In this paper, the vibration of a three screw pump was studied. Firstly the vibration response of the pump was tested. Then the FE model of the pump was constructed and the modals of it were calculated. The exactness of the result was confirmed by the testing modals and the reasonable of the FE model was verified at the same time. Finally, the force acted on rotors due to pressure was calculated by the mathematical method of surface integral. The force was loaded on the FE model and the force response was predicted, which represented the basic vibration of the screw pump. Based on the work above, the vibration spectrum of the screw pump was analyzed.

In this paper the vibration of a screw pump unit was studied. Firstly the modal of this pump unit was calculated, which was possible thank to the exact finite element model. And the exactness of the result was verified by comparing with the testing one. Based on the correct simulation modal, the load is identified using the experimental results, and the accuracy of the identification is confirmed using the response error. Combined the response spectrum, the load spectrum and the modal analysis results, the causes and control methods of the screw unit's vibration are analyzed. Finally, according to the foregoing calculation results, the system is simulated and optimized. The identified load is loaded on the optimized structure. The responses calculated are compared with the original structure and the optimized results are evaluated.

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.

Abstract. With the global environment worsening and the consciousness of protecting environment strengthening, the limitation of noxious gas from diesel engines is becoming more and more strictly. Selective catalytic reduction (SCR) aftertreatment system has been applied to reduce Nitrogen Oxides (NOx) as a key technology. The urea solution injected into the tailpipe decomposes to ammonia, which will react with NOx on the surface of SCR catalyst. The main purpose of this paper is to study the effect of different concentrations of NO, NO2 and NH3 on the reactions taking place with SCR catalyst by simulation. Based on mass transfer equations and chemical kinetics the simulation results predict the concentrations of NO, NO2 and NH3 accurately. The mass conservation equations of species are solved by the software MATLAB. Some regulations can be revealed to improve the NOx conversion efficiency and reduced the NH3 slip.

The mixing degree of ammonia and exhaust gas has significant effect on the NOx conversion efficiency of SCR (selective catalytic reduction) system. It is essential to investigate the structure of urea nozzle since it considerably impacts the atomization of urea water solution. This paper simulated the process of urea spray by the software FIRE and analyzed the influence of spray characteristics such as nozzle hole number, nozzle hole chamfering as well as the spray angle on the atomization of urea water solution. Simulation results can indicate the optimal nozzle for a certain circumstance which is beneficial to the engineering design.