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Research Papers: Internal Combustion Engines

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

[+] Author and Article Information
Amin Reihani

Department of Mechanical Engineering,
University of Michigan,
G.G. Brown Laboratory, 2350 Hayward,
Ann Arbor, MI 48109
e-mail: areihani@umich.edu

Brent Patterson

Department of Chemical Engineering,
University of Michigan,
3074 H.H. Dow 2300, Hayward Street,
Ann Arbor, MI 48109-2136
e-mail: patbre@umich.edu

John Hoard

Department of Mechanical Engineering,
University of Michigan,
1231 Beal Avenue,
1012 Lay Autolab, Ann Arbor, MI 48109
e-mail: hoardjw@umich.edu

Galen B. Fisher

Department of Chemical Engineering,
University of Michigan,
3170 H.H. Dow 2300, Hayward Street,
Ann Arbor, MI 48109-2136
e-mail: gbfisher@umich.edu

Joseph R. Theis

Ford Motor Company,
2101 Village Road,
Dearborn, MI 48124
e-mail: jtheis@ford.com

Christine K. Lambert

Ford Motor Company,
2101 Village Road,
Dearborn, MI 48124
e-mail: clamber9@ford.com

1Corresponding author.

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 16, 2017; final manuscript received February 27, 2017; published online April 25, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(10), 102805 (Apr 25, 2017) (7 pages) Paper No: GTP-17-1068; doi: 10.1115/1.4036295 History: Received February 16, 2017; Revised February 27, 2017

Lean NOx traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based selective catalytic reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400 °C needs to be improved. Rapidly pulsed reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) (Bisaiji et al., 2011, “Development of Di-Air—A New Diesel deNOx System by Adsorbed Intermediate Reductants,” SAE Int. J. Fuels Lubr., 5(1), pp. 380–388). Four important parameters were identified to maximize NOx conversion while minimizing fuel penalty associated with hydrocarbon injections in RPR operation: (1) flow field and reductant mixing uniformity, (2) pulsing parameters including the pulse frequency, duty cycle, and magnitude, (3) reductant type, and (4) catalyst composition, including the type and loading of precious metal and NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150 °C and 650 °C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. Under RPR conditions, H2, CO, C12H26, and C2H4 provided approximately 80% NOx conversion at 500 °C; however, at 600 °C the conversions were significantly lower. The NOx conversion with C3H8 was low across the entire temperature range. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of 280–630 °C. This suggested that the high-temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

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References

Figures

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Fig. 1

Schematics of the RPR test rig

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Fig. 2

Graphical definition of pulse duty cycle (DC)

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Fig. 3

NOx conversion curves of RPR using different reductants at concentrations listed in Table 3, and pulsing parameters: P = 3 s, DC = 15%, and λpulse = 0.75

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Fig. 4

(a) NOx conversion and (b) ethylene conversion curves using ethylene as the reductant at concentrations listed in Table 3, different pulsing periods, DC = 15%, and λpulse = 0.75 using a degraded LNT sample

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Fig. 5

(a) Ammonia selectivity and (b) CO out concentration using ethylene as the reductant at concentrations listed in Table 3, different pulsing periods of P = 1 s, 3 s, 10 s, DC = 15%, and λpulse = 0.75

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Fig. 6

NOx conversion using dodecane as the reductant at concentrations listed in Table 3, at different pulsing periods, DC = 15%, and λpulse = 0.75

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Fig. 7

(a) Ammonia selectivity and (b) CO out concentration using vaporized dodecane as the reductant at concentrations listed in Table 3, different pulsing periods of P = 1 s, 2 s, 3 s, 6 s, DC = 15%, and λpulse = 0.75

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Fig. 8

(a) NOx and propylene conversion and (b) CO concentration and NH3 selectivity using propylene as the reductant at concentrations listed in Table 1, P = 3 s, DC = 15%, and λpulse = 0.75

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