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Research Papers: Internal Combustion Engines

Characteristic Response of a Production Diesel Oxidation Catalyst Exposed to Lean and Rich PCI Exhaust

[+] Author and Article Information
Timothy J. Jacobs

 Texas A&M University, College Station, TX 77843-3123tjjacobs@tamu.edu

Dennis N. Assanis

 University of Michigan, Ann Arbor, MI 48109-2121assanis@umich.edu

J. Eng. Gas Turbines Power 130(4), 042805 (Apr 29, 2008) (9 pages) doi:10.1115/1.2906174 History: Received October 24, 2007; Revised November 07, 2007; Published April 29, 2008

Although low-temperature premixed compression ignition (PCI) combustion in a light-duty diesel engine offers dramatic and simultaneous reductions in nitric oxides (NOx) and soot, associated increases in unburned hydrocarbons (HC) and carbon monoxide (CO) become unacceptable. Production diesel oxidation catalysts (DOCs) are effective in oxidizing the increased levels of HC and CO under lean combustion conditions. However, the low-temperature∕high CO combination under rich PCI conditions, designed as a lean NOx trap (LNT) regeneration mode, generally renders the DOC ineffective. The objectives of this study are to characterize the oxidizing efficiency of a production DOC under lean and rich PCI conditions, and attempt to identify probable causes for the observed ineffectiveness under rich PCI. The study uses several tests to characterize the behavior of the DOC under lean PCI and rich PCI combustion conditions, including (1) steady-state feed gas characterization, (2) transient feed gas characterization, (3) air injection (4) insulated air-fuel sweep, and (5) combustion mode switching. The DOC never becomes effective under rich PCI for any of the tests, suggesting that the platinum-based catalyst may be incorrect for use with rich PCI. Furthermore, combustion mode switching between lean PCI and rich PCI (mimicking LNT loading and regeneration) demonstrates diminishing effectiveness of the DOC during and after continuous mode transitioning.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

NOx and smoke concentrations at the three studied diesel combustion modes

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Figure 2

EI‐NOx and EI-PM emissions at the three studied diesel combustion modes. EI‐NOx and EI-PM standards are based on US EPA Tier 2, Bin 5 regulations (26), assuming a vehicle fuel economy of 36miles∕gal.

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Figure 3

HC and CO conversion efficiencies and concentrations at the three studied diesel combustion modes

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Figure 4

Precatalyst exhaust temperature and space velocity at the three studied diesel combustion modes

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Figure 5

CH4∕HC ratio and O2 concentration at the three studied diesel combustion modes

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Figure 6

Pre- and postcatalyst exhaust temperatures versus time as combustion switches from the heating mode to lean PCI (at time=0)

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Figure 7

Pre- and postcatalyst CO concentrations versus time as combustion switches from the heating mode to lean PCI (at time=0)

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Figure 8

Pre- and postcatalyst HC concentrations versus time as combustion switches from the heating mode to lean PCI (at time=0)

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Figure 9

Pre- and postcatalyst exhaust temperatures versus time as combustion switches from the heating mode to rich PCI (at time=0)

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Figure 10

Pre- and postcatalyst CO concentrations versus time as combustion switches from the heating mode to rich PCI (at time=0)

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Figure 11

Pre- and postcatalyst HC concentrations versus time as combustion switches from the heating mode to rich PCI (at time=0)

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Figure 12

Precatalyst exhaust temperatures versus AF ratio for insulated and noninsulated exhaust systems

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Figure 13

CO conversion efficiency versus AF ratio for insulated and noninsulated exhaust systems

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Figure 14

HC conversion efficiency versus AF ratio for insulated and noninsulated exhaust systems

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Figure 15

AF ratio versus time for lean PCI∕rich PCI mode switching. Engine operates lean PCI for 60s, switches to rich PCI for 5s, and returns to lean PCI.

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Figure 16

Postcatalyst exhaust temperatures versus time for lean PCI∕rich PCI mode switching. Engine operates lean PCI for 60s, switches to rich PCI for 5s, and returns to lean PCI.

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Figure 17

Postcatalyst (and precatalyst) CO concentrations versus time for lean PCI∕rich PCI mode switching. Engine operates lean PCI for 60s, switches to rich PCI for 5s, and returns to lean PCI.

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Figure 18

Postcatalyst (and precatalyst) HC concentrations versus time for lean PCI∕rich PCI mode switching. Engine operates lean PCI for 60s, switches to rich PCI for 5s, and returns to lean PCI.

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