This work was aimed to study droplet combustion which was a foundation of spray combustion. Combustion characteristics of BUT00 (pure biodiesel) and BUT50 (50% n-butanol and 50% biodiesel by mass) were investigated using droplet suspension technology under 1 bar and 900 K. One flame was observed for BUT00 while two flames were observed for BUM50. The flame of BUT00 underwent successively faint luminosity, bright luminosity, soot aggregate and soot spread. The first flame of BUT50 was faint and the second one was similar to that of BUT00 because they were caused by n-butanol and biodiesel combustion respectively. Before the auto-ignition of BUT00, (D/D-0)(2) was approximately unchanged at 1.0 and similarity degree (SD) was higher than 97%. Temperature growth rate (TGR) decreased first quickly and then slowly. After the auto-ignition of BUTOO, (D/D-0)(2) sharply decreased and SD was in the range of 90-97%. The flame heating led to the increase of TGR. For BUT50, obvious fluctuations were found in (D/D-0)(2), SD and TGD. The SD of BUT50 was generally lower than 97%. The (D/D-0)(2) of BUT50 included transient heating, fluctuation evaporation and equilibrium evaporation phases. Some characteristic parameters were deterministic although (D/D-0)(2) in fluctuation evaporation phase was a non-deterministic process. (C) 2018 Elsevier Ltd. All rights reserved.