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Research Papers: Internal Combustion Engines

Lubricant-Derived Ash Properties and Their Effects on Diesel Particulate Filter Pressure-Drop Performance

[+] Author and Article Information
Alexander Sappok, Victor W. Wong

Sloan Automotive Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139

J. Eng. Gas Turbines Power 133(3), 032805 (Nov 09, 2010) (12 pages) doi:10.1115/1.4001944 History: Received December 15, 2009; Revised February 05, 2010; Published November 09, 2010; Online November 09, 2010

Diesel particulate filters (DPFs) have seen widespread use in on- and off-road applications as an effective means for meeting increasingly stringent particle emission regulations. Over time, incombustible material or ash, primarily derived from metallic additives in the engine lubricant, accumulates in the DPF. Ash accumulation leads to increased flow restriction and an associated increase in pressure-drop across the particulate filter, negatively impacting engine performance and fuel economy and eventually requiring periodic filter service or replacement. While the adverse effects of ash accumulation on DPF performance are well known, the underlying mechanisms controlling these effects are not. The results of this work show ash accumulation and distribution in the DPF as a dynamic process with each stage of ash accumulation altering the filter’s pressure-drop response. Through a combined approach employing targeted experiments and comparison with the existing knowledge base, this work further demonstrates the significant effect ash deposits have on DPF pressure-drop sensitivity to soot accumulation. Ash deposits reduce the available filtration area, resulting in locally elevated soot loads and higher exhaust gas velocities through the filter, altering the conditions under which the soot is deposited and ultimately controlling the filter’s pressure-drop characteristics. In this study, a novel accelerated ash loading system was employed to generate the ash and load the DPFs under carefully controlled exhaust conditions. The ash loading system was coupled to the exhaust of a Cummins ISB diesel engine, allowing for accelerated ash loading and DPF performance evaluation with realistic exhaust conditions. Following DPF performance evaluation, the filters were subjected to a detailed post-mortem analysis in which key ash properties were measured and quantified. The experimental results, coupled with the ash property measurements, provide additional insight into the underlying physical mechanisms controlling ash properties, ash/soot interactions, and their effects on DPF performance.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup showing accelerated ash loading system mounted beside the Cummins ISB

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Figure 2

DPF sample locations for post-mortem analysis and measurement of ash layer thickness

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Figure 3

DPF pressure-drop as a function of filter ash loading and equivalent on-road exposure. Letters refer to the location of ash deposition depicted in the inset.

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Figure 4

Measured ash layer thickness profiles for DPFs containing 42 g/l and 12.5 g/l ash

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Figure 5

Comparison of channel ash accumulation of 57 mm from DPF face for (a) DPF containing 12.5 g/l ash and (b) DPF containing 42 g/l ash and 133 mm from DPF face for (c) DPF containing 12.5 g/l ash and (d) DPF containing 42 g/l ash

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Figure 6

Comparison of ash packing density for DPFs containing 12.5 g/l ash and 42 g/l ash generated in the laboratory using CJ-4 oil and periodic regeneration

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Figure 7

Radial packing density variation within the ash end plug for a DPF containing 42 g/l ash

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Figure 8

Ash compositional analysis measured via XRD

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Figure 9

DPF pressure-drop profiles as a function of space velocity for the clean and ash loaded cases

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Figure 10

DPF pressure-drop due to flow through ash layer and substrate as a function of wall velocity, computed from the measured ash deposition profiles, for the ash loaded cases

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Figure 11

Comparison of individual soot and ash effects on DPF pressure-drop as a function of material loading

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Figure 12

DPF pressure-drop as a function of soot accumulation for various stages of ash loading at 20,000 h−1 space velocity

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Figure 13

DPF pressure-drop as a function of soot accumulation for a DPF containing no ash at 20,000 h−1 space velocity

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Figure 14

Shift in pressure-drop curves adjusted to account for ash accumulation in DPF channels

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Figure 15

Pressure-drop sensitivity adjusted to account for the DPF volume occupied by ash

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Figure 16

Measured and predicted soot layer packing density variation as a function of wall velocity and soot load. Adapted from Ref. 14.

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Figure 17

Evolution of ash deposition and buildup in DPF channels with time

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Figure 18

SEM images showing ash accumulation on the DPF surface and ash deposit structures

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Figure 19

Configuration of accelerated ash loading and aftertreatment aging system

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