Nowadays, many researches are being carried out to replace the diesel by alternative fuels. Biodiesel and ethanol are strong candidates for this purpose. However, the experimental study of the combustion of biofuels in engines is not an easy task. Due to the large differences between the properties of the new fuels and the conventional diesel, radical changes may be needed in current engines, developed specifically for the fossil fuel. So, the experimental study of ethanol compression ignition (CI) combustion is not simple to be obtained in conventional engines. Therefore, some experimental apparatus, such as a rapid compression machine (RCM), are useful to conduct this kind of study. This paper describes the RCM adaptations made in order to run CI combustion tests using Ethanol-Powered (ED95) and Diesel (S50) for different compression ratios and injection timing. The RCM was equipped with a high pressure common-rail diesel injection system, a piezoelectric sensor, its amplifier and a high speed camera. The idea is to use the results obtained with this system in the future to adapt engines and make correlations with engine tests. The main objective is to develop new technologies to guide the design of new engines and new fuel formulation, quickly reducing the time and costs in the development process. The results show the behavior of combustion with varying the compression ratio and the injection timing. The moment of injection associated with higher compression ratios allows the optimization of the combustion process, increasing thermal efficiency, thus reducing emissions of exhaust gases. © 2013 SAE INTERNATIONAL.