Gum Formation in Gasoline and Its Blends: A Review

Abstract

Gasoline is a volatile mixture of hydrocarbons that is used in spark-ignition (SI) engines. It is a complex mixture composed of olefinic, paraffinic, naphthenic, and aromatic hydrocarbons (C 4 −C 12 ), among other substances in a smaller concentration. In several countries, such as Brazil, ethanol is used pure as a renewable fuel for SI engines, especially in flex fuel engines, and/or an additive to improve the octane number of gasoline. During storage, some classes of hydrocarbons in gasoline blends, particularly olefins and diolefins, are able to slowly react, at ambient temperatures, with the oxygen in the air. The formed oxidation products are responsible for the formation of an insoluble solid, commonly called deposits or gums, which sticks to the metal surfaces along the vehicle-fuel system, from the tank to the combustion chamber. Accumulation of these products can cause engine wear and can have adverse effects on engine efficiency, performance, emission, and durability. Consequently, it is necessary to predict gasoline blend behavior and prevent gum formation, improving gasoline quality and using additives. Even if the number of publications dedicated to gum formation in gasoline blends is reduced, results available in the literature for other fuels can be applied to the gasoline issue. This review intends to define more precise fuel stability concepts and what is considered a gum. It also aims to present the oxidation mechanism involved in gum formation, determine the main parameters influencing gum deposition in gasoline blends, and describe the experimental tools available to measure gum content.

Evaluation of Red Onion Skin Extract as Inhibitor for Gum Formation in Gas Condensates

“…Gum refers to the resinous, non-volatile, high molecular weight polymeric material formed in fuels in storage or when exposed to high temperature conditions during combustion in engines [1]. Gum formation and inhibition in refined petroleum products such as gasoline, diesel and aviation fuel has been extensively studied as a result of its impact on product storability and engine performance but similar studies on gas condensates are scarce [2][3][4][5][6].…”

“…Gum formation is believed to be a free-radical chain polymerization process mediated by peroxy radicals [1,3]. The presence of trace heavy metals such as iron, copper, cobalt and manganese is known to increase the rate of gum formation because heavy metals facilitate the production of peroxides by catalyzing the decomposition of hydroperoxide [1]. Resins and asphaltenes although present in low concentration in condensates, increase the potential for gum formation in condensates due to their large polycondensed heteroaromatic structures.…”

Certainties and challenges in modeling unwashed and washed gums formation in Brazilian gasoline–ethanol blends

“…(4), (5), or (6)). The formation of high molar mass species with long carbon chain results of these three reactions (A'reff, 2011;De la Puente and Sedran, 2004;Heneghan and Zabarnick, 1994;Pradelle et al, 2015a;Roan and Boehman, 2004).…”

“…Literature showed that the stability of hydrocarbons decreases in the order of paraffins, naphthenes, isoparaffins, aromatics, monoolefins (in particular, cyclic and branched olefins), aromatic olefins and diolefins, especially conjugated compounds (De la Puente and Sedran, 2004;Gilbert, 2004;Nagpal et al, 1994Nagpal et al, , 1995aNagpal et al, , 1995bPasa, 2006, 2007;Pradelle et al, 2015a;Rahimi et al, 1998;Teixeira et al, 2007). The oxidation rate is proportional to the concentration of atmospheric oxygen absorbed by the fuel (Schwartz et al, 1968a(Schwartz et al, , 1968bShatalov and Seregin, 2009;Stavinoha et al, 1990).…”

“…Traces of ions from transition metal strongly catalyze gum formation, since they facilitate the formation of radical by decomposition of hydroperoxides. The literature showed that metallic ions with an oxidation state of +1 (for instance, copper, iron, cobalt, and manganese ions) are the most efficient catalyst (Ackermann, 1969;Nery et al, 2003;Souza et al, 2005;Pereira and Pasa, 2005;Pradelle et al, 2015a;Streva et al, 2011;Teixeira et al, 2007).…”