Heat release process in a free volume combustion chamber and in porous reactors has been analyzed in a wide range of initial pressures and temperatures under Diesel engine-like conditions. For investigating of this kind of reactions a special combustion chamber characterized by a constant volume and adiabatic conditions has been used as an engine simulator. formation must be considered together with chemistry of low- and high-temperature oxidation. The resulting pressure history in both porous reactors and in free volume significantly depends on the initial pressure and temperature. At lower initial temperatures the process in porous reactors is accelerated. There are five characteristic regions of the process characterized by different delay time, reaction rate and number of recognizable oxidation reactions. Combustion in porous reactor is characterized by heat accumulation in solid phase of porous structure and results in reduced pressure peaks and lowered combustion temperature. This depends on reactor heat capacity, pore density, specific surface area, pore structure and heat transport. Low- and high-temperature oxidation processes of Diesel sprays as performed in porous reactors are similar in nature to those in free volume combustion chamber.