Semester

Fall

Date of Graduation

2011

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Mridul Gautam

Abstract

One of the most effective methods to control diesel particulate matter (PM) emissions from heavy duty diesel engines is to use wall flow diesel particulate filters (DPF). It is still a major challenge to get an accurate estimation of soot loading, which is crucial for the engine afterteratment assembly optimization. In the recent past, several advanced computational models of DPF filtration and regeneration have been presented to assess the cost effective optimization of future particulate trap systems. They are characterized by different degree of detail and computational costs, depending on the specific application (i.e diagnostics, control, system design, component design etc).;The objective of this study is to compare in detail a two dimensional (2-D) approach with a one dimensional (1-D) approach, thus giving a better insight of the variation of properties over the DPF length. This task has been archived by extending an in-house developed 1-D numerical soot model to the next dimension to understand the impact of 2-D representation to predict both steady state and transient behavior of a catalyzed diesel particulate filter (CDPF). Performance of the model was evaluated using three key parameters: pressure drop, filter outlet temperature and soot mass retained in the filter during both active and continuous regeneration events. Quasi-steady state conservation of mass, momentum and energy equations were solved numerically using finite difference methods adopting a spatially uniform mesh. The results obtained from the current model were compared with the 1-D code to evaluate the general validity of assumptions made in the latter, especially DPF loading status prediction.;The model was validated using the data gathered at the West Virginia University Engine and Emissions Research Laboratory (WVU-EERL) using a model year 2004 Mack MP7-355E Diesel engine coupled to a Johnson Matthey catalyzed diesel particulate filter (CDPF) exercised over a 13 mode European stationary cycle (ESC) followed by two federal transient cycles (FTP). A constant set of model tuning parameters were maintained for the sake of general validation of simplifying assumptions of the 1-D code.;The analysis shows that the predicted pressure drop across the DPF is in good agreement with the data obtained at EERL in both steady state and transient cycles. It is also shown that the soot accumulates mainly in the frontal and rear parts across the filter length under given soot concentrations. The model is capable of tracking DPF soot mass satisfactorily with a maximum discrepancy of 3.47g during steady state cycle. A 7.95% decrease in soot layer thickness can be seen in the front portion of the DPF during the transient cycle mainly due to O2 assisted regeneration at elevated temperatures. Both 1-D and 2-D models produce similar results during the loading phase. However, the current model is able to capture regeneration phase of the FTP cycle more descriptively than the 1-D model. The discrepancy of the reported total soot mass estimation between two models was 2.12%. The distribution corresponding to the 1-D model is representative of soot layer distribution given by the 2-D model at one tenth distance away from the DPF front face. 1-D model representation is effective towards PM prediction, although presenting considerable axial effects at higher DPF temperatures.

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