Design and Simulation of Two Stroke Engines

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Design and Simulation of Two-Stroke Engines < DC LU cr D CO CO LU CC Q. 1 n . ^r 0.9 - MEASURED 0.8 - A J *-- 1 1 • 1 1 1 1 fV 1 \*-, \ ^ MEASURED TIME, seconds -\ • 1 •— - 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Fig. 2.33 Measured and calculated pressures at station 2. The correlation of measured and calculated mass is also good. The criterion used is the ratio of the final to the initial cylinder mass. The calculated and the measured values are 1.308 and 1.311, respectively, which is an error of 0.2%. As with the exhaust process in (i) above, no wave action other than friction reflections impinged on the port to influence the cylinder emptying process. The main event is the creation of the intake pulse as a wave of expansion, the peak of which is passing station 1 at 0.004 second. It reflects at the open end as a compression wave and the peak returns to station 1 at 0.0383 second. The basic theory of the motion of finite amplitude waves is discussed in Sec. 2.1.4 and of reflections of expansion waves at a plain open end in Sec. 2.8.3. As the reference acoustic velocity in air at 20°C is 343 m/s, which is estimated to be the average propagation velocity on the simplistic grounds that the expansion wave travels as much below sonic velocity as the compression wave is supersonic above it, the expected return point in time by a very simple computation is: time t = 0.004 + 2(5901-317) 1000 x 343 = 0.0366 second This approximate calculation can be seen to give an answer which is similar to the experimental value. In Figs. 2.31 to 2.33 the individual waves can be seen clearly. The creation of the induction pulse is accurate as can be seen in Figs. 2.31 and 2.32. Later it passes station 2 after 0.01 second. Steepening of the tail of the expansion wave has occurred as discussed in Sec. 2.1.5. It will be seen that a shock did not develop on the wave at any time. The effect of friction is presented in Fig. 2.58(b) which expands the time scale for the time period between 0.007 and 0.01 second. The close correlation between the measured and calculated pressures, and the residual waves attributable to the friction reflections after 0.0085 second causing the sub-atmospheric pressure on the traces, is now observable by zooming in on this time period. As for friction causing deterioration of the peak of the pressure wave, as it passed station 1 it had a measured peak pressure ratio of 0.864 (calculated at 0.859) and when it passed station 2 it had increased to 0.871 (calculated at 0.876). The theoretical discussion on this subject is contained in Sec. 2.3. 176
Chapter 2 - Gas Flow through Two-Stroke Engines It can be seen that the GPB modeling method provides a very accurate pressure-time history of the recorded events for the motion of expansion waves and of the induction process into a cylinder. However, it was the "less than perfect" theoretical correlation with this experiment which led to the study on discharge coefficients [5.25]. 2.19.3 A sudden expansion attached to the QUB SP apparatus The experiment simulates an exhaust process with a straight pipe incorporating a sudden expansion attached to the cylinder. Fig. 2.34 shows a straight aluminum pipe of 3.394 m and 25-mm internal diameter attached to the port, followed by a 2.655 m length of 80-mm-diameter pipe ending at the atmosphere. There are pressure transducers attached to the pipe at stations 1, 2 and 3 at the length locations indicated. The basic theory of pressure wave reflections at sudden expansions and contractions is given in Sees. 2.10 and 2.12. CYLC • < — • « — STATION 1 STATION 2 S T A i° 55 ?5 f r r 317 • 3097 3394 ' *" T70*3 N 3 6049 Fig. 2.34 QUB SP rig with a sudden expansion attached. The cylinder was filled with air and the initial cylinder pressure and temperature were 1.5 bar and 293 K. In Figs. 2.35 to 2.37 are the measured pressure-time records in the cylinder and at stations 1, 2 and 3. The results of the computations using the GPB modeling method are shown in the same figures, and the correlation is very good. Differences that can be discerned between measurement and computation are indicated on the figure. In Fig. 2.35 the basic action of reflection at a sudden expansion is observed. The exhaust pulse passes the pressure transducer at station 1 at 0.004 second and the sudden expansion in SUDDEN EXPANSION 0.01 0.02 0.03 0.04 0.05 0.06 2.35 Measured and calculated pressures at station 1. Ill >•
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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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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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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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