Using Ejector Diluters to Sample Vehicle Exhaust at Elevated Pressures and Temperatures

This paper presents an alternative and relatively simple method which allows the use of ordinary ejector-type diluters over a wide range of sample inlet conditions including elevated pressures and temperatures. After calibration of the ejector diluter, the dilution can be accurately characterized using only the pressures at the inlet and the outlet of the diluter and the sample temperature. The method is based on a semi-empirical, stationary model taking into account the critical parameters needed to predict the dilution factor. Under steady state operation it achieves accuracies estimated to be below +/- 8% (95% confidence interval) for diluter inlet pressures in the range of 1000 - 4000 mbar absolute and temperatures between 20 - 200 degrees C. Performance under actual vehicle testing conditions is evaluated upstream of the DPF for a diesel vehicle run on a chassis dynamometer. Model predicted time resolved dilution factors were compared against oxygen tracer gas measurements for both steady state and transient operation, and confirmed the +/- 8% accuracy estimate.