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Over the past decades, researchers from different countries that produce oil or not, have intensified their research in order to develop more efficient systems. It is not unknown to the world that the main source of energy used in transport is the diesel oil, to be more economical and more efficient. For this reason, various sectors of transport and fuel producers are developing new technologies in order to replace fossil fuels with other renewable sources. Nowadays it is possible to find on the market engines that run on blends of diesel and other renewable fuels and systems that work with mixtures of ethanol and additives. To be able to use ethanol in compression ignition engines, the main problem to be overcome is the poor flammability of the ethanol under compression ignition conditions. This problem is generally attributed to the high enthalpy of vaporization of ethanol and the need for higher autoignition temperatures when compared to diesel.

Gasoline is a volatile, inflammable mixture composed of olefinic, paraffinic, naphthenic and aromatic C4-12 hydrocarbons. Gasoline presents low contents of oxygenates and traces of sulfur, nitrogen and metals which introduce instability. In several countries, like Brazil, ethanol is used as an alternative fuel and as an octane improver. Nevertheless, hydrocarbons present in the fuel slowly react at room temperatures with atmospheric oxygen and with each other. This promotes changes in their physical-chemical characteristics. The process is observed throughout all the fuel production and use chain, increasing fuel density. These resinous, polymeric, insoluble and nonvolatile materials that are formed with high molar mass, commonly called gums, form deposits along the vehicle fuel system. Their accumulation can cause engine wear and have adverse effects on engine efficiency, performance and durability.

The period between the start of fuel injection into the combustion chamber and the start of combustion it's known as Ignition Delay (ID) or Delay Time. Delay period in the diesel engine exerts a very great influence on both engine design and performance. Functionally, the ID can be divided into two parts: the physical and chemical delay. The physical delay, it is the time between the beginning of injection and the attainment of chemical reaction conditions. During this period, the fuel is atomized, vaporized, mixed with air and raised to self-ignition temperature. Viscosity governs the physical delay of fuel combustion process, for low viscosity fuels, the physical delay tends to be small and vice versa. The chemical delay, during this period reactions start slowly and the accelerate until inflammation or ignitions takes place. Generally, chemical delay is larger than the physical delay.

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.