Design and Simulation of Two Stroke Engines

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Design and Simulation of Two-Stroke Engines The functions in Eqs. 2.2.9 and 2.2.10 reveal the non-isentropic nature of the flow. For example, an isentropic compression would give the following relation between pressure and density: _P_ Po — This is clearly quite different from that deduced for the moving shock wave in Eq. A2.2.10. The non-isentropic functions relating pressure, temperature and density for a moving shock wave are often named in the literature as the Rankine-Hugoniot equations. They arise again in the discussion in Sec. 2.2.4. 204
Chapter 2 - Gas Flow through Two-Stroke Engines Appendix A2.3 Coefficients of discharge in unsteady gas flow In various sections of this chapter, such as Sees. 2.12, 2.16, 2.17, and 2.19, a coefficient of discharge, Cd, is employed to describe the effective area of flow through a restriction encountered at the throat of a valve or port at a cylinder, or of flow past a throttle or venturi section in an inlet duct. Indeed a map of measured coefficients of discharge, Cd, is displayed in Fig. 2.27. It will be observed from this map that it is recorded over a wide range of pressure ratios and over the full range of port-to-pipe-area ratio, k, from zero to unity. The area ratio, k, is defined as: throat area Af Area ratio, k = = —- rA9 o i\ pipe area Ap (fu.J.i) Where the geometry under scrutiny is a port in the cylinder wall of a two-stroke engine and is being opened or closed by the piston moving within that cylinder, it is relatively easy to determine the effective throat and pipe areas in question. All such areas are those regarded as normal to the direction of the particle flow. In some circumstances these areas are more difficult to determine, such as a poppet valve in an engine cylinder, and this matter will be dealt with more completely below. A poppet valve is not a valving device found exclusively in a four-stroke engine, as many two-stroke engines have used them for the control of both inlet and exhaust flow. Measurement of coefficient of discharge The experimental set-up for these measurements varies widely but the principle is illustrated in Fig. A2.3. The cylinder of the engine is mounted on a steady flow rig and the experimentally determined air mass flow rate, rhex, is measured at various pressure drops from the cylinder to the pipe for outflow, or vice-versa for inflow, through the aperture of area, At> leading from the cylinder to the pipe of area, Ap. The illustration shows a two-stroke engine cylinder with the piston held stationary giving a geometric port area, At, feeding an exhaust pipe with an inner diameter, djS, and where the flow is coming from, or going to, a pipe where the diameter is dp. It involves the measurement of the pressures and temperatures, pO, To, within the cylinder and at the pipe point, p2, T2, respectively. In the illustration, the flow is suction from the atmosphere, giving "exhaust" flow to the exhaust pipe, and so the cylinder pressure and temperature are the atmospheric conditions, po and To- The values of pressure and temperature within the cylinder are regarded as stagnation values, i.e., the particle velocity is so low as to be considered zero, and at the pipe point they are the static values. The mass rate of flow of the gas, rhex, for the experiment is measured by a meter, such as a laminar flow meter or an orifice designed to ISO, BS, DIN or ASME standards. The experiment is normally conducted using air as the flow medium. The theoretical mass flow rate, rhis, is traditionally determined [2.7] using isentropic nozzle theory between the cylinder and the throat for outflow, or pipe and throat for inflow, using the measured state conditions in the cylinder, at the throat, or in the pipe, which are pi and Ti, pt and Tt, or P2 and T2, respectively, and using the nomenclature associated with 205
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Design and Simulation of Two-Stroke
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A Second Mulled Toast When as a stu
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Acknowledgments As explained in the
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Table of Contents Nomenclature xv C
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Table of Contents 2.10.1 Flow at pi
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Table of Contents 3.5.3.1 The use o
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Table of Contents 6.1.3 The effect
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Nomenclature NAME SYMBOL UNIT (SI)
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speed of rotation speed of rotation
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attenuation or transmission loss wa
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Chapter 4 Combustion in Two-Stroke
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Chapter 4 - Combustion in Two-Strok
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a stratilpl o tions to ivior. If m
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CD 30 -, W 20 - LU CO iS _J LU OC 1
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181 also x3 = — = 0.905 x6 = 2.17
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to be cur .3.20) .3.21) .3.22) for
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3.23) com- :on is hhas has a /eng-
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stroke .3.29) mean me to 3land ssio
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a LU z: en 3 CO a LU z EC D m O ho
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CD 1.2 -i 1.0 - di „„ LU 0.8 cc
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CO —> 111" cc LU < LU _J LU CC £
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Combustion in compression-ignition
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stroke ari more often lseful lental
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lat the ssi ;tribu- ELEVATION VIEWS
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CYLINDER HEAD TYPE IS CENTRAL BORE,
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CO E 50 40 - O O _i Hi > I CO 30 Z)
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CURRENT INPUT DATA FOR 2-STROKE 'SP
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Cylin- PP £ Pa- tics of Paper Chap
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vfitro- ;titi >tants 1970. i(In- Ch
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£2 = Pi P2 I Pi J Chapter 4 - Comb
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CHAINSAW AT 9600 rpm. Chapter 4- Co
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LLI •z. O N -z. 0.21 -, 0.20 DC 0
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Chapter 7 Reduction of Fuel Consump
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Chapter 7 • Reduction of Fuel Con
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Chapter 7 - Reduction of Fuel Consu
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0.35 • 0.34 LU ° 0.33 - c 03 DC
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§ 2000
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y, ,6 Chapter 7 - Reduction of Fuel
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Chapter 7- Reduction of Fuel Consum
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INLET FOR r AIR AND FUEL Chapter 7
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Chapter 8 Reduction of Noise Emissi
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Chapter 8 • Reduction of Noise Em
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Chapter 8 - Reduction of Noise Emis
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• • / . • Appendix Listing of
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Active radical (AR) combustion and
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initial conditions, assumptions reg
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in two-stroke engine (schematic dia
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exhaust timing control valve, effec
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I Exhaust emissions/exhaust gas ana
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Exhaust systems (continued) untuned
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gas constant/universal gas constant
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in crankcase heat transfer analysis
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Mercury Marine air-assisted fuel in
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I PISTON POSITION (computer program
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Pressure wave reflection (in pipes)
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local acoustic velocity, 60 local M
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Simulation, engine See Computer mod
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temperature vs. crankshaft angle (c
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work per thermodynamic (Otto) cycle
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Design and Simulation of Two Stroke Engines

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