Surface area, pore size distribution and microstructure of combustion engine deposits

The structural characteristics of combustion engine deposits produced from fuels with 22-44% aromatics by volume have been studied using Raman spectro scopy and gas sorption techniques. The lateral sizes of graphitic crystalli tes were found to increase slightly with the aromatic content of the fuel u sed. The surface areas of the deposits were evaluated using the BET and DR theories. Density functional theory (DFT) and mercury porosimetry were used to evaluate pore size distributions. The deposits have large internal surf ace areas (in the approximate range 110-300 m(2)/g) and their structures ar e highly porous. The average pore sizes of the largely microporous deposits do not depend on the aromatic content of the precursor fuel. Walls of pore s with widths of about 0.5 nm are primarily responsible for the majority of the internal surface area found in the deposits. Heat treatment at tempera tures above 573 K results in increased surface areas because the release of small hydrocarbon fragments from the deposits opens pores which were not a ccessible following heat treatment at lower temperatures. (C) 1999 Elsevier Science Ltd. All rights reserved.