Li Xinling, Zhao Pengcheng
College of Smart Energy, Shanghai Jiao Tong University, Shanghai, 200240, China.
Institute of Eco-Chongming (IEC), Shanghai, 202162, China.
Environ Sci Pollut Res Int. 2025 May;32(23):14086-14096. doi: 10.1007/s11356-025-36511-3. Epub 2025 May 19.
As one of the most effective ways of reducing nitrogen oxides (NO) emission, exhaust gas recirculation (EGR) has been widely used in diesel engines. However, EGR generally shows adversely effective in particulate matter (PM) emissions. The chemical composition of the PM with the application of EGR is not well identified because few previous publications focus on this topic, especially for high EGR rate cases. In this paper, emission characteristics of organic carbon (OC, OC-OC), elemental carbon (EC, EC-EC), and particulate semi-volatile organic compounds (SVOCs) including 18 n-alkanes and 20 polycyclic aromatic hydrocarbons (PAHs) for a common-rail diesel engine at mild and high EGR rate conditions (up to maximum achievable level while maintaining stable combustion) were analyzed at four steady-state conditions comprehensively. It can be clearly observed that EGR rate instead of load and speed significantly affects the EC emission under the experimental conditions. EC emission increase with increasing EGR rate, which is divided to two sections, i.e., slight increase from 0 to 30% (mild EGR rate) and sharp increase from 30 to 45% (high EGR rate). TC is dominated by OC, OC, and EC at low EGR rate, and the fraction of EC evidently increases with increasing EGR rate. It is observed that TC is heavily dominated by EC at highest EGR rate ranges, which corresponds to the lower heat release rates (lower HRR at higher EGR rate) and lower air-fuel ratio at these conditions. All the target PAHs increase with increasing EGR rate at the four operation modes. The adverse effect of EGR on PAH emission is less significant than EC emission. Moreover, the effect of EGR rate on the PAH ring distribution is not significant. Both of total ∑C-C and ∑C-C emission rates evidently increase at high EGR rate condition in comparison with those at baseline and mild EGR condition cases, which indicates that both fuel-derived and oil-derived n-alkanes exhibit higher emission rate at high EGR conditions compared with those at baseline and mild EGR condition. The application of EGR helped with other controlling strategies (e.g., fuel injection, after-treatment device) is suggested to suppress the carbonaceous PM formation for the modern common-rail diesel engine.
作为减少氮氧化物（NO）排放的最有效方法之一，废气再循环（EGR）已在柴油发动机中广泛应用。然而，EGR通常对颗粒物（PM）排放显示出不利影响。由于以前很少有出版物关注这一主题，特别是对于高EGR率的情况，因此应用EGR时PM的化学成分尚未得到很好的识别。本文全面分析了一台共轨柴油发动机在轻度和高EGR率条件下（达到最大可实现水平同时保持稳定燃烧），在四个稳态工况下有机碳（OC，OC-OC）、元素碳（EC，EC-EC）以及包括18种正构烷烃和20种多环芳烃（PAHs）的颗粒半挥发性有机化合物（SVOCs）的排放特性。可以清楚地观察到，在实验条件下，EGR率而非负荷和转速对EC排放有显著影响。EC排放随EGR率增加而增加，可分为两个阶段，即从0到30%（轻度EGR率）略有增加，从30到45%（高EGR率）急剧增加。在低EGR率下，总碳（TC）以OC、OC和EC为主，且EC的比例随EGR率增加而明显增加。据观察，在最高EGR率范围内，TC主要由EC主导，这对应于较低的热释放率（高EGR率下较低的HRR）和这些工况下较低的空燃比。在四种运行模式下，所有目标PAHs均随EGR率增加而增加。EGR对PAH排放的不利影响不如对EC排放显著。此外，EGR率对PAH环分布的影响不显著。与基线和轻度EGR工况相比，在高EGR率工况下，总∑C-C和∑C-C排放率均明显增加，这表明与基线和轻度EGR工况相比，燃料衍生和机油衍生的正构烷烃在高EGR条件下均表现出更高的排放率。建议将EGR与其他控制策略（如燃油喷射、后处理装置）结合应用，以抑制现代共轨柴油发动机中碳质PM的形成。
