Catalyst Ammonia Storage Measurements Using Radio Frequency Sensing

[+] Author and Article Information
Jonathan Aguilar

University of Massachusetts Lowell, Lowell, MA, USA

Leslie Bromberg

Massachusetts Institute of Technology, Cambridge, MA, USA

Alexander Sappok

CTS Corporation, Malden, MA, USA

Paul Ragaller

CTS Corporation, Malden, MA, USA

Jean Atehortua

CTS Corporation, Malden, MA, USA

Xiaojin Liu

CTS Corporation, Malden, MA, USA

1Corresponding author.

ASME doi:10.1115/1.4040198 History: Received March 15, 2018; Revised April 30, 2018


Motivated by increasingly strict NOx limits, engine manufacturers have adopted selective catalytic reduction (SCR) technology to reduce engine-out NOx. In the SCR process, nitrogen oxides (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.

Copyright (c) 2018 by ASME
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