Research Papers: Internal Combustion Engines

Catalyst Ammonia Storage Measurements Using Radio Frequency Sensing1

[+] Author and Article Information
Jonathan Aguilar

Mechanical Engineering,
University of Massachusetts Lowell,
Lowell, MA 01854
e-mail: Jonathan_Aguilar@student.uml.edu

Leslie Bromberg

Plasma Science and Fusion Center,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: Brom@psfc.mit.edu

Alexander Sappok

CTS Corporation,
Malden, MA 02148
e-mail: Alexander.Sappok@ctscorp.com

Paul Ragaller

CTS Corporation,
Malden, MA 02148
e-mail: Paul.Ragaller@ctscorp.com

Jean Atehortua

CTS Corporation,
Malden, MA 02148
e-mail: Jean.Atehortua@ctscorp.com

Xiaojin Liu

CTS Corporation,
Malden, MA 02148
e-mail: Xiaojin.Liu@ctscorp.com

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 15, 2018; final manuscript received April 30, 2018; published online July 9, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(11), 112805 (Jul 09, 2018) (7 pages) Paper No: GTP-18-1131; doi: 10.1115/1.4040198 History: Received March 15, 2018; Revised April 30, 2018

Motivated by increasingly strict nitrogen oxides (NOx) limits, engine manufacturers have adopted selective catalytic reduction (SCR) technology to reduce engine-out NOx. In the SCR process, NOx react with ammonia (NH3) to form nitrogen and water vapor. The reaction is influenced by several variables, including stored ammonia on the catalyst, exhaust gas composition, and catalyst temperature. Currently, measurements from NOx and/or NH3 sensors upstream and downstream of the SCR are used with predictive models to estimate ammonia storage levels on the catalyst and control urea dosing. This study investigated a radio frequency (RF)-based method to directly monitor the ammonia storage state of the SCR. This approach utilizes the catalyst as a cavity resonator, in which an RF antenna excites electromagnetic waves within the cavity to monitor changes in the catalyst state. Ammonia storage causes changes in the dielectric properties of the catalyst, which directly impacts the RF signal. Changes in the RF signal relative to stored ammonia (NH3) were evaluated over a wide range of frequencies, temperatures, and exhaust conditions. The RF response to NH3 storage, desorption, and oxidation on the SCR was well correlated with changes in the catalyst state. Calibrated RF measurements demonstrate the ability to monitor the adsorption state of the SCR to within 10% of the sensor full scale. The results indicate direct measurement of SCR ammonia storage levels, and resulting catalyst feedback control, via RF sensing to have significant potential for optimizing the SCR system to improve NOx conversion and decrease urea consumption.

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Fig. 1

Catalyst housing with RF antennas inserted upstream and downstream of the SCR sample

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Fig. 2

Simulated electric field distribution at a resonant frequency of 3.9 GHz for the SCR catalyst core samples used in this study

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Fig. 3

Comparison of the simulated and experimental resonances modes, a–e, within the metallic catalyst housing

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Fig. 4

RF transmission measurements showing both empty and loaded catalyst states of the SCR. Resonant modes are labeled a–d.

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Fig. 5

Electric field distribution within the catalyst housing at a resonant frequency of 5.31 GHz

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Fig. 6

Laboratory bench reactor layout showing system and main components for catalyst RF measurements

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Fig. 7

Laboratory Bench Reactor showing LabVIEW interface and Keysight RF Analyzer with two antennas

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Fig. 8

Experimental procedure showing ammonia injection rate at 300 ppm and ammonia slip at the outlet of the SCR

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Fig. 9

RF resonance curves with and without stored ammonia on the catalyst

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Fig. 10

Ammonia slip profile at a constant ammonia feed rate of 320 ppm and increasing temperatures

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Fig. 11

RF parameter as a function of time at temperatures of (a) 200 °C, (b) 250 °C, (b) 300 °C, and (d) 350 °C. The inlet ammonia feed rate is also shown for reference.

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Fig. 12

Ammonia storage, NH3 slip, and oxidation with a constant flow and NH3 feed rate at 250 °C

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Fig. 13

Ammonia inventory as a function of time based on NH3 slip and oxidation with increasing temperature and ammonia feed rate of 320 ppm

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Fig. 14

NH3 inventory comparison with the RF parameter at a temperature of 200 °C and constant ammonia feed rate of 320 ppm

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Fig. 15

Raw RF parameter as a function of NH3 inventory with increasing temperatures from 200–350 °C and a constant ammonia feed rate of 320 ppm

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Fig. 16

Measured NH3 RF catalyst storage state as a function of the calculated NH3 inventory over a temperature range of 200–350 °C and a constant ammonia feed rate of 320 ppm

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Fig. 17

RF measurement error for the calibration data presented in Fig. 16

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Fig. 18

Correlation between NH3 Inventory and normalized RF parameter with temperatures from 200 to 350 °C with a constant ammonia feed rate of 320 ppm

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Fig. 19

Upstream and downstream ammonia measurements along with the corresponding RF signal for a flow rate of (a) 40,000 1/h and (b) 80,000 1/h



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