Methods for reconstruction of transient emissions from heavy-duty vehicles.

摘要

Emissions measurement analyzers give out a response that may not reflect the true instantaneous engine-out emissions. Currently, the heavy-duty diesel engines are being certified for emissions measured in a thirty second time window with certain specification requirements for the analyzers. Since these measured emissions values may not be the same as the true instantaneous emissions, integrated values for the thirty second windows may be affected by analyzer response.;This document presents and examines reconstruction techniques to estimate instantaneous heavy-duty engine-out emissions. These techniques will take as the input, the continuous set of emissions data and approximate dispersion characteristics of the analyzer employed in measuring the continuous data. For this purpose, this research dealt with understanding and modeling the transient dynamics (dispersion function) of the analyzers and the sampling system to establish a relationship between the measured and instantaneous heavy-duty emissions.;Four methods of reconstruction were presented in this study: Sequential Inversion Technique (SIT), Differential Coefficients Method (DCM), Inverse Fast Fourier Transform (IFFT) and Modified Deconvolution Technique (MDT). The application of each method in reconstructing real-time emissions data was presented. While SIT failed in practical applications, each of the other three methods was shown to offer advantage in the post-processing of the measured emissions data. DCM accounted for the small errors in the computation of the analyzer dispersion function. IFFT was able to reconstruct just as well as DCM; however the Fast Fourier Transform of the dispersion function should be high enough to ensure stability of the method. In other words, the dispersion function should not have elements that were almost equal to zero for the method to be stable. Both the DCM and IFFT improved the correlation of emissions with power by an average of about 2%. MDT employs fitting a gamma distribution to the dispersion function and searches for the best possible distribution within a prescribed range to improve the reconstruction. With emissions reconstruction using MDT, the improvement of correlation of emissions with power was approximately about 3%.;The measured continuous data of CO2 mass flow rate from the New Flyer 2006 transit bus was divided into several operating bins, each bin having a specific speed and acceleration range. MDT was used to generate continuous reconstructed emissions from the measured continuous data. This reconstructed data is again divided into identical bins following a similar procedure. By comparing the two sets of bins, it was found that at low accelerations, the average mass flow rate of the measured CO2 was lesser than that of the reconstructed CO2. However, the reverse was found true at high accelerations.;This work could enhance the existing inventory models, help the calibrators appreciate the affect of time dispersion and can take the certifiers one step closer to estimating the true transient emissions by compensating for the distortion of the measurement systems.