内燃机示功图的曲线拟合修正研究

A Study of correcting curve fitting method in indicator diagrams of internal combustion engines

内燃机示功图含有与内燃机性能相关的丰富信息,它不仅可以反映内燃机的热力转换过程和工作状态,而且可以获得各缸平均指示压力、指示功和最高爆发压力等重要性能指标.但是在内燃机设计阶段绘制示功图的时候,循环各主要阶段的多变指数都需要合理地设定,并且各阶段曲线需要平滑顺接起来,尤其是在最高爆压处的曲线拟合要求更为严格.通过对三种曲线拟合方案进行对比,最终选择三角函数作为内燃机急燃期阶段的拟合曲线函数.

An engine indictor diagram contains much information on the engine’s performance.It not only shows the thermodynamic cycle and work state of the engine,but also includes the parameters such as the average indicated pressure,indicated power and the maximal blast pressure.However the polytropic exponents of main working cycle should be set reasonable before drawing the indicator diagram in the designing of IC engines,and every stage should also be connected with flat curves,especially on the position of peak pressure.Three different methods are used to fit the curves in fast burning period orderly.The result shows that the trigonometric function is adaptive to fit the curves.