WHTC工况下PN10和PN23计数器粒子数排放测量差异分析

Analysis of PN emission measurement difference between PN10 and PN23 counters under WHTC conditions

为探究当前主流的PN23计数器与更先进的PN10计数器测量结果差异,选取一台符合国Ⅵ排放标准的柴油发动机进行世界统一瞬态循环(World Harmonized Transient Cycle,WHTC)工况排放试验。该发动机可配置两套标定功率数据。使用最小测试粒径分别为23 nm和10 nm的粒子数(Particulate Number,PN)计数器同时测取PN排放数,分析对比PN排放结果,并总结排放规律。结果显示:标定功率为316 kW和430 kW的WHTC循环PN10计数器粒子数排放结果比PN23计数器分别高约27.48%和27.46%;WHTC循环第1145 s后,PN10计数器粒子数浓度显著高于PN23计数器,中等以上负荷、稳定转速工况更利于23 nm以下粒子生成;转速高于1000 r/min时,PN10计数器测得的粒子数浓度比PN23计数器明显更高;随着负荷增加,直径为10~23 nm的粒子数浓度先增加后减少。发动机在上述工况下运行时,PN23计数器测量值显著低于PN10计数器,该差异最终导致循环排放结果相对不准确。

To study the difference in measurement results between the current PN23 counter and the more advanced PN10 counter,and analyze the PN emission characteristics of diesel engines under different rated power,a series of comparative tests are carried out.A diesel engine that complies with China VI emission standard is selected for the WHTC condition emission test.The engine can be equipped with two data sets of power.PN emission values are measured by PN counters with minimum detected size of 23 nm and 10 nm at the same time respectively.Test results such as total PN emissions in a cycle and specific emissions are analyzed and compared.Emission characteristics measured by different PN counters are summarized.The results show that the emission results of the PN10 counter in WHTC condition with a rated power of 316 kW and 430 kW are about 27.48%and 27.46%higher than those of the PN23 counter respectively.From 1145 s after the start of the WHTC condition,the PN emission volume concentration measured by the PN10 counter is significantly higher than that of the PN23 counter,and the measured data of two sets of calibrated power all show this rule.It means there are more conducive to the formation of PN below 23 nm in Medium load and stable engine speed conditions.When the speed is higher than 1000 r/min,the value of PN emission volume concentration measured by the PN10 counter is significantly higher than that measured by the PN23 counter.The emission volume concentration of PN with a diameter of 10 nm to 23 nm increase first and then decreases with load increase.We find that under the stable conditions of medium load and medium-high speed,the current PN23 counter has a significantly lower measurement value than the PN10 counter,which makes the measurement result of the total cycle of the PN23 counter inaccurate.