Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resi...Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reaction-bonded is one of important sintering technology of ceramics structural parts. The preparation of reaction-bonded silicon carbide (RBSC) is based on a reaction sintering process, whereby a compacted body of α-SiC and carbon (graphite) powders is heated in contact with liquid silicon or gas silicon, which impregnates the body, converting the carbon (graphite) to β-SiC which bonds the original alpha grain. This process is characterized by low temperature and a short time sintering, and being appropriate to the preparation of large size and complex-shaped components, and so on. Besides, during compacting process of reaction sintering, it can maintain a stable dimension of ceramics parts. Therefore, the method of reaction-bonded silicon carbide ceramics has been identified as a technology suitable for producing complicated and highly exact dimensions’ ceramics parts. In this paper, the method of reaction-bonded silicon carbide was applied to the manufacturing of a complex-shaped spacecraft combustion chamber of SiC ceramics. SiC and carbon powder of 4～30 μm were chosen as the raw materials, green compacts containing appropriate wt.% carbon were formed using the mold press method, sintering was performed in a graphite electric furnace under an argon atmosphere. It was introduced in detail that the technological parameters and technological flow of reaction sintering silicon carbide ceramics. At the same time, physical and mechanical experiments such as bending strength, coefficient of thermal expansion, coefficient of thermal conductivity, gastight property, heat resisting property etc. have been carried out. The results demonstrated that spacecraft combustion chamber made from reaction sintering of silicon carbide ceramics is feasible and the results of experiment is satisfactory. The strength of high-temperature structural parts made by reaction sintered SiC varied with silicon content; Under the this article testing condition, the optimum silicon content is 10.5% for the part investigated. The method of reaction sintered SiC ceramics is suitable for manufacturing of complicated spacecraft parts with a working temperature of 1 500 ℃.展开更多
基于一台高压缩比四缸增压直喷(gasoline direct injection,GDI)发动机和预燃室湍流射流点火(turbulent jet ignition,TJI)系统,开展中低负荷稀燃特性试验研究。研究结果表明:预燃室射流点火的燃烧稳定性存在着明显的负荷边界;在平均指...基于一台高压缩比四缸增压直喷(gasoline direct injection,GDI)发动机和预燃室湍流射流点火(turbulent jet ignition,TJI)系统,开展中低负荷稀燃特性试验研究。研究结果表明:预燃室射流点火的燃烧稳定性存在着明显的负荷边界;在平均指示压力(indicated mean effective pressure,IMEP)为0.4 MPa的低负荷,预燃室射流点火的缸压和瞬时放热率峰值较常规火花点火(spark ignition,SI)下降明显,峰值相位后移,滞燃期长;在平均指示压力为0.7 MPa时其平均指示压力循环波动率(coefficient of variation,COV)达5%;在平均指示压力为1.1 MPa的最佳指示燃油消耗率工况,预燃室射流点火的稀燃边界、指示燃油消耗率、排放等可以达到和常规火花点火相当的水平。中低负荷下,随着负荷增加,预燃室射流点火的滞燃期缩短,燃烧重心提前,燃烧稳定性改善,全碳氢(total hydrocarbon,THC)和CO排放降低。高能点火可以缩短预燃室射流点火的滞燃期,加快燃烧速度,提高燃烧稳定性,改善排放。展开更多
为验证被动预燃室技术在商用缸内直喷(gasoline direct injection,GDI)发动机中的应用潜力,采用三阶段喷射策略研究了预燃室点火发动机在增压稀薄燃烧环境中的热效率、燃烧特性(累计放热量达到总放热量的50%对应的曲轴转角CA50、爆震指...为验证被动预燃室技术在商用缸内直喷(gasoline direct injection,GDI)发动机中的应用潜力,采用三阶段喷射策略研究了预燃室点火发动机在增压稀薄燃烧环境中的热效率、燃烧特性(累计放热量达到总放热量的50%对应的曲轴转角CA50、爆震指数和循环变动系数)和排放特性,建立了三维仿真模型进行模拟。结果表明,在高负荷条件下,平均爆震指数可控制在0.20~0.34 MPa之间,循环变动系数可控制在3.0%~3.5%之间;当指示平均有效压力(indi⁃cated mean effective pressure,IMEP)在1.0 MPa~1.4 MPa范围内,指示热效率均能达到40%以上;负荷增加时,氮氧化物呈下降趋势,碳氢化合物和一氧化碳排放略有增加。展开更多
