Abstract: Fuel additives and fuel additive compositions are described comprising: (i) at least one fuel-soluble detergent/dispersant which is (a) a fuel-soluble salt, amide, imide, oxazoline and/or ester, or a mixture thereof, of a long chain aliphatic hydrocarbon-substituted dicarboxylic acid or its anhydride, (b) a long chain aliphatic hydrocarbon having a polyamine attached directly thereto, and/or (c) a Mannich condensation product formed by condensing a long chain aliphatic hydrocarbon-substituted phenol with an aldehyde, and an amine; wherein the long chain hydrocarbon group in (a), (b) and (c) is a polymer of at least one C.sub.2 to C.sub.10 monoolefin, said polymer having a number average molecular weight of at least about 300; (ii) a fuel-soluble cyclopentadienyl complex of a transition metal; and (iii) a fuel-soluble liquid carrier or additive induction aid. These compositions in use enable surprising improvements in intake valve deposit control as well as other advantages.

Abstract: The combination of a fuel-soluble succinimide detergent/dispersant, a fuel-soluble liquid carrier or induction aid therefor, and a fuel-soluble cyclopentadienyl manganese tricarbonyl compound can sharply reduce the formation or accumulation of engine deposits such as intake valve deposits in internal combustion engines. In fact, such compositions can function synergistically whereby the effectiveness of a highly effective succinimide-based deposit control additive can be improved by the addition thereto of the manganese compound, the latter not known to be a substance that reduces deposits.

Abstract: NO.sub.x emissions are reduced in two stages during operation of an engine equipped with an exhaust gas catalyst system. In the first stage, a reduction in NO.sub.x emissions is effected in the exhaust leaving the combustion chamber. In the second stage a further reduction in NO.sub.x emissions is effected in the exhaust passing through the exhaust catalyst system. Both of the two-stage reductions are brought about in the same way, namely (a) by use of a fuel composition containing at least one fuel-soluble cyclopentadienyl manganese tricarbonyl compound in an amount equivalent to up to 1/32 gram of manganese per gallon of fuel; and (b) by enhancing the NO.sub.x control activity of at least the catalyst by prior operation of the engine on such fuel composition, either intermittently or continuously. Such prior operation constitutes a run-in or conditioning stage of sufficient total duration (continuous or interrupted) so that substantial reductions in NO.sub.