Design and Simulation of Two-Stroke Engines List of Chapters: Nomenclature Chapter 1 Introduction to the Two-Stroke Engine 1.0 Introd Introduction to the two-stroke cycle 1.1 The fundamental method of operation of a simple two-stroke 1.2 Methods of the cylinder 1.2.1 Loop 1.2.2 Cross 1.2.3 Uniflow 1.2.4 Scavenging not employing the crankcase as an air pump 1.3 Valving and porting control of the exhaust, scavenge and inlet processes 1.3.1 Poppet valves 1.3.2 Disc valves 1.3.3 Reed valves 1.3.4 Port timing events 1.4 Engine and porting geometry 1.4.1 Swept volume 1.4.2 Compression ratio 1.4.3 Piston position with respect to crankshaft angle 1.4.4 Computer program, Prog.1.1, PISTON POSITION 1.4.5 Computer program, Prog.1.2, LOOP ENGINE DRAW 1.4.6 Computer program, Prog.1.3, QUB CROSS ENGINE DRAW 1.5 Definitions of thermodynamic terms used in connection with design and testing 1.5.1 Scavenge ratio and delivery ratio 1.5.2 Scavenging efficiency and purity 1.5.3 Trapping efficiency 1.5.4 Charging efficiency 1.5.5 Air-to-fuel ratio 1.5.6 Cylinder trapping conditions 1.5.7 Heat released during the burning process 1.5.8 The thermodynamic cycle for the two-stroke 1.5.9 The concept of mean effective pressure 1.5.10 Introd Power and torque and fuel consumption 1.6 Laboratory testing of two-stroke 1.6.1 Laboratory testing for power, torque, mean effective pressure and specific fuel consumption 1.6.2 Laboratory testing for exhaust emissions from two-stroke 1.6.3 Trapping efficiency from exhaust gas analysis 1.7 Potential power output of two-stroke 1.7.1 Influence of piston speed on the rate of rotation 1.7.2 Influence of type on power output Subscript notation for Chapter 1 References for Chapter 1 Chapter 2 Gas Flow through Two-Stroke Engines 2.0 Introd Introduction 2.1 Motion of pressure waves in a pipe 2.1.1 Nomenclature for pressure waves 2.1.2 Propagation velocities of acoustic pressure waves 2.1.3 Propagation and particle velocities of finite amplitude waves
2.1.4 Propagation and particle velocities of finite amplitude waves in air 2.1.5 Distortion of the wave profile 2.1.6 The properties of gases 2.2 Motion of oppositely moving pressure waves in a pipe 2.2.1 Superposition of oppositely moving waves 2.2.2 Wave propagation during superposition 2.2.3 Mass flow rate during wave superposition 2.2.4 Supersonic particle velocity during wave superposition 2.3 Friction loss and friction heating during pressure wave propagation 2.3.1 Friction factor during pressure wave propagation 2.3.2 Friction loss during pressure wave propagation in bends in pipes 2.4 Heat transfer during pressure wave propagation 2.5 Wave reflections at discontinuities in gas properties 2.6 Reflection of pressure waves 2.6.1 Notation for reflection and transmission of pressure waves in pipes 2.7 Reflection of a pressure wave at a closed end in a pipe 2.8 Reflection of a pressure wave at an open end in a pipe 2.8.1 Reflection of a compression wave at an open end in a pipe 2.8.2 Reflection of an expansion wave at a bellmouth open end in a pipe 2.8.3 Reflection of an expansion wave at a plain open end in a pipe 2.9 An introduction to reflection of pressure waves at a sudden area change 2.10 Introd Reflection of pressure waves at an expansion in pipe area 2.10 Introd.1 Flow at pipe expansions where sonic particle velocity is 2.11 Reflection of pressure waves at a contraction in pipe area 2.11.1 Flow at pipe contractions where sonic particle velocity is 2.12 Reflection of waves at a restriction between differing pipe areas 2.12.1 Flow at pipe restrictions where sonic particle velocity is 2.12.2 Examples of flow at pipe expansions, contractions and restrictions 2.13 An introduction to reflections of pressure waves at branches in a pipe 2.14 The complete solution of reflections of pressure waves at pipe branches 2.14.1 The accuracy of simple and more complex branched pipe theories 2.15 Reflection of pressure waves in tapered pipes 2.15.1 Separation of the flow from the walls of a diffuser 2.16 Reflection of pressure waves in pipes for outflow from a cylinder 2.16.1 Outflow from a cylinder where sonic particle velocity is 2.16.2 Numerical examples of outflow from a cylinder 2.17 Reflection of pressure waves in pipes for inflow to a cylinder 2.17.1 Inflow to a cylinder where sonic particle velocity is 2.17.2 Numerical examples of inflow into a cylinder 2.18 The simulation of by the computation of unsteady gas flow 2.18.1 The basis of the GPB computation model 2.18.2 Selecting the time increment for each step of the calculation 2.18.3 The wave transmission during the time increment, dt 2.18.4 The interpolation procedure for wave transmission through a mesh 2.18.5 Singularities during the interpolation procedure
