SAE R-104-1990 The Basic Design of Two-Stroke Engines (To Purchase Call 1-800-854-7179 USA Canada or 303-397-7956 Worldwide).pdf

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1、.11* * a a g a g a * *a g a a a, * *g ag g g a g*E a g a s gao a, * g g g a g * a g g a oo a a g a * ag g g - g Dg * *g g o a L; g these remarks will be clearly identified as such. The totality ofthebook isjust as applicable to the design ofthe diesel as it is to the gasoline engine, forthe only rea

2、l difference is themethodology of the combustion process. It is to behoped that the reader derives asmuch usefrom the analytic packages as does the author. The author has always been somewhat lazy ofmind and so has found the accurate repetitive nature ofthe computer solution to be a great saviour of

3、 mental perspiration. At the same time, and since his schooldays, he has been fascinatedwiththetwo-stroke cycleengineand itsdevelopment andimprovement. In those far-off days in the late 1950s, the racing two-stroke motorcycle was a music-hall joke, whereas a two-stroke engined car won the Monte Carl

4、o Rally. Today, there are no two-stroke engined cars and four-stroke engines areno longer competitive in Grand Prix motorcycle racing! Is tomorrow, or the twenty-first century, going to produce yet another volte-face? Theauthorhasalsohadtheinestimableprivilegeofbeingaroundatpreciselythat point inhis

5、torywhen itbecamepossible to unravelthetechnology ofenginedesign from the unscientific black art which had surrounded it since the time ofOtto and Clerk. That unravelling occurred because the digital computer permitted the programming ofthe fundamental unsteady gas-dynamic theory whichhadbeen in exi

6、stence since the time ofRayleigh, Kelvin, Stokes and Taylor. The marriage of these two interests, computers and two-stroke engines, has produced this book and the material within it. For those in this worldwho are of a like mind, this book should prove to be useful. ivAcknowledgements The first ackn

7、owledgement is to thosewho enthusedme duringmy schooldays on the subject of internal combustion engines in general, and motorcycles in particular.They setmeontheroadto athoroughly satisfyingresearchcareerwhich has never seen ahintofboredom.Thetwo individuals were,my fatherwhohaden- thusiasticallyown

8、edmanymotorcycles inhisyouth,andMr.RupertCameron,who hadownedbutoneandhadridden iteverywhere-a 1925 350ccRover.Ofthetwo, RupertCameronwasthegreaterinfluence, forhewasawalkinglibraryoftheGrand Prix races of the twenties and thirties and would talk of engine design, and engineering design, inthemostkn

9、owledgeablemanner.Hewas actually the senior naval architect at Harland andWolffs shipyard in Belfast andwas responsible for the design ofsome ofthe grandest liners ever to sail the oceans. Ihave toacknowledge that thisbookwouldnotbe writtentodaybutforthegood fortune that brought Dr. Frank Wallace (P

10、rofessor at Bath University since 1965) to Belfast in the very year that I wished to do postgraduate research. At that time, FrankWallacewas one ofperhaps adozenpeople in theworldwhocomprehended unsteady gas dynamics, which was the subject area I already knew I had to understand ifIwasevertobeacompe

11、tentenginedesigner.However,FrankWallace taughtmesomething else as wellbyexample, andthat isacademic integrity. Others willjudgehow well I leamed either lesson. ProfessorBernardCrosslanddeserves aspecialmention,forhebecametheHead ofthe Department ofMechanical Engineering atQUB in thesame year I start

12、ed as a doctoral research student. His drive and initiative set the tone for the engineering research which has continued atQUB until the present day. Theword engineering in the previous sentence is underlined because he instilled in me, and a complete generation, that real “know-how“ comes from usi

13、ng the best theoretical science available, at the same time as conducting related experiments ofaproduct design, manufacture, build and test nature. That he became, in latter years, a Fellow ofthe Royal Society, a Fellow of the Fellowship of Engineering and a President of the Institution ofMechanica

14、l Engineers seems no more than justice. I have been very fortunate in my early education to have had teachers of mathematicswho taughtme the subject not only with enthusiasm but,muchmore importantly, from the point ofview of application. I refer particularly to Mr. T. H. Benson atLameGrammarSchoolan

