An investigation into catalysts to improve the low temperature performance of an SCR

Selective catalytic reduction with NH3 is considered as one of the most effective technologies controlling NOx emission. Metal Fe based catalysts were used in the investigation to improve the low temperature performance of NOx conversion. The temperature range studied was between 150 degrees C and 350 degrees C with the interval of 50 degrees C. The honeycomb catalysts were prepared by an impregnation method. The study also included characterization of catalysts by BET, XRD, H2-TPR, SEM and XPS methods. It is found an increase in metal Fe content from 2 to 6 % wt. offers an improvement in the catalytic performance. However, a further increment in Fe content will result in a decrease in its performance. More than 90 % NOx conversion rate could be achieved over the Fe-based honeycomb catalyst at a low temperature by doping with Ni and Zr metal with different weights. Among all the catalysts studied, the mixed metal catalyst of Fe-Ni-Zr is found the most potential one, not only because of its higher NOx conversion rate at a low temperature, but also because of its wider operation temperature window. The effect of gas hourly space velocity (GHSV) was also investigated in the study and results show as GHSV increases that reduction of NOx is decreased

Studying on the emission characteristic of a diesel engine by simulation

At present, the problem of environment pollution draws people's attention increasingly. The international communities and organizations established relevant laws to restrict the emission and reduce the harm to human being and environment. In this paper, a numerical simulation model for diesel engine was established by GT-POWER in order to study the NO, CO and HC emissions characteristic of the diesel engine and the model was validated by experimental data. Based on the model, the variable parameters including injection timing, intake air temperature, compression ratio and EGR ratio were carried out. The simulation results showed that with the decrease of CA BTDC, intake air temperature, compression ratio and EGR ratio respectively, the NO emission decreased. However, the CO and hydrocarbon emissions increased

An investigation into catalysts to improve low temperature performance in the selective catalytic reduction of NO with NH3

Selective catalytic reduction with NH3 is considered one of the most effective technologies controlling NOx emission. Metal Fe-based catalysts were used in the investigation to improve low temperature performance of NOx conversion. The temperature range studied was betweet 15 degrees C and 350 degrees C in increments of 50 degrees C. The honeycomb catalysts were prepared by an impregnation method. The study also included characterisation of catalysts by BET, XRD, H2-TPR and XPS methods. It was found that an increase in metal Fe content from 2 to 6% wt offered an improvement in the catalytic performance. However, a further increase in Fe content resulted in a decrease in its performance. More than 90% NOx conversion rate could be achieved over the Fe-based honeycomb catalyst at a low temperature by doping with different weights of Ni and Zr metals. Amongst all the catalysts studied, the mixed metal catalyst of Fe-Ni-Zr was the one with most potential. This was because of its higher NOx conversion rate at a low temperature and also because of its wider operating temperature window. The effect of gas hourly space velocity (GHSV) was also investigated and the results showed that as GHSV increased, the reduction of NOx decreased

Study on the mixing performance of static mixers in selective catalytic reduction (SCR) systems

Selective catalytic reduction (SCR) is a promising technique for reducing nitrogen oxide (NOx) emissions from diesel engines. Static mixers are widely used in SCR systems before reactors to promote the mixing of ammonia and exhaust streams. This work aims to investigate the effects of the location of static mixers and the volume ratio of two species on mixing quality using the computational fluid dynamics (CFD) method. The simulation results show that a more homogenous ammonia distribution can be achieved at the exit of the pipe if static mixers are placed close to the ammonia injection point or if more ammonia is injected. Another phenomenon found in the study is that the mixing performance of an identical static mixer may behave discrepantly under different flow conditions if using B and C as the evaluating indexes for mixing homogenization

Investigation on accuracy of numerical simulation of aerodynamic noise of single-stage axial fan

