Evaluation of soot emission and wall heat loss for the fuels with high aromatic contents using the coupled analysis of chemical luminescence images with heat flux

The stricter regulations on the sulfur content of marine fuel oil in the general sea area that came into effect in January 2020 have led to a prediction of the increase of light cycle oil with high aromatic contents. The higher aromatic content is expected to result in higher soot in the exhaust gas. During combustion, soot emits radiant heat because of blackbody radiation, some of which passes through the walls of the combustion chamber and is released outside. Therefore, the exhaust emission characteristics and wall heat loss are affected if soot formation during combustion differs depending on the aromatic content of the fuel oil. This study developed an analytical method that combines the temporal and spatial distributions of C 2 and OH radicals (these species contribute to soot formation and oxidation) to evaluate the emission and wall heat loss characteristics of different aromatics in fuel oils via combustion and heat flux analysis. The method was applied to test fuels containing different aromatic contents. Two test fuels containing 60 vol% each of toluene (monocyclic) and 1-methylnaphthalene (bicyclic) were evaluated in a rapid compression machine with a 100 mm wall-to-wall distance combustion chamber. The results suggested that the differences in soot emissions were observed because of differences in aromatics, and no differences in the wall heat flux were observed. The distributions of C 2 and OH radical luminescence intensities between the walls were examined, and the differences in soot production were attributed to differences in the C 2 radical production upstream of the flame in the region of low air entrainment. The lack of difference in the heat flux between the test fuels can be attributed to the the differences in the C 2 and OH luminescence intensities, which are related to the heat release rate and heat flux, being almost nonexistent near the walls.