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The utilization of fuel microemulsions helps in reducing harmful emissions, enhancing combustion efficiency, and preserving conventional fuels. This study is focused on the effect of the properties and phase behavior of water-in-diesel and water-in-biodiesel microemulsions that can be used as an alternative fuel on the droplet impingement dynamics of such fluids on a heated wall in the film boiling regime. The microemulsions represent complex fluids consisting of diesel fuel–rapeseed oil blends and distilled water with different mixture volume ratios. The emulsification is carried out using a mixture of a surfactant [isononylphenol poly(ethylene glycol) ether, PEG-6] and a co-surfactant (2-ethylhexanol) with a volume ratio of 9/1. The study considers the efficiency of the fuel samples in terms of the temperature-dependent viscosity and aggregate thermal stability as well as the quantitative characteristics of the spreading drop breakup, namely, mean diameter and number of ejected droplets. The fuel efficiency factor is derived to reveal the optimal samples. We test the phase behavior of the water–diesel fuel/rapeseed oil–PEG-6/2-ethylhexanol system in a wide temperature range. Comprehensive viscosity tests are carried out within the temperature ranges of stability to check the viscosity values of the developed microemulsions against the viscosity of the conventional diesel fuels.