Design and Simulation of Two Stroke Engines

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Chapter 7 - Reduction of Fuel Consumption and Exhaust Emissions speed regions, which characterize most urban emissions test cycles for automobiles, they are superior in every regard to those recorded for the single-cylinder unit. 7.5 Compression-ignition engines Very little has been said above about diesel engines. It is only comparatively recently, and principally in Europe, that there has been any renewed interest in the topic. In one area at least, the diesel is immediately superior to the two-stroke gasoline engine, for it conducts stratified combustion at all speeds and loads with no difficulty and at high efficiency! For an automobile, or for a truck, the externally scavenged engine should be re-examined from a design standpoint for its ability to take advantage of new knowledge, new materials, new supercharger or turbocharger designs, or new injection systems. This has already started, and the outcome is that this design and development area is being revisited. Early indications are that higher power density, better thermal efficiency and better exhaust emissions are possible for the automobile, the bus, the tractor or the truck. In Europe, there is already a high proportion of on-road vehicles fitted with turbocharged four-stroke cycle diesel engines, most of which have, to American eyes, astonishing performance characteristics. It is quite conceivable that a 2-liter, two-stroke diesel car engine would have a flat bmep curve of 7.5 bar from 1000 to 4500 rpm and have a (best point) specific fuel consumption of 250 g/kWh, as an IDI design. If combustion can be attained as a DI engine, then that bmep is raised to 8.3 bar and the bsfc drops to 210 g/kWh. Both these designs have the inherently low HC emission common to all diesel engines, but the two-stroke engine has bsNOx levels below 1.6 g/kWh. The bmep information translates into peak power outputs of 112 kW and 125 kW for the IDI and the DI engine, respectively, which means that they would out-accelerate equivalent gasoline-engined vehicles due to the shape of the torque curve, may even have a higher terminal speed, and will certainly post considerably superior fuel consumption figures for both urban and highway driving. Needless to add, as QUB has had a long history of R&D in diesel engines in general, and two-stroke diesel engines in particular, much activity is devoted to the theoretical and experimental advancement of these concepts. 7.6 Concluding comments It is too early in the development history of two-stroke engines for precise conclusions to be drawn regarding their future role; this process has really been in progress only for some thirty years. Nevertheless, the general level of improvement in performance characteristics of the simple engine has been greatly enhanced by new research and development techniques for cycle calculation, scavenging and combustion design, fueling methods and exhaust tuning; much has been learned in the last half-decade [7.36]. Even more remarkable are the performance characteristics of some of the advanced two-stroke engines aimed at future automotive applications, some with behavioral characteristics at the first experimental attempt which rival or exceed those available from current four-stroke engine practice. Often, some of these new two-stroke engines are produced on research budgets and by engineering teams whose size is a mere fraction of that being devoted to the onward development of an existing four-stroke production engine. The end of this century, and the turn of the next, is going to be 531
Design and Simulation of Two-Stroke Engines a very important period in the development of the two-stroke cycle engine and it is not impossible that an automobile fitted with such an engine will be in series production before the end of this millenium. In that context, the prophetic remark passed by Professor Dr.h.c. Alfred Jante, in an SAE paper [3.5] presented in May 1968, is particularly significant: "The stricter that the exhaust emissions standards become, the more the two-stroke engine will regain importance." References for Chapter 7 7.1 G. Batoni, "An Investigation into the Future of Two-Stroke Motorcycle Engine," SAE Paper No. 780710, Society of Automotive Engineers, Warrendale, Pa., 1978. 7.2 T. Sato, M. Nakayama, "Gasoline Direct Injection for a Loop-Scavenged Two-Stroke Cycle Engine," SAE Paper No. 871690, Society of Automotive Engineers, Warrendale, Pa., 1987. 7.3 K. Tsuchiya, S. Hirano, M. Okamura, T Gotoh, "Emission Control of Two-Stroke Motorcycle Engines by the Butterfly Exhaust Valve," SAE Paper No. 800973, Society of Automotive Engineers, Warrendale, Pa., 1980. 7.4 N. Hata, T. Iio, "Improvement of the Two-Stroke Engine Performance with the Yamaha Power Valve System," SAE Paper No. 810922, Society of Automotive Engineers, Warrendale, Pa., 1981. 7.5 S. Ohigashi, "Exhaust Pipe Contraction in Two-Stroke Engines," Japanese Patent No. Showa 38-19659, 1963. 7.6 H. Nishizaki, S. Koyama, "EK34 Type Engine and Idle Silence Valve for Subaru Rex," Internal Combustion Engines, Vol 11, No 128, Sept. 1972. 7.7 S. Ishihara, "An Experimental Development of a New U-Cylinder Uniflow Scavenged Engine," SAE Paper No. 850181, Society of Automotive Engineers, Warrendale, Pa., 1985. 7.8 S. Onishi, S.H. Jo, PD. Jo, S. Kato, "Multi-Layer Stratified Scavenging (MULS)—A New Scavenging Method for Two-Stroke Engine," SAE Paper No. 840420, Society of Automotive Engineers, Warrendale, Pa., 1984. 7.9 G.P. Blair, B.W. Hill, A.J. Miller, S.P Nickell, "Reduction of Fuel Consumption of a Spark-Ignition Two-Stroke Cycle Engine," SAE Paper No. 830093, Society of Automotive Engineers, Warrendale, Pa., 1983. 7.10 B.W. Hill, G.P. Blair, "Further Tests on Reducing Fuel Consumption with a Carburetted Two-Stroke Cycle Engine," SAE Paper No. 831303, Society of Automotive Engineers, Warrendale, Pa., 1983. 7.11 H. Uchiyama, T Chiku, S. Sayo, "Emission Control of Two-Stroke Automobile Engine," SAE Paper No. 770766, Society of Automotive Engineers, Warrendale, Pa., 1977. 7.12 M. Nuti, "Direct Fuel Injection: An Opportunity for Two-Stroke SI Engines in Road Vehicle Use," SAE Paper No. 860170, Society of Automotive Engineers, Warrendale, Pa., 1986. 7.13 N.J. Beck, R.L. Barkhimer, M.A. Calkins, W.P Johnson, W.E. Weseloh, "Direct Digital Control of Electronic Unit Injectors," SAE Paper No. 840273, Society of Automotive Engineers, Warrendale, Pa., 1084. 532
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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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S.S.F.C. , C./SHP-HS Chapter 7 - Re
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Chapter 8 - Reduction of Noise Emis
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1 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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