Faculty of Mechanical and Energy Engineering, Shahid Beheshti University, Tehran, Iran.
Environ Sci Pollut Res Int. 2020 May;27(14):16929-16939. doi: 10.1007/s11356-020-08266-6. Epub 2020 Mar 6.
Because of their direct contact with society, urban buses are prioritized targets for air quality improvement. In this study, a sample group of in-use urban old buses powered by compressed natural gas (CNG) and diesel engines was chosen for particle emission analysis. The CNG buses do not have any type of after-treatment, while diesel ones are equipped with a diesel particulate filter (DPF). To measure the lung deposited surface area (LDSA), a possible physical metric of exhaust particles' toxicity, a diffusion charger-based analyzer was utilized. The measurements were done at different engine speeds in stationary conditions. The results revealed that although the particle mass emission of CNG buses remains at a low level, the number of emitted particles for 75% of the CNG buses (depending on their maintenance conditions) is 10 to 100 times more than the retrofitted diesel ones, with the range of 10 to 10 p/cm. The rest 25% of the CNG buses were performing the same as the retrofitted diesel ones in terms of exhaust particle number in the range of 10 p/cm. In addition, the lowest LDSA parameter at low idle engine speed was measured to be 97.8 and 229.4 μm/cm for a CNG and a DPF retrofitted diesel bus, respectively. This result indicates the same and even lower LDSA and surface area and thus the lower possible toxic potentiality of exhaust particles of CNG buses compared to diesel vehicles at DPF downstream. Investigation on the different behavior of the CNG buses in the emission of particles showed the correlation of some aging parameters such as lubricant oil aging mileage with the released particles and the importance of periodic maintenance interval. Graphical abstract.
由于与社会的直接接触，城市公交车是优先考虑改善空气质量的目标。在本研究中，选择了一组使用中的压缩天然气（CNG）和柴油发动机的城市旧公交车进行颗粒排放分析。CNG 公交车没有任何类型的后处理装置，而柴油车则配备了柴油颗粒过滤器（DPF）。为了测量肺沉积表面积（LDSA），一种可能的废气颗粒毒性物理指标，使用了基于扩散充电器的分析仪。在静止状态下，在不同的发动机转速下进行了测量。结果表明，尽管 CNG 公交车的颗粒质量排放量保持在较低水平，但 75%的 CNG 公交车（取决于其维护条件）排放的颗粒数量是经过改装的柴油车的 10 到 100 倍，范围在 10 到 10 p/cm。其余 25%的 CNG 公交车在废气颗粒数量方面与经过改装的柴油车相同，范围在 10 p/cm。此外，在低怠速发动机转速下，测得的最低 LDSA 参数分别为 97.8 和 229.4μm/cm，分别为 CNG 和 DPF 改装的柴油公交车。这一结果表明，与 DPF 下游的柴油车相比，CNG 公交车的废气颗粒具有相同甚至更低的 LDSA 和表面积，因此潜在毒性可能更低。对 CNG 公交车在排放颗粒方面的不同行为的调查表明，一些老化参数（如润滑油老化里程）与释放的颗粒之间存在相关性，定期维护间隔的重要性。
