## 1 Introduction
[11] found that phase behavior is substantially improved when the transition of dieseline (10% volume gasoline) from liquid to liquid\(-\)vapor and then to the supercritical fluid state and gasoline also prevents diesel coking. [PERSON] et al. [12] presented a methodology for effectively evaluating the performance of diesel fuel surrogates in representing real diesel fuel thermophysical properties. The researchers estimated the critical temperature of diesel fuel to be 717-745 K. This result is important for the design of supercritical fuel delivery and injection systems. [PERSON] [13; 14] explored the thermophysical properties of diesel fuel surrogates in supercritical state and proposed the use of statistical parameters, such as absolute average of relative error and sum of average residues, to evaluate the accuracy of the surrogates. In our previous study, we estimated the critical temperature and pressure of gasoline by using the values 550.4 K and 3.092 MPa, respectively [15]. Thus far, most of the research on supercritical fuels is based on the rocket engine, whereas investigations of supercritical fuels in internal combustion engine applications are rare. [PERSON] et al. [16] proposed a modifying mechanism for simulating supercritical gasoline, this mechanism contains 103 species and 201 reactions and is obtained by modifying the pre-exponential factors of key reactions and adding key reactions on the basis of the original mechanism proposed by our research program. [PERSON] claimed that the delivery of a diesel fuel-diluent mixture in supercritical state increases engine efficiency and reduces NO\({}_{\rm X}\) and PM by avoiding two-phase reactions in fuel-rich regions [17; 18; 19]. [PERSON] et al. [20; 21] studied the combustion and emission performance of supercritical fuel via experiments. They found that the emission of soot particles and NO is improved in the supercritical fuel condition of a single cylinder and obtained the trend of NO and soot emission with the change in fuel temperature. [PERSON] et al. [22] discovered that supercritical gasoline combustion combined with exhaust gas recirculation results in low emissions and high thermal efficiency of single-cylinder engines under all operating conditions, and the maximum indicated thermal efficiency is 45%. [PERSON] [23]explored the combustion effect of supercritical-state diesel and concluded that combustion efficiency is improved, and fuel economy is increased to 20%. [PERSON] et al. [24; 25; 26], through their aviation kerosene Jet-A research, established a supercritical calculation model and a calculation method for the physical parameters of supercritical-state fuel. This study provides an effective theoretical basis and guidance for follow-up studies. Diesel and gasoline (diesel mass fraction 10%) was selected as the research object in the current study due to the combined advantages of easy diffusion, small viscosity coefficient, good flow capability, and short combustion time of supercritical fuel. On the basis of the special physical properties of supercritical fuel and supercritical injection technology, a simulation of supercritical fuel combustion was conducted under a high compression-ignition ratio in an internal combustion engine. To our knowledge, no study has been conducted on the combustion of supercritical fuel in internal combustion engines. In this work, we explored flow and temperature fields and the quality score distribution of supercritical and subcritical fuels in the cylinder. Thus, different combustion and diffusion characteristics of supercritical and subcritical fuels were revealed.