Modern Engines and Power Generators

Rankin Kennedy

Description

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. IN this Volume the Heat Engine, in which the working fluid is a true gas or air, is described in all its forms.

Sujets

• Sciences et techniques

Informations

• Publié par: Forgotten Books
• Date de parution: 27 novembre 2019
• Nombre de lectures: 0
• EAN13: 9780243664085
• Langue: English
• Poids de l'ouvrage: 18 Mo

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I N this t h e Heat E which the worngine in k ingflor air uid is a true i s described i n all its forms The simple hot air engine described in its only useful types for small powers I t has stil l a fi The constant pressureespecially for water raising eld usefulness gradual combustion type of i nternal combustion e gine in the D iesel E ngine come gai n to the front whether it is to be the permanent standard type or not it has scienti fi c interest We have also to note the new water piston engine of Vogt s invention This is a remarkable departure from common practice The gas or internal combustion turbine is of vast interest and briefly referred to many advanced engineers are engaged on the problem but little is known of results obtained I nternal combustion M arine E ngines for small powers are common but no serious attempts have been made to introduce it for mercantile or naval shipping any scale its uses at present being mostly for pleasure sporting purposes in launc h es But the time is ripe for greater things now be made with certainty safety and C And these producers present no diheapness in gas producers ficulties in the thei r appl ication to m arine propulsion by engines The significant fact to enginee rs that less than lb of com mon bituminous slack coal can do the work of lbs of the best Welsh steam coal and a horse power obtained for one twentieth of a penny per hour This opens up a new fi enormous magnitudeeld for the gas engine of L arge gas engines are now common enough on land working with producer gas and furnace gases with satisfactory results The mode of action and general design and oil engines of di erent makes are all very similar the di ference i s only in detail s out of all the classes in use it should be possible at this date to eliminate a number of them and come to some standard designs embodying the good points of al l of them The larger engines are more likely to arrivefirst at a standard type the market for large powers is rapidly growing branch of manufacturing engineering business o ers a more brilliant future than that of the internal combustion prime mover not even electrical engineering The internal combustion engine is a prime mover electrical engines are only power transmitters replacing belts pull eys and shafting The growth of the internal combustion engine and the gas producer providing at a very cheap rate has been very sl ow but very sure And at this moment no steam plant of any design or make produce horse power hour at the same low cost as the gas producer and engine And the di erence will be greater still in favour of gas whe n the turbine is perfected This part of the work is t herefore of g r eat interest to all engineers and those concerned about the fuel supply of the future

Pr e a c e The questions regarding stroke or stroke engines compared with each other have yet to be settled also the question between the gradual introduction and of the fuel at very high compression or the compression to moderate extent and subsequent explosion has also to be settled The Author inclines to the idea that gradual combustion of fuel with moderate compression of pure air and a stroke cycle will prevail for oil engines of large powers This subject will be still further considered i n next Volume M any thanks are due to the variousfirms for i nformation and illustrations of their engines readily and willingly given regarding their specialities Next Volume wil l deal with Pri me M overs on Wheels Portable Traction Road and Rail L ocomotives and M otor Cars with Coal Petrol Oil as fuel and S team Gas and E working mediumlectricity the AN KI N K E N N E D Y R

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C H A P T E I I I R S T OK E E N GI NE S S T OK E E N NE S G ENE A T O S I NTE N A C O B S T O N W A TE P S T O N A N D E N G NE S A N D E N GI NE S MA I NE I NTE N A C O B S T O N E N GI NE S LA G E MA I NE E N GI NE E S IG N MA I NE P O D E S I G N T O N E N G NE S I NTE N A C O B S T I O N E N GI NE S T A TE S V A IO S T Y PE S E N G NE S

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B AK E H O S E P OW E CY I N D E F E N GI NE B AK E H O S E P OW E D O B E CY I N D E D I E S E E N I NE B AK E H O S E P OW E S N G E CY I N D E CY C E K T I N E N GI NE M O D E N B A S T F N A C E E N GI NE WO KI N B OWI N G CY I N D E B A S T S PP Y R I C H A D S O N W E S T GA TH M I DD E S B O G H B AK E H O S E P O WE W E S T I N G H O S E E N G NE H O S E P OW E S T O K P O T E N GI NE WI TH F A T F A E A N D O T S I D E S I D E MA I NE E N GI NE WI TH H E E S H AW R E V E S I N G F T I O N C T C H S H A T A N D P O PE E J T H O NE Y O T LO N D O N H O S E P OW E P E I E E N GI NE P OW E

