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Ammonium Nitrate Formation and Decomposition on an Extruded Vanadium-Based SCR Catalyst

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Christopher Keturakis, Z. Gerald Liu
  • Technical Paper
  • 2020-01-1320
To be published on 2020-04-14 by SAE International in United States
In this study, the formation and decomposition of ammonium nitrate (AN) on a state-of-the-art extruded vanadium-based SCR catalyst (V-SCR) under simulated exhaust conditions has been evaluated. Results show that AN readily forms and accumulates at temperatures below 200°C when exposed to NH3 and NO2. The rate of AN accumulation increases with decreasing temperature. A new low temperature NH3 release peak (not present following NH3 storage conditions with NH3 only) becomes apparent after AN accumulation at 100 and 125°C. This new NH3 release, with a peak release temperature of approximately 180°C, is evaluated in detail to better determine its origin. BET surface area, and thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC), and reactor-based experiments are all used to characterize AN formed on the V-SCR catalyst in comparison to pure AN. Experiments on pure AN crystals reveal that the new low temperature NH3 peak is attributable to the release of NH3 from AN that is not related to AN volatilization, since this does not occur until above T > 200°C.This study expands the present understanding of AN formation…
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A Case Study of a Cu-SSZ-13 SCR Catalyst Poisoned by Real-World High Sulfur Diesel Fuel

Cummins Emission Solutions-Yuanzhou Xi, Nathan Ottinger, Christopher Keturakis, Z. Gerald Liu
  • Technical Paper
  • 2020-01-1319
To be published on 2020-04-14 by SAE International in United States
To meet increasingly stringent diesel engine emission regulations, diesel engines are required to use ultra-low sulfur diesel (ULSD) and are equipped with advanced aftertreatment systems. Cu-SSZ-13 zeolite catalysts are widely used as selective catalytic reduction (SCR) catalysts due to their high NOx reduction and excellent hydrothermal stability. However, active Cu sites of Cu-SSZ-13 catalysts can be poisoned by exposure to engine exhaust sulfur species. This poison effect can be mitigated with the use of ULSD and high temperature exposure from engine operation. On the other hand, ULSD is still not universally available where regulations require it, and vehicles may inadvertently operate with high sulfur diesel fuel (HSD) in some locations. The high concentration of exhaust sulfur species resulting from HSD combustion may rapidly poison the Cu-SSZ-13 SCR catalyst. In this study, the catalytic performance of a sulfur poisoned Cu-SSZ-13 SCR catalyst is analyzed. Results show that the as received SCR catalyst displays substantially low NOx conversion below 350 °C. A thermal treatment at 550 °C can recover most of its lost performance. Temperature programmed desorption…
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Low-Temperature NH3 Storage, Isothermal Desorption, Reactive Consumption, and Thermal Release from Cu-SSZ-13 and V2O5-WO3/TiO2 Selective Catalytic Reduction Catalysts

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Christopher Keturakis, Z. Gerald Liu
Published 2019-04-02 by SAE International in United States
Worldwide, regulations continue to drive reductions in brake-specific emissions of nitric oxide (NO) and nitrogen dioxide (NO2) from on-highway and nonroad diesel engines. NOx, formed as a byproduct of the combustion of fossil fuels (e.g., natural gas, gasoline, diesel, etc.), can be converted to dinitrogen (N2) through ammonia (NH3) selective catalytic reduction (SCR). In this study, we closely examine the low-temperature storage, isothermal desorption, reactive consumption, and thermal release of NH3 on commercial Cu-SSZ-13 and V2O5-WO3/TiO2 SCR catalysts. Catalyst core-reactor, N2 adsorption (BET) surface area, and in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) experiments are utilized to investigate the fundamental chemical processes relevant to low-temperature (T < 250°C) NH3 SCR. Results show that NH3 stored at low-temperature continuously, yet slowly releases from the SCR catalysts, and that nearly all of the weakly bound NH3 stored on Cu2+ sites of the Cu-SSZ-13 catalyst will isothermally desorb from the catalyst in the absence of NOx. However, in the presence of NOx, a large fraction of this weakly bound NH3 will react with NOx, contributing to the…
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Experimental Study of Impact of Ash and Soot on Tail Pipe Particle Number

