A Lubricant Formulation for Lower Unburnt Hydrocarbon Emissions

Engine-out emissions of unburnt hydrocarbons from spark ignition engines are attributable to a number of mechanisms, occurring during the engine cycle, by which fuel escapes combustion. These include absorption of fuel components into the bore lubricating oil film during compression, and subsequent desorption into hot combustion gases throughout expansion. A proportion of the hydrocarbons desorbed will then be emitted, either as unburnt or partially oxidised fuel. This mechanism has been studied by a number of workers, and estimates of its importance vary from