Comparison of the performance of real-time PM mass and number instrumentation for vehicle exhaust measurements

Four dynamic PM measurement instruments (EEPS3090, DMS500, DMM230, AVL483) are studied in terms of their usability for diesel exhaust measurements under transient and steady state conditions. Measurements for various engine and exhaust aftertreatment strategies as well as on a Combustion Aerosol Standard (CAST) were conducted. The utilized sampling concepts comprised pre-DPF, tailpipe and CVS tunnel measurements. All results obtained from the two particle size spectrometers (EEPS3090 and DMS500) were compared to corresponding SMPS and CPC values, while the PM mass measurement instruments (DMM230 and AVL483) were compared to filter data. In addition, PM mass was estimated from the transient particle size spectra of EEPS3090 and DMS500, assuming different particle density functions, and was also compared to the corresponding filter data. All instruments were suitable to resolve fast changes in PM emissions. The linearity and repeatability for each of the instruments was found to be good over a wide range of PM concentrations for both steady state and transient conditions. However, for low mass emissions below 5 mg/km, the relative deviations between the DMM230 and the AVL483 compared to the filter data were significant. The size distributions measured by the two spectral instruments deviated from the corresponding SMPS results especially for particles at the upper and lower end of the measured size range. The concentration of larger particles seems to be underestimated by the EEPS3090 and the DMS500. The comparison between mass emissions calculated from the size spectra of these instruments using typical diesel soot effective densities (fractal dimension 2.3) and the corresponding filter values suggest the EEPS3090 and DMS500 to significantly underestimate the particle volume. This also indicates a miscalculation of the number of larger particles by EEPS3090 and DMS500. For an assumed size independent effective particle density of ρ_eff (D_p) = 1 g/cm³ a reasonable agreement of PM masses between the spectral instruments and the filter values could be achieved.