Cummins Emission Solutions-Harsha Shankar Surenahalli, Jacob Backhaus, Qiang Liu
Cummins Inc-Rayomand Dabhoiwala, Todd Martin
Published 2019-04-02 by SAE International in United States
Tailpipe particle number (PN) emission limits for heavy-duty diesel engines have been introduced as part of the off-highway Stage V standards. To meet the required limits a diesel particulate filter (DPF) with high filtration efficiency is required. The DPF relies on formation of a soot cake layer on the channel walls to achieve this high filtration efficiency. Off highway Stage V certification cycles are significantly higher in temperature than their on-highway counterparts, leading to difficulty in creating and maintaining a soot cake in the DPF. Hence for these applications meeting particle number requirements is challenging.To meet the high filtration efficiency requirements the DPF will have to reduce mean pore size, pore standard deviation, and increase wall thickness, in turn increasing backpressure, which results in a fuel consumption penalty. Another option is to evaluate the impact of temperature stable ash accumulation on DPF filtration efficiency. This paper discusses the ability of ash and soot to improve PN filtration.
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Design and Durability of Vanadium-SCR Catalytic Aftertreatment System to Meet Tier 4 Emission Regulations in a Locomotive Application

Cummins Emission Solutions-Alaa Kababji, Atul Abhyankar, Huiling Li
Cummins Power Systems-S.M. Boopathi
Published 2019-02-21 by SAE International in United States
An advanced exhaust aftertreatment system (ATS) for Tier 4 compliant locomotive applications was successfully designed and developed for use on Cummins QSK95 engines. The engine and ATS were introduced in late 2016. This system provided nitrogen oxides (NOx) reduction capability in excess of 95%. Vanadia-based selective catalytic reduction (V-SCR) extruded catalyst technology was chosen over other readily available component technologies such as diesel oxidation catalyst (DOC) or a combination of DOC and SCR systems to address the stringent Tier 4 standards. In addition to NOx reduction, substantial oxidation of gaseous hydrocarbons (HCs) from unburnt fuel and lubricating oil soluble organic fraction (SOF) was also achieved. This dual functionality (oxidation and reduction capability) was one of the key factors in adopting this technology as the prime path and rendering it suitable for the harsh locomotive application environment. The properties and performance of the chosen Johnson Matthey Inc. (JMI) extruded V-SCR catalyst are described in this article. In-house developed analysis led design (ALD) and computational fluid dynamics (CFD) tools were utilized to design the ATS package and…
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CFD Modeling of Tailpipe NOx Sensor Accuracy

SAE International Journal of Engines

Cummins Emission Solutions-Apoorv Kalyankar, Achuth Munnannur, Z. Gerald Liu
  • Journal Article
  • 03-11-04-0029
Published 2018-08-08 by SAE International in United States
In a modern diesel aftertreatment system, a sensor for nitrogen oxides (NOx) placed downstream of the selective catalytic reduction (SCR) catalyst is necessary to determine if the tailpipe NOx concentration remains below the applicable On-board diagnostic (OBD) threshold. Typically the same NOx sensor also provides feedback to the dosing control module to adjust diesel exhaust fluid (DEF) dosing rate thereby controlling tailpipe NOx and ammonia emissions. However, feedback signal sent by the tailpipe NOx sensor may not always be accurate due to reasons including non-uniformity in NOx and ammonia distributions at SCR outlet. Flow based metrics from computational fluid dynamics (CFD) analyses, that are typically used to qualitatively assess NOx sensor accuracy in different designs are often inadequate. In this work, an improved CFD analysis procedure has been developed for assessing NOx sensor accuracy. This approach enables a direct comparison of NOx sensor accuracy between different sampling probe and sensor designs. This improved modeling approach was first validated against test data without spray effects by injecting gaseous NOx in a 5″ pipe. The impact of…
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NO2 Formation and Mitigation in an Advanced Diesel Aftertreatment System

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Niklas Schmidt, Z. Gerald Liu
Published 2018-04-03 by SAE International in United States
Nitrogen dioxide (NO2) is known to pose a risk to human health and contributes to the formation of ground level ozone. In recognition of its human health implications, the American Conference of Governmental Industrial Hygienists (ACGIH) set a Threshold Limit Value (TLV) of 0.2 ppmv NO2 in 2012. For mobile sources, NO2 is regulated as a component of NOx (NO + NO2). In addition, the European Commission has indicated it is considering separate Euro 6 light-duty diesel and Euro VI heavy-duty diesel NO2 emissions limits likely to mitigate the formation of ground level ozone in urban areas. In this study, we conduct component-level reactor-based experiments to understand the effects that various aftertreatment catalyst technologies including diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR) catalyst and ammonia oxidation (AMOX) catalyst have on the formation and mitigation of NO2 emissions. Finally, emissions from a nonroad Tier 4 Final/Stage IV engine equipped with an advanced aftertreatment system are analyzed to understand the effect of real-world engine operating conditions on NO2 emissions. Experiments were conducted…
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The Dynamics of Methane and NOx Removal by a Three-Way Catalyst: A Transient Response Study

