The performance of a compression ignition (CI) engine run with alternative fuel is inferior to when it is run with petro-diesel resulting in lower power, higher fuel consumption and higher carbon deposits. This is due to the poorer properties of the alternative fuel for the CI engine compared to petro-diesel, for instance, higher viscosity. Due to this factor, this research has grouped these fuels as higher viscous fuels (HVFs). In order to solve or reduce the problem of higher viscosity, this paper presents research that has sought to improve the in-cylinder airflow characteristics by using a guide vane so that the evaporation, diffusion, mixing and combustion processes can be stimulated eventually improving or at least reducing the problem. The in-cylinder airflow was studied using ANSYS-CFX with the help of SolidWorks. Firstly, the validated base model replicated from the generator of a CI engine was prepared. Then, 10 guide vane models with various numbers of vanes were adapted to simulate the in-cylinder airflow characteristics. The results of in-cylinder turbulence kinetic energy (TKE) and velocity were presented and discussed. This research found that four vanes was the optimized number of vanes since it improved approximately 10% of the average in-cylinder TKE and approximately 20% of the average in-cylinder velocity.