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Considering helical gear transmission's economic performance and drive reliability, construct multi-objective optimization model of the helical gear transmission with taking normal module, teeth number of small helical gear, helix angle and the gear width coefficient as design variables and taking the volume of small and large helical gear and opposite number of overlap ratio as objective functions. Propose multi-objective optimization design method based on coalition cooperative game theory where the two design goals are seen as two game players. By calculating the impact factor of design variables to objective functions and fuzzy clustering, the design variables are divided into strategy space of game players. Each game player takes its own revenue function as target and does single objective optimization in its own strategy space in order to get its own best strategy. The best strategies of all players form a combination of one round game and the optimal solution can be obtained through several game rounds. Example results show the effectiveness of game method.

In this paper, the Urea-SCR system is first introduced; then change of the urea solution concentration under different temperatures with time lapsing is given. Meanwhile, conditions for the urea crystallization are analyzed and SCR converter adaptability is tested under high sulfur environment on engine test bench. As the efficiency of NOx conversion is not significantly reduced after aging and the activity of the catalyst is very little damaged by dense sulfur content in fuel, SCR catalyst is able to adapt to the application of high-sulfur-contained fuel environment in our country.

A three-dimensional model of a diesel Urea-SCR（Selective Catalytic Reduction）catalytic converter system was set up with aid of CFD software AVL FIRE coupled with available knowledge of SCR chemical reaction kinetics. Basing on the validation of the spray injection model of Urea-water-solution, the numerical simulation was made to get the distribution of pressure, velocity, temperature and species concentration in the converter and NOxconversion in different conditions by considering the injection and evaporation of the urea-water-solution, the thermal decomposition and hydrolysis into ammonia and the surface catalytic reactions in the monolith. The simulated results have some reference meaning for improving NOxconversion efficiency and optimizing the diesel SCR catalytic converter.

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