The prediction accuracy of turbomachinery aerodynamic noise, particularly in relation to broadband noise with uncertain factors, has long been a challenging issue. Previous studies have not fully comprehended the factors influencing its prediction accuracy, lacking an objective and comprehensive evaluation method. An improved approach combining orthogonal experiment design and principal component analysis is employed to address these limitations. The evaluation method expands the noise metrics and provides a comprehensive assessment of the accuracy of numerical simulation for aerodynamic noise. The evaluation method is utilized to optimize and quantitatively analyze the impact of the refinement size of the core area on noise prediction for single-stage axial fans. Subsequently, the three metrics, namely, Z1, Z2, and broadband noise Z3, are integrated using PCA to form a new integrated optimal metric Ztotal. The influence of different refinement sizes, particularly on Ztotal, is quantitatively examined. The findings reveal that the mesh size of the stator wake (D area) exhibits the most significant influence on noise prediction accuracy, with a calculated weight of 81.3% on noise accuracy. Furthermore, a comprehensive investigation is conducted on the influence of turbulence models and the wall Y+ value on aerodynamic noise. Detached-eddy simulation and large eddy simulation demonstrate effective capabilities in simulating both upstream and downstream turbulent flow characteristics of the stator, enabling accurate prediction of broadband noise. This study presents a set of numerical simulation schemes that achieve precise prediction of turbomachinery aerodynamic noise

Simulation research on aerodynamic noise characteristics of a compressor under different working conditions

The shear stress transport turbulence model is employed to conduct a detailed study of flow characteristics at the highest efficiency point and near-stall point in a full-channel 1.5-stage compressor in this paper. The simulation results for the compressor's total pressure ratio and efficiency exhibit good agreement with experimental data. Emphasis is placed on examining the internal flow structure in the tip area of the compressor rotor under near-stall conditions. The results reveal that significant differences in flow structure primarily occur in the tip area as the compressor approaches stall. Specifically, a reduction in turbulent kinetic energy is observed in a region spanning approximately 20%–60% of the chord length on the rotor suction face near-stall conditions. Two additional peak frequencies, at 0.8 and 1.6 times the blade passage frequency, are observed, and the intricate flow phenomena are elaborated at the near-stall point. The near-stall point exhibits greater noise levels than the highest efficiency point, where the intensity of the surface source increases by more than 10 dB, peaking at 20 dB. This additional peak serves as a significant supplementary noise source near the stall point, leading to a maximum increase of 33.3 dB in the free radiated sound power. The acoustic response within the duct indicates that the compressor operating at the near-stall point continues to produce substantial noise on the actual test bench, showing an average increase of 6 dB in noise levels, and the distribution of the additional peak single-tone noise at the entrance significantly differs from that observed at the highest efficiency point

An investigation into catalysts for improving low temperature performance of an SCR in a diesel engine exhaust system

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Investigation of emission characteristic of a diesel engine by simulation

This paper presented results of a study on emission characteristics of diesel engines. A numerical simulation model for a diesel engine was established by GT-POWER. Emission species studied include of NO, CO and HC. The developed model was validated by engine tests under laboratory condition. Based on the model, the simulation changing the variable parameters including injection timing, intake air temperature and EGR (exhaust gas recirculation) ratio were carried out to study their effect on emissions. The simulation results showed that with the decrease of CA BTDC, intake air temperature, compression ratio and EGR ratio respectively, the NO emission decreased. However, the CO and HC emissions increased

Investigation on the effect of ammonia distribution on selective catalytic reduction conversion efficiency

The effect of ammonia distribution upstream selective catalytic reduction converter on selective catalytic reduction conversion efficiency has been studied in this paper. The results indicate that the more uniform ammonia concentration distribution upstream converter is, the higher NO_x reduction rate and lower NH₃ slip can be achieved. By using static mixers fixed in the pipeline upstream converter, ammonia and exhaust streams can be mixed effectively on the limitation of mixing distance for marine selective catalytic reduction system. Different kinds of static mixers could lead to different degree of mixing between ammonia and exhaust streams, which will affect selective catalytic reduction conversion efficiency directly. Then comparing with the complete mixing degrees of ammonia and exhaust streams, selective catalytic reduction conversion efficiency can be used as an evaluation index for static mixers. Based on CFD method, the effect of mixing degrees of different static mixers on selective catalytic reduction conversion efficiency can be obtained by simulating current commercial catalysts with several different kinds of static mixers such as GK mixer, SK mixer, contour mixer, star-shaped mixer. The trend of NO_x reduction rate and NH_x slip changing with ammonia distribution and velocity distribution before selective catalytic reduction catalyst layers can be summarized by analyzing the simulating data. The results can be used to help engineering applications