Effects of fuel additives on the microstructure of combustion engine deposits

Abstract

The microstructure of spark-ignition (SI) engine deposits produced from fuels with two commonly used gasoline additives, polyether amine and polybutene amine, were studied by gas adsorption technique and Raman spectroscopy. The lateral sizes of graphitic crystallites were found to increase upon addition of the additives. The surface areas of the deposits were evaluated using the BET and DR theories. Density functional theory was used to evaluate pore size distribution. The majority of the internal surface area of the deposits is due to narrow pores of widths of about 0.5 nm. The surface area of the deposits decreases with increased concentration of the additives, and this process is more efficient for polybutene amines than polyether amines. The structure of the deposits removed from the combustion chamber’s cylinder heads is more porous than that of piston top deposits. Likewise, intake valve deposits were seen to be less porous than combustion chamber deposits.