15、dtoMr. Scottduringmyundergraduate studies at The Queens University of Belfast. They gave me a lifelong interest in the application ofmathematics to problem solving which has never faded. The next acknowledgement is to those who conceived and produced the Macintosh computer. Without that machine, on

16、which I have typed this entire manuscript, drawnevery figurewhich is notfromSAE archives, anddeveloped all ofthecomputerprograms, therewouldbenobook. In short,the entirebook,andthe theoretical base for much of it, is there because the Macintosh has such superbly integratedhardwareandsoftwaresothathu

17、geworkloadscanbetackledrapidlyand efficiently. vThe Basic Design ofTwo-Stroke Engines Itwouldberemiss ofmenottothankmany ofthe present generation ofdoctoral research students, andmyfourcolleaguesinvolvedinreciprocatingengineresearch anddevelopment atQUB,Drs.Douglas, Fleck,Goulburn andKenny,whoreadth

18、is book during its formation and offeredmany helpful suggestions on improving the text. To one ofour technicians atQUB, David Holland, a special mention must be made for his expert production ofmany of the photographs which illustrate this book. As the flyleafpoem says, gentlemen, take a bow. Gordon

19、 P. Blair, The Queens University of Belfast, May 1989. viTable of Contents CHAPTER 1 INTRODUCTIONTOTHETWO-STROKE ENGINE 1 1.0 Introduction to the two-stroke cycle engine 1 1.1 The fundamental method of operation of a simple two-stroke engine 6 1.2 Methods ofscavenging the cylinder 9 1.2.1 Loop scave

20、nging 9 1.2.2 Cross scavenging 10 1.2.3 Uniflow scavenging 12 1.2.4 Scavenging without employing the crankcase as an airpump 13 1.3 Valving and porting control of the exhaust, scavenge and inlet processes 17 1.3.1 Poppet valves 18 1.3.2 Disc valves 18 1.3.3 Reed valves 19 1.3.4 Port timing events 20

21、 1.4 Engine and porting geometry 21 1.4.0.1 Units used throughout the book 22 1.4.0.2 Computerprograms presented throughout the book 22 1.4.1 Swept volume 23 1.4.2 Compression ratio 23 1.4.3 Piston position with respect to crankshaft angle 24 1.4.4 Computer program, Prog.1.1, PISTONPOSITION 25 1.4.5

22、 Computer program, Prog.1.2,LOOPENGINEDRAW 25 1.4.6 Computer program, Prog.1.3,QUB CROSS ENGINEDRAW 27 1.5 Definitions ofthermodynamic terms in connection with two-stroke engines 28 1.5.1 Scavenge ratio and delivery ratio 28 1.5.2 Scavenging efficiency and purity 29 1.5.3 Trapping efficiency 30 1.5.

23、4 Charging efficiency 30 1.5.5 Air-to-fuel ratio 31 1.5.6 Cylinder trapping conditions 32 1.5.7 Heat released during the burning process 32 1.5.8 The thermodynamic cycle for the two-stroke engine 32 1.5.9 The concept ofmean effective pressure 34 1.5.10 Power and torque and fuel consumption 36 1.6 La

24、boratory Testing oftwo-stroke engines 37 1.6.1 Laboratory testing for performance characteristics 37 1.6.2 Laboratory testing for exhaust emissions from two-stroke engines 40 1.6.3 Trapping efficiency from exhaust gas analysis 42 *vi VllThe Basic Design ofTwo-Stroke Engines 1.7 Potential power outpu

25、t oftwo-stroke engines 44 1.7.1 Influence ofpiston speed on the engine rate of rotation 45 1.7.2 Influence ofengine type on power output 46 NOTATION forCHAPTER 1 47 REFERENCES forCHAPTER 1 48 CHAPTER 2 GASFLOWTHROUGHTWO-STROKEENGINES 51 2.0 Introduction 51 2.1 Motion ofpressure waves in a pipe 54 2.

