Design and Simulation of Two Stroke Engines

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Design and Simulation of Two-Stroke Engines The properties of the gas subscripted as 2 in Fig. 2.16 or 2.18 are the properties of the gas in the mesh 1 used here as the illustration. At the conclusion of the computation for boundary conditions at the "box," using the theory of Sees. 2.16 and 2.17, the amplitude of the reflected pressure wave, pr2, is provided. So too for outflow is the entropy gain in the form of the reference temperature, To2- In nomenclature terms, this reflected pressure wave is the "missing" pressure wave value at the lefthand of mesh 1 to permit the computation to proceed to the next time step. 1 X R - ( \ QX1 Pr2 Po (2.18.43) One important final point must be made in this section regarding the rather remote possibility of encountering supersonic particle velocity in any of the pipe systems during the superposition process at any mesh point. By the end of this section you have been brought to the point where the amplitudes of all of the left and right moving pressure waves have been established at both ends of all meshes within the ducting of the engine. At this juncture it is necessary to search each of these mesh positions for the potential occurrence of supersonic particle velocity in the manner described completely in Sec. 2.2.4 and, if found, apply the corrective action of a weak shock to give the necessary subsonic particle velocity (Sees. 2.15- 2.17). Unsteady gas flow does not permit supersonic particle velocity. It is self-evident that the particles cannot move faster than the disturbance which is giving them the signal to move. 2.18.9 Mass and energy transport along the duct during a time step In the real flow situation the energy and mass transport is conducted at the molecular level. Computational facilities are not large enough to accomplish this, so it is carried out in a mesh grid spacing of some 10 to 25 mm, a size commonly used in automotive engines. The size of mesh length is deduced by making the simple assumption that the calculation time step, dt, should translate to an advance of about 1° or 2° crank angle for any engine design. Within each mesh space, as shown in Fig. 2.20, the properties of the gas contained are assumed to be known at the start of a time step. During the subsequent time step, dt, as a result of the wave transmission, particles and energy are going to be transported from mesh space to mesh space, and heat transfer is going to occur by internal means, such as friction or a catalyst, or by external means through the walls of the duct. To determine the effect of all of these mechanisms, the First Law of Thermodynamics is employed, and the situation is sketched in Figs. 2.23 and 2.24. Here the energy transport across the boundaries for the mesh space J will have unique values depending on the particle directions of this transport. This is illustrated in Fig. 2.23, where four different cases are shown to be possible. The four cases will be described below. All pressures, particle velocities and densities are, by definition, for the superposition situation at the physical location at the appropriate end of the mesh J. The left-hand end of any mesh is denoted as the "in" side and the righthand end as the "out" side for flow of mass and energy and as a sign convention when apply- 156
^ •c o Q. CO a +—> co •>, 92 £T °-§ cC^ fico E^x: c 0) CD — . CO CO CO CO O So E co mesh J mesh J CASE1 mass flow, enthalpy and purity of gas with properties of mesh (J) CASE 2 mass flow, enthalpy and purity of gas with properties of mesh (J-1) Chapter 2 - Gas Flow through Two-Stroke Engines Po To mesh J CASE 3 mass flow, enthalpy and purity of gas with properties of mesh (J+1) CASE 4 mass flow, enthalpy and purity of gas with properties of mesh (J) mesh J ^ ^ mesh J Fig. 2.23 Mass, energy and gas species transport at mesh J during time interval dt. heat transfer across the space boundary A T, w Y dQh « • ' left dm dH dKE n Y R space m P T U II P Y R friction heating dQf catalyst dQint right dm dH dKE IT Y R t= o CO c *"* £> %$ y r- CD ^ §> *- . CO co 93 co o O E co Fig. 2.24 The mesh J which encounters mass and energy transfer during time dt. 157 •w,
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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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Design and Simulation ofTwo'Stroke
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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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^ s C£ Q 2^ E Q. Q_ z' o ISSI HCEM
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o > z~ Q w CO UJ w g x O z o z o m
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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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o Q_ Ld < CD 15-, 10- Chapter 7 - R
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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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1 Chapter 8 - Reduction of Noise Em
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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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Roots blower in turbocharged/superc
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Scavenging (continued) scavenging e
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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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