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There is individual droplet burning phenomenon in spray flames but the ignition prediction and criteria are lack of both experimental and theoretical study. In the paper, firstly based on the energy balance analysis method, two new droplet ignition models were proposed by analyzing the single droplet evaporation and ignition process in relatively static high temperature air environment, which models can be used to predict the droplet ignition boundaries. Then, the single droplet of RP3 aviation kerosene, common kerosene and diesel was suspended in static air environment with ambient temperature from 855K to 1085K to test the ignition limits of the fuel droplet. The experimental ignition boundary was obtained by measuring and recording the minimum ignitable initial diameters of the experimental droplet in every temperature condition. The experimental results show that the ignitable minimum initial diameter of the fuel droplet decreases along with the increase of ambient temperature. And at the same ambient temperature, the minimum ignitable initial diameter of common kerosene droplet is the biggest, then is diesel and RP3 aviation kerosene is the smallest. Finally, the predicted ignition boundaries of the two new models were compared with the experimental data. And the comparison results show that the models’ predictions are in good agreement with the experimental data, whose error is within 10%. INTRODUCTION Spray combustion is widespread in the current combustion system, such as gas turbine engines, rocket engines, diesel engines and industrial furnaces( Kom and Sharma 2002 ). In these systems, the fuel is atomized into a large number of droplets to accelerate evaporation process and increase combustion efficiency by increasing the surface area. As the basic elements of fuel sprays, fundamental research on single droplet characteristics is a good stare of spray combustion characteristics. The single droplet ignition phenomenon has been observed in the liquid fuel spray flames(Zhou 1961; Chiu and Liu1977; Chiu2000). Russo and Gomez(2006) studied the experimental instantaneous photos of ethanol/argon/oxygen flames. Both droplet evaporation with premixed flame amongst droplets mode and single droplet burning with individual diffusion flame mode existed in the spray flame. Agoston et al(1957)experimentally studied isolated acetone droplets ignition/burning characteristics in convection environment. The experimental results showed different combustion regimes of an isolated droplet, such as stationary envelope flame, envelope flame around a moving droplet, wake flame and boundary-layer flame. Many researchers have investigated droplet ignition characteristics by both experimental research and numerical simulation study under different environmental parameters with different fuels. There are also studies on the droplet ignition under microgravity conditions and microexplosion phenomenon during ignition period(Chen et al2016). Rah (1986)mainly studied the ignition process of n-dodecane droplets. They found that the soot formation can be suppressed by delaying the ignition and the formation of an envelope flame around the droplets. Sangiovanni and Kesten(1975)using furfuryl alcohol and butyl alcohol investigated the influence of ambient temperature, oxygen concentration, droplet relative velocity, droplet size, and fuel type on single droplet ignition. They found that ignition delay time increases when ambient temperature and fuel volatility decrease and the droplet initial diameter increase. Chiu and

Single Droplet Ignition Models Based on Energy Balance Analysis and Validation