The world recognizes that the main source of energy used in transportation is diesel oil since it is economical and efficient; however, unfortunately, it is not a renewable resource and pollutes the environment. Today, although n-butanol has been used in blends with diesel oil with great results, there is still dependence on the use of fossil fuels. Hence, the effects of n-butanol as an ignition improver for hydrous ethanol were studied for its properties and the fact that this fuel alcohol may be produced by renewable sources, making it possible to replace diesel oil with a biofuel. To study the combustion characteristics of the ethanol/n-butanol blend, a rapid compression machine was used under different test conditions (compression ratio and start of injection). The mass fractions of n-butanol used in the blends were 10% and 15%, and the test results were compared with those of other fuels, i.e., diesel oil S10 and an ethanol/additive blend, developed by SEKAB and named ED95. The test results show a similar behavior for both blends with n-butanol. Therefore, the ethanol/n-butanol blend (10%) (w/w) may be used in compression ignition systems after some modification, such as increasing the compression ratio (above 27:1) and injection pressure and advancing the start of injection.