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为了提高发动机的有效热效率,必须尽量减少各种损失,例如理论热效率中的冷却损失和摩擦损失。然而,除了减少各种损失外还必须提高理论热效率。在努力提高商用车用大型柴油机有效热效率的工作中,重点研究关注了影响发动机理论热效率的2个重要因素:压缩比和比热比。根据这2个因素所起的作用而进行理论热力学循环分析,预计将压缩比从基本发动机的17提高到26,并增加比热比,使理论热效率得到显著的提高。利用1台单缸发动机研究了上述2个因素对指示热效率和有效热效率的影响。通过改变燃烧室容积来改变几何压缩比,通过外部供气系统调节过量空气和EGR率来控制缸内气体的比热比。由初步理论分析得知,理论热效率可提高8%(较高压缩比和较高比热比相结合时),指示热效率和有效热效率分别可提高6%和4%。
In order to increase the effective thermal efficiency of the engine, various losses, such as cooling loss and friction loss in theoretical thermal efficiency, must be minimized. However, in addition to reducing various losses, it is also necessary to increase the theoretical thermal efficiency. In an effort to improve the effective thermal efficiency of a large diesel engine for commercial vehicles, two important factors that affect the theoretical thermal efficiency of the engine are focused on: the compression ratio and the specific heat ratio. According to the role played by these two factors, a theoretical thermodynamic cycle analysis is carried out. It is expected that the compression ratio will be increased from 17 to 26 for the basic engine and the specific heat ratio will be increased, so that the theoretical thermal efficiency will be remarkably improved. The effects of the above two factors on the indicated thermal efficiency and the effective thermal efficiency were studied using a single-cylinder engine. By varying the volume of the combustion chamber to change the geometric compression ratio, the external air supply system to adjust the excess air and EGR rate to control the specific heat ratio of gas cylinder. According to the preliminary theoretical analysis, the theoretical thermal efficiency can be increased by 8% (when the high compression ratio is combined with the higher specific heat ratio), indicating that the thermal efficiency and the effective thermal efficiency can be increased by 6% and 4% respectively.