Design and Simulation of Two Stroke Engines

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Design and Simulation of Two-Stroke Engines DC LU DC D CO CO UJ cc Q. DC UJ DC D CO CO UJ DC Q_ 1.2 1.1 - ,.A_ 0.9 1.2 CONVERGENT CONE CALCULATED TIME, seconds 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Fig. 2.47 Measured and calculated pressures at station 1. 1.1 - 1.0 CONVERGENT CONE CALCULATED TIME, seconds 0.9 0.00 0.01 0.02 0.03 0.04 0.05 0.06 1.2 H 1.1 H DC UJ DC CO CO UJ DC 0_ 1.0 0.9 Fig. 2.48 Measured and calculated pressures at station 2. CONVERGENT CONE MEASURED TIME, seconds 0.8 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Fig. 2.49 Measured and calculated pressures at station 3. Fig. 2.41 for the sudden expansion. This was not the case in the previous section, when it was observed that the tapered diffuser pipe had distorted the profile of the exhaust pulse into a shock front as it reached the station 3 pressure transducer. It is germane to this discussion, and it is fully covered in the theoretical analysis in Sees. 2.10, 2.12 and 2.15, that a process in a diffuser is non-isentropic whereas that in a nozzle is isentropic. Shock formation in Fig. 2.45 184
Chapter 2 - Gas Flow through Two-Stroke Engines is clearly a manifestation of non-isentropic behavior while the undistorted profile emanating from the nozzle in Fig. 2.49 is obviously more efficient. Even the profile in Fig. 2.37 of the transmitted exhaust pulse onward from the sudden expansion exhibits elements of steep-front formation. It is also interesting to compare the amplitudes of the transmitted and reflected waves, as the nozzle should be more efficient at this than a sudden contraction. The peak of the compression wave from the tapered pipe undergoing superposition at 0.02 second at station 1 is 1.105 atm; for the sudden contraction it is weaker at 1.08 atm. The peak of the transmitted wave from the converging tapered pipe passing station 3 undisturbed at 0.012 second is 1.155 atm; for the sudden contraction it is 1.12 atm or an exhaust pulse of reduced strength is delivered onward down the pipe system. One final word on the above sections, which reiterates many of the theoretical considerations from Sees. 2.10, 2.12 and 2.15, is that area changes, which in discussion are labeled loosely as "cones," "nozzles," "diffusers," etc., are only accurate as nomenclature when taken in the context of the direction of the particle velocity at that instant of the discussion. In short, what is a nozzle for a particle traveling rightward at one instant in time is a diffuser to another traveling leftward in another time frame. 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 steeply tapered pipe segment within ducting. Taking heed of the warning in the previous paragraph, note that the word nozzle is not mentioned in this last statement. 2.19.7 A longer divergent tapered pipe attached to the QUB SP apparatus The experiment simulates an exhaust process with a straight pipe attached to the cylinder and incorporating a long divergent taper attached at the end of that straight pipe. Fig. 2.50 shows a straight aluminum pipe of 3.417 m and 25-mm internal diameter attached to the port, followed by a 600 mm length of tapered pipe at 8° included angle to 109-mm diameter at the open end to the atmosphere. This form of steep taper is very commonly found within the ducting of IC engines, including the diffuser outlet sections of highly tuned four-stroke engines. They are often referred to as "megaphones" for obvious reasons. There is a pressure transducer attached to the pipe at the length location indicated. The basic theory of pressure wave reflections in tapered pipes is presented in Sec. 2.15. The cylinder was filled with air and the initial cylinder pressure and temperature were 2.0 bar and 293 K. In Figs. 2.51 to 2.53 are the (same) measured pressure-time record at the pressure transducer location. The megaphone acts as an expansion to the area of the pipe system and sends a strong expansion wave reflection back from it. This is chased back along the pipe system by the reflection at the atmosphere of the residue of the exhaust pulse which makes it to the open end. It returns as an expansion wave, but now strengthening as it nozzles its way back to the smaller area of the parallel pipe leading back to the cylinder. It is observed arriving back at the pressure transducer at 0.021 second in Figs. 2.51 to 2.53 in a virtually undisturbed condition apart from residual friction waves. The original exhaust pulse has a pressure ratio of 1.55 and the suction reflection has a peak of 0.63 atm. The suction reflection has a shock wave at its tail, a feature already observed regarding the action of tapered pipes in Sec. 2.19.5. It will be seen from the discussion below that the superposition of oppositely 185
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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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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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