Design and Simulation of Two Stroke Engines

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Chapter 7 • Reduction of Fuel Consumption and Exhaust Emissions spring, and the fuel awaiting final injection is heated within this space by conduction from the cylinder head; this period is shown in Fig. 7.50(c). At the appropriate juncture, the main (outwardly opening) poppet valve is activated by its solenoid and the high-pressure air supply can now act upon the stored fuel and spray it into the combustion chamber; this is shown in Fig. 7.50(d). The poppet is closed by its solenoid through electronic triggering, but it is further assisted by a spring to return to its seat, as in Fig. 7.50(a). This completes the cycle of operation. The spray which is created by such an "aerosol" method is particularly fine, and (a) BOTH NEEDLES ON THEIR SEATS (b) FUEL SOLENOID LIFTS NEEDLE AND SPRAYS FUEL INTO SAC (c) FUEL NEEDLE RESEATS (d) AIR SOLENOID LIFTS POPPET AND THE AIR ATOMIZES THE FUEL INTO THE CYLINDER Fig. 7.50 Sequence of events in the operation of an air-blast fuel injector. 517
Design and Simulation of Two-Stroke Engines droplet sizes in the range of 3-20 um SMD have been reported for these devices [7.34, 7.28]. Studies of the spray formation in such injectors have been provided by Ikeda [7.50] and by Emerson [7.43]. The spray pattern from an air-assisted injector, designed and manufactured at QUB for in-house R&D, is shown in Plate 7.3. It can be seen to have a wider hollow cone shape than the narrower cone emanating from liquid injection, shown in Plate 7.2. These are general comments, for it is possible to shape differently the spray patterns of most injector nozzles. The QUB air-assisted injector has a SMD value of between 3 and 12 um over the full range of required delivery. An indication of the types of fuel sprays emanating from well-optimized fuel injectors are shown in Plates 7.4 and 7.5, for liquid and air-assisted fuel injectors, respectively. The "hollow-cone" nature of their spray patterns can be seen very clearly. Actually, the device emanating from IFP [7.18], and discussed in Sec. 7.4.1, is a mechanical means of accomplishing the same ends, albeit with a greater mass of air present during the heating phase, but the final delivery to the cylinder is at a lower velocity than that produced by the air-blast injector. The advantage of the air-assisted injector is that it potentially eliminates one of the liquid injector's annoying deficiencies, that of "dribbling" or leaving a droplet on the nozzle exit at low flow rates. This "dribble" produces misfire and excessive HC emission. A potential disadvantage is that the long-term reliability and accuracy of fuel delivery of the air-assisted injector is open to question. Solenoids exposed to high temperatures are not known for precision long-term retention of their electromagnetic behavior, and this would be unacceptable in vehicle service. That is why the injector is occasionally seen placed lower in the cylinder wall, or angled up from the transfer ports in some designs [7.17], i.e., away from, and not Plate 7.3 The spray pattern from a QUB-designed air-assisted fuel injection system. 518
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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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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 8 - Reduction of Noise Emis
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Chapter 8 • Reduction of Noise Em
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H Chapter 8 - Reduction of Noise Em
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Name F R Chapter 8 • Reduction of
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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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