2.18.6 Changes due to friction and heat transfer during a computation step 2.18.7 Wave reflections at the intermesh boundaries after a time step 2.18.8 Wave reflections at the ends of a pipe after a time step 2.18.9 Mass and energy transport along the duct during a time step 2.18.10 Introd The thermodynamics of cylinders and plenums during a time step 2.18.11 Air flow, work, and heat transfer during the modeling process 2.18.12 The modeling of using the GPB finite system method 2.19 The correlation of the GPB finite system simulation with experiments 2.19.1 The QUB SP (single pulse) unsteady gas flow experimental 2.19.2 A straight parallel pipe attached to the QUB SP 2.19.3 A sudden expansion attached to the QUB SP 2.19.4 A sudden contraction attached to the QUB SP 2.19.5 A divergent tapered pipe attached to the QUB SP 2.19.6 A convergent tapered pipe attached to the QUB SP 2.19.7 A longer divergent tapered pipe attached to the QUB SP 2.19.8 A pipe with a gas discontinuity attached to the QUB SP 2.20 Introd Computation time 2.21 Concluding remarks References for Chapter 2 Appendix A2.1 The derivation of the particle velocity for unsteady gas flow Appendix A2.2 Moving shock waves in unsteady gas flow Appendix A2.3 Coefficients of discharge in unsteady gas flow Chapter 3 Scavenging the Two-Stroke Engine 3.0 Introd Introduction 3.1 Fundamental theory 3.1.1 Perfect displacement 3.1.2 Perfect mixing 3.1.3 Combinations of perfect mixing and perfect displacement 3.1.4 Inclusion of short-circuiting of scavenge air flow in theoretical models 3.1.5 The application of simple theoretical models 3.2 Experimentation in flow 3.2.1 The Jante experimental method of scavenge flow assessment 3.2.2 Principles for successful experimental simulation of flow 3.2.3 Absolute test methods for the determination of efficiency 3.2.4 Comparison of loop, cross and uniflow 3.3 Comparison of experiment and theory of flow 3.3.1 Analysis of experiments on the QUB single-cylinder gas rig 3.3.2 A simple theoretical model which correlates with experiments 3.3.3 Connecting a volumetric model with simulation 3.3.4 Determining the exit properties by mass 3.4 Computational fluid dynamics 3.5 Scavenge port design 3.5.1 Uniflow 3.5.2 Conventional cross 3.5.3 Unconventional cross 3.5.3.1 The use of Prog.3.3(a) GPB CROSS PORTS 3.5.4 QUB type cross 3.5.4.1 The use of Prog.3.3(b) QUB CROSS PORTS
Chapter 4 3.5.5 Loop 3.5.5.1 The main transfer port 3.5.5.2 Rear ports and radial side ports 3.5.5.3 Side ports 3.5.5.4 Inner wall of the transfer ports 3.5.5.5 Effect of bore-tostroke ratio on loop 3.5.5.6 Effect of cylinder size on loop 3.5.5.7 The use of Prog.3.4, LOOP SCAVENGE DESIGN 3.5.6 Loop design for external 3.5.6.1 The use of Prog.3.5 BLOWN PORTS 3.6 Scavenging design and development References for Chapter 3 Combustion in Two-Stroke Engines 4.0Introd Introduction 4.1 The spark-ignition 4.1.1 Initiation of ignition 4.1.2 Air-fuel mixture limits for flammability 4.1.3 Effect of efficiency on flammability 4.1.4 Detonation or abnormal 4.1.5 Homogeneous and stratified 4.1.6 Compression ignition 4.2 Heat released by 4.2.1 The chamber 4.2.2 Heat release prediction from cylinder pressure diagram 4.2.3 Heat release from a two-stroke loop-scavenged 4.2.4 Combustion efficiency 4.3 Heat availability and heat transfer during the closed cycle 4.3.1 Properties of fuels 4.3.2 Properties of exhaust gas and products 4.3.2.1 Stoichiometry and equivalence ratio 4.3.2.2 Rich mixture 4.3.2.3 Lean mixture 4.3.2.4 Effects of dissociation 4.3.2.5 The relationship between and exhaust emissions 4.3.3 Heat availability during the closed cycle 4.3.4 Heat transfer during the closed cycle 4.3.5 Internal heat loss by fuel vaporization 4.3.6 Heat release data for sparkignition 4.3.7 Heat release data for compression-ignition 4.3.7.1 The direct injection diesel (DI) 4.3.7.2 The indirect injection diesel (IDI) 4.4 Modeling 4.4.1 A simple closed cycle model within simulations 4.4.2 A closed cycle model within simulations 4.4.3 A one-dimensional model of flame propagation in sparkignition 4.4.4 Three-dimensional model for spark-ignition 4.5 Squish be 4.5.1 A simple theoretical analysis of squish velocity 4.5.2 Evaluation of squish velocity by computer 4.5.3 Design of chambers to include squish effects 4.6 Design of c the required clearance volume 4.7 Some gener chambers for particular applications 4.7.1 Stratified charge 4.7.2 Homogeneous charge References for Chapter 4 Appendix A4.1 Exhaust emissions Appendix A4.2 A simple two-zone model
