The lift-off flame of gasoline/diesel blend fuel spray in controllable active thermo-atmosphere (CATA) was captured by a high speed camera to investigate the auto-ignition characteristics of blend fuel, meanwhile a database for further simulation work was provided. The experimental results showed that the influence of co-flow temperature on spray lift-off flame has two opposite trends: Under higher co-flow temperature, the flame lift-off height increases with the increase of blended ratio of diesel, and the ignition delay gets longer; when the co-flow temperature is lower, the increment of diesel ratio in blend fuel leads to decrement in lift-off height, and the auto-ignition delay becomes shorter. According to the results, the equilibrium temperature "Te'' was defined to represent the co-flow temperature, where diesel and gasoline ignited spontaneously, and under the test conditions of this paper, it is around 1117 K. The exact value of equilibrium temperature of diesel and gasoline fuel under the conditions of an internal combustion engine (ICE) still needs to be verified by further experimental studies, but the change rules and trend of the equilibrium temperature that proposed in this paper should be applicable to real engines. (C) 2014 Elsevier Ltd. All rights reserved.