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

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

Study on mixing, modelling and control of an SCR system

In recent years, more and more research attention has been paid to the NOx emissions caused by marine diesel engines. Selective catalytic reduction (SCR) system has been proven to be an effective technology for the removal of NOx emitted from marine diesel engines. In order to comply with stringent International Maritime Organization (IMO) Tier III NOx emission regulations, a number of engine manufacturers have developed their own SCR systems with an option of installing SCR reactors before or after the turbines of engine turbochargers. This thesis focuses on modelling of evaporation and decomposition of urea-water-solution (UWS) droplets, design and optimisation of static mixers, modelling of an SCR reactor and developing model-based urea dosing control strategy.The amount of ammonia converted from UWS has a significant effect on the NOx removal efficiency of SCR systems. Due to a limited installation space for SCR systems on board, choosing the location of urea injection nozzle appropriately has become a critical issue for SCR system design. An evaporation and decomposition model of UWS droplets has been developed in this research in order to determine the total depletion time of a UWS droplet, which is helpful to calculate the proper length between the urea nozzle and reactor of an SCR system.In order to achieve a high NOx removal rate and reduce the quantity of NH₃ slip, static mixers are commonly used before SCR reactors to improve the mixing between ammonia and exhaust gases. 4 novel static mixers have been designed and the performance of the mixers is compared in the study. An experiment has been conducted to validate the mixing performance and pressure loss of the static mixers developed. It shows that there is a satisfied agreement between the simulation and experiment results.A mathematical model of SCR reactors has been established. The unknown parameters of the model are identified by minimising the error between the model predicted and measured values of both the temperature and the species concentration after the SCR reactor. The SCR reactor model is further used in a simulation for the purpose of developing model-based urea dosing control strategies.A state observer is used to determine the actual states in the reactor which supplies the mandatory information for developing model-based urea dosing control strategies. The NH₃ cross-sensitivity of NOx sensors can be described by a linear equation. The simulation results of the observer show that the NH₃ cross-sensitivity of NOx sensors can be neglected when estimating the actual states of the reactor if NH₃ is of a low concentration in the exhaust.In recent years, more and more research attention has been paid to the NOx emissions caused by marine diesel engines. Selective catalytic reduction (SCR) system has been proven to be an effective technology for the removal of NOx emitted from marine diesel engines. In order to comply with stringent International Maritime Organization (IMO) Tier III NOx emission regulations, a number of engine manufacturers have developed their own SCR systems with an option of installing SCR reactors before or after the turbines of engine turbochargers. This thesis focuses on modelling of evaporation and decomposition of urea-water-solution (UWS) droplets, design and optimisation of static mixers, modelling of an SCR reactor and developing model-based urea dosing control strategy.The amount of ammonia converted from UWS has a significant effect on the NOx removal efficiency of SCR systems. Due to a limited installation space for SCR systems on board, choosing the location of urea injection nozzle appropriately has become a critical issue for SCR system design. An evaporation and decomposition model of UWS droplets has been developed in this research in order to determine the total depletion time of a UWS droplet, which is helpful to calculate the proper length between the urea nozzle and reactor of an SCR system.In order to achieve a high NOx removal rate and reduce the quantity of NH₃ slip, static mixers are commonly used before SCR reactors to improve the mixing between ammonia and exhaust gases. 4 novel static mixers have been designed and the performance of the mixers is compared in the study. An experiment has been conducted to validate the mixing performance and pressure loss of the static mixers developed. It shows that there is a satisfied agreement between the simulation and experiment results.A mathematical model of SCR reactors has been established. The unknown parameters of the model are identified by minimising the error between the model predicted and measured values of both the temperature and the species concentration after the SCR reactor. The SCR reactor model is further used in a simulation for the purpose of developing model-based urea dosing control strategies.A state observer is used to determine the actual states in the reactor which supplies the mandatory information for developing model-based urea dosing control strategies. The NH₃ cross-sensitivity of NOx sensors can be described by a linear equation. The simulation results of the observer show that the NH₃ cross-sensitivity of NOx sensors can be neglected when estimating the actual states of the reactor if NH₃ is of a low concentration in the exhaust

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

Optimization of the location of injector in urea-selective catalytic reduction system

Urea–water solution (UWS) has been widely used in selective catalytic reduction (SCR) system as reductant to generate ammonia. The position where UWS nozzle should be located is a concerned issue and worth a deep investigation. Although UWS droplet evaporates and decomposes once it has been sprayed from the nozzle, the decomposition of droplet may be still incomplete if the distance between nozzle and reactor is not long enough. Thus, the incomplete decomposed UWS droplets will collect at the entrance of reactor, which is not beneficial for droplet evaporation, system flow and SCR efficiency. This paper presents the position where UWS nozzle should be placed from the perspective of evaporation and decomposition of UWS droplet. A numerical model of UWS droplet evaporation and decomposition was established in this paper and the droplet displacement is solved by adding droplet motion equation to the simulation model. The results can provide a practical help for designing a urea-SCR system

Genetic Diversity Analysis of Genotype 2 Porcine Reproductive and Respiratory Syndrome Viruses Emerging in Recent Years in China

Porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by its extensive genetic diversity. Here we analyzed 101 sequences of NSP2 hypervariable region, 123 ORF3 sequences, and 118 ORF5 sequences from 128 PRRSV-positive clinical samples collected in different areas of China during 2008–early 2012. The results indicated that the amino acid identities of the three genes among these sequences were 87.6%–100%, 92.5%–100%, and 77%–100%, respectively. Meanwhile, 4 novel patterns of deletion and insertion in NSP2 region or GP5 were first found. The phylogenetic analysis on these 3 genes revealed that the Chinese PRRSV strains could be divided into three subgroups; majority of genes analyzed here were clustered in subgroup 3 with multiple branches; the strains with 30-aa deletion in NSP2-coding region were still the dominant virus in the field. Further phylogenetic analysis on four obtained complete genomic sequences showed that they were clustered into different branches with the Chinese corresponding representative strains. Our analyses suggest that the genetic diversity of genotype 2 PRRSV in the field displays a tendency of increasing in recent years in China, and the 30-aa deletion in NSP2-coding region should be no longer defined as the molecular marker of the Chinese HP-PRRSV

Unique epitopes recognized by monoclonal antibodies against HP-PRRSV: deep understanding of antigenic structure and virus-antibody interaction.

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) is a member of the genus Arterivirus within the family Arteriviridae. N and GP3 proteins are the immunodominance regions of the PRRSV viral proteins. To identify the B-cell linear antigenic epitopes within HP-PRRSV N and GP3 proteins, two monoclonal antibodies (mAbs) against N and GP3 proteins were generated and characterized, designated as 3D7 and 1F10 respectively. The mAb 3D7 recognized only HuN4-F112 not the corresponding virulent strain (HuN4-F5). It also recognized two other commercial vaccines (JXA1-R and TJM-F92), but not two other HP-PRRSV strains (HNZJJ-F1 and HLJMZ-F2). The B-cell epitope recognized by the mAb 3D7 was localized to N protein amino acids 7-33. Western blot showed that the only difference amino acid between HuN4-F112-N and HuN4-F5-N did not change the mAb 3D7 recognization to N protein. The epitope targeted by the mAb 1F10 was mapped by truncated proteins. We found a new epitope (68-76aa) can be recognized by the mAb. However, the epitope could not be recognized by the positive sera, suggesting the epitope could not induce antibody in pigs. These results should extend our understanding of the antigenic structure of the N protein and antigen-antibody reactions of the GP3 protein in different species