Design and Simulation of Two Stroke Engines

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6. £ -Q 500 n | "I) 400 -Q 300 1000 6 -i 4 - 1000 Chapter 7 • Reduction of Fuel Consumption and Exhaust Emissions QUB270 CROSS SCAVENGED ENGINE WOT, 3000 rpm AIRHEAD CLOSED 2000 3000 4000 ENGINE SPEED, rpm AIRHEAD 50% OPEN AIRHEAD 100% OPEN 5000 Fig. 7.45 Effect of airhead on engine torque QUB270 CROSS SCAVENGED ENGINE WOT, 3000 rpm 2000 3000 4000 ENGINE SPEED, rpm AIRHEAD CLOSED AIRHEAD 50% OPEN AIRHEAD 100% OPEN 1 5000 Fig. 7.46 Effect of airhead on specific fuel consumption. overall air flow rate with the throttle valve in the airhead inlet either fully closed, or at onehalf open, or fully open. The bmep is virtually unchanged in all three cases, although some extra air flow, leading to a minor torque increase, is visible at the highest engine speed of 5000 rpm. In Figs. 7.46 and 7.47, there is a noticeable improvement in bsfc and bsHC at engine speeds of 2000 rpm and above. The reduction in hydrocarbon emissions ranges from 55% at 2500 rpm to 20% at 5000 rpm. The reduction in brake specific fuel consumption ranges from 20% at 2500 rpm to 5% at 5000 rpm. 511
Design and Simulation of Two-Stroke Engines 200 -, Q E 150 sz I d 100 i w 50 QUB270 CROSS SCAVENGED ENGINE WOT, 3000 rpm 1000 2000 3000 4000 5000 ENGINE SPEED, rpm AIRHEAD CLOSED Fig. 7.47 Effect of airhead on hydrocarbon emissions. AIRHEAD 50% OPEN AIRHEAD 100% OPEN While these are significant findings, the absolute levels of bsHC minimize at 60 g/kWh, which is considerably above the 25 g/kWh theoretically achieved by the low bmep optimization process described above for the simple two-stroke engine. It is not impossible to consider a combination of the two approaches. One of the advantages of the airhead approach is that lost charge from the exhaust port tends to contain bypassed charge with a leaner air-to-fuel ratio than with homogeneous charging. This provides excess oxygen in the exhaust system and would improve the conversion efficiency of the pollutants by an oxidation catalyst placed in it. 7.4.2 Homogeneous charging with stratified combustion As was pointed out earlier, direct in-cylinder fuel injection is one of the obvious methods of reducing, or even eliminating, the loss of fuel to the exhaust port during the scavenge process. Fig. 7.30 illustrates the positioning of such a fuel injector for the combustion of gasoline in a spark-ignition engine. Figs. 4.1(b) and 4.9 show the positioning of injectors for the injection of fuel into a compression-ignition engine, for it must not be forgotten that this engine falls directly, and more convincingly in the view of some, into this category. Gasoline injection into spark-ignition engines The potential difficulties of evaporating a fuel spray in time for a homogeneous combustion process to occur have been debated. The even more fundamental problem of attaining good flammability characteristics at light load and speed in a homogeneous combustion process has also been addressed. What, then, are the known experimental facts about in-cylinder fuel injection? Is the combustion process homogeneous, or does the desirable possibility of stratified burning at light load and speed exist? Does the fuel vaporize in time to burn in an efficient manner? The answers to these questions are contained in the technical papers published by several authors; answers to the question of cost and design approach for tradition- 512
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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 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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