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The Scavenging Flow Field in a Crankcase-Compression Two-Stroke Engine - A Three-Dimensional Laser-Velocimetry Survey
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Abstract
Transfer-port and in-cylinder flow fields have been mapped in a crankcase-compression, loop-scavenged two-stroke engine under motored conditions (1600 r/min; delivery ratio: 0.5). The impulsive, high-velocity flow (initially ≳2200 m/s) issuing from the transfer ports is fairly uniform and symmetric in space. The resulting in-cylinder flow field displays a classic scavenging loop pattern, but is complex and asymmetric. The data also characterize backflow from the cylinder into the transfer ports and the spin-up and breakdown of the scavenging-loop vortex during compression. The detailed LDV results provide some quantitative support for the widely used Jante scavenging test.
FOR THE GREATER PART OF A CENTURY, the scavenging process has been recognized as critical to the performance of two-stroke-cycle engines. Much of our understanding of the scavenging process (see Blair's book [1] for a comprehensive treatment) has been obtained through physical reasoning, thermodynamic and gas-dynamic analysis, and global measurements (e.g., scavenging efficiency and trapping efficiency as a function of delivery ratio). Flow visualization with both air and water as the working fluids (e.g., [2, 3]) has also contributed substantially. For loop-scavenged engines, the Jante test [4], which maps the axial-air-velocity distribution at the top of the cylinder (with the head removed), provides both a relative indicator of scavenging performance and some physical insight into the spatial character of the scavenging flow field. This semi-quantitative, empirical procedure is used in the development of virtually all such engines.
Despite the acknowledged importance of the scavenging process, there exists little quantitative experimental information on the flow fields in practical loop-scavenged two-stroke engines. In contrast, there have been many experimental studies of in-cylinder flow fields in four-stroke engines (cf. the reviews of Refs. [5], [6] and [7]). For the most part, previous velocity measurements in two-stroke engines either have examined the heavy-duty uniflow configuration [8, 9] or have been confined to the cylinder's TDC clearance volume [10], [11], [12], [13], [14] and [15]. These studies therefore offer limited insight into the velocity fields involved in the gas-exchange processes of interest here. The flow field in the single-cylinder research engine developed at Princeton University has been characterized extensively (e.g., [16], [17], [18] and [19]), but the engine's porting is atypical, and it does not scavenge well [20]. Detailed LDV measurements of the port-efflux velocity field in a two-port, loop-scavenged model engine have recently been carried out under both steady flow [21] and motored (blown, 200 r/min) conditions [22] at The Queen's University of Belfast; little in-cylinder velocity data have been presented, however [21].
An automotive two-stroke engine must operate efficiently over a broad speed-load range. In this context, the importance of detailed, quantitative knowledge of the flow fields is underscored by recent three-dimensional computational-fluid-dynamics (CFD) studies of scavenging and combustion in loop-scavenged two-stroke engines [23], [24], [25] and [26]. These studies predict that the scavenging effectiveness, mixture formation, and combustion can be sensitive to details of both the port-inflow velocities and the in-cylinder velocity field. In a crankcase-compression engine, moreover, these scavenging flow fields can vary with speed and load.
In view of the paucity of pertinent experimental data and the potential importance of the information, we undertook systematic, three-dimensional measurements of the spatial structure and temporal evolution of the scavenging flows in a crankcase-compression, loop-scavenged two-stroke-cycle engine, examining both the in-cylinder flow field and the flow entering the cylinder through the faces of the transfer ports. A principal objective of this study was to obtain physical insight and engineering guidance. The quantitative results should also prove helpful both in confirming the three-dimensional CFD codes used to model such engines and in providing boundary-condition information for these computations.1
The organization of the paper follows the usual order. §1 describes the experimental apparatus. The results are presented and discussed in the next two sections, which cover the formation (§2) and subsequent evolution and destruction (§3) of the scavenging loop, respectively. In §4, LDV and Jante-test results are compared, after which the conclusions of the study are summarized (§6). The appendices provide additional details of the LDV and engine-airflow systems.
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Fansler, T. and French, D., "The Scavenging Flow Field in a Crankcase-Compression Two-Stroke Engine - A Three-Dimensional Laser-Velocimetry Survey," SAE Technical Paper 920417, 1992, https://doi.org/10.4271/920417.Also In
References
- Blair G. P The Basic Design of Two-Stroke Engines SAE Warrendale, PA 1990
- Risk W. “Experimental Studies of the Mixing Processes and Flow Configurations in Two-Cycle Engine Scavenging.” Proc. I. Mech. E. 172 417 437 1958
