandmissgovernorisused,andthelatterformthereforeistobepreferred,especiallyonsmallengines,wherethedifferencebetweentheindicatedpowerandthebrakepowerisalways,evenunderthebestconditions,fairlygreat.)

Inthiscasethegovernor leveronlyoperates thegasvalve; theairvalvebeingopenedoneverychargingorsuctionstroke,whethergasisadmittedornot.

Anotherapplicationof thecentrifugalgovernor is tosuspendadistancepieceon theendof thegovernorlever,sothatatnormalspeedthisdistancepieceisinterposedbetweenthegasvalvespindleand the lever operating it. In that case the gas valvewill be opened. But if the speed is above the

normal, the distance piece will be raised clear of the valve spindle, and the opening mechanism(drivenbyacamonthesideshaft)willsimplymoveforwardandrecedeagainwithoutevertouchingthegasvalve.

Thereareanynumberofmovementswhichhavebeen,andtherearemanymorewhichcouldbe,devisedtogivethesameresult;anditdependsprincipallyupontheformofengineinquestionwhichdeviceweadopt.

Thesimplestandmostdirectactionis,however,alwaysthebest;complicatedmechanismistobedeprecated,especiallyonsmallengines.Forthisreasonistheinertiagovernormoregenerallyfittedtosuchengines.

FIG.25.

Asimpleformofthisgovernorisshowninfig.25.ThegasvalveVisshownonitsseating.ItisscrewedintoapeckerblockB,andpinnedasshown.Thelattershouldbeofcaststeel,temperedtoastrawcolour;orifmildsteelorironisused,itmustbewellcase-hardened,inordertoresistwear.ThepeckerP(alsotemperedhard)ismountedonthecast-ironweightW,whichinturnispivotedonthevalveleverL.ItwillbeseenthattheweightW(whichisonlyheldinthepositionshownbythespringS)will tend to lagbehindwhenasuddenupwardmotion is imparted to the leverL.Thus itdependsuponthedegreeofsuddennesswithwhichLmoveswhetherthepeckerPremainsinthesamerelativeposition to the lever as the latter travelsupwardsandengageswith thepeckerblockB,orwhether itmisses itandsimplyslidesover the faceof theblock.Theadjustmentof thespringS iseffectedbyscrewinguporslackingoutthemillednutsT;andonthedegreetowhichthisspringiscompresseddependsthesensitivenessofthegovernor,andconsequentlythespeedoftheengine.Toobtain accurate and steadygoverningwith this typeofmechanism it is essential that theweight beperfectlyfreeonitsspindle,andthatnothingbutthespringSholds,ortendstohold,itinthepositionshown.Onthisaccount it isadvisabletoprovidea"lip"onthepeckerblock,asshown,tokeeptheareaofcontactassmallaspossible.Thiseffectuallypreventsanysticking,shouldasuperfluityofoilhappentogetoneitherblockorpecker.ForsimilarreasonsthereshouldbesomeclearancebetweenAandthepecker,i.e.,thelattershouldonlybearatonepointandnotbedflatagainstA.

Anotherformofinertiagovernorisshowninfig.26ofthehitandmisstype,whichisemployedbyMessrsCapel&Co.onmanyoftheirengines.

Itconsistsofthreemainparts—thebrassarmLcarriedonastudD,onwhichitisfreetomove;theweightW,whichcarriesthepeckerPpivotedattheupperendofL;andthepeckerblockB,whichengagesthepeckerwhentheenginerequiresachargeofgas.

ThegoverningactionisdependentupontheshapeoftheoperatingcamfromXtoY.(Inthecasealready dealt with, the lever L serves to operate both air and gas valves, and so one cam only isnecessary; but in this instance thegasvalve is operatedby a separate cam, and agreater nicetyofadjustmentisobtainable.)

