Gasoline Additive Requirements for Today's Smaller Engines

The performance and driveability of today's smaller engines, particularly those with port fuel injectors, often are adversely affected by deposits at various places throughout the fuel induction system. These deposits can, however, be controlled by the use of optimal detergent additives, which are surface-active agents containing polar heads and hydrocarbon tails. For convenience in discussion, the gasoline detergents may be divided into two groups: low and high molecular weight. Low molecular weight detergents typically are more effective in forming protective films on metal surfaces, and high molecular weight detergents are more effective in dispersing deposit precursors. The performance of a particular low molecular weight detergent and a particular high molecular weight detergent is compared herein in carburetor, port fuel injector and intake valve tests. The low molecular weight detergent is effective in keeping the carburetor and port fuel injectors clean, and it also is partially effective in the clean-up of dirty port fuel injectors; however, it is concentration limited because of possible accumulation on intake valves. The high molecular weight detergent is effective not only in keeping carburetors and port fuel injectors clean, but also in the clean-up of injector deposits. When used in combination with a polymeric carrier fluid, the high molecular weight detergent also provides effective control of intake valve deposits. For optimal overall intake system cleanliness in today's smaller engines, the preferred detergent products are of higher molecular weight than those typically used in previous years when carburetor cleanliness was the major detergent performance requirement.