Abstract: Use of a Fischer-Tropsch derived gas oil, and/or of a fuel composition containing it in operating a diesel engine and/or a vehicle which is driven by a diesel engine is provided, to clean a diesel engine. Method for assessing a diesel fuel composition, involving measurement of engine fouling levels is also provided. Use of a Fischer-Tropsch derived gas oil in a diesel fuel composition, optionally together with a detergent, to reduce and/or clean up engine fouling is also described.

Abstract: A process for upgrading a liquid hydrocarbon transportation fuel is provided, wherein an inlet stream of liquid hydrocarbon transportation fuel, preferably diesel or gasoline base fuel is contacted with a non-porous or nano-filtration membrane and a first liquid hydrocarbon outlet stream is recovered as the retentate and a second liquid hydrocarbon outlet stream is recovered as the permeate. The retentate is more than 70 weight % of the inlet stream. The inlet stream and the first and the second outlet stream each fulfil the requirements for base fuel without further treatment.

Abstract: Use of a Fischer-Tropsch derived fuel in a fuel composition, for the purpose of reducing the amount of additives, in particular antifoaming and/or dehazing additives, in the composition is disclosed. The Fischer-Tropsch fuel may be used to reduce the amount of silicon containing additives in the composition, or generally to reduce silicon levels, and in turn to reduce loss of efficiency of fuel atomization and/or combustion in a fuel consuming system which is running on the fuel composition, and/or to reduce build up of deposits, in particular silicon deposits, in such a system.