If thespeedof theengine is sufficientlyhigh, thearmL is thrust forwardat sucha rate that theweightWtends to lagbehind,with theresult thatP israisedabovethenotchinB,asshownbythedotted lines indrawing.On theotherhand,when thespeed is too low, thearmLwillnotbe thrustforwardwithsogreatadegreeofsuddenness,theweightWwillhavetimetomovewithL,andtherelative position ofW and P to L will remain the same. Hence, in the first case, when a furtherforwardmovement isgiven toLby thecam, thepeckerP isclearofB,andomits toopen thegasvalveV; in the second case, P engageswithB, and the gas valve is held open during the time theportionofcamYtoZispassingovertherollerRonarmL.

Thegreatdrawbacktosomeformsofgovernorsisnotthattheyfailtogovernwellwhennew,butthatnoprovisionismadetoensurethemworkingsteadilywhenabitworn.Theshapeofthecamhaseverythingtodowiththeregularworkingofthisformofgovernor.

Supposing our cam was of the shape

FIG.26.

shown in fig. 27, i.e., the governing andopening portion all in one curve, it wouldcause thepecker tomoveboth forward andinanupward direction at the same time, sothat at themoment of engagingB, Pmightstill be moving in an upward direction,which would cause uncertainty of action,especially if the tips of the engagingmembers were at all blunt through wear;and, in all probability, P would fly off Bafterpartiallyopeningthegasvalve.

This behaviour is very undesirable, asthesmallquantityofgassoadmitted to thecylinderisquiteuseless,andasheerwasteisincurred. With the governing arrangementshowninfig.26, this troubledoesnotexist.Thecamissodesignedthat thefirst risefromXtoAdetermineswhetherornotthevalveistobeopened;thecurvefromAtoYisstruckfromthecentreofthesideshaft;thus,duringthatportionoftherevolutionthearmLisstationary,andthepeckeratthesameinstant takesupadefinitepositioneither in thenotch inBoron topof it,and is readytoopenthevalveifthespeedoftheengineissuchastorequireanexplosion,orsimplytoslideoverthetop of B, allowing the valve to remain closed. It is most interesting to observe the action of thisgovernor;whenanenginefittedwithoneisrunningveryslowly,thethreedistinctmovementsofthepeckerPmaybeclearlydiscernedastherespectiveportionsofthecampassoverthesmallrollerR.

FIG.27.

FIG.28.

CHAPTERVII

CAMSANDVALVESETTINGS

Withthegas,aswithanyotherkindofengine,thevalvesettingsareofprimaryimportance.Onverysmallenginesitisoftenthecasethatonlytheexhaustvalveisoperatedmechanically.

Again,thereareseveralwell-knownmakeswhichoperatethegasandexhaustmechanicallywhiletheairvalveisopenedbysuctionalone.Thoughopinionsdifferastowhichisthebestcoursetotake,there can be little doubt that, with all three valves mechanically operated, a greater nicety ofadjustmentisobtainablethanwouldbeotherwisepossible.Andprovidedtheworkingpartsareneatlymadeandfinished,theywilltakebutlittlepowertodrivethem;andsuchlosswouldbecompensatedby the additional power and efficiency obtained from the engine, due to satisfactory and correctadjustment.

In fig. 28 we give a diagram showing the exact positions of the crank when the gas, air, andexhaust valves open and close respectively, under normal conditions ofworking. The solid circlerepresents the first revolution of the crank shaft, starting from the commencement of the suctionstroke,and thedottedcircle thesecond revolution,duringwhich theexplosionandexhaust strokestakeplace;thedottedhorizontallineshowsthepositionofcrankatthebackandfrontdeadcentres.

Asaclearconceptionofwhycertainthingshappenundercertainconditionsismostdesirable,wewill firstdescribe theoperationofmarkingoff thecamswhichoperate therespectivevalvelevers,andthendiscusstheeffectofvarious"settings"ofthevalvesontherunningoftheengine.

