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9.4. Stability
9.4.1. Existent (?washed?) Gum
Petrol can slowly oxidise in the presence of air to form undesirable oxidation products such as
peroxides or gums. These products are soluble in the fuel, but can appear as sticky residue
when the petrol evaporates. The residues can deposit on carburettors, injectors, intake port
valves and impact the vehicle's performance. These problems can be managed through a
specification on existent gum.
Gums are typically specified as either washed or unwashed. Unwashed gum is measured by
evaporating a sample of petrol and weighing the residue. This not only measures the gum
formation, but it also measures the additives (detergents etc). To determine the inherent gum,
the sample is then washed with a solvent, which removes the additives - this is ?washed gum?.
9.4.2. Induction period
Induction period is an indication of storage stability. Fuels with poor stability will form
insolubles that can block fuel filters. Petrol oxidises in the presence of air and water,
particularly if the fuel contains non-hydrotreated cracked products, which are relatively
unstable. High temperatures also accelerate the oxidation of petrol. Further, petrol degrades
when in contact with copper or zinc because these two metals actively promote oxidation of
petrol. Accordingly, prolonged storage of fuel in such an environment can result in the
oxidation of petrol to form undesirable gums and sediment. Such undesirables can cause filter
plugging, combustion chamber deposit formation, and gumming or lacquering of injection
system components with resultant sticking and wear.
Sau citeste intregul articol aici:
http://www.environment.gov.au/atmosphere/f...pubs/paper4.pdfInteresant paragraful despre guma care se depune. Aia care omoara carburatoare si injectoare.