Numerical analysis of NOx reduction for compact design in marine urea-SCR system

Abstract Lean gasoline engine operation provides clear efficiency benefits relative to conventional stoichiometric combustion approaches. One of the key hurdles to the widespread, practical implementation of lean gasoline combustion remains the challenge of lean NOx control. One of the potential approaches for controlling NOx emission from lean gasoline engines is the so-called passive selective catalytic reduction (SCR) system. In such systems, periods of rich operation generate ammonia over a three-way catalyst (TWC), which is then adsorbed on the downstream SCR and consumed during lean operation. Brief periods of rich operation must occur in response to the depletion of stored ammonia on the SCR, which requires reliable measurements of the SCR ammonia inventory. Presently, lean exhaust system controls rely on a variety of gas sensors mounted up- and downstream of the catalysts, and which only provide an indirect inference of the operation state. In this study, a radio frequency (RF) sensor was used to provide a direction measurement of the amount of ammonia adsorbed on the SCR in real-time. The RF sensor was calibrated and deployed on a BMW N43B20 4-cylinder lean gasoline engine equipped with a passive SCR system. Brief periods of rich operation performed at lambda values between 0.98 and 0.99 generated the ammonia, subsequently stored on the SCR for consumption during periods of lean operation. The experiments compared real-time measurements of SCR ammonia inventory from the RF sensor with estimates of ammonia coverage derived from exhaust gas composition measurements upstream and downstream of the catalyst. The results showed a high degree of correlation between the RF measurements and SCR ammonia storage inventory, and demonstrated NOx conversion efficiencies above 98%, confirming the feasibility of the concept. Relative to stoichiometric operation, lean-gasoline operation resulted in fuel efficiency gains of up to 10%, which may be further improved through direct feedback control from the RF sensor to optimize lean–rich cycling based on actual, measured SCR ammonia levels.

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Investigation of Urea Uniformity with Different Types of Urea Injectors in an SCR System

Catalysts ◽

10.3390/catal10111269 ◽

2020 ◽

Vol 10 (11) ◽

pp. 1269

Author(s):

Muhammad Khristamto Aditya Wardana ◽

Kwangchul Oh ◽

Ocktaeck Lim

Keyword(s):

Diesel Engine ◽

Catalytic Reduction ◽

Nox Reduction ◽

Heavy Duty ◽

Ammonia Gas ◽

Experimental Parameters ◽

Heavy Duty Diesel Engine ◽

Heavy Duty Diesel ◽

Scr System

Heavy-duty diesel engines in highway use account for more than 40% of total particulate and nitrogen oxide (NOx) emissions around the world. Selective catalytic reduction (SCR) is a method with effective results to reduce this problem. This research deals with problems in the urea evaporation process and ammonia gas distribution in an SCR system. The studied system used two types of urea injectors to elucidate the quality of ammonia uniformity in the SCR system, and a 12,000-cc heavy-duty diesel engine was used for experimentation to reduce NOx in the system. The uniformity of the generated quantities of ammonia was sampled at the catalyst inlet using a gas sensor. The ammonia samples from the two types of urea injectors were compared in experimental and simulation results, where the simulation conditions were based on experimental parameters and were performed using the commercial CFD (computational fluid dynamics) code of STAR-CCM+. This study produces temperatures of 371 to 374 °C to assist the vaporization phenomena of two injectors, the gas pattern informs the distributions of ammonia in the system, and the high ammonia quantity from the I-type urea injector and high quality of ammonia uniformity from the L-type urea injector can produce different results for NOx reduction efficiency quality after the catalyst process. The investigations showed the performance of two types of injectors and catalysts in the SCR system in a heavy-duty diesel engine.