SAE International Journal of Engines

Cummins Emission Solutions-Yuanzhou Xi, Nathan Ottinger, Z. Gerald Liu
  • Journal Article
  • 2018-01-1270
Published 2018-04-03 by SAE International in United States
Natural gas-powered engines are widely used due to their low fuel cost and in general their lower emissions than conventional diesel engines. In order to comply with emissions regulations, an aftertreatment system is utilized to treat exhaust from natural gas engines. Stoichiometric burn natural gas engines use three-way catalyst (TWC) technology to simultaneously remove NOx, CO, and hydrocarbon (HC). Removal of methane, one of the major HC emissions from natural gas engines, is difficult due to its high stability, posing a challenge for existing TWC technologies. In this work, degreened (DG), standard bench cycle (SBC)-aged TWC catalysts and a DG Pd-based oxidation catalyst (OC) were evaluated and compared under a variety of lean/rich gas cycling conditions, simulating stoichiometric natural gas engine emissions. Transient response techniques were applied to reveal the effect of the oxygen storage component on the performance of DG TWC as well as upon SBC aging in comparison to DG OC. It is illustrated that the oxygen storage component of TWC can extend the rich phase’s high conversion efficiency of both CH4 and…
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Formation and Decomposition of Ammonium Nitrate on an Ammonia Oxidation Catalyst

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Z. Gerald Liu
Published 2018-04-03 by SAE International in United States
Achieving high NOx conversion at low-temperature (T ≤ 200 °C) is a topic of active research due to potential reductions in regulated NOx emissions from diesel engines. At these temperatures, ammonium nitrate may form as a result of interactions between NH3 and NO2. Ammonium nitrate formation can reduce the availability of NH3 for NOx conversion and block active catalyst sites. The thermal decomposition of ammonium nitrate may result in the formation of N2O, a regulated Greenhouse Gas (GHG). In this study, we investigate the formation and thermal and chemical decomposition of ammonium nitrate on a state-of-the-art dual-layer ammonia oxidation (AMOX) catalyst. Reactor-based constant-temperature ammonium nitrate formation, temperature programmed desorption (TPD), and NO titration experiments are used to characterize formation and decomposition. N2 adsorption and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) experiments are also conducted to elucidate the physical and chemical impacts of ammonium nitrate formation on the AMOX catalyst. The insights provided herein support the diesel aftertreatment communities’ ongoing efforts to understand low-temperature chemical processes such as ammonium salt formation and their impact on emissions.
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Sustained Low Temperature NOx Reduction

Cummins Emission Solutions-Sade Ruffin
Cummins Inc.-Yuhui Zha, Michael Cunningham, Yadan Tang, Anand Srinivasan, Jinyong Luo, John Heichelbech, Venkata Lakkireddy, Aleksey Yezerets
Published 2018-04-03 by SAE International in United States
Sustained NOx reduction at low temperatures, especially in the 150-200 °C range, shares some similarities with the more commonly discussed cold-start challenge, however, poses a number of additional and distinct technical problems. In this project, we set a bold target of achieving and maintaining 90% NOx conversion at the SCR catalyst inlet temperature of 150 °C. This project is intended to push the boundaries of the existing technologies, while staying within the realm of realistic future practical implementation.In order to meet the resulting challenges at the levels of catalyst fundamentals, system components, and system integration, Cummins has partnered with the DOE, Johnson Matthey, and Pacific Northwest National Lab and initiated the Sustained Low-Temperature NOx Reduction program at the beginning of 2015 and completed in 2017. Through this collaboration, we are exploring catalyst formulations and catalyst architectures with enhanced catalytic activity at 150 °C; opportunities to approach the desirable ratio of NO and NO2 in the SCR feed gas; options for robust low-temperature reductant delivery; and the requirements for the overall system integration. This paper will provide…
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