Assuming that we are still dealing with theOtto cycle engine, the cam or side shaft willrevolveatpreciselyhalf thespeedofthecrankshaft.This2 to1motion isobtainedbymeansof toothed wheels, or a screw gear. In theformer case, where plain or bevel cog-wheelsareemployed, theone fixedon thecrankshaftmustbeexactlyhalfthediameteroftheoneonthe side shaft, i.e., it must have one half thenumberof teeth.On theotherhand, if a screwgear is used, the relative diameters of the twowheelsmayvary,butthepitchoftheteethontheone must be twice that of the other. Thesewheels sometimes have the teeth or thread

formedinthecasting,andsometimestheyarecutafteraplaincastinghasbeenmade.Thelatterkindare,needlesstosay,betterthantheformer,whichoftenrequirefilingupinordertomakeeverytoothalike,andensuresweetrunning.

Weknowalready inwhat positionsour crankhas to be at theopening and closingof the threevalves,andwiththeaidofthediagram,fig.28,wecandeterminethesizeofthecams.Infig.29,Sisthe side shaft to which the cams have to be keyed, R the roller on valve lever, the latter beingrepresentedbythecentrelinesLL,asallwerequiretofindisthemotionthisleverwilltransmittothevalve,thespindleofwhichisshownatV.

Fig.30showsdiagrammaticallythepositionofcrankattheopeningandclosingoftheairvalve.Fromthisweseethattheanglethroughwhichthecranktravelsduringthetimetheairvalveisopenisequal to the obtuse angleABC.Now, as the side shaft S revolves at half the speed of crank, it isobviousthattheformerwilltravelthroughonlyhalfthatangleinthesamespaceoftime,i.e.,throughanangleequal toABD.WecannowtransferthisangleontoS,fig.29,anddrawtwolinesSE,SF,cuttinga circleGHJ, representing thebackof the cam,which latterpasses in frontof the rollerRwithoutcausinganymovementoftheleverL.

FIG.29.

FIG.30.

FIG.31.

ItwillbeseenthatbydrawingalineformingatangenttothecircleGHJatFandanotheratE,andproducing these, theywillmeet at pointK. Consequently, as the side shaft rotates in the directionindicated,theleverLwillbegintoopenthevalveVwhenthecamisinthepositionshowninfig.29,reachamaximumopeningatK,and finallyclosewhen thecamhasmovedso thatpointE isnowwhereFwas.With a camof this shape, however, a considerable portionof the strokewouldhavepassedbeforethevalvewasraisedanyappreciabledistanceoffitsseat;itwouldonlybefullyopenforaninstant,viz.,whenKwaspassingoverR,andwouldbegintocloseagaindirectly.

Moreover,iftheenginewererunningatevenaslowspeed,themotionimpartedtoleverLwouldbeindefinite;andthis,especiallyifthegovernorisfittedtotheairvalvelever,asinfig.25,isveryundesirable.Therefore,toobtainadefiniteopeningwemustsetoutthecam,asshowninfig.31.Inthisdiagramtherollerisshownstandingclearofthebackofcambyabout1⁄16in.AlineMNisthendrawn,formingatangenttobothrollerRandcircleGHJatpointsFandOrespectively.Thisgivesustheopeningportionofcam.ThenfromthecentreSwithradiusSFdescribethearcFE(showndottedinfig.31),andsetoff theanglerequired(ABD,fig.30),aspreviouslyexplained.ThroughpointEdrawalineformingatangenttocircleGHJ,andproduceittowardsP.Thislinegivesustheclosingportionof cam.ThedistanceW is of coursevariable, according to the amountof liftwegive thevalve.Bycomparingthesetwodiagramsitwillbeseenthatinbothcasesthevalvewillbeopenedthesame length of time, but in first case the motion will be indefinite and uncertain. In practice thecornersareroundedoffsomewhat,inordertoobtainasteadymotion;andwhentheaircamisalsothe governing cam, it is advisable to round off the opening face, as indicated in fig. 32.Upon theshape of this face both the sensitiveness and the life of the governor gear depends. If it is nicelyroundedoff, giving agradual rise, very little tension (or compression, as the casemaybe) of thecontrolling spring will be necessary to give the required speed to engine; whereas, if the rise issudden,thespringwillhavetobescreweduptighter,and,ifunevenandlumpy(i.e.,notafaircurve),theresultwill,ofcourse,beerraticgoverning.

