Ammonia Generation and Utilization in a Passive SCR (TWC+SCR) System on Lean Gasoline Engine

2016 ◽  
Vol 9 (2) ◽  
pp. 1289-1295 ◽  
Author(s):  
Vitaly Y. Prikhodko ◽  
James E. Parks ◽  
Josh A. Pihl ◽  
Todd J. Toops
Keyword(s):  
Gasoline Engine ◽  
Scr System ◽  
Lean Gasoline ◽  
Passive Scr

scholarly journals Direct Measurement of Ammonia Storage on Passive SCR Systems for Lean Gasoline NOx Reduction Using Radio Frequency Sensing

2019 ◽  
Author(s):  
Paul Ragaller ◽  
Josh Mandelbaum ◽  
Luc Lapenta ◽  
Alexander Sappok ◽  
Josh Pihl ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Real Time ◽  
Gasoline Engine ◽  
Nox Reduction ◽  
Practical Implementation ◽  
Engine Operation ◽  
Ammonia Storage ◽  
Scr System ◽  
Lean Gasoline ◽  
Passive Scr

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.

TWC-SCR Aftertreatment System Evaluation for a Lean Burn Gasoline Engine Operating in HCCI, SACI, and SI Combustion Modes

2016 ◽  
Author(s):  
Jordan Easter ◽  
Stanislav V. Bohac
Keyword(s):  
Conversion Efficiency ◽  
Gasoline Engine ◽  
Fuel Efficiency ◽  
Compression Ignition ◽  
Scr Catalyst ◽  
Advanced Combustion ◽  
Nox Conversion ◽  
Combustion Modes ◽  
Scr System ◽  
Nox Conversion Efficiency

Low temperature and dilute Homogenous Charge Compression Ignition (HCCI) and Spark Assisted Compression Ignition (SACI) can improve fuel economy and reduce engine-out NOx emissions to very low values, often less than 30 ppm. However, these combustion modes are unable to achieve stringent future regulations such as SULEV 30 without the use of lean aftertreatment. Though active selective catalytic reduction (SCR) with urea injection and lean NOx traps (LNT) have been investigated as options for lean gasoline engines, a passive TWC-SCR system is investigated in this work because it avoids the urea storage and dosing hardware of a urea SCR system, and the high precious metal cost of an LNT. The TWC-SCR concept uses periodic rich operation to produce NH3 over a TWC to be stored on an SCR catalyst for subsequent NOx conversion during lean operation. In this work a laboratory study was performed with a modified 2.0 L gasoline engine that was cycled between lean HCCI and rich SACI operation, or between lean and rich SI (spark ignited) combustion, to evaluate NOx conversion and reduced fuel consumption. Different lambda values during rich operation and different times held in rich operation were investigated. Results are compared to a baseline case in which the engine is always operated at stoichiometric conditions. SCR system simulations are also presented that compare system performance for different levels of stored NH3. With the configuration used in this study, lean/rich HCCI/SACI operation showed a maximum NOx conversion efficiency of 10%, while lean/rich SI operation showed a maximum NOx conversion efficiency of 60%. However, if the low conversion efficiency of lean/rich HCCI/SACI operation could be improved through higher brick temperatures or additional SCR bricks, simulation results indicate TWC-SCR aftertreatment has the potential to provide near-zero SCR-out NOx concentration and increased system fuel efficiency. In these simulations, fuel efficiency improvement relative to stoichiometric SI were 7 to15% for lean/rich HCCI/SACI with zero tailpipe NOx and −1 to 5% for lean/rich SI with zero tailpipe NOx emissions. Although previous work indicated increased time for NH3 to start forming over the TWC during rich operation, less NH3 production over the TWC per fuel amount, and increased NH3 slip over the SCR catalyst for advanced combustion systems, if NOx conversion efficiency could be enhanced, improvements in fuel economy and low engine-out NOx from advanced combustion modes would more than make up for these disadvantages.

