Water-in-diesel emulsion plays a vital role in the reduction of NOx and PM emissions. Spray droplet micro-explosion is a crucial aspect that requires indepth investigation to provide a detailed analysis of the fuel atomisation and combustion. This study is one of the foremost attempts to examine the microscopic spray atomisation and evaluate the emulsified fuel droplet behaviour. A set of water-in-diesel emulsions is prepared and tested in a constant volume chamber in an evaporating condition. The microscopy lens is attached to a high-speed camera, and high spatial and temporal resolutions through a LED system are used for the visualisation. A purpose-built algorithm is utilised for the spray measurements. The measurements indicate that the emulsified fuel penetrates farthest with a wider cone angle compared to the neat-diesel. The initial spray development suggests droplet puffing/micro-explosion. An observation of a highly deformed droplet shape is caused by droplet puffing/micro-explosion. The Sauter mean diameter (SMD) value increases with the increase in water content due to the water evaporation inside the droplet is greater than the drop off caused by droplet evaporation, suggesting that the spray droplets may undergo puffing/micro-explosion in a short time. © 2021 Elsevier Ltd