FIG.32.

Acertainamountofclearanceshouldalwaysbeprovidedbetweentherollerandthebackofcam(compare figs. 29 and 31), that is, the roller should not bear against the cam, except during that

FIG.33.

portionof thestrokeinwhichit isactuallyoperatingthevalve,viz., fromFtoE(fig.31).Asmallstop interposed between the lever and some convenient part of the engine, such as the side-shaftbracketbearing,answersthispurpose.

FIG.34.

Thesizeandshapeoftheexhaustcamisfoundinthesamemannerasabovedescribed;theanglethroughwhichitoperatesisgreaterthanthatoftheaircam,andisshowninfig.33.Afairmarginshould be allowed for filing ormachining these castings up; the shape and sizes arrived at by theabovedescribedmethodbeing finishedmeasurements. Fig. 34gives the outline of an exhaust camworkedoutfromthesettingdiagram,fig.33.

FIG.35.

FIG.37.

FIG.41.

FIG.42.

Wemaynowconsidertherelativepositionsthesetwocamswilloccupywhenkeyeduponthesideshaft.Assumingthatwehavebothcamsfinishedtothepropershapeandsize,andthekeywaycutinthesideshaft,wecancommencetomarkoffthepositionofkeywayintheaircam.Withthecrankinthepositionshowninfig.35,theaircamisslippedontothesideshaftandbrought to thepositionshowninfig.32.Thekeywaybeingalreadycutinthesideshaft,thepositionforthatinthecammaybescribedoff,asshownbydottedlines(fig.32),thecamremoved,andthekeywaycut.Itisaswell,however,tocheckthismarkbyturningthecrankroundtopositionshowninfig.37,i.e.,theclosingofairvalve.Thesideshaftwillalsoturnthroughexactlyhalfthisangle,sothatwhenthecamisagainslippedonthelatter,thescribermarksandkeywayinshaftshouldbeexactlyinline,astheywereinfig. 32, and the fall of the cam—the closing portion—should just be touching roller R, but notsufficienttokeepthevalveopen(seefig.38).TheslightestmovementofthecrankfromthispointinaforwarddirectionshouldresultinalittleplaybeingfeltintheleverL,assumingthatthecamisalsomovedjustenoughtokeepthescribermarksinlinewiththeexistingkeyway.

FIG.36.

FIG.38.

FIG.39.

Bytheseoperationsitwillbeatonceevidentwhetherthecamistoolargeortoosmall.Supposingitistoosmall,wewillobtaintwosetsofmarksindicatingthepositionofkeyway,asshowninfig.39,anditisobviousthatwemustgivetheleverlessplaybyscrewingupthesetscrewsshowninfig.11.Theeffectofthisistocausethevalvetoopenearlierandcloselaterthanitwouldiftheplayweregreater; as it would were the operating portion of cam larger. A minimum amount of play mustalwaysbeallowed,however.Whentwosetsofmarksareobtained, themeanmustbe takenandthekeywaycutasshownbythethicklinesinfig.39.Theexhaustcaminlargerenginesisusuallymadewithaswellingontheopeningportion,asshowninfig.40,sothatthevalveisveryslightlyopenedsometimebeforethecrankhasreachedthepositionshowninfig.41.Fig.42showspositionofcrankatthecloseofexhaustvalve,andthetwolast-mentioneddiagramscorrespondwiththetwopositionsinwhichtheexhaustcamisshowninfig.34.Thesmalllumponthebackofexhaustcam,fig.40,isonlyrequiredonenginesabove3B.H.P.torelievethecompressiononthecompressionstrokewhenstartingup.BymovingtherollerRonvalveleverlongitudinally,sothatitengagesbothpartsofcamastheypassinfrontofit,theexhaustvalveisheldopenduringasmallportionofthecompressionstroke,usuallyclosingwhenthecrankhasreachedthebottomcentre.

