An optical study on spray and combustion characteristics of ternary hydrogenated catalytic biodiesel/methanol/n-octanol blends; part I: Spray morphology, ignition delay, and flame lift-off length

Abstract A fundamental study on spray morphology, ignition delay, and flame lift-off length of two ternary hydrogenated catalytic biodiesel (HCB)/methanol/n-octanol blends were carried out by performing visualization tests through high-speed Schlieren and OH* chemiluminescence simultaneously within a quiescent combustion chamber. The two ternary mixtures are 68% by volume HCB, 17% octanol, and 15% methanol, as well as 58% HCB, 17% octanol, and 25% methanol, which are denoted as M15 and M25 respectively. It was found that the mixture stability of HCB/methanol is significantly enhanced using n-octanol as the co-solvent. The pure HCB (M0) was also tested under the same operating conditions as references. All the sprays were injected into the chamber through an injector equipped with a single-hole nozzle. Experimental results show that spray of M0 presents a faster penetration, following by M15 and M25, which is mainly caused by the shorter ignition delay of M0; With the increase of methanol percentage in the blends, the stoichiometric fuel mass fraction increases because of the high oxygen content of methanol, which contributes to a longer ignition delay; There are two factors of the blended fuel properties affecting flame lift-off length, namely stoichiometric fuel mass fraction and cetane number. It was found the cetane number plays a much more important role than that of stoichiometric fuel mass fraction on lift-off length.