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Coefficients of Discharge at the Aperatures of Engines
ISSN: 0148-7191, e-ISSN: 2688-3627
Published September 01, 1995 by SAE International in United States
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This paper reports on the experimental evaluation of certain aspects concerning the mathematical modelling of pressure wave propagation in engine ducting. A particular aspect is the coefficient of discharge of the various ports, valves or apertures of the ducting connected to the cylinder of an engine or to the atmosphere. The traditional method for the deduction of the coefficients of discharge employs steady flow experimentation. While the traditional experimental method may well be totally adequate, it is postulated in this paper that the traditional theoretical approach to the deduction of the discharge coefficient from the measured data leads to serious inaccuracies if incorporated within an engine simulation by computer. An accurate theoretical method for the calculation of the discharge coefficient from measured data is proposed.
The paper presents experimental results for the coefficients of discharge for several duct end geometries such as orifices, plain ends, bellmouths and the exhaust port of a two-stroke engine cylinder, and demonstrates that the conventional method for the deduction of the coefficient of discharge may be used only as a comparator for these geometries but leads to serious computational errors if used within a computer simulation. The paper contrasts and compares the values of coefficients of discharge determined by the postulated and the traditional methods, based on the same experimental measurements for the several duct end geometries.
The paper presents further theoretical confirmation that the postulated theoretical approach is justified and accurate, by comparison of the predictions of measured flow rates by the postulated and the traditional theories with the theoretical results from a CFD analysis of an identical duct end geometry. The CFD analysis and the postulated theoretical approach match almost perfectly whereas the traditional method does not.
CitationBlair, G., Lau, H., Cartwright, A., Raghunathan, B. et al., "Coefficients of Discharge at the Aperatures of Engines," SAE Technical Paper 952138, 1995, https://doi.org/10.4271/952138.
Design and Emissions of Small Two- and Four-Stroke Engines
Number: SP-1112 ; Published: 1995-09-01
Number: SP-1112 ; Published: 1995-09-01
- Kirkpatrick S.J., Blair G.P., Fleck R., McMullan R.K., “Experimental Evaluation of 1D Computer Codes for the Simulation of Unsteady Gas Flow Through Engines - a First Phase”, SAE International Off-Highway Meeting, Milwaukee, September 1994, SAE Paper no. 941685, pp. 18.
- Blair G.P., “An Alternative Method for the Prediction of Unsteady Gas Flow through the Reciprocating Internal Combustion Engine”, Society of Automotive Engineers International Off-Highway & Powerplant Congress, Milwaukee, Wisconsin, September 9-12, 1991, SAE Paper No.911850 and also in SP883, p 137-162.
- Blair G.P., “Correlation of an Alternative Method for the Prediction of Engine Performance Characteristics with Measured Data”, Society of Automotive Engineers, International Congress, Detroit, Michigan, March 1993, SAE paper No.930501, pp20.
- Blair G.P., “Correlation o Measured and Calculated Performance Characteristics of Motorcycle Engines”, Funfe Zweiradtagung, Technische Universität, Graz, Austria, 22-23 April 1993, p5-16
- Blair G.P., Magee S.J., “Non-Isentropic Analysis of Varying Area Flow in Engine Ducting”, Society of Automotive Engineers International Off-Highway & Powerplant Congress, Milwaukee, Wisconsin, September 13-16, 1993, SAE Paper No.932399, p77-94.
- Blair G.P., “Non-Isentropic Analysis of Branched Flow in Engine Ducting”, Society of Automotive Engineers, International Congress, Detroit, Michigan, March 1994, SAE paper No.940395, p55-72.
- Blair G.P., Kirkpatrick S.J., Fleck R., “Experimental Validation of 1-D Modelling Codes for a Pipe Containing Gas of Varying Properties”, Society of Automotive Engineers, International Congress, Detroit, Michigan, March 1995, SAE paper No.950275, p93-106.
- Blair G.P., Kirkpatrick S.J., Mackey D.O., Fleck R., “Experimental Validation of 1-D Modelling Codes for a Pipe System Containing Area Discontinuities”, Society of Automotive Engineers, International Congress, Detroit, Michigan, March 1995, SAE paper No.950276, p 107-120.
- Blair G.P., “Design and Simulation of Two-Stroke Cycle, Engines”, in preparation, SAE, Warrendale, Pennsylvania, in 1996.
- Bingham J.F., “Unsteady Gas Flow in the Manifolds of Multicylinder Automotive Engines”, PhD Thesis, The Queen's University of Belfast, October 1983.
- Blair G.P., McConnell J.H., “Unsteady Gas Flow Through High-Specific-Output 4-Stroke Cycle Engines”, SAE Farm, Construction & Industrial Machinery and Powerplant Meetings, Milwaukee, September 1974, SAE Paper no. 740736.
- Agnew D.D., “What is limiting engine air flow. Using Normalised Steady Air Flow Bench Data”, SAE Motorsports Engineering Conference, Dearborn, December 1994, SAE Paper no. 942477.
- Cartwright A., Fleck R., “A Detailed Investigation of Exhaust System Design in High Performance Two-Stroke Engines”, SAE Motorsports Engineering Conference, Dearborn, December 1994, SAE Paper no. 942515.
- Schlichting H., “Boundary Layer Theory” McGraw-Hill, 6th Edition, New York, 1968.