Referringagaintofig.26,thisgasorgovernorcammaybesetout,andthekeywaymarkedonthesameprinciple as alreadydescribed for the air and exhaust valves.An endviewof the three camskeyeduponthesideshaftisgiveninfig.40A.Insmallenginesit isconvenienttohavetheairandexhaustcamsmadeinonecasting,whenonekeyonlywillberequired.Onsomeengines,insteadofemploying a movable roller or valve lever, the exhaust cam is fitted on side shaft with a"feather"—i.e., a headless key—and the cam being capable of longitudinal movement, suchmovementbeingcontrolledbyasmallleverorhandle,calledthehalf-compressionlever.

FIG.40

FIG.40A

Having once thoroughly grasped theimportantpartthecamsplayintheworkingof the engine, it will be an easy matter toadjust the valve settings, and to keep themadjusted correctly. The effect of a wrongsettingwillthenbestrikinglyapparent.Onsmallenginesaseparatecamtooperatethegasvalveisnotanecessity;andthepracticeoffittingthegasvalvespindle(orthepecker,theeffectwouldbethesame)withadeviceforincreasingordiminishingitslength,isalsounnecessaryandunsound.

Thewearonawell-designedgasvalveoperatingmechanismispracticallynil;andeveniftherewaswear,theeffectwouldbetocausethevalvetoopenatriflelaterandclosesoonerthanitwouldotherwise,i.e.,itwouldremainopenashortertimeduringeachchargingstroke.Thisinturn(otherconditionsremainingthesame)wouldgiveusaweakermixture;andalthoughtooweakamixtureispreferabletoatoorichone,weshouldhavetoadoptsomemeansofincreasingtherichnessofthemixture;otherwisethemaximumpoweroftheenginewouldsoonbeseentodiminish.

Toget themixturenormalagainwemusteitherenlargethegasinletorcutdowntheair-supplysomewhat,andsokeeptheproportionsthesame.Thatistosay,thequalityofthemixtureisdependentupontherelativedimensionofthegasandairinlets.Weknowbyactualtrialthatifatthecompletionof the charging stroke the pressure in the cylinder is approximately that of the atmosphere, betterresultsareobtained thanwhen thepressure isconsiderablybelowthatof theatmosphere.Thus, thelargerwemaketheinletports(butstillretainingcorrectrelativedimensions)themorereadilywillthemixturebedrawnintothecylinderasthepistonmovesforward,tendingtocreateavacuum.Ofthetwocoursesopentoustoretainagoodmixtureitispreferabletoopenoutthegas-supply,forbycutting down the air-supply, and sucking the gas in, due to the partial vacuum being formed, weshould be keeping the proportions correct at the expense of reducing the total volume of theexplosivemixture(morestrictlyspeaking,thedensityofthecharge)admittedtothecylinder.

Under normal conditions it is not necessary to create a high vacuum to suck the gas into thecylinder,butitisaswelltounderstandwhatresultswewouldtendtoproduce,didweworkonthese

lines.Ofcourse,withsmallhigh-speedenginesfittedwithsuctionairvalve,thevacuumishigherthanitwouldbeinslow-speedengineswithmechanicallyoperatedvalves.Ifwetakeanextremecaseasanexample,where,togetanygastospeakofintothecylindertheair-supplywouldhavetobecutdownorthrottledtoanabnormalextent,wewillrealiseatoncethatsuchasmallquantityofbothairandgas would have been drawn in, and consequently the mixture would be so rarefied that on thecompressionstrokethepressurewouldpossiblybeextremelylowandtotallyinadequatetoproduceefficient working. Moreover, working at such a high vacuum as this would not only prevent usobtaininganormalexplosioninthecylinder,butwouldupsettheworkingoftheexhaustvalve.Thelatterbeinghelddownonitsseatduringthesuctionstrokebymeansofaspiralspringwouldbeliftedoffitsseatbysuction(thepartialvacuuminthecylinder),andanyburntgaseswhichhappenedtobehangingaboutintheexhaustportorpipewouldbedrawnintothecylinderagain,andtendtodamptheensuingexplosion.Tooearlyclosingof theexhaustshouldbeavoidedalmostas rigorouslyastoolate.Thelatterwillaffecttheworkinginasimilarwaytotheexhaustbeingliftedonthechargingstrokebysuction;ontheotherhand,ifitclosestoosoon,theentirevolumeofburntgaseswillnothavebeensweptoutofthecylinder,andtheeffectwillagainbetodampthefollowingexplosion.

