壁流式DPF热再生时颗粒层结构特征的氧化演变机理和颗粒排放特性研究

Diesel particulate filters (DPFs) are widely applied to effectively reduce the soot emission from diesel engine. The emitted particles from DPF greatly increase during its thermal regeneration process, which seriously exceed the emission standard and urgently need to be controlled. The emitted particles during the thermal regeneration process are strongly correlated with the oxidation process of deposited soot layer inside the DPF channels. Firstly, this project is firstly based on the oxidation process of single soot particle, measuring the evolution mechanism of its micro-construction characteristics and investigating the co-oxidation mechanism of NO2 on particle oxidation to reveal the influence mechanism of oxidation process of single soot particle on uniform oxidation process of soot layer. Secondly, based on a visualization single channel experimental bench, using the online and offline measuring method to investigate the oxidation evolution mechanism of soot layer construction characteristics during its gas-solid oxidation and solid-solid catalytic oxidation process, and to investigate the back-diffusion mechanism of solid-solid catalytic oxidation, and to investigate the non-uniform oxidation phenomenon of the deposited soot layer. Thirdly, the influences mechanism of soot layer construction characteristics on the particle penetration and second particle generation are investigated, and the effects of sulfate and hydrocarbon substances are taken into account to determine the mutual influence relationship of each sources of emitted regeneration particle. Finally, the empirical correlation models of soot layer oxidation process and the regeneration particle emission are built, and the model validation are carried out using the experimental results. The conduction of this project can not only help to deeply reveal the oxidation mechanism of soot layer and understand the emitted particle performance, but also provide important theoretical basis and application reference for controlling the emitted particle during thermal regeneration process.

壁流式柴油机颗粒捕集器（DPF）可有效降低柴油机颗粒排放，但其热再生时颗粒排放陡增，超标严重，急需控制。再生时的颗粒排放与DPF内沉积颗粒层的氧化燃烧密切相关。本项目首先从单个碳烟颗粒的氧化燃烧入手，分析其微观结构特征的演变规律，探索NO2对颗粒的协同氧化作用，揭示碳烟颗粒氧化过程对颗粒层均匀氧化的作用机理。其次，基于可视化单通道实验台，采用在线和离线测量结合的方法，探索颗粒层结构特征在气固氧化和固固催化氧化时的演变规律，揭示逆向扩散的催化氧化机理和颗粒层不均匀氧化规律。再次，探索颗粒层结构特征对颗粒穿透和二次颗粒生成的影响机理，同时考察硫酸盐和碳氢物质对再生颗粒排放的影响，确定各颗粒来源之间的相互影响关系。最后，建立颗粒层氧化和再生颗粒排放的实验关联模型，并进行模型验证。项目研究既有助于深入阐明颗粒层的氧化燃烧过程以及再生颗粒排放特性，又能为控制再生颗粒排放提供重要的理论基础和应用参考。

壁流式柴油机颗粒捕集器（DPF）可有效降低柴油机颗粒排放，但其热再生时颗粒排放陡增，超标严重，急需控制。再生时的颗粒排放与DPF内沉积颗粒层的氧化燃烧密切相关。本项目首先从单个碳烟颗粒的氧化燃烧入手，分析其微观结构特征的演变规律，探索NO2对颗粒的协同氧化作用，揭示碳烟颗粒氧化过程对颗粒层均匀氧化的作用机理。其次，基于可视化单通道实验台，采用在线和离线测量结合的方法，探索颗粒层结构特征在气固氧化和固固催化氧化时的演变规律，揭示逆向扩散的催化氧化机理和颗粒层不均匀氧化规律。再次，探索颗粒层结构特征对颗粒穿透和二次颗粒生成的影响机理，同时考察硫酸盐和碳氢物质对再生颗粒排放的影响，确定各颗粒来源之间的相互影响关系。最后，建立颗粒层氧化和再生颗粒排放的实验关联模型，并进行模型验证。. 通过项目研究发现：NO2与O2对炭黑氧化具有明显的协同作用。在Pt催化作用下，NO2与O2对炭黑氧化的协同作用更明显，使得炭黑氧化活化能更低。但NO2也存在最优的浓度窗口。老化作用可以提升炭黑颗粒的氧化活性，降低活化能。发现了颗粒的沉积过程分为四个阶段（深床期、长树期、搭桥期和颗粒层期），丰富了颗粒在DPF内部的“三阶段（深床期，过渡期和颗粒层期）”沉积理论。碳黑颗粒层在DPF过滤表面的氧化过程可以分为三个阶段：压降缓慢下降、明显下降和再次缓慢下降；颗粒层厚度基本保持不变、明显下降和缓慢下降。探明了CDPF壁面上活性氧的逆向扩散距离。DPF再生时升温阶段由于高温气流携带，可以将已沉积的颗粒吹出，形成颗粒释放峰。在高温再生阶段，可以使得已沉积颗粒氧化变小，导致出口颗粒排放峰。DPF再生存在快速再生期。DPF再生出口排放与颗粒沉积分布具有较大的相关性。再生期，热点形成期（快速再生期）导致颗粒大量释放；而无热点形成，无明显的颗粒释放现象。. 该项目研究既有助于深入阐明颗粒层的氧化燃烧过程以及再生颗粒排放特性，又能为控制再生颗粒排放提供重要的理论基础和应用参考。