Effects of initial oil temperature on exothermic properties of horizontal spray combustion with transformer oil

This study experimentally investigates the effect of different initial oil temperatures on the horizontal spray combustion characteristics of transformer oil, and the results show that the heat release rate increases with initial temperature, and it becomes less sensitive to the initial oil temperature as the mass flow rate increases. Only 0.45 %–1.61 % of the heat provided by combustion is used to heat the unburned oil droplets. Combustion can be self-sustained for a long time when the percentage of heat required for oil heating and evaporation is h ≤ 1.22 %, while self-extinction of combustion occurs when h ≥ 1.29 %. At low mass flow rate, the effect of increasing oil temperature on combustion efficiency is significant, and with the increase of mass flow rate, the effect of ambient oxygen depletion on combustion efficiency is dominant, and the combustion efficiency prediction model η=1/[1+(1.01130(0.0176−m)(416−T)−1)+160(m−0.0097)] closely aligns with experimental data. Additionally, flame surface area (S) and heat release rate (Q) are linearly related (Q = 119S). This relationship indicates higher heat release per unit flame area compared to gas laminar flames and battery jet flames, due to improved air-fuel mixing in the turbulent spray flame. The combustion efficiency prediction model proposed in this study is applicable only to self-sustaining combustion in open spaces involving horizontal transformer oil sprays without any external heat source.