Progress in experimental investigations on evaporation characteristics of a fuel droplet

Investigating the evaporation characteristics of a fuel droplet is critical for understanding spray and combustion processes, which provides valuable information and guidance for optimizing engine performance. This paper systematically reviews the droplet evaporation characteristics of various fuels. Firstly, experimental methods for fuel droplet evaporation are introduced, including flying droplet, suspension and levitation, of which the latter two are the most widely applied due to their simple setups and convenient measurements. Secondly, droplet evaporation mechanisms of different fuels are comprehensively discussed. The evaporation process of single-component fuel droplets includes transient heating and equilibrium evaporation phases. Miscible and immis-cible multi-component fuel droplets could experience puffing and micro-explosion phenomena, which increase droplet surface area and evaporation rate. Droplet evaporation may be the best when light component con-centration is around 50% due to the strongest puffing and micro-explosion. The water droplets in emulsified fuel are slightly superheated by 0-30 C when micro-explosion occurs. Nanoparticles could enhance droplet evap-oration at low concentrations (0-1.25%) but inhibit droplet evaporation at higher concentrations. Finally, future research directions of fuel droplets are elaborated. More advanced experimental and numerical methods should be developed. Meanwhile, investigations on droplet evaporation should be combined with spray and combustion.