文摘Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reaction-bonded is one of important sintering technology of ceramics structural parts. The preparation of reaction-bonded silicon carbide (RBSC) is based on a reaction sintering process, whereby a compacted body of α-SiC and carbon (graphite) powders is heated in contact with liquid silicon or gas silicon, which impregnates the body, converting the carbon (graphite) to β-SiC which bonds the original alpha grain. This process is characterized by low temperature and a short time sintering, and being appropriate to the preparation of large size and complex-shaped components, and so on. Besides, during compacting process of reaction sintering, it can maintain a stable dimension of ceramics parts. Therefore, the method of reaction-bonded silicon carbide ceramics has been identified as a technology suitable for producing complicated and highly exact dimensions’ ceramics parts. In this paper, the method of reaction-bonded silicon carbide was applied to the manufacturing of a complex-shaped spacecraft combustion chamber of SiC ceramics. SiC and carbon powder of 4～30 μm were chosen as the raw materials, green compacts containing appropriate wt.% carbon were formed using the mold press method, sintering was performed in a graphite electric furnace under an argon atmosphere. It was introduced in detail that the technological parameters and technological flow of reaction sintering silicon carbide ceramics. At the same time, physical and mechanical experiments such as bending strength, coefficient of thermal expansion, coefficient of thermal conductivity, gastight property, heat resisting property etc. have been carried out. The results demonstrated that spacecraft combustion chamber made from reaction sintering of silicon carbide ceramics is feasible and the results of experiment is satisfactory. The strength of high-temperature structural parts made by reaction sintered SiC varied with silicon content; Under the this article testing condition, the optimum silicon content is 10.5% for the part investigated. The method of reaction sintered SiC ceramics is suitable for manufacturing of complicated spacecraft parts with a working temperature of 1 500 ℃.
文摘基于一台高压缩比四缸增压直喷(gasoline direct injection,GDI)发动机和预燃室湍流射流点火(turbulent jet ignition,TJI)系统,开展中低负荷稀燃特性试验研究。研究结果表明:预燃室射流点火的燃烧稳定性存在着明显的负荷边界;在平均指示压力(indicated mean effective pressure,IMEP)为0.4 MPa的低负荷,预燃室射流点火的缸压和瞬时放热率峰值较常规火花点火(spark ignition,SI)下降明显,峰值相位后移,滞燃期长;在平均指示压力为0.7 MPa时其平均指示压力循环波动率(coefficient of variation,COV)达5%;在平均指示压力为1.1 MPa的最佳指示燃油消耗率工况,预燃室射流点火的稀燃边界、指示燃油消耗率、排放等可以达到和常规火花点火相当的水平。中低负荷下,随着负荷增加,预燃室射流点火的滞燃期缩短,燃烧重心提前,燃烧稳定性改善,全碳氢(total hydrocarbon,THC)和CO排放降低。高能点火可以缩短预燃室射流点火的滞燃期,加快燃烧速度,提高燃烧稳定性,改善排放。
文摘为验证被动预燃室技术在商用缸内直喷(gasoline direct injection,GDI)发动机中的应用潜力,采用三阶段喷射策略研究了预燃室点火发动机在增压稀薄燃烧环境中的热效率、燃烧特性(累计放热量达到总放热量的50%对应的曲轴转角CA50、爆震指数和循环变动系数)和排放特性,建立了三维仿真模型进行模拟。结果表明,在高负荷条件下,平均爆震指数可控制在0.20~0.34 MPa之间,循环变动系数可控制在3.0%~3.5%之间;当指示平均有效压力(indi⁃cated mean effective pressure,IMEP)在1.0 MPa~1.4 MPa范围内,指示热效率均能达到40%以上;负荷增加时,氮氧化物呈下降趋势,碳氢化合物和一氧化碳排放略有增加。
