Optical study on spray, combustion and flame characteristics of n-hexanol/diesel blends under various diesel engine-like conditions

As a long-chain alcohol, n-hexanol has attracted increasing attention recently. Soot emissions are shown to reduce effectively when n-hexanol is blended into diesel, but the mechanisms of this have not been revealed through spray combustion. Therefore this study is aimed to investigate the spray, combustion and flame characteristics of n-hexanol/diesel blends using optical diagnostics. Diesel containing 20% and 50% of n-hexanol by volume were tested and compared with pure diesel. Results indicate that when n-hexanol is blended into diesel, the spray characteristics improve greatly while peak of the combustion pressure suffers a slightly drop at most test conditions. Moreover, the combustion duration is always shortened when n-hexanol is mixed into diesel. Additionally, the fuel blends always exhibit a longer flame lift-off length than that of pure diesel, which together with their shortened liquid penetration length may have the potential to enlarge the mixing region and therefore improve the fuel mixing level. The results also show that the peaks of the spatial integrated natural luminosity for the fuel blends are noticeably lower. And as the amount of the n-hexanol blended into diesel increases, the peaks of the spatial integrated natural luminosity get even lower. That indicates n-hexanol is capable of achieving a low-soot combustion by being directly blended into diesel.