缸内流场扰动对快速压缩机着火中间物种采样测量影响的数值研究

The effect of in-cylinder airflow disturbances in the rapid compression machine on the species sampling accuracy remains unclear when fuel autoignition exhibits a negative temperature coefficient (NTC) effect. To solve this problem, this study establishes a numerical model for species sampling during fuel autoignition, and delves into the combined effect of NTC and airflow disturbances on the species sampling accuracy during the autoignition of a n-butane mixture, by controlling different piston crevice volumes to generate airflow disturbances of different intensities within the combustion chamber. The results show that due to the NTC effect of the fuel, both of the typical sampling methods exhibit a reverse dilution phenomenon, where the sampling concentration of the fuel is lower than expected, while that of intermediate species is higher than expected. This reverse dilution offsets the systematic errors of the sampling methods, resulting in a reduced sensitivity of the species sampling accuracy to airflow disturbances in the NTC region. Suppressing airflow disturbances within the combustion chamber is generally beneficial to the increase in the sampling accuracy. However, in an absolutely undisturbed flow field, the sampling error of the whole quenching method may even increase slightly due to the effect of the thermal boundary layer. This study provides valuable reference for the design of species sampling experiments and the uncertainty analysis of experimental data during fuel autoignition.