Pradelle, F., Braga, S., Martins, A., Turkovics, F. et al., "Experimental Study of the Influence of Ethanol Concentration and Temperature on Gum Formation during Prolonged Storage of Brazilian Gasoline-Ethanol Blends," SAE Technical Paper 2015-36-0169, 2015, doi:10.4271/2015-36-0169.
Gasoline is a volatile, inflammable mixture composed of olefinic, paraffinic, naphthenic and aromatic C4-12 hydrocarbons. Gasoline presents low contents of oxygenates and traces of sulfur, nitrogen and metals which introduce instability. In several countries, like Brazil, ethanol is used as an alternative fuel and as an octane improver. Nevertheless, hydrocarbons present in the fuel slowly react at room temperatures with atmospheric oxygen and with each other. This promotes changes in their physical-chemical characteristics. The process is observed throughout all the fuel production and use chain, increasing fuel density. These resinous, polymeric, insoluble and nonvolatile materials that are formed with high molar mass, commonly called gums, form deposits along the vehicle fuel system. Their accumulation can cause engine wear and have adverse effects on engine efficiency, performance and durability. The formation of gums in gasoline depends on the gasoline composition, absorbed oxygen content and storage conditions (temperature and aging period). The presence of ethanol in gasoline seems to have a dilution effect. The exact mechanisms are not fully known, but it is agreed that they involve a series of free radical chain processes. This work studied the influence of aging period, temperature and addition of aqueous ethanol concentration on Brazilian E20 gasoline-ethanol blend properties. Density, kinematic viscosity, induction period and washed gum content as well as water content were evaluated. It intended to determine critical conditions where the fuel does not meet the specifications required for engine use, using predictive mathematic models given by two Doehlert experimental designs with three factors.