Study on Direct Measurement of Diesel Exhaust Gas Flow Rate: Transient Characteristics of Ultrasonic Exhaust Gas Flowmeter

The partial flow dilution system is one of the typical measurement systems for particulate matter emission from diesel engines. In this system, exhaust gas at a transient flow rate should be transferred to a dilution tunnel at a constant split ratio of exhaust gas. The current partial flow dilution system is used under steady-state engine operating conditions in lieu of direct flow rate measurement of exhaust gas. Therefore development of an exhaust gas flowmeter is indispensable in the partial flow dilution system for transient engine operating conditions. An ultrasonic exhaust gas flowmeter had been developed. As for the developed ultrasonic exhaust gas flowmeter, the transient characteristics measuring exactly and instantaneously temperature, pressure and velocity that are the components of the exhaust gas mass flow rate, has not been perfectly verified. We have inspected the transient characteristics of the developed ultrasonic exhaust gas flowmeter by using a laser Doppler velocimeter and numerical calculation. Consequently, an ultrasonic exhaust gas flowmeter has been confirmed to be capable of measuring the exhaust gas flow rate with sufficient transient characteristics.