軽油-水エマルジョンの噴霧火炎におけるミクロ爆発の観測:　第3報，油申分散水滴径の違いが火炎構造に及ばす影響

摘要

近年，アジアにおけるエネルギー消費の大幅な増加rnに伴い，環境問題が大きな課題となっている．その中rnでも車両，一般産業，船舶と幅広く用いられているデrnィーゼル機関ではNO_xやPMといった排気ガスへの対rn策が求められている．rnエマルジョン燃焼法は燃焼性の改善とNO_x排出量rnの低減を同時に達成できる燃焼技術とされており，こrnれは，その特徴的現象である油滴のミクロ爆発によるrn二次微粒化，水添加による燃焼温度の低下，および水rn蒸気と燃焼ガスとの水性ガス反応によるものと考えrnられている．%Microexplosions of light oil-water emulsified fuel droplets were successfully documented using a high-speed video camera with laser illumination. The local frequency of explosion occurrence, temperature profile and exhaust gas emission were measured in spray flames of water-in oil type emulsion formed using an air-assist atomizer with a ring pilot burner. Those results indicate that the flame structure changes as the water droplet diameter in the emulsion fuel was varied, even if the fuel components and their fractions were same. When fuel includes water droplets, whose median diameter was around 75 μm, HC and CO emissions were reduced as compared to those for the fuel of smaller water droplet content. It is probable that if the water droplet diameter is uniform, avalanch-ing microexplosions occur at certain local region in the flame, and the water content vaporizes almost at once and extinguishes the flame. It leads to HC and CO emission increase. When the water droplet diameters are large, atomizer atomizes those ; therefore, emulsion droplets include various size of water droplet in the flame. Consequently, the avalanching microexplosion occurrence is avoided, and HC and CO emissions are reduced.