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.

References

References
1.
Official Journal of the European Union
,
2007
, “
Regulation (EC) No. 715/2007 of the European Parliament and of the Council of 20 June 2007
,” Paper No. 32007R0715.
2.
ARB
,
2013
, “
Staff Report: Initial Statement of Reasons for Proposed Rule Making
,” Air Resources, Board, Sacramento, CA, accessed Dec. 12, 2013, https://www.arb.ca.gov/regact/2013/hdghg2013/hdghg2013isor.pdf
3.
Majewski
,
W. A.
,
2015
, “
SCR Systems for Mobile Engines
,” DieselNet, accessed May 2, 2016, from https://www.dieselnet.com/tech/cat_scr_mobile.php
4.
Cavataio
,
G.
,
Girard
,
J.
, and
Lambert
,
C.
,
2009
, “
Cu/Zeolite SCR on High Porosity Filters: Laboratory and Engine Performance Evaluations
,”
SAE
Paper No. 2009-01-0897.
5.
Hannu
,
J.
, and
Majewski
,
W. A.
,
2015
, “
Urea Dosing Control
,” DieselNet, accessed May 2, 2016, https://www.dieselnet.com/tech/cat_scr_mobile_control.php
6.
Majewski
,
W. A.
,
2015
, “
Urea Dosing and Injection Systems
,” DieselNet, accessed May 2, 2016, https://www.dieselnet.com/tech/cat_scr_mobile_urea_dosing.php
7.
Majewski
,
W. A.
,
2015
, “
Selective Catalytic Reduction
,” DieselNet, accessed May 2, 2016, https://www.dieselnet.com/tech/cat_scr.php
8.
Kleemann
,
M.
,
Elsener
,
M.
,
Koebel
,
M.
, and
Wokaun
,
A.
,
2000
, “
Hydrolysis of Isocyanic Acid on SCR Catalysts
,”
Ind. Eng. Chem. Res.
,
39
(
11
), pp.
4120
4126
.
9.
Cavataio
,
G.
,
Girard
,
J.
,
Patterson
,
J.
,
Montreuil
,
C.
, et al. .,
2007
, “
Laboratory Testing of Urea-SCR Formulations to Meet Tier 2 Bin 5 Emissions
,”
SAE
Paper No. 2007-01-1575.
10.
Rauch
,
D.
,
Kubinski
,
D.
,
Cavataio
,
G.
,
Upadhyay
,
D.
, and
Moos
,
R.
,
2015
, “
Ammonia Loading Detection of Zeolite SCR Catalysts Using a Radio Frequency Based Method
,”
SAE Int. J. Engines
,
8
(
3
), pp.
1126
1135
.
11.
Sappok
,
A.
,
Ragaller
,
P.
,
Bromberg
,
L.
,
Herman
,
A.
,
Prikhodko
,
V.
,
Parks
,
J.
, and
Storey
,
J.
,
2017
, “
On-Board Particulate Filter Failure Prevention and Failure Diagnostics Using Radio Frequency Sensing
,”
SAE Int. J. Engines
,
10
(
4
), pp. 1667–1682.
12.
Sappok
,
A.
,
Ragaller
,
P.
,
Bromberg
,
L.
,
Prikhodko
,
V.
,
Storey
,
J.
, and
Parks
,
J.
,
2016
, “
Real-Time Engine and After treatment System Control Using Fast Response Particulate Filter Sensors
,”
SAE
Paper No. 2016-01-0918.
13.
Sappok
,
A.
,
Ragaller
,
P.
,
Bromberg
,
L.
,
Gunasekaran
,
N.
,
Warkins
,
J.
, and
Wilhelm
,
R.
,
2016
, “
Particulate Filter Soot Load Measurements Using Radio Frequency Sensors and Potential for Improved Filter Management
,”
SAE
Paper No. 2016-01-0943.
14.
Moos
,
R.
,
2015
, “
Microwave-Based Catalyst State Diagnosis—State of the Art and Future Perspectives
,”
SAE Int. J. Engines
,
8
(
3
), pp.
1240
1245
.
15.
Sappok
,
A.
, and
Bromberg
,
L.
,
2013
, “
Development of Radio Frequency Sensing for In-Situ Diesel Particulate Filter State Monitoring and After Treatment System Control
,”
ASME
Paper No. ICEF2013-19199.
You do not currently have access to this content.