Design and Simulation of Two Stroke Engines

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Chapter 7 - Reduction of Fuel Consumption and Exhaust Emissions start and duration of the metering of fuel into the injector body are referred to as "start of fuel" (SOF) and "fuel duration" (FD), respectively. Similarly, the start and duration of the airassisted injection process are referred to as "start of air" (SOA) and "air duration" (AD), respectively. The engine is also tested with the "perfect carburetor," i.e., an electronic fuel injector (EFT) mounted in the inlet tract so that the engine is homogeneously charged at all times. The word "perfect" is used in the sense that the operator can dial in any air-to-fuel ratio desired. The engine is tested at full load at 3000 rpm, and at 1600 rpm at part load, with both stratified and homogeneous charging, i.e., ABI or EFI installed; the results of these tests are found in Figs. 7.52-7.55 and 7.56-7.59, respectively, over a very wide range of trapped airfuel ratios, AFRt. Ignition timing is always set at MBT (minimum advance for best torque). For the full load tests, stratified charging is recorded for three SOA timings, namely 110°, 125° and 140° atdc, and the air duration is 2 ms. For the part load tests, stratified charging is recorded for three SOA timings, namely 215°, 230° and 245° atdc, and the air duration is 5 ms. In the entire test series, presented in Figs. 7.52-7.59, the profile of the relevant performance parameter for homogeneous charging can be compared with previous test results in Figs. 7.3-7.8 and theoretical results in Figs. 7.13-7.18. However, here in Figs. 7.55 and 7.59 is also shown the brake specific emissions of oxides of nitrogen with respect to air-to-fuel ratio, which can be compared for profile with theoretical computer simulations in Fig. A4.3. During full load (wot) operation, the SOA timing preceded exhaust port closure by 1 IS MS 0 . However, the SOA timings do not include any allowance for air solenoid delay. Tests conducted with a Hall effect sensor on the injector show that the poppet valve opening is delayed by approximately 2.5 ms. Therefore, the actual poppet valve opening occurred approximately 45° later than the nominal SOA timing. Nevertheless, it is clear that during this test a substantial proportion of the fuel is injected prior to exhaust port closure. The wot results, presented in Figs. 7.52-7.55, show that the air-assisted direct-injection system pro- 03 CL .*: c£ E 600 -, 500 400 QUB 500 RESEARCH ENGINE AIR-ASSISTED FUEL INJECTION 10 12 - — i 14 —r- 16 TRAPPED AIR-TO-FUEL RATIO SOA125 ^SOAHO —i 18 Fig. 7.52 Effect of fueling on bmep at full load, 3000 rpm. 523
Design and Simulation ofTwo-StroJ" Engines CD w -O 600 -i 500 400 - 300 200 QUB 500 RESEARCH ENGINE SOA140 EFI 1 1 1 1 1 1 r 10 12 14 16 TRAPPED AIR-TO-FUEL RATIO SOA125 SOA110 Fig. 7.53 Effect of fueling on bsfc at full load, 3000 rpm. 200 n o> 100 • O I w 10 QUB 500 RESEARCH ENGINE 18 AIR-ASSISTED FUEL INJECTION SOA110 i 12 - — i 14 —T" 16 TRAPPED AIR-TO-FUEL RATIO SOA125 SOA140 — i 18 Fig. 7.54 Effect of fueling on bsHC at full load, 3000 rpm. duced very significant improvements in fuel economy and hydrocarbon emissions over homogeneous charging (EFI). The minimum bsfc is reduced from 424 g/kWh to 293 g/kWh, and the minimum bsHC is reduced from 150 g/kWh to 19 g/kWh. These improvements are accompanied by a marginal increase in bmep, due to the additional air supply through the injector. The results also illustrate the influence of SOA timing. Later injection gives an inadequate time for preparation of the mixture, and a consequent deterioration in combustion efficiency. 524
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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 7 - Reduction of Fuel Consu
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Chapter 8 • Reduction of Noise Em
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Chapter 8 - Reduction of Noise Emis
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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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