Abstract Growing interest of the European Union to introduce new emission regulations seeking to lower the particle cut-off size down to the current limit set at 23 nm, has made crucial to achieve an extensive comprehension on their nature. In this regard, it is necessary to deepen their knowledge under different engine technologies, operating conditions, fuel properties and after-treatment devices and how their measure is affected by the sampling and dilution procedure. This paper provides a study on the sub-23 nm particles emitted from a small direct/port fuel injection, spark ignition engine fueled with gasoline, ethanol and a 30% v/v ethanol/gasoline blend, at different operating conditions. Particles were measured both upstream and downstream of a three-way catalyst. The conditions of the sampling were changed in order to investigate the volatile organic fraction. For this purpose, the exhaust gas sample was diluted through a Particulate Measurement Programme compliant system. The temperature of the first dilution stage and of evaporation chamber were changed to discriminate the volatile compounds by enhancing the condensation and the nucleation processes. An engine Exhaust Particle Sizer was used for the sizing and the counting of the particles in the range 5.6–560 nm. The results show a strong dependence of the sub-23 nm particle emissions from the engine operating condition and the fuel type. A moderate impact of the three-way catalyst was instead observed. Moreover, a significant effect of the dilution parameters in the sampling system was noted pointing out the importance to define an appropriate protocol for the measurement of the sub-23 nm particles.

中文翻译：

---

以汽油、乙醇和 30%v/v 乙醇混合物为燃料的 PFI/DI 火花点火发动机中亚 23 nm 颗粒及其挥发性有机成分 (VOF) 的研究

摘要 欧盟对引入新的排放法规的兴趣日益浓厚，以寻求将粒子截止尺寸降低到目前设定的 23 nm 限制，这对于实现对其性质的广泛理解变得至关重要。在这方面，有必要加深他们在不同发动机技术、运行条件、燃料特性和后处理装置下的知识，以及他们的测量如何受到采样和稀释程序的影响。本文研究了在不同操作条件下，以汽油、乙醇和 30% v/v 乙醇/汽油混合物为燃料的小型直接/端口燃料喷射火花点火发动机发出的亚 23 nm 颗粒。在三元催化剂的上游和下游都测量了颗粒。改变取样条件以研究挥发性有机组分。为此，废气样品通过符合微粒测量程序的系统进行稀释。改变第一稀释阶段和蒸发室的温度以通过增强冷凝和成核过程来区分挥发性化合物。发动机排气粒度仪用于对 5.6-560 nm 范围内的颗粒进行分级和计数。结果表明，来自发动机运行条件和燃料类型的亚 23 nm 颗粒排放有很强的依赖性。相反，观察到三元催化剂的适度影响。而且，