Research On The Performance Of VNT Diesel Engine And The Optimization Of Vehicle Matching Based On Work Conditions Of Buses

City buses are an important part of urban public transport system, which is closely related with residents’ lives. However, with the rapid growth of city size and population, the number of buses is greatly increased, leading to a lot of energy consumption and polluting the environment. As a result, in order to improve the dynamic properties and economy of buses and reduce emissions, the following work had been done:(1)The typical buses and its use area was selected, collecting and analyzing the operating data of engine and vehicle, the characteristics of the buses were extracted.(2)The test system of VNT engine performance is developed for investigating the effects of VNT opening degree on fuel consumption rate, supercharging pressure, intake flow rate, exhaust smoke and temperature under various engine speeds and loads. Then, the basic properties of the VNT engine was compared with the original engine. Results showed that under low and middle speed, dynamic properties and economy of engine was significantly improved, which was suitable for buses.(3)The VNT was applied into buses and verified. The data of vehicle and engine was collected. Dynamic properties and economy of buses was evaluated by comparing the results. Results showed that in terms of the dynamic property of initial acceleration, VNT vehicle was improved by 13 to 15%, the fuel consumption at constant speed was decreased by 4 to 7%, and the reduction of actual fuel consumption is about 6%;(4)The AVL-CRUISE software was employed to establish a simulation model of a 9m-bus. The model was revised and verified based on the above test data of dynamic properties and economy. Then, this model was used to investigate the effects of transmission systems with different speed ratios based on VNT engine. Results showed that the original vehicle configuration(five-speed gearbox + 4.875 main reduction ratio) is capable of both dynamic properties and economy, while the comprehensive fuel consumption of the configuration(five-speed gearbox + 4.67 main reduction ratio) was decreases by 1.84%. Compared with the original bus with bypass valve turbocharger, the comprehensive fuel consumption was decreased by 6 to 7%;(5) For the 11.5m-bus with 6J VNT engine, the dynamic properties and economy of it was analyzed and evaluated. Compared with the typical configuration with 6G engine, results showed that the project including 6J engine, VNT and the optimized reduction ratio could satisfy the 11.5m-bus. Compared with the original 6G engine configuration, this project had more excellent dynamic properties and economy.