Chapter 5 Computer Modeling of Engines 5.0 Introd Introduction 5.1 Structure of a computer model 5.2 Physical geometry required for an model 5.2.1 The porting of the cylinder controlled by the piston motion 5.2.2 The porting of the cylinder controlled externally 5.2.3 The intake ducting 5.2.4 The exhaust ducting 5.3 Heat transfer within the crankcase 5.4 Mechanical friction losses of two-stroke 5.5 The thermodynamic and gas-dynamic simulation 5.5.1 The simulation of a chainsaw 5.5.2 The simulation of a racing motorcycle 5.5.3 The simulation of a multicylinder 5.6 Concluding remarks References for Chapter 5 Appendix A5.1 The flow areas through poppet valves Chapter 6 Empirical Assistance for the Designer 6.0 Introd Introduction 6.1 Design of porting to meet a given performance characteristic 6.1.1 Specific time areas of ports in two-stroke 6.1.2 The determination of specific time area of porting 6.1.3 The effect of changes of specific time area in a chainsaw 6.2 Some practical considerations in the design process 6.2.1 The acquisition of the basic dimensions 6.2.2 The width criteria for the porting 6.2.3 The port timing criteria for the 6.2.4 Empiricism in general 6.2.5 The selection of the exhaust system dimensions 6.2.6 Concluding remarks on data selection 6.3 Empirical design of reed valves for twostroke 6.3.1 The empirical design of reed valve induction systems 6.3.2 The use of specific time area information in reed valve design 6.3.3 The design process programmed into a package, Prog.6.4 6.3.4 Concluding remarks on reed valve design 6.4 Empirical design of disc valves for twostroke 6.4.1 Specific time area analysis of disc valve systems 6.4.2 A computer solution for disc valve design, Prog.6.5 6.5 Concluding remarks References for Chapter 6 Chapter 7 Reduction of Fuel Consumption and Exhaust Emissions 7.0 Introd Introduction 7.1 Some fundamentals of and emissions 7.1.1 Homogeneous and stratified and charging 7.2 The simple two-stroke 7.2.1 Typical performance characteristics of simple 7.2.1.1 Measured performance data from QUB 40ntrod0 research 7.2.1.2 Typical performance maps for simple twostroke 7.3 Optimizing fuel economy and emissions for the simple two-stroke 7.3.1 The effect of on performance and emissions 7.3.2 The effect of air-fuel ratio 7.3.3 The effect of optimization at a reduced delivery ratio 7.3.4 The optimization of 7.3.5 Conclusions regarding the simple two-stroke 7.4 The more complex two-stroke 7.4.1 Stratified charging with homogeneous 7.4.2 Homogeneous charging with
stratified 7.5 Compression-ignition 7.6 Concluding comments References for Chapter 7 Appendix A7.1 The effect of compression ratio on performance characteristics and exhaust emissions Chapter 8 Reduction of Noise Emission from Two-Stroke Engines 8.0 Introd Introduction 8.1 Noise 8.1.1 Transmission of sound 8.1.2 Intensity and loudness of sound 8.1.3 Loudness when there are several sources of sound 8.1.4 Measurement of noise and the noise-frequency spectrum 8.2 Noise sources in a simple two-stroke 8.3 Silencing the exhaust and inlet system 8.4 Some fundamentals of silencer design 8.4.1 The theoretical work of Coates 8.4.2 The experimental work of Coates 8.4.3 Future work for the prediction of silencer behavior 8.5 Acoustic theory for silencer attenuation characteristics 8.5.1 The diffusing type of exhaust silencer 8.5.2 The side-resonant type of exhaust silencer 8.5.3 The absorption type of exhaust silencer 8.5.4 The laminar flow exhaust silencer 8.5.5 Silencing the intake system 8.5.6 Engine simulation to include the noise characteristics 8.5.7 Shaping the ports to reduce high-frequency noise 8.6 Silencing the tuned exhaust system 8.6.1 A design for a silenced expansion chamber exhaust system 8.7 Concluding remarks on noise reduction References for Chapter 8 Postscript Appendix Listing of Computer Programs Index