| Our country consumes a large amount of oil resources, while our country’s resources are insufficient to meet our own consumption. The traditional auto industry depends on oil resources seriously. Therefore, the diversification of energy has become the mainstream trend in the development of auto industry. In these alternative sources of energy, natural gas is regarded as the most promising alternative fuel for the engines of vehicle by many research institutions for its abundant energy reserves, higher octane number, lower level of pollution and lower price. According to the condition of the use of fuel in internal combustion engine, natural gas can be divided into the following three kinds:the single fuel engine, the fuel engine with two functions and the dual fuel engine. Among them, the dual fuel engine has a broader perspective owing to the improvement in the defect of inconvenient transportation of natural gas.With the deep study of dual fuel engines and the improvement of science and technology, dual fuel engines are gradually changed from the characteristic of low compression ratio and low gas replacement rate toward the high compression ratio and high gas replacement rate. The advanced technology in dual fuel engines is pilot-ignited technology. With the help of software STAR-CD, this paper is mainly about the study of macro parameter and the analysis of the rules in micro field in CA6DL2-35E5RB natural gas/diesel. The purpose is to fulfill the pilot-ignited technology of diesel through the change of the shape of combustion chamber, and to get the high replacement without the occurrence of knocking. The results show that:1. The burning of diesel first takes place at the wall of combustion chamber, and then the fire appears at the different part of the chamber. It means that the fire starts at the different parts and appears at the different time. After that, the high-temperature zone spread from the wall of combustion chamber to the center part. The burning of nature gas bases on the core where the diesel is burning. Nature gas burns in the different part of the combustion chamber with an asymmetric form. This is caused by the non-uniformity of air flow, and with the increase of natural gas substitution rate, the maximum cylinder pressure drops, the engine output power decreases and NO emissions are declining.2. At the condition of the same compression ratio, lateral clearance and tip clearance, only the shape of combustion chamber is changed, in which the#1is the original machine, also can be called omega combustor;2#is the cylindrical combustion chamber;3-1#is the petals combustion chamber. Through the comparison, the original machine has the lower emission of the natural gas, while the emission of Soot is comparatively high. Such a phenomenon shows that combustion state of natural gas is high while diesel’s state is low, which determine that the original machine can not get good quality of burning at high rate of substitution. For if it is at high rate of substitution, the amount of diesel decreases. However the burning quality of diesel is poor which will affect the burning process of natural gas directly, so it is unavoidable to control the high emission of Soot in the single fuel engines. On the contrary, diesel has the good burning quality in the petal combustion chamber. This sets the foundation for pilot-ignited technology of diesel and solves the problem of high emission of Soot in single fuel engines. At the same time, this highlights the advantages of dual fuel engines and the combustion rate of natural gas can be achieved by controlling the reasonable flow in cylinder.3. Petal combustion chamber has different position of emission. Such differencewill influence the performance of engine power, economy and emission. Four injection angles are chosen. That is0°,-7.5°,-15°and-22.5°. Though the analyses of its macro parameters and micro field and the optimal selection, we get that-22.5°is the best emissive angle. |
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