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N A L O U S T O L U SS U A T N N S E R C R E R E E E E Volume I theflt with in which the heatuid momentum or impulse engines are deal is util ised by the expansion theflproducing a high velocity of theuid freely fluid itself and the momentum of theflthe high velocity is converted into an impulsiveuid at force by impact upon vanes or blades or upon otherflui s I t is equally economical whether momentum or pressure produces power I n pressure engines theflor colduid is admitted n either a hot behind a movable piston i condition I n thefibe steam rst case it may er or hot gases from a boil furnacefrom a Under pressure thefluid presses the piston and moves it a certain distance when the supply offltheuid is and the expansion fluid completes the stroke of the piston at the end of the stroke thefluid is released and escapes I n the second case gas is enclosed i n a cylinder heat is applied to the external surface of the cylinder the gas expands and moves a piston through some distance The then displaced into a cool ing cylinder called a refrigerator it contracts upon cooling the piston returns and the gas is again heated expanded and the piston l ifted again This is a type of engine i n which the fuel combustion prod ucing the heat occurs outside the working cylinder and piston I n another type of engine air and fuel mixed together i n proper proportion for complete combustion are admitted to a cylinder behind a piston and then ignited The combustion produces a sudden rise in pressure which propels the piston I n a modifisuccessfully to work upon a di ferented form the latter type is now made cycl e Ai r is compressed behind a piston to such a pressure that it becomes nearly red hot At the end o f the compression fuel is injected and ignites maintaining the pressure as the piston moves forward and the gases expand The student of thermodynamics has a vast amount of work before him in the science of heat but the engineer after all has been little assisted in perfecting heat engines by the scientific theoretical treatment gases by heatthe expansion of James Watt laid down the conditions for successfully employing expanding gases i n a cylinder to prod uce power and no improvements since made have in any way advanced us beyond the fact that the gas expands and in doing so pushes the piston

M od e rn E ngine s along and becomes itself reduced in temperature by an amount o f heat absorbed i n order to maintai n its increasing volume The relations between heat pressure and volume of gases may be here brie y examined from an elementary point of vie First then let us take a non conducting cylinder and piston as in Fig square foot in area of bore and suppose the piston small in weight hat neglect weight L bottom The pressures onet the piston stand in the cylinder foot from the each side of the piston will be equal to the atmospheric press ure lbs per square i nch or x lbs total Air expand s part of its volume for every degree Centigrade of temperature rise hence i f apply heat to the cylinder until the air belo the piston rises to from the experiment starting from zero evidently its volume will be doubled and the piston raised foot high agains the of atmosp eric pressure Work equal to foot l bs has been done The thermal units required to raise the temperature from to is equal to the weight of air specific heat of air at constant pressure I n this case the heat only i ncreases the vol ume and does not increase the pressure and the temperature remains constant S this principle work on shall see ome engines At and atmospheric pressure cubic foot of air weighs and at constant pressure the specific heat of unitshence thermal air is And these units have been used up as follows Raising the temperature o f the air L highifting the lbs oot Now want to know the value of these two e fects How many units were expe nded upon thefiI f rst and second wefiout we would nd this then know many foot lbs work be done by thermal unit very important result A thermal unit is the quantity of heat required to raise lb of water Fah r in Britain or C in metrical units J oul e determined the mechanical equivalent for both scales by experiment and found it equal to foot lbs in Fah renheit scale and foot lbs i n Centigrade scale To return to our experiment it will be easily seen that i f we begi n agai n with air at and the pistonfiit cannot xed that foot from the bottom of move at the cylinder and apply heat to raise the temperature of the air to as before tha we will have no work done but al l the heat expended on raising the temperature of the ai r only The air is kept at constant volume and its pressure rises Under these conditions the specific heat of the air is much less than it under constant pressure The thermal units expended are equal to This quantity of heat must therefore have been expended wholly in raising t he temperature of the ai r from to C hence in thefirst experiment we got for internal foot lbs external work lift foot external work S foot lbso that one thermal unit produces work equal to AB S O L UT E T E M P E RATU R E I f a gas contracts of its volume for every degree Centigrade through which its temperature is lowered it evident that it would vanish altogether at a temperature of below zero this temperature has been called the absolute zero The diagram Fig illustrates this in Fahrenheit s scale in which the absolute zero is is the temperature scale F freezing point B boil ing point By careful ments we know the ratio of the volume of air at F to the volume at B ere

H e a t E ngines ore it we draw at right angles to two lines BA and F E proportional to the volumes the air at these temperatures and then join and produce it to at a point this point will be equal to equal degrees or division of the line showing the contraction the air to nothing at below F Naturally contraction to nothing is physically impossible As a matter fact the airfirst on reducing its temperature and then freezes solid that may presume it would still be a sol id at absolute zero H owever that may be it is very convenient to reckon gaseous volumes and pressures from absolute zero hat if from F or thermometer zero and zero then Fah r cale and C scale The law of e x spansion of gases by heat i then in a formul e

where C is a constant depending upon the kind gas expanded I S OTH E R M A L A N D AD IABATI C E PA N S I ON P A T To understand these terms may return to simple cylinder and piston experiments and suppose have a cyli nder and piston as shown FIG Di g T tu ee pe i n Fig with a diagram alongside of it The piston is as before square foot i n area and foot from end of the cylinder and there fixed The we now heat the air totemperature of the air to begin with is zero C without allowing the piston to move The pressure wil l rise from per square foot to lbs or lbs per square inch I f release the piston it will be pushed forward and the air will expand falling in pressure as Shown by the curved line in the diagram This the curve of pressures found by drawing verticals fro each of the equal divisions of the stroke and marking them in height corresponding to the pressures P at these points found by formul and joining their upper ends by the curve a constant Con tant Then at the point the pressure on the piston atmospheres and its volume ivisions hence at poin t Constant Then at point P V

Approximate mean pressure