为了研究影响发动机动态试验直采测试结果的主要因素，在理论分析的基础上，利用一台柴油机，通过改变不同的测试参数，结合直采和全流稀采结果进行对比分析。结果表明：全流稀采结果受测试参数的变化影响较小；直采测试排气组分瞬时浓度与排气质量流量按照转换时间对齐与否是影响排放结果准确性的关键因素；排气管长度变化会导致转换时间改变，该影响可通过测试CO2延迟予以修正；直采采样频率较低时，直采结果相对全流稀采结果偏差的散差会变大；空气流量计后管道长度变化对直采结果的影响较小。

In order to study the main influencing factors of direct sampling results for engine dynamic test, a diesel engine was used to compare direct and fullflow constant volume sampling results by changing different test parameters based on the theoretical analysis. The results showed that the fullflow constant volume sampling test results were less affected by the changes of test parameters. Whether the realtime concentration of direct sampling exhaust aligned with the exhaust mass flow or not according to conversion time was the key factor for the accuracy of emission test results. The change of exhaust pipe length would lead to different conversion time, which could be corrected by testing CO2 delay. Compared with the fullflow constant volume sampling, the dispersion of direct sampling test results were large at the low direct sampling frequency. The change of pipe length after air flow meter had minor influence on the direct sampling test results.