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Effects of SCR System on Nox Reduction in Heavy Duty Diesel Engine Fuelled with Diesel and Alcohol Blends

Advances in Automobile Engineering ◽

10.4172/2167-7670.1000139 ◽

2016 ◽

Vol 05 (02) ◽

Cited By ~ 1

Author(s):

Ceyla Ozgur ◽

Kadir Aydin

Keyword(s):

Diesel Engine ◽

Nox Reduction ◽

Heavy Duty ◽

Heavy Duty Diesel Engine ◽

Heavy Duty Diesel ◽

Scr System

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Modelling and parametric investigation of NOx reduction by oxidation precatalyst-assisted ammonia-selective catalytic reduction

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/09544070jauto1099 ◽

2009 ◽

Vol 223 (9) ◽

pp. 1193-1206 ◽

Cited By ~ 4

Author(s):

S-C Jung ◽

W-S Yoon

Keyword(s):

Selective Catalytic Reduction ◽

Low Temperatures ◽

Catalytic Reduction ◽

Nox Reduction ◽

Volume Ratio ◽

Kinetic Scheme ◽

Space Velocity ◽

Gas Temperature ◽

Scr System ◽

Very High

Nitrogen oxide (NO x) reduction by the selective catalytic reduction (SCR) system assisted by an oxidation precatalyst is modelled and analytically investigated. The Langmuir—Hinshelwood SCR kinetic scheme with vanadium-based catalyst and ammonia (NH3) reductant in conjunction with the NO—NO2 conversion reaction over a platinum-based catalyst is used. The effects of the ratio of the oxidation precatalyst to the SCR monolith volume, the gas temperature, the space velocity, and the NH3-to-NO x concentration ratio on the de-NO x performance are parametrically examined. The oxidation precatalyst promotes NO x conversion at low temperatures. At intermediate temperatures, the NO x reduction is either activated or deactivated with increase in the space velocity. A higher oxidation precatalyst-to-SCR monolith volume ratio tends to promote the NO x reduction of higher space velocities. At high temperatures, the de-NO x efficiency is very high and insensitive to the space velocity. The NO x conversion efficiency depends on the NH3-to-NO x ratio at low temperatures.

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Dynamic Characteristics of a Urea SCR System for NOx Reduction in Diesel Engine

Journal of the Korean Society of Marine Engineering ◽

10.5916/jkosme.2007.31.3.235 ◽

2007 ◽

Vol 31 (3) ◽

pp. 235-242 ◽

Cited By ~ 5

Author(s):

Jeong-Gil Nam ◽

Jae-Sung Choi

Keyword(s):

Diesel Engine ◽

Dynamic Characteristics ◽

Nox Reduction ◽

Scr System

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The Development and Implementation of Model-Based Control Algorithm of Urea-SCR Dosing System for Improving De-NOx Performance and Reducing NH3-Slip

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D ◽

10.1115/ajk2011-23011 ◽

2011 ◽

Author(s):

Soo-Jin Jeong ◽

Woo-Seung Kim ◽

Jung-Kwon Park ◽

Ho-Kil Lee ◽

Se-Doo Oh

Keyword(s):

Control Algorithm ◽

Catalytic Reduction ◽

Fluid Model ◽

Nox Reduction ◽

Reaction Model ◽

Urea Solution ◽

Model Based Control ◽

Model Based ◽

Nh3 Emission ◽

Scr System

The selective catalytic reduction (SCR) system is a highly-effective aftertreatment device for NOx reduction of diesel engines. Generally, the ammonia (NH3) was generated from reaction mechanism of SCR in the SCR system using the liquid urea as the reluctant. Therefore, the precise urea dosing control is a very important key for NOx and NH3 slip reduction in the SCR system. This paper investigated NOx and NH3 emission characteristics of urea-SCR dosing system based on model-based control algorithm in order to reduce NOx. In the map-based control algorithm, target amount of urea solution was determined by mass flow rate of exhaust gas obtained from engine rpm, torque and O2 for feed-back control NOx concentration should be measured by NOx sensor. Moreover, this algorithm cannot estimate NH3 absorbed on the catalyst Hence, the urea injection can be too rich or too lean. In this study, the model-based control algorithm was developed and evaluated based on the analytic model for SCR system. The channel thermo-fluid model coupled with finely tuned chemical reaction model was applied to this control algorithm. The vehicle test was carried out by using map-based and model-based control algorithms in the NEDC mode in order to evaluate the performance of the model based control algorithm.

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