26、1.1 Nomenclature for pressure waves 54 2.1.2 Acoustic pressure waves and their propagation velocity 56 2.1.3 Finite amplitude waves 57 2.1.4 Propagation and particle velocities of finite amplitude waves in air 59 2.1.4.1 The compression wave 59 2.1.4.2 The expansion wave 61 2.1.5 Distortion ofthe wa

27、ve profile 62 2.2 Motion ofoppositely moving pressure waves in a pipe 62 2.2.1 Superposition of oppositely moving waves 63 2.2.2 Reflection of pressure waves 66 2.3 Reflections ofpressure waves in pipes 68 2.3.1 Reflection of a pressure wave at a closed end in a pipe 68 2.3.2 Reflection of a pressur

28、e wave at an open end in a pipe 69 2.3.2.1 Compression waves 69 2.3.2.2 Expansion waves 70 2.3.3 Reflection of pressure waves in pipes at a cylinder boundary 71 2.3.3.1 Outflow 74 2.3.3.2 Inflow 75 2.3.4 Reflection ofpressure waves in a pipe at a sudden area change 76 2.3.5 Reflections ofpressure wa

29、ves at branches in a pipe 79 2.4 Computational methods for unsteady gas flow 81 2.4.1 Riemann variable calculation offlow in a pipe 81 2.4.1.2 a and B characteristics 81 2.4.1.3 The mesh layout in a pipe 84 2.4.1.4 Reflection of characteristics at the pipe ends 84 2.4.1.5 Interpolation ofa and B val

30、ues at each mesh point 85 2.4.2 The computation ofcylinder state conditions at each time step 87 2.5 Illustration ofunsteady gas flow into and out of a cylinder 91 2.5.1 Simulation ofexhaust outflow with Prog.2.1,EXHAUST 94 2.5.2 Simulation ofcrankcase inflow with Prog.2.2, INDUCTION 103 2.6 Unstead

31、y gas flow and the two-stroke engine 111 NOTATION forCHAPTER 2 111 REFERENCES forCHAPTER 2 112 viiiTable ofContents CHAPTER 3 SCAVENGINGTHETWO-STROKEENGINE 115 3.0 Introduction 115 3.1 Fundamental theory 115 3.1.1 Perfect displacement scavenging 117 3.1.2 Perfect mixing scavenging 117 3.1.3 Combinat

32、ions ofperfect mixing and perfect displacement scavenging 118 3.1.4 Inclusion of short-circuiting of scavenge air flow in theoretical models 118 3.1.5 The application of simple theoretical scavenging models 119 3.2 Experimentation in scavenging flow 121 3.2.1 The Jante expenmental method of scavenge

33、 flow assessment 122 3.2.2 Principles for successful experimental simulation of scavenging flow 126 3.2.3 Absolute test methods for the determination of scavenging efficiency 127 3.2.4 Comparison ofloop, cross and uniflow scavenging 130 3.3 Comparison ofexperiment and theory ofscavenging flow 135 3.

34、3.1 Analysis ofexperiments on theQUB single-cycle gas scavenging rig 135 3.3.2 A simple theoretical scavenging model to correlate with experiments 138 3.4 Computational Fluid Dynamics (CFD) 143 3.5 Scavenge port design 149 3.5.1 Uniflow scavenging 150 3.5.2 Conventional cross scavenging 151 3.5.3 QU

35、B type cross scavenging 155 3.5.4 Loop scavenging 157 3.5.4.1 The main transferport 159 3.5.4.2 Rear ports and radial side ports 160 3.5.4.3 Side ports 160 3.5.4.4 The use of Prog.3.4,LOOPSCAVENGEDESIGN 160 NOTATION forCHAPTER 3 162 REFERENCES forCHAPTER 3 164 CHAPTER 4 COMBUSTION INTWO-STROKEENGINES 167 4.0 Introduction 167 4.1 The spark ignition process 168 4.1.1 Initiation of ignition 168 4.1.2 Air-fuel mixture limits for flammability 169 4.1.3 Effect of scavenging efficiency on flammability 171 4.1.4 Detonation or abnormal combustion 171 4.1.5 Homogeneous and stratified combustion 173 ix