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EGR flow rate measurements on production engines are commonly made using orifices or flow nozzles. These devices increase the exhaust pressure resulting in an increase in fuel consumption. Further, they are accurate and recommended only for steady state flow, and not pulsating flow encountered in engines. In this work measurements made at the EGR cooler, such as the pressure drop across it and the inlet and outlet temperatures, have been examined for their ability to predict mass flow rate through the cooler. Direct measurements of pulsating flow through an EGR cooler were made by routing all of the engine exhaust flow through the cooler while making accurate measurements of the air and fuel flowing into the engine. Based on dimensional arguments, the flow resistance of the EGR cooler was characterized by a loss coefficient within the standard head loss energy equation.

Orifices, flow nozzles and arbitrarily shaped flow obstructing flow measurement devices are widely used to estimate EGR flow rates in engines, and also used to model flow restricting components like valves in engine analysis tools such as GT-Power. The standard assumptions about the flow discharge coefficient and its variation with Reynolds number are based on investigations of orifices across steady non-pulsating flows, widely reported in literature. In this work, the discharge coefficient for steady state pulsating flow as well as accelerating pulsating flow, commonly encountered during steady state and dynamic engine operation respectively, were investigated by installing an orifice on the exhaust side of a naturally aspirated diesel engine, while making reference flow measurements with a Laminar Flow Element on the intake side.