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Reconstruction of Time-Resolved Vehicle Emissions Measurements by Deconvolution
Abstract:
A thorough understanding of vehicle exhaust aftertreatment system performance requires time-resolved emissions measurements that accurately follow driving transients, and that are correctly time-aligned with exhaust temperature and flow measurements. The transient response of conventional gas analyzers is characterized by both a time delay and an attenuation of high-frequency signal components. The distortion that this imposes on transient emissions measurements causes significant errors in instantaneous calculations of aftertreatment system efficiency, and thus in modal mass analysis. This creates difficulties in mathematical modeling of emissions system performance and in optimization of powertrain control strategies, leading to suboptimal aftertreatment system designs.
A mathematical method is presented which improves the response time of emissions measurements. This begins with development of a model of gas transport and mixing within the sampling and measurement system. Deconvolution techniques are described which solve the inverse of the model, i.e. the input to the system is estimated when the output is known. In this way, an improved signal is reconstructed by removing the effects of the transient response of the measurement system. Model parameters are estimated by exciting the system with a series of square pulses and fitting the model response to the resulting data. Finally, reconstruction is applied to transient vehicle emissions data, showing significant recovery of detail.