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Utilization of biofuels to vehicles is attracting attention globally from viewpoints of preventing global warming, effectively utilizing the resources, and achieving the local invigoration. Representative examples are bioethanol and biodiesel. This study highlights biodiesel and hydrotreated vegetable oil (HVO) in view of reducing greenhouse gas emission from heavy-duty diesel vehicles. Biodiesel is FAME obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. As already reported, FAME has fuel properties different from conventional diesel fuel, resulting in about 10% increase in NOx emission [1],[2],[3]. Suppression of such increase in the NOx emission during operating with biodiesel requires adjustment of the combustion control technology, such as fuel injection control and EGR, to the use of biodiesel.

Exciplex-based planar fluorescence technique was applied for two-dimensional visualization of the fuel spray including the region close to the nozzle tip. A spray doped with small amount of naphthalene and TMPD was discharged from a diesel nozzle into a pressurized gaseous nitrogen inside the test chamber installed with glass windows. The fuel spray was also allowed to evaporate in high temperature gaseous environments produced by combustion of the homogeneous mixture of methane and air in the test chamber. Photographs of the temporally frozen two dimensional image of the fuel spray were processed using an image analyzer. The image in the longitudinal cross section passing through the center axis of the spray demonstrated that the high density portion of liquid fuel appeared almost periodically downstream and that the axial distance between the neighboring high density portion increased with an increase in the downstream distance.