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A CFD simulation of the flow within a motored two-port loop-scavenged two-stroke engine is described. The simulation is carried out using the STAR-CD CFD code and employs a multi-block approach to simulate the flow within the transfer duct, cylinder, and exhaust duct. A moving mesh with cell layer activation-deactivation is used to represent the reciprocating piston motion. Predictions of the flow within the cylinder and at the transfer port are presented over the open cycle and are compared to an existing measured velocity field for an engine speed of 600 rpm and a delivery ratio of unity. The results show the in-cylinder flow to have a highly complex structure dominated by recirculating flow features. The in-cylinder flow is considerably affected by reverse flow through the exhaust port at exhaust port opening, and is not seen to fully establish until after bottom dead centre.

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.