The authors have proposed a novel approach regarding fuel design methodology targeting at both Diesel and Gasoline engines and demonstrated that the fuels designed based on this approach were effective to achieve high thermal efficiency and low pollutants emissions. Here, flash boiling spray is applied to improve the spray atomization and evaporation processes by using several kinds of mixed fuels with relatively low injection pressure. This paper is a review covering concerned our previous researches and new experimental results of superheated mixed Diesel like spray, with focusing on spray dynamics. In the mixed fuels, additives or lower boiling point fuels, such as CO2, gas fuel and Gasoline component, are mixed into higher boiling point fuel such as Diesel gas oil, through vapor-liquid equilibrium with a formation of two-phase region in pressure-temperature diagram, where liquid and vapor phases of both components are mixed in. In this scheme, the authors intend to control both physical process, that is the fuel vapor formation rate or spatial vapor distribution, and chemical processes, those are the mixture ignition, emission reduction of NOx and PM, and HC burn out. Then it is easy for mixed fuel to obtain flash boiling spray due to the formation of two-phase region on P-T diagram and it provides the relatively lean and homogeneous vapor mixture. In the experiments, the authors conducted the mixed fuel application studies for actual diesel combustion field by use of mixed fuel consisting of liquefied CO2 as an additive and n-tridecane as a typical component of gas oil, and mixed fuel of Gas or Gasoline component and Gas oil component to control evaporation process. Further, experiments of mixed fuel heating were conducted to realize the prompt evaporation spray due to partially flashing effect and supercritical Diesel like spray feature.