Measurement and Characterization of Pulsating Flow through an Orifice Placed in Located in the Exhaust Stream of a Diesel Engine 2019-01-1176
Flow discharge coefficients for orifices and other flow obstructions are widely used in the automotive industry, for example to measure EGR flow rate or to model flow through exhaust/intake valves. All such situations involve pulsating flows, but no systematic studies investigating the flow resistance of pulsating flows existing in internal combustion engines exist, and behavior similar to non-pulsating flow is assumed. This work expands on a preliminary investigation that found that the discharge coefficient of a square-edged orifice placed in the exhaust stream of a four-cylinder naturally aspirated diesel engine increased continuously with Reynolds numbers, contrary to steady non-pulsating flow where the discharge coefficient is assumed to be approximately constant at high Reynolds numbers. Sixty three data high Reynold number data points spanning the speed-load space of the engine, including choked and non-choked flow were investigated, all of them at high Reynolds number. Wide variation in discharge coefficients between 06-0.9 was observed, with no correlation with Reynolds number. Dimensionless parameters were identified to characterize the discharge coefficient. The most important variable common to these dimensionless parameters was the standard deviation of the pulsating pressure differential signal, while the frequency of pulsation was not found to be important. Based on these results, it can be concluded that accurate measurement or modeling of pulsating flows requires knowledge of the magnitude of pulsation.