Abstract:

Under the national goal of “carbon peaking and carbon neutrality”, the carbon-free alternative utilization of fossil fuels has become very important. Metal fuels are a new type of carbon-free fuels, among which micron iron powder is considered to be the most potential metal fuel. However, the current understanding of the combustion mechanism of iron powder is still in its infancy. In order to study the combustion characteristics of single iron particle, a new type of iron powder burner was designed based on the principle of vibration-entrainment flow. It realizes the single iron particle supply and ensures its rapid combustion in a hot environment. The ignition and combustion processes of single iron particle with the diameter mainly distributed within 50 μm to 65 μm in the fuel-lean methane/air flame environment were investigated. It was observed that the combustion process of single iron particle was mainly divided into three stages: combustion retardation, normal combustion and product solidification. The combustion history of single iron particle was captured by using a high-speed digital camera, and typical combustion brightness anomalies were found. The sharp variation of the motion speed of iron particle was observed in the later period of combustion. In addition, the intermediate and final products of combustion were analyzed. It indicates that single iron particle melts in the initial of combustion, then the gas generates and expands during the combustion process, and the product particle bursts and becomes a hollow thin-walled sphere eventually.

Key words: micrometer scale, iron powder, entrained flow, renewable energy, multiphase reaction, combustion

摘要：

在国家“双碳”目标下，化石燃料的无碳替代利用变得十分重要。金属燃料是一类新型的无碳燃料，其中微米铁粉被认为是最具潜力的金属燃料。然而，目前对铁粉燃烧机理的理解尚处于起步阶段。为了研究单颗粒铁粉的燃烧特性，基于振动-夹带流原理设计了一种新型铁粉燃烧器，实现了单颗粒铁粉稳定供给，并在热氛围中快速燃烧。研究了粒径主要集中在50~65 μm内的单颗粒铁粉在稀燃甲烷/空气热氛围中点燃和燃烧过程。观察到单颗粒铁粉的燃烧过程主要分为燃烧迟滞、正常燃烧和产物凝固三个阶段。采用高速摄像机拍摄了单个铁粉颗粒的燃烧历程，发现了典型的燃烧亮度反常现象，同时观察到铁粉颗粒的运动速度在燃烧后期发生突变。另外，通过对燃烧中间产物与最终产物进行采样分析，表明单颗粒铁粉在燃烧初期发生熔化，在燃烧过程中产生气体并膨胀，最终发生破裂形成空心薄壁球体。

关键词: 微米尺度, 铁粉, 夹带流, 再生能源, 多相反应, 燃烧