This document discusses theoretical investigations of injection pressure in a four-stroke diesel engine using alcohol as fuel. A computer program was developed to simulate the engine's performance with diesel and at different alcohol injection pressures ranging from 180 to 160 bar. The results showed that an injection pressure of 165 bar for alcohol produced higher brake thermal efficiency and indicated thermal efficiency that were closest to diesel fuel. It was concluded that alcohol can be used in diesel engines with an injection pressure of 165 bar as it allows an optimum amount of alcohol to be injected while compensating for alcohol's low viscosity.