How is flow measurement accomplished?

Exhaust flow is indirectly measured using engine operation parameters, known engine and fuel properties, and exhaust gas concentrations. This technique has been patented and successfully validated by repeated laboratory comparisons. Engine operation parameters can be acquired through the available Engine Control Unit diagnostic port for J1939, J1708, and OBDII protocols or by an array of sensors temporarily, non-intrusively, and passively attached to the engine.