Thegasvalveopensjustafterthecrankisabovethebackcentreandclosesjustbeforethefrontcentreisreached,thatis,openingalittleaftertheairvalveandclosingashadebeforeit,thuseveryparticleofgasisusedinthecylinder,duetoadraughtofairbeingdrawninafterthegasvalvehasbeenclosed.

Thesettingsofthevalvebeingofprimaryimportance,nomatterwhatsizeenginewearedealingwith,andbeingalsothemostconfusingmatterforanyoneunacquaintedwithgasenginestograsp,itwillnotbeoutofplacetosuggestasimplemethodofcheckingthesesettings.

Let us begin by pulling the fly-wheel round backwards until we feel the piston is on thecompressionstroke,thenfromthispoint—thecrankbeingabout45°abovethefrontcentre—pullthewheel rounduntil thecrank is in theposition for theexhaustopening (see fig.28). In thispositionthereshouldbebuttheslightestplayin theexhaust lever,showingthat thevalveis justonpointofopening;andbykeepingone'shandontheleverwhilstthefly-wheelispulledroundveryslowly(itisagoodplantogetsomeoneelsetodothepullinground),itispossibletoascertaintheprecisepointatwhichthevalveopens.Nextpullroundtillthecrankisinthepositionfortheairvalveopening,andobservethatitissetcorrectly.Thengoontoatrifleabovethebackcentre,wheretheexhaustvalveshouldclose,andsoontilltheopeningandclosingofeachvalvehasbeenchecked.Itwillbenoticedthattheair,andsometimesthegas,valveopensbeforetheexhaustcloses.Thisoverlapisnecessary;anditwillbefoundthatthesmallertheengineandthehigherthespeedthegreaterthisoverlapwillbetoobtaingoodresults,althoughagooddealofindividualjudgmentmustbeusedinsettlingtheexactamountofoverlap,as therequisiteamountmay, toget thebestresults,varyindifferentenginesofpreciselythesamedimensionsandtype.

Whendealingwithengineswhichhavenoseparategasvalve—thegasbeingadmittedwiththeair,which is sometimes the casewithvery small engines—the abovenotes referring to thegas settingindependently,will,ofcourse,notholdgood.

Itmaybementionedwithregardto the lumpontheopeningsideof theexhaustcam, that this ifoverdoneisfoundtobedetrimentalonlargeengines,andevenonsmallones.Ifitistoolarge,itwillcausebothexhaustvalveandseattobecomeburntandpitted,duetothesurfacebeingexposedtotheexceedinglyhightemperatureoftheexpandinggases.Ifitistoolarge,itisequivalenttoopeningtheexhaustvalvetooearly,andtheeffectisthesame,viz.,awasteofpoweranddamagetothevalveanditsseat.

FIG.43.

FIG.44.—BrakeTesting.

Themethodofgrindinginthevalvestotheirseatswithemerypowderandoilissowellknownthat no further description is needed here.We give, however, in fig. 43 a sketch showing a veryexpeditiouswayofdealingwithverybadlywornorburntseats.Thesketchexplainsitself.Suchatoolisreadilymade;eventhecuttercouldbeturnedandfileduptoshapeandthenhardenedathome.Bylightlytappinginthetapercotterpinlittlebylittle,sufficientpressureisputonthecuttertomakeitaneasymattertocompletelyre-faceanoldseatorformanewone.AT-wrenchor"tommy"canbeusedtoworkthecutterspindle.Thelowerpartofthelattermustbethesamediameterastheexistingvalvespindle;thebushactsasaguide;andasthebevelofthecuttershouldbethesameasthatofthevalve,averylittlegrindinginwithemerypowderisrequiredtofinishthejoboff.

