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Direct measurement of dilution air volume in a Constant Volume emission sampling system may be used to calculate tailpipe exhaust volume, and the total dilution ratio in the CVS. A Remote Mixing Tee (RMT) often includes a subsonic venturi (SSV) flowmeter in series with the dilution air duct. The venturi meter results in a flow restriction and significant pressure drop in the dilution air pipe. An ultrasonic flow meter for a similar dilution air volume offers little flow restriction and negligible pressure drop in the air duct. In this investigation, an ultrasonic flow meter (UFM) replaces the subsonic venturi in a Remote Mixing Tee. The measurement uncertainty and accuracy of the UFM is determined by comparing the real time flow rates and integrated total dilution air volume from the UFM and the dilution air SSV in the RMT. Vehicle tests include FTP and NEDC test cycles with a 3.8L V6 reference vehicle.

An experimental study was performed to investigate diesel particulate filter (DPF) performance during filtration with the use of real-time measurement equipment. Three operating conditions of a single-cylinder 2.3-liter D.I. heavy-duty diesel engine were selected to generate distinct types of diesel particulate matter (PM) in terms of chemical composition, concentration, and size distribution. Four substrates, with a range of geometric and physical parameters, were studied to observe the effect on filtration characteristics. Real-time filtration performance indicators such as pressure drop and filtration efficiency were investigated using real-time PM size distribution and a mass analyzer. Types of filtration efficiency included: mass-based, number-based, and fractional (based on particle diameter). In addition, time integrated measurements were taken with a Rupprecht & Patashnick Tapered Element Oscillating Microbalance (TEOM), Teflon and quartz filters.