scholarly journals Analysis of the NOx storage behaviour during cold start of modern SCR flow-through substrates and SCR on-filter substrates

Author(s):  
Deinhofer Lukas ◽  
Maurer Michael ◽  
Barnstedt Gert ◽  
Keber Andreas

AbstractSelective catalytic reduction (SCR) systems are the state-of-the-art technology to reduce nitrogen oxide emissions (NOx) of modern diesel engines. The system behaviour is well understood in the common temperature working area. However, the system properties below light-off temperature are less well known and offer a wide scope for further investigations. Vehicle measurements show that under specific conditions during cold start, NOx can be partially stored and converted on on-filter and flow-through SCR catalysts. The purpose of this work was in a first step to analyse the main influence parameters on the NOx storage behaviour. Therefore, synthetic gas test bench measurements have been carried out, varying the gas concentrations, temperature, and gas hourly space velocity (GHSV). These investigations showed that the NOx storage effect strongly depends on the NH3 level stored in the catalyst, GHSV, the adsorbed water (H2O) on the catalyst, and the temperature of the catalyst. Further influence parameters such as the gas composition with focus on carbon monoxide (CO), short-chain hydrocarbons and long-chain hydrocarbons have been analysed on a synthetic gas test bench. Depending on operating conditions, a significant amount of NOx can be stored on a dry catalyst during the cold start phase. The water vapor from the combustion condenses on the cold exhaust pipe during the first seconds, or up to a few minutes after a cold start. As the water vapor reaches the surface of the catalyst, it condenses and adsorbs onto it, leading to a sudden temperature rise. This exothermal reaction causes the stored NOx to be desorbed, and furthermore it is partially reduced by the NH3 stored in the catalyst.

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Guido Belforte ◽  
Andrea Manuello Bertetto ◽  
Luigi Mazza

A study was carried out to evaluate behavior and performance of vortex triodes. In particular, the study investigated the geometries and operating conditions which minimize the control flow capable of intercepting the supply flow. The study was conducted experimentally using a specially designed test bench on prototypes operating with water. The geometric parameters which influence vortex valve performance were identified and varied so as to minimize the ratio between control and supply flows. The paper presents a semi-empirical formula to predict vortex valve performance. In particular, the formula takes valve outlet geometry and the shape of outlet diffusers into account.


2014 ◽  
Vol 42 (1) ◽  
pp. 2-15
Author(s):  
Johannes Gültlinger ◽  
Frank Gauterin ◽  
Christian Brandau ◽  
Jan Schlittenhard ◽  
Burkhard Wies

ABSTRACT The use of studded tires has been a subject of controversy from the time they came into market. While studded tires contribute to traffic safety under severe winter conditions by increasing tire friction on icy roads, they also cause damage to the road surface when running on bare roads. Consequently, one of the main challenges in studded tire development is to reduce road wear while still ensuring a good grip on ice. Therefore, a research project was initiated to gain understanding about the mechanisms and influencing parameters involved in road wear by studded tires. A test method using the institute's internal drum test bench was developed. Furthermore, mechanisms causing road wear by studded tires were derived from basic analytical models. These mechanisms were used to identify the main parameters influencing road wear by studded tires. Using experimental results obtained with the test method developed, the expected influences were verified. Vehicle driving speed and stud mass were found to be major factors influencing road wear. This can be explained by the stud impact as a dominant mechanism. By means of the test method presented, quantified and comparable data for road wear caused by studded tires under controllable conditions can be obtained. The mechanisms allow predicting the influence of tire construction and variable operating conditions on road wear.


2020 ◽  
Vol 26 (3) ◽  
pp. 126-130
Author(s):  
Krasimir Kalev

AbstractA schematic diagram of a hydraulic drive system is provided to stabilize the speed of the working body by compensating for volumetric losses in the hydraulic motor. The diagram shows the inclusion of an originally developed self-adjusting choke whose flow rate in the inlet pressure change range tends to reverse - with increasing pressure the flow through it decreases. Dependent on the hydraulic characteristics of the hydraulic motor and the specific operating conditions.


