Combustion of Tetradecane and Tetradecane/ α-Methylnaphthalene in a Diesel Engine with Regard to Soot and PAH Formation

Abstract

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 C₂H₂ concentration

The effect of the fuel aromaticity on the evolution of pyrolysis and oxidation processes in a diesel engine, and in particular on the formation of soot, PAH and other pollutants has been studied by comparing the results obtained in tetradecane combustion with those obtained by adding 10 vol.% of α-methylnaphthalene to tetradecane and running the engine in the same operating conditions. An increased formation of C₂H₂ and CO, as a consequence of the α-methylnaphthalene addition to tetradecane, was found and explained on the basis of the peculiar mechanism of aromatic oxidation. The larger formation of C₂H₂ could be responsible for the higher formation of PAH, high molecular weight species and soot found when a-methylnaphthalene was added to tetradecane.

Key words:

• Soot
• polycyclic aromatic hydrocarbons
• diesel combustion