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Some Fundamental Aspects of the Discharge Coefficients of Cylinder Porting and Ducting Restrictions
ISSN: 0148-7191, e-ISSN: 2688-3627
Published February 23, 1998 by SAE International in United States
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This paper reports on the experimental evaluation of the coefficient of discharge of ports in the cylinder wall of a two-stroke engine and of restrictions within engine ducting. It is required to know such discharge coefficients, as a function of the area of the restriction and the pressure ratio across it, so that in the mathematical modelling process at each juncture during the open cycle, accuracy can be obtained for the mass flow rates of gases, the magnitude of pressure waves created, and the effect on the internal engine thermodynamics. The discharge coefficients, Cd, are required for both inflow and outflow, i.e in both directions, at all such cylinder apertures or ducting restrictions. A fundamental experimental study is conducted of the effect of size of the engine ducting on the discharge coefficient of the cylinder porting aperture and it is found to have no significant influence. The general applicability of this conclusion in design and simulation practice is debated. A study of the discharge coefficients of restrictions or throttles within engine ducting is carried out and the ensuing map is determined to be significantly dissimilar in profile to that of all published data on engine porting or valving.
CitationBlair, G., McBurney, D., McDonald, P., McKernan, P. et al., "Some Fundamental Aspects of the Discharge Coefficients of Cylinder Porting and Ducting Restrictions," SAE Technical Paper 980764, 1998, https://doi.org/10.4271/980764.
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- Blair G.P. Drouin F.M.M. “Relationship between Discharge Coefficients and Accuracy of Engine Simulation” SAE Motorsports Engineering Conference Dearborn, Michigan December 1996 SAE paper No. 962527 151 163
- Jante A. “Scavenging and Other Problems of Two-Stroke Cycle Spark-Ignition Engines” SAE Mid-Year Meeting Detroit, Michigan May 1968 SAE paper No. 680468 101 122
- Fleck R. Cartwright A. “Coefficients of Discharge in High Performance Two-Stroke Engines” SAE Motorsports Engineering Conference Dearborn, Michigan December 1996 SAE paper No. 962534 165 176