Explosions of the premixed gaseous or liquid fuel are just part of energy output. Transient reaction flow beyond the premixed zone are the premise of occurrence of chain hazards. This work proposed a model including two-phase propylene oxide/air mixtures, and first examined the flame range and energy output beyond the premixed zone. Propylene oxide/air mixtures at different initial droplet sizes and concentrations were simulated inside and outside a premixed tube of diameter 0.06 m and length 1 m. Results show that sustaining combustion of vapor diffused outwards the premixed region can increase the range of flame range. Given the initial conditions of fuel concentration and initial dispersity, flame ranges beyond the premed zone for pure gas, initial droplet size 50 mu m and 100 mu m are 0.03 m, 0.08 m and 0.1 m, respectively. At different fuel concentrations and the same initial diameter 100 gm, the lengths of flame range beyond the premixed zone at 100 g/m(3), 200 g/m(3) and 300 g/m(3) are 0, 0.16 m and 0.18 m, respectively. Oscillatory pressure plateau was intuitively observed with large droplet size or at fuel-rich conditions - the more the droplet size or fuel concentration, the more uneven the reaction rate. (C) 2019 The Authors. Published by Elsevier Ltd.