EGR和稀燃对甲醇发动机燃烧及排放特性的影响

在废气再循环(EGR)和稀燃策略下,以一台进气道喷射点燃式大功率甲醇发动机为试验对象,研究了两种稀释策略及复合稀释对甲醇发动机性能、燃烧及排放特性的影响。试验结果表明：在相同的稀释率下,稀燃比EGR能拥有更高的缸压峰值、更短的燃烧持续期、更低的燃油消耗率和更高的有效热效率。稀燃策略在降低HC和CO排放方面效果较为显著,而EGR策略能更为有效地降低NO_x排放。在未燃甲醇和甲醛排放方面,稀燃策略效果都较好。与EGR单独稀释相比,复合稀释能显著提高甲醇发动机的有效热效率。复合稀释对HC排放的影响较小,在降低CO排放方面和过量空气稀释效果相似,优于EGR稀释,最大降低幅度高达80.3%;拥有更好的抑制NO_x排放的效果,最大降低幅度为97%。复合稀释时,未燃甲醇排放与EGR单独稀释时相当,高于过量空气单独稀释;高稀释程度复合稀释时,甲醛排放有所下降。     

Approach for Reliability Evaluation of Cross-Linked Polyethylene Under Combined Thermal and Vibration Stresses

Based on Wiener process model, a new approach for reliability evaluation of cross-linked polyethylene(XLPE) is proposed to improve the lifetime evaluation reliability of XLPE under multi-stressing conditions and study the failure probability distribution. In this paper, two accelerated aging tests are carried out under combined thermal and vibration conditions. The volume resistance degradation data of XLPE samples are tested with a24 h interval under the accelerated stressing conditions at(130℃, 12 m/s~2) and(150℃, 8.5 m/s~2), respectively.Nonlinear degradation data obtained from the experiment are transformed to linear intermediate-variable values using time scaling function, and then linearized degradation data are calculated and evaluated on the basis of linear Wiener process model. Considering traditional Arrhenius equation and inverse power criterion, parameters of the linear Wiener model are estimated according to the maximum likelihood function. The relationship curves on probability density and reliability are given, and the lifetime distribution of XLPE under different stressing conditions is also obtained for evaluating the reliability of XLPE insulation. Finally, the life expectancy of XLPE is 17.9 a under an allowance temperature of 90℃ and an actual vibration acceleration of 0.5 m/s~2. The approach and results in this paper may be used for reliability assessment of high-voltage multiple samples or apparatuses.