Ethanol has gradually become a commonly used additive in diesel to reduce the carbon foot print of the combustion products. In the process of production, transportation and storage, once the accidental leaked ethanol-diesel blend fuel is ignited, the flame will spread very fast and cause great threaten to people's lives and properties, the combustion properties of ethanol-diesel blends is thus a matter of great concern to us. A set of experiments was conducted to study the effects of fuel depth and ullage height on liquid flame spread of diesel and 5% ethanol-diesel. Results showed that as the fuel depth increases under ullage effect, the flame spread rate increases first and then maintain constant. For 5% ethanol-diesel, the flame spread rate decreases monotonously and then tends to be unchanged with ullage height due to the higher combustion efficiency and oxygen content of ethanol-diesel. For deep pools, the surface velocity increases with fuel depth. Moreover, the flash flame pulsation frequency is weakly affected by the fuel depth and presents a negative relationship with ullage height. The study on these issues may have the potential to benefit the current safety production, utilization and management of the energy of ethanol diesel blends. (C) 2018 Elsevier Ltd. All rights reserved.