Simultaneous Optimization of Configuration and Control for a Passive SCR System

2018 ◽  
Author(s):  
Pingen Chen ◽  
Qinghua Lin
Keyword(s):  
Catalytic Reduction ◽  
Simultaneous Optimization ◽  
Computationally Efficient ◽  
System Architectures ◽  
Aftertreatment System ◽  
In Series ◽  
System Configurations ◽  
Scr System ◽  
And Control ◽  
Passive Scr

The configuration and control of aftertreatment systems have a significant impact on their functionalities and emission control performance. The traditional aftertreatment system configurations, i.e., connections from one aftertreatment subsystem to another subsystem in series, are simple but generally do not yield the optimal aftertreatment system performance. New aftertreatment configurations, in conjunction with new engine and aftertreatment control, can significantly improve engine efficiency and emission reduction performance. However, new configuration design requires human intuition and in-depth knowledge of engine and aftertreatment system design and control. The purpose of this study is to develop a general systematic and computationally-efficient method which enables automated and simultaneous optimization of passive selective catalytic reduction (SCR) system architectures and the associated non-uniform cylinder-to-cylinder combustion (NUCCC) controls based on a newly proposed highly reconfigurable passive SCR model structure and integer partition theory. The proposed method is general enough to account for passive SCR systems with two or more TWC stages. We demonstrate through this case study that the optimized passive SCR configuration, in conjunction with the optimized NUCCC control, can reduce the NH3 specific fuel consumption by up to 21.90%.

Optimization of Mode Switching Timing Control for a Lean-Burn Gasoline Engine With a Prototype Passive SCR System

2018 ◽  
Author(s):  
Dakota Strange ◽  
Pingen Chen ◽  
Vitaly Y. Prikhodko ◽  
James E. Parks
Keyword(s):  
Gasoline Engine ◽  
Nox Reduction ◽  
Cost Effective ◽  
Nox Storage ◽  
Mode Switching ◽  
Timing Control ◽  
Lean Burn ◽  
Gasoline Engines ◽  
Effective Manner ◽  
Passive Scr

Passive selective catalytic reduction (SCR) has emerged as a promising NOx reduction technology for highly-efficient lean-burn gasoline engines to meet stringent NOx emission regulation in a cost-effective manner. In this study, a prototype passive SCR which includes an upstream three-way catalyst (TWC) with added NOx storage component, and a downstream urealess SCR catalyst, was investigated. Engine experiments were conducted to investigate and quantify the dynamic NOx storage/release behaviors as well as dynamic NH3 generation behavior on the new TWC with added NOx storage component. Then, the lean/rich mode-switching timing control was optimized to minimize the fuel penalty associated with passive SCR operation. Simulation results show that, compared to the baseline mode-switching timing control, the optimized control can reduce the passive SCR-related fuel penalty by 6.7%. Such an optimized mode-switching timing control strategy is rather instrumental in realizing significant fuel efficiency benefits for lean-burn gasoline engines coupled with cost-effective passive SCR systems.

scholarly journals Passive SCR for lean gasoline NOX control: Engine-based strategies to minimize fuel penalty associated with catalytic NH3 generation

2016 ◽  
Vol 267 ◽  
pp. 202-209 ◽  
Author(s):  
Vitaly Y. Prikhodko ◽  
James E. Parks ◽  
Josh A. Pihl ◽  
Todd J. Toops
Keyword(s):  
Nox Control ◽  
Lean Gasoline ◽  
Passive Scr

scholarly journals A New Generation Lean Gasoline Engine for Premium Vehicle CO2 Reduction

2021 ◽  
Author(s):  
Richard Osborne ◽  
Andrew Lane ◽  
Niall Turner ◽  
John Geddes ◽  
Penny Atkins ◽  
...  
Keyword(s):  
Gasoline Engine ◽  
Co2 Reduction ◽  
New Generation ◽  
Lean Gasoline
Sign in / Sign up

Export Citation Format

Share Document