Droplet combustion behavior of oxidatively degraded methyl laurate and methyl oleate in microgravity
Droplet combustion behavior of oxidatively degraded methyl laurate and methyl oleate in microgravity
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DOI：
10.1016/j.combustflame.2019.12.042
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发表时间：
2020-04
影响因子：
4.4
通讯作者：
S. Ando;Yuxiang Wu;S. Nakaya;M. Tsue
中科院分区：
文献类型：
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作者：
S. Ando;Yuxiang Wu;S. Nakaya;M. Tsue
研究了微重力条件下脂肪酸甲酯降解产物和未降解产物的液滴燃烧行为。以月桂酸甲酯（LME）和油酸甲酯（OME）为代表进行了加速氧化试验，评价了FAME的粘度和组成变化。Rancimat方法用于在100 °C下氧化燃料6或24小时。粘度和组成分别用乌氏粘度计和气相色谱-质谱仪（GC-MS）测量。结果表明，在氧化过程中，仅OME生成了多种氧化产物，且氧化产物的生成量随氧化时间的延长而增加。此外，降解OME的粘度高于未降解OME的粘度，这可能归因于氧化产物的形成。随后，在微重力条件下，在0.1MPa、750 °C、富CO2气氛下进行了液滴燃烧实验。根据液滴直径平方和瞬时燃速的变化规律，分析了液滴的燃烧特性。结果表明，LME和正癸烷的瞬时燃速在燃烧过程中基本保持不变，说明烃类和不饱和FAME燃料性质的差异对瞬时燃速的变化没有影响。相反，在蒸发和燃烧期间，降解OME的液滴表现出膨化。这表明，在降解燃料中形成了具有不同挥发性的氧化产物，从而导致了膨化。随着氧化的进行，由于粘度的增加，液体和蒸汽通过膨化的释放速率降低，这导致膨化更频繁。随着初始液滴直径的增大，气泡形成时间增加，这是由于液滴热容的增大。相反，气泡形成的时间并没有随着氧化时间而急剧变化，这可能是由于在氧化试验期间热容的有限变化。本研究针对大海洋生态系统和大海洋生态系统的液滴燃烧行为，着重于氧化的影响。
Droplet combustion behavior of degraded and non-degraded fatty acid methyl ester (FAME) were studied under microgravity condition. Accelerated oxidation tests were conducted for methyl laurate (LME) and methyl oleate (OME) as representatives of FAME, and the changes in viscosities and compositions were evaluated. The Rancimat method was employed for oxidizing fuels at 100 °C for 6 or 24 h. The viscosities and compositions were measured with an Ubbelohde viscometer and a gas chromatography-mass spectrometer (GC–MS), respectively. Results showed that various oxidation products were formed only for OME during the oxidation test, and the amounts increased with an increase in the oxidation time. In addition, viscosities of degraded OME were higher than those of non-degraded OME, which would be attributable to the formation of oxidation products. Subsequently, the droplet combustion experiment was performed at 0.1 MPa, 750 °C in CO2-rich atmosphere under microgravity. Droplet combustion behavior was analyzed in terms of evolutions of droplet diameter squared and the instantaneous burning rate. As a result, the instantaneous burning rate of LME maintained almost constant during its combustion period as well as n-decane, which indicates that the behavior of instantaneous burning rate was not influenced by the difference in fuel properties between hydrocarbon and unsaturated FAME. In contrast, the droplet of degraded OME exhibited puffing during the evaporation and combustion periods. This indicates that oxidation products with various volatilities were formed in the degraded fuels, which resulted in puffing. As oxidation proceeded, the release rate of liquid and vapor by puffing decreased owing to the increased viscosity, which causes puffing more frequently. Furthermore, the time of bubble formation increased with an increase in the initial droplet diameter owing to an increase of the heat capacity of the droplet. On the contrary, the time of bubble formation did not vary drastically with the oxidation time, which was probably owing to a limited change in the heat capacity during the oxidation test. This study addresses the droplet burning behavior of LMEs and OMEs with an emphasis on the effects of oxidation.