- Ohigashi S. Kashiwada Y. “A Study on the Scavenging Air Flow through the Scavenging Ports.” Bull. JSME 9 777 784 1966
- Jante A. Scavenging and Other Problems of Two-Stroke-Cycle Spark-Ignition Engines SAE Paper 680468 1968
- Arcoumanis C. Whitelaw J. H. “Fluid Mechanics of Internal Combustion Engines - A Review.” Proc. I. Mech. E. 201C 57 74 1987
- Rask R. B. “Laser Doppler Anemometer Measurements of Mean Velocity and Turbulence in Internal Combustion Engines.” Intl. Conf. on Applics. of Lasers and Electro-Optics Boston Nov. 12-15 1984 GM Research Laboratories Publication GMR-4839 October 3 1984
- Fansler T. D. “Photon-Correlation Laser Velocimetry in Reciprocating-Engine Research.” Abbiss J. B. Smart A. E. Photon Correlation Techniques and Applications , Opt. Soc. Amer. Conf. Proc. Ser. 1 1988
- Sung N. W. Patterson D. J. Air Motion in a Two-Stroke Engine Cylinder - The Effects of Exhaust Geometry SAE Paper 820751 1982
- Kido H. Tajima H. Matsumoto A. “LDV Measurement of Axial Distributions of In-Cylinder Gas Velocities.” JSME Intl. J. Ser. II 32 78 84 1989
- Ohigashi S. Hamamoto Y. Tanabe S. “Gas Flow Velocity in Inlet Pipe, Exhaust Pipe and Cylinder of Two-Stroke Cycle Engine.” Bull. JSME 14 470 482 1969
- Obokata T. Matsuo N. Hireno Y. LDV Measurements of Pipe Flows in a Small Two-Cycle Spark-Ignition Engine SAE Paper 840425 1984
- Obokata T. Hanada N. Kurabayashi T. Velocity and Turbulence Measurements in a Combustion Chamber of S.I. Engine under Motored and Firing Operations by LDA with Fiber-Optic Pick-Up SAE Paper 870166 1987
- Reddy K. V. Ganesan V. Gopalakrishnan K. V. Under the Roof of the Cylinder Head - An Experimental Study of the In-Cylinder Air Movement in a Two-Stroke Spark-Ignition Engine SAE Paper 860166 1986
- Lee K. H. Ohira T. Nakajima T. Matsumoto R. “Measurement of Gas Flow Velocity in the Combustion Chamber of a Two-Stroke S.I. Engine by a Laser Doppler Velocimeter.” JSME Intl. J., Series II 33 163 170 1990
- Ikeda Y. Hikosaka M. Nakajima T. Ohhira T Scavenging Flow Measurement in a Fired Two-Stroke Engine by Fiber LDV SAE Paper 910670 1991
- Liou T.-M. Hall M. J. Santavicca D. A. Bracco F. V. Laser Doppler Anemometer Measurements in Valved and Ported Engines SAE Paper 840375 1984
- Hall M. J. Bracco F. V. A Study of Velocities and Turbulence Intensities in Firing and Motored Engines SAE Paper 870453 1987
- Fraser R. A. Bracco F. V. Cycle-Resolved LDV Integral Length-Scale Measurements Investigating Clearance-Height Scaling, Isotropy, and Homogeneity in an I. C. Engine SAE Paper 890615 1989
- Bardsley M. E. A. Gajdezcko B. Boulouchos K. Chehroudi B. Bracco F. V. Measurements of the Three components of the Velocity in the Intake Ports of an I.C. Engine SAE Paper 890792 1989
- Andrews M. A. Bracco F. V. The Use of Intake and Exhaust Measurements with Computer Simulations to Investigate the Evolution of the Internal Plow Field in a Ported Engine SAE Paper 910262 1991
- Smyth J. G. Kenny R. G. Blair G. P. Steady Flow Analysis of the Scavenging Process in a Loop-Scavenged Two-Stroke Engine - A Theoretical and Experimental Study SAE Paper 881267 1988
- Smyth J. G. Kenny R. G. Blair G. P. Motored and Steady-Flow Boundary Conditions Applied to the Prediction of Scavenging Flow in a Loop-Scavenged Two-Stroke-Cycle Engine SAE Paper 900800 1990
- Ahmadi-Befrui B. Brandstatter W. Kratochwill H. Multidimensional Calculation of the Flow Processes in a Loop-Scavenged Two-Stroke-Cycle Engine SAE Paper 890841 1989
- Ahmadi-Befrui B. Kratochwill H. “Multidimensional Calculation of Combustion in a Loop-Scavenged Two-Stroke-Cycle Engine,” Proc. Intl. Symp. on Diagnostics & Modeling of Combustion in Internal Combustion Engines (COMODIA) 465 474 Kyoto September 3-5 1990
- Fabre A. Ferreira C. “Three Dimensional Modeling of Flow and Mixture Preparation in a Two Stroke Engine.” Proc. Intl. Symp. on Diagnostics & Modeling of Combustion in Internal Combustion Engines (COMODIA) 475 480 Kyoto September 3-5 1990
- Kuo T. W. Reitz R. D. Three-Dimensional Computations of Combustion in Premixed-Charge and Fuel-Injected Two-Stroke Engines SAE Paper 920425 1992
- Amsden A. A. O'Rourke P. J. Butler T. D. Meintjes K. Fansler T. D. Comparisons of Computed and Measured Three-Dimensional Velocity Fields in a Motored Two-Stroke Engine SAE Paper 920418 1992
- Diwakar R. Fansler T. D. French D. T. Ghandhi J. B. Dasch C. J. Heffelfinger D. M. Liquid and Vapor Fuel Distributions from an Air-Assist Injector - An Experimental and Computational Study SAE Paper 920422 1992
- Hilbert H. S. Falco R. E. Measurements of Flows During Scavenging in a Two-Stroke Engine SAE Paper 910671 1991
- Gosman A. D. Tsui Y. Y. Vafidis C. Flow in a Model Engine with a Shrouded Valve - A Combined Experimental and Computational Study SAE Paper 850498 1985
- Haworth D. C. El Tahry S. H. Huebler M. S. Chang S. Multidimensional Port-and-Cylinder Flow Calculations for Two- and Four-Valve-per-Cylinder Engines: Influence of Intake Configuration on Flow Structure SAE Paper 900255 1990
- Arcoumanis C. Hu Z. Vafidis C. Whitelaw J. H. Tumbling Motion: A Mechanism for Turbulence Enhancement in Spark-Ignition Engines SAE Paper 900060 1990
- Khalighi B. Intake-Generated Swirl and Tumble Motions in a Four-Valve Engine - Flow Visualization and Particle Tracking Velocimetry SAE Paper 900059 1990
- Abbiss J. B. “The Structure of the Doppler-Difference Signal and the Analysis of Its Autocorrelation Function.” Physica Scripta 19 388 395 1979