The combustion process of tetradecane in a direct injection diesel engine has been studied by means of fast sampling and chemical analysis of the combustion products collected inside the diesel chamber during the early stages of the combustion cycle. Soot and acetylene were the major pyrolytic products and both of their concentration rapidly increased just after the ignition point, although acetylene reached its maximum concentration before the maximum of soot. Polycyclic aromatic hydrocarbons were minor pyrolytic species produced during the combustion cycle and accounted for less than 20% of the heavy organic material, referred to as high molecular weight species, whose concentration was more than one order of magnitude lower than soot and C2H2concentration