Author(s):  
Joonguen Park ◽  
Shinku Lee ◽  
Sunyoung Kim ◽  
Joongmyeon Bae

This paper discusses a numerical analysis of the heat and mass transfer characteristics in an autothermal methane reformer. Assuming local thermal equilibrium between the bulk gas and the surface of the catalyst, a one-medium approach for the porous medium analysis was incorporated. Also, the mass transfer between the bulk gas and the catalyst’s surface was neglected due to the relatively low gas velocity. For the catalytic surface reaction, the Langmuir–Hinshelwood model was incorporated in which methane (CH4) is reformed to hydrogen-rich gases by the autothermal reforming (ATR) reaction. Full combustion, steam reforming, water-gas shift, and direct steam reforming reactions were included in the chemical reaction model. Mass, momentum, energy, and species balance equations were simultaneously calculated with the chemical reactions for the multiphysics analysis. By varying the four operating conditions (inlet temperature, oxygen to carbon ratio (OCR), steam to carbon ratio, and gas hourly space velocity (GHSV)), the performance of the ATR reactor was estimated by the numerical calculations. The SR reaction rate was improved by an increased inlet temperature. The reforming efficiency and the fuel conversion reached their maximum values at an OCR of 0.7. When the GHSV was increased, the reforming efficiency increased but the large pressure drop may decrease the system efficiency. From these results, we can estimate the optimal operating conditions for the production of large amounts of hydrogen from methane.


Author(s):  
Juan Yin ◽  
Yi-wu Weng

This paper investigated performance characteristics analysis of catalytic combustion by utilizing 1-D models incorporated heat and mass transfer correlations. The 1-D numerical results were compared with 2-D models studies and experimental data. The performance characteristics were mainly the effects of operating conditions on methane conversion rate. The comparable analysis confirmed that 1-D model can success in predicting performance of catalytic combustion when empiric inter-phase heat and mass transfer correlations are used and appropriate operating conditions are chosen.


2018 ◽  
Vol 10 (12) ◽  
pp. 168781401881536 ◽  
Author(s):  
Yong Zhou ◽  
Xiaogang Zhou

The reliable and repeatable experimental ground testing of aircraft actuator is an essential phase before flight testing. It is not an easy task to simulate the alternating aerodynamic forces on actuators reasonably and accurately in a laboratory. In this article, an experimental test bench is designed to simulate the aerodynamic forces by a hydraulic actuator, which replicates the operating conditions that the actuator will encounter in service. In order to improve the force control performance, a feed-forward compensator and a fuzzy proportional–integral–derivative controller are designed. Both simulation and experimental results show that the designed method can improve the control performance.


2018 ◽  
Vol 116 ◽  
pp. 57-61 ◽  
Author(s):  
Yao Shi ◽  
Pei Zhang ◽  
Tuotuo Fang ◽  
Erhao Gao ◽  
Fujuan Xi ◽  
...  

Author(s):  
Yuping Wang ◽  
Mark Pellerin ◽  
Pravansu Mohanty ◽  
Subrata Sengupta

This paper focuses on the gas flow study of an ejector used in applications where moist gases are being entrained. Two parts of work are presented. In the first part, characteristics of gas flow inside an ejector, as well as the ejector's performance under various operating and geometric configurations, were studied with a three-dimensional computational model. Measurements were also performed for validation of the model. In the second part, focus was given to the potential condensation or desublimation phenomena that may occur inside an ejector when water vapor is included in the entrained stream. Experiments using light-attenuation method were performed to verify the presence of a second phase; then, the onset of phase change and the phase distribution were obtained numerically. A two-dimensional axis-symmetric model was developed based on the model used in the first part. User-defined functions were used to implement the phase-change criteria and particle prediction. A series of simulations were performed with various amounts of water vapor added into the entrained flow. It was found that both frost particles and water condensate could form inside the mixing tube depending on the operating conditions and water vapor concentrations. When the concentration exceeds 3% by mass, water vapor could condense throughout the mixing tube. Some preliminary results of the second phase particles formed, e.g., critical sizes and distributions, were also obtained to assist with the design and optimization of gas ejectors used in similar applications.


2000 ◽  
Vol 123 (1) ◽  
pp. 117-124 ◽  
Author(s):  
H.-Q. Liu ◽  
N. G. Chalhoub ◽  
N. Henein

A nonlinear dynamic model is developed in this study to simulate the overall performance of a naturally aspirated, single cylinder, four-stroke, direct injection diesel engine under cold start and fully warmed-up conditions. The model considers the filling and emptying processes of the cylinder, blowby, intake, and exhaust manifolds. A single zone combustion model is implemented and the heat transfer in the cylinder, intake, and exhaust manifolds are accounted for. Moreover, the derivations include the dynamics of the crank-slider mechanism and employ an empirical model to estimate the instantaneous frictional losses in different engine components. The formulation is coded in modular form whereby each module, which represents a single process in the engine, is introduced as a single block in an overall Simulink engine model. The numerical accuracy of the Simulink model is verified by comparing its results to those generated by integrating the engine formulation using IMSL stiff integration routines. The engine model is validated by the close match between the predicted and measured cylinder gas pressure and engine instantaneous speed under motoring, steady-state, and transient cold start operating conditions.


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