Design and Characterization of an Isokinetic Sampling Train for Particle Size Measurements Using Exhaust Gas Recirculation

摘要

A particulate sampling train has been constructed which satisfies the conflicting requirements of isokinetic sample extraction and constant flowrate through an inertial sizing device. Its design allows a variable fraction of the filtered exhaust gas to be added to the sample upstream of the inertial sampler in order to maintain a preselected flowrate through this device while the gas flowrate into the sampling nozzle is adjusted to remain isokinetic with the local duct velocity. The prototype train was constructed by relatively simple modifications of a commercially available Method 5 sampling system, and much of the sampling technique is identical with Method 5 protocol. The train was tested by comparison of parallel runs in the EPA/SRI wind tunnel using redispersed flyash. In the first series of runs the EGR train without inertial sizing device sampled simultaneously with a colocated Method 17 sampling train. The average ratio of the measured mass concentrations was 1,003, with a standard deviation of 0.046. A second series of parallel isokinetic samples was taken using a dual cyclone sampler. The average mass concentration ratio for these runs was 0.988, with a standard deviation of 0.057.