微重力燃烧研究进展

RESEARCH ADVANCES ON MICROGRAVITY COMBUSTION

认识燃烧过程是安全、高效、洁净地利用能源的基础.但是,常重力条件下的浮力对流和重力沉降使得燃烧现象变得复杂.而微重力条件下这些影响几乎消失,这简化了对燃烧的研究.在加深对地面燃烧过程和载人航天器火灾安全问题的认识的推动下,经过近半个世纪特别是最近10多年的发展,微重力燃烧研究已经涵盖了预混气体、气体扩散、液滴、颗粒和粉尘燃烧、燃料表面的火焰传播等燃烧学科的各个领域.研究中实现了球对称液滴燃烧、不受沉降影响的粉尘燃烧、静止或低速对流环境中的燃烧,观察到了火球、自熄灭火焰等现象,阐明了碳黑形成中的热泳力效应、可燃极限与火焰稳定性等机理.加深了对燃烧现象,特别是对辐射效应的理解:在预混气体、气体扩散、液滴等多种火焰中,除了停留时间过短引起的吹熄极限外,还存在辐射热损失过大引起的冷熄极限,后者只能在微重力条件下观测到.部分研究成果已经进入教材.而火焰在微重力下不同于常重力下的现象,对载人航天器火灾安全具有重要意义.考虑到我国的现实情况和国内外的研究现状,建议将煤炭颗粒和粉尘的燃烧、与碳黑相关的机理、辐射效应、化学动力学等作为我国微重力燃烧的主要研究方向.

Understanding the combustion process is essential for the energy utilization in a safe, efficient and clean way. However, in normal gravity, the buoyant convection and gravitational sedimentation make the process complicated. Such effects nearly disappear in microgravity, which will simplify the research on combustion. In view of the combustion process occured on ground and the fire safety problem for manned spacecraft, the research on microgravity combustion involves various fields of combustion science, including premixed gas combustion, gaseous diffusion combustion, droplet combustion, particle combustion, dust combustion and flame spread over fuel surface, during the development of about a half century, especially the last decade. Through the research, the droplet combustion with spherical symmetry, dust combustion without sedimentation effect and combustion in quiescent or low speed convection environment have been realized, the flame ball, self-extinguishing flame and other phenomena were observed, and the thermophoresis effect during soot formation, flammability limit and flame instability and other mechanism were clarified. The research has deepened the knowledge of combustion phenomenon and especially deepened the understanding on radiation effect. It is shown that, for premixed gas combustion, gaseous diffusion combustion and droplet combustion, there is also the quenching extinction limit caused by large radiative heat loss, besides the blowoff extinction limit caused by short residence time. The former can be found only under microgravity condition. Some of these results have already been absorbed into the textbook. The fact that the combustion under microgravity shows different characteristics from that under normal gravity is important for fire safety for manned spacecraft. Acounting for the condition of our country and present research advances, the coal particle combustion, the dust combustion, the mechanism related to soot, radiation effect and chemical dynamics would serve as the promising future directions.