Modeling study of active regeneration of a catalyzed particulate filter using one-dimensional DOC and CPF models

The catalyzed particulate filter (CPF), used in conjunction with a diesel oxidation catalyst (DOC) is an important aftertreatment device used to meet Environmental Protection Agency (EPA) heavy duty diesel emission standards for particulate matter (PM). Numerical modeling of these exhaust after-treatment devices decreases the time and cost of development involved. Modeling CPF active regeneration gives insight into the PM oxidation kinetics, which helps in reducing the regeneration fuel penalty. As seen from experimental data, active regeneration of the CPF results in a significant temperature increase into the CPF (up to 8°C/sec) which affects the oxidation rate of particulate matter (PM). PM oxidation during active regeneration was determined to be a function of filter PM loading, inlet temperature and inlet hydrocarbon concentration. This paper focuses on the development and calibration of a 1-dimensional, MATLAB/Simulink DOC model and its use with a CPF model appropriate for studying active regeneration strategies. The DOC model accurately captures DOC behavior when the exhaust gas HC concentration is at the elevated levels observed during CPF active regeneration. Experimental data were used to calibrate the DOC model during CPF active regeneration using a numerical optimization approach. The DOC model is used to predict the time-varying outlet HC concentrations which are then used as input to a 1-D CPF model. The CPF model is an improved version of the model described in Premchand et al. [1] with several important differences including: HC and CO oxidation, reversible NO oxidation/NO2 dissociation reaction, PM cake layer permeability, PM cake layer density, improvements in the filtration model, wall and gas temperature prediction and time-varying HC concentration into the CPF. The CPF modeling effort focuses on using the DOC outlet HC concentration and calibrating the sub-models that have a significant effect on the active regeneration pressure drop across the CPF, including: HC oxidation, PM cake permeability, substrate wall PM and PM cake oxidation and filtration. Comparisons are made between simulated and experimental values of the pressure drop across the CPF and the PM oxidized during loading, regeneration and post-loading, CPF outlet temperatures and CPF outlet gaseous emission concentrations for the selected load cases. An optimization has been done using the reaction rate from the CPF model to find thermal PM activation energy and pre exponential factors. Active regeneration experimental data acquired by Chilumukuru et al. [2] with a 2007 production Cummins regenerative particulate filter has been used for this study. The experimental matrix consists of three CPF inlet temperatures (525, 550 and 600°C), three filter loadings (1.1, 2.2 and 4.1 g/1) and PM oxidation levels of 40 and 70% of the PM retained at the end of loading. Accurate estimates of the DOC inlet HC levels are critical for accurate DOC and CPF model temperature predictions. A combined direct/indirect HC measurement approach was used. Emission FID HC measurements were adjusted using a DOC/CPF energy balance based on DOC and CPF inlet and outlet temperature measurements