Design and Simulation of Two Stroke Engines

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Design and Simulation of Two-Stroke Engines CYLC d=25 mm [P — taper=8 * 1705 3417 * 9 d=109mm 4017 Fig. 2.50 QUB SP rig with a megaphone exhaust attached. moving expansion and compression waves gives very high particle velocities within the pipe and diffuser system, in excess of a Mach number of 0.7. Consider the strong suction wave evident in the figures at 0.02 second; if it arrives at the exhaust valves or ports of an engine, particularly a four-stroke engine during the long valve overlap period of a high-performance unit, it can induce a considerable flow of air through the combustion chamber, removing the residue of the combustion products, and initiate a high volumetric efficiency. The earlier discussion in Sec. 2.8.1 alludes to this potential for the enhanced cyclic charging of an engine with air. 1.6 = 1.2 H 111 DC CO W 0.8 - Q. 0.6 < DC W cc z> CO CO LU CL Q. MEGAPHONE EXHAUST TIME, seconds 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Fig. 2.51 Measured and calculated pressures with Mach 0.5 criterion. 1.6 1.4 1.2 1.0 0.8 0.6 MEGAPHONE EXHAUST 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Fig. 2.52 Measured and calculated pressures with Mach 0.6 criterion. 186
1.6 >& 1.4 - LU Q. 1.2 - 1.0 Chapter 2 • Gas Flow through Two-Stroke Engines MEGAPHONE EXHAUST 0.6 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Fig. 2.53 Measured and calculated pressures with Mach 0.7 criterion. The result of the computations using the GPB modeling method are shown on the same figures with the theoretical criterion for flow separation from the walls of a diffuser, as debated in Sec. 2.15.1, differing in each of the three figures. Recall from the discussion in that section, and by examining the criterion declared in Eq. 2.15.5, that gas particle flow separation from the walls of a diffuser will induce deterioration of the amplitude of the reflection of a compression wave as it traverses a diffuser. The taper of 8° included angle employed here would be considered in steady gas flow to be sufficiently steep as to give particle flow separation from the walls. The theory used to produce the computations in Figs. 2.51 to 2.53 was programmed to record the gas particle velocity at every mesh within the diffuser section. The Eq. 2.15.3 statement was implemented at every mesh at every time step, except that the computational switch was set at a Mach number of 0.5 when computing the theory shown in Fig. 2.51, at a Mach number of 0.6 for the theory plotted in Fig. 2.52, and at a Mach number of 0.7 for the theory presented in Fig. 2.53. It will be seen that the criterion presented in Eq. 2.15.5 provides the accuracy required. It is also clear that any computational method which cannot accommodate such a fluid mechanic modification of its thermodynamics will inevitably provide considerable inaccuracy. Total reliance on the momentum equation alone for this calculation gives a reflected wave amplitude at the pressure transducer of 0.5 atm. It is also clear that flow separation from the walls occurs only at very high Mach numbers. As the criterion of Eq. 2.15.5 is employed for the creation of the theory in Figs. 2.43 to 2.45, where the taper angle is at 12.8° included, it is a reasonable assumption that wall taper angle in unsteady gas flow is not the most critical factor. The differences between measurement and computation are indicated on each figure. It can be observed that the GPB finite system modeling gives a very accurate representation of the measured events for the reflection of compression pressure waves at a tapered pipe ending at the atmosphere. 2.19.8 A pipe with a gas discontinuity attached to the QUB SP apparatus The experiment simulates an exhaust process with a straight pipe attached to the cylinder. Fig. 2.54 shows a straight aluminum pipe of 5.913 m and 25-mm internal diameter attached to the port and ending at a closed end with no exit to the atmosphere. There are pressure transducers attached to the pipe at stations 1, 2 and 3 at the length locations indicated. However, at 187
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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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0.35 • 0.34 LU ° 0.33 - c 03 DC
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§ 2000
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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 01 III cr cc LU Q. LU h- LU Z o N
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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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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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