In fig. 44 we give a diagram showing themethod of testing for Brake H.P. of engine, as it isfrequentlyinterestingtomakesuchasimpletestafteranyalterationsoradjustmentshavebeenmade.

Twospringbalancesanda ropeor cord (according to the sizeof theengine), fittedwitha fewwood blocks as shown in section, fig. 44, to keep the rope on the rim of fly-wheel, is all that isrequiredforthistest.ThefollowingformulamaybeusedforarrivingattheB.H.P.:—

B.H.P.=(S1−S2)3·14×DxR/33000

S1=Readinginlbs.ofspringbalanceNo.1.

S2=Readinginlbs.ofspringbalanceNo.2.

D=Diameteroffly-wheelanddiameterofbrakeropeinfeet.

R=Revolutionsoffly-wheelperminute.

As3·14×D/33000willalwaysremainthesameforanygivenengineandgear,wemaycallthatexpressionC;thentheB.H.P.maybewritten—

B.H.P.=(S1−S2)CR.

CHAPTERVIII

OILENGINES

Thesmalloilengineispracticallythesameasthegasengine,withtheadditionofavaporiserforconvertingtheoil intogas,orvapour, tobeexplodedinthecylinder;consequentlytheonemaybeconvertedintotheotherinmanycaseswithoutmuchtrouble.Thedifficultyofproducinganefficientoil engine liesprincipally indevisinga satisfactoryand reliablevapouriser—onewhichwillworkequallywellunderallloads.Theheatsuppliedtothechambermustbesufficienttovaporisetheoil,but not great enough todecompose it.There arevariousmethodsofvaporising theoil, andmanytypesofvaporisersareemployedtoattainthesameend.Therearesomeinwhichachargeofoilisdrawnbysuctionintoahotchamberinwhichitisconvertedintovapourandatthesametimemixedwithasmallquantityofhotair;thisrichmixtureisthenpassedintothecombustionchamberoftheengine,inthesamemannerascoal-gaswouldbe,whereitisfurtherdilutedwithmoreairdrawninthroughtheairvalve.Otherarrangementscauseajetofoiltobeinjectedintoachambercontaininghotair,intheformofspray,whichimmediatelyconvertstheoilintovapour,andisthenpassedintothecylinder,compressed,andfired.Then,again,wecanpumpoilthroughasprayingnippleintothevapouriser(whichiskeptatasuitabletemperature)whilstthecylinderisbeingfilledwithaironthesuction stroke. On the following compression stroke the air is driven into the vapouriser, whichcommunicateswith the cylinder through a narrow neck, andmixes intimatelywith the oil vapour.Gradually,asthepressurerises,duetocompression,thechargebecomesmoreandmoreexplosive,untilatthecompletionofthisstrokeithasattainedtheproperproportionsofairandoilvapour,andisfiredbythetemperatureofthevapouriserandthatcausedbyahighcompression;thatis,thechargeis fired automatically; and once the engine is running, no heating lamp is required to keep thevapouriseratthecorrecttemperature.Itisnecessary,however,toraiseittotheworkabletemperatureatstarting.ThisisknownastheHornsby-Akroydmethod.

