Influence of time-alignment on the calculation of mass emissions on a chassis rolls dynamometer

Time-alignment sensitivity studies have been carried out to assess the accuracy of instantaneous mass NOx emissions on a chassis rolls dynamometer. The work is part of a larger project aimed at measuring passive NOx catalyst conversion efficiencies. Instantaneous NOx emissions are examined in relation to the NEDC vehicle speed trace at multi-sampling points, and phase and time alignment issues are highlighted and discussed. It has been found that a small mismatch of the vehicle speed trace to the instantaneous mass of emissions of \mP2 seconds can lead to results indicating that the conversion efficiency is anywhere between 0-20%. Finally, examples are presented showing the difficulties of attempting to adjust the time alignment of raw emissions data.