基于多维模型的天然气发动机敲缸趋势数值研究

研究了天然气发动机关键参数对敲缸趋势的影响。将自点火和两步湍流燃烧两个子模型集成在发动机缸内流体动力学多维模型程序KIVA-3V中,采用数值计算与试验相结合的方法修正多维模型,然后调整操作条件使发动机处于敲缸状态,解析点火提前角、压缩比、涡流比和等价率四个参数对敲缸时刻(KOCA)和敲缸强度(KI)的影响。研究表明:压缩比下降,敲缸强度明显下降。点火提前角增大,敲缸时刻提前,并且敲缸强度增加。当等价率从0.72增加到0.78,敲缸强度增加,敲缸时刻提前;而当等价率从0.78到0.92,敲缸强度增加,发生时刻反而推后。当涡流比从0.0到2.0变化时,敲缸时刻提前;而从2.0到3.11,敲缸时刻反而推后。压缩比对敲缸趋势影响最大,其次是等价率,相比之下,点火提前角和涡流比的影响较小。

Numerical Study of Knock Trend of Natural Gas Engine Based on a Multidimensional Model

This paper investigated the effects of several key factors in natural gas engines on knock trend.Firstly,both autoignition and two step turbulent combustion submodels were coupled to multidimensional model code(KIVA-3V) used in the calculation of in-cylinder flow dynamics for engines.Then, multidimensional model was modified by combining numerical calculation with experiments.Thirdly,the computing knock of engines was simulated after adjusting the operating conditions.Finally,the effects of such factors as ignition timing,compression ratio,swirl ratio and equivalence ratio on the knock occurrence crank angle(KOCA) and knock intensity(KI) were analyzed.The results are shown as followings: KI declines obviously as compression ratio does;KOCA occurs early and KI increases with the adding of ignition timing;KI rises and KOCA occurs early while the equivalence ratio changes from 0.72 to 0.78,but KI rises and KOCA occurs latterly while it does from 0.78 to 0.92 and KOCA happens early as swirl ratio is adjusted from 0.0 to 2.0,but it does latterly as swirl ratio changes from 2.0 to 3.11.It is concluded that the effect of compression ratio on KOCA and KI is the most sensitive,equivalence ratio second,ignition timing and swirl ratio the least.