Capel'sarrangementisalsosimpleandefficient,andhastheadditionaladvantageofbeingcapableof being fitted to their existinggas engines, the conversionbeingmade in a very short time.ThisvapouriserconsistsprimarilyofatubularcastingA,ontheoutsideofwhichareformedaseriesofvertical ribs, shown inplan, fig.46, running towithina shortdistanceof the flangeatoneend, asshowninthesection,fig.45,thusprovidinganannularspaceCbetweentheupperendsoftheribsandtheflange.ThiscastingisenclosedbyanoutercasingB,whichfitswellover the inner tube. Ithasalsoanumberofsmallholesdrillednearthelowerendcommunicatingwiththechannelsbetweentheribs.Thus itwillbeseen thatwhen thegasvalve isopenedandsuction takesplace,air isdrawninthroughtheseholes,passesupintotheannularspaceCbelowthetopflange,fromtheretravelstotheopposite side of vapouriser, andmixeswith the oilwhich is also being drawn in through a smallnipperatN,fig.45.Boththenpassbetweenaseriesofpegs,wheretheybecomethoroughlymixed,andfinallypassontotheinletvalveV,fig.47,andsointothecylinder,wherethecompletechargeismixedupandcompressedand fired in theusualmanner. Iron ignition tubesmaybeused, andoneheatinglampservesadoublepurposeinkeepingthetubeandvapouriserhotatthesametime.This

FIG.46.

FIG.45.

lampisfedbymeansofapumpactuatedfromthesideshaft.Theplungerofthepumpisloadedwithaspiralspring,whichmaybeadjustedtogiveanydesiredpressure,andiskeptconstantandsteadybymeansofanairvessel.Thispumpisshowninfig.48.Itisactuatedbymeansofarodandleverfromthesideshaftofengine.TheplungerPworksinabarrelB,whichiscarriedbyasmallreservoirR,thelatterbeingincommunicationwiththemainoiltankbymeansofthepipeH.

FIG.47.

FIG.48.

FIG.49.

FIG.50.

FIG.51.

Theplunger is loadedwithaspiralspring,andhasaballvalve,asshown.Intermediatebetweenthissmallreservoirandthemainoiltankisanothersetofvalves,showninfig.49.Itwillbeseenthatthesuctionofthepumpwilldrawtheoilup,thesmallandlowerballvalve,ofcourse,allowingittopassfreely.Onthedownstrokethelowervalvewillbeautomaticallyclosed,andtheoilwillbeputunderpressure,thisbeingdeterminedbytheloadontheplungervalve,whichisadjustablebymeansofthescrewS,fig.48.WhentherequiredpressureinthepipeP,figs.45and49,hasbeenattained,theplunger valve lifts on each stroke and the surplus oil flows through the plunger into the smallreservoirR.ThelatterisataboutthesamelevelasanotherstillsmallerreservoirM(showninfigs.47and50),aflowofoilbeingestablishedbetweenthetwobymeansofapipeQ(seefigs.48and50).InthereservoirRisfittedanoverflowpipe,sothattheoilcannotrisebeyondacertainlevel;hencethe headof oil in the smaller oneM is always constant.On the suction stroke a partial vacuum isformedintheenginecylinder,consequentlythepressureinthevapouriserdropssomewhatbelowthatoftheatmosphere,andthissmalldifferenceinpressureisenoughtocausetheoiltoriseinthesmallpassageX,fig.45,beyonditsnormallevel,andoverflowintothevapourisingchamber,aspreviouslydescribed.ThevalveornipperNisshownopeninthediagram,fig.45,andallthatisrequiredtostoptheenginewhenrunningistodropthesmallhandleL,fig.45,whenthevalvewillclose,duetothespringS.Theairvesselshowninfig.49isincommunicationwiththepipeleadingtotheblowlamp.Apressuregaugecanalsobefitted,althoughitisnotinanywayanecessity.

Theratchetwheelandpawlshowninfig.48arepartofthelubricator.Thewheeldrivesabrassorgun-metalplug,producinganintermittentrotarymotion.Theplughasasmallholeinitsperiphery,

whichbecomesfilledwithoilwhenitisattheupperpartofitstravel,andemptiestheoiloutintoadischargepipeT,when it is inverted,and is then ledawayandapplied to thepistonat therequiredspot.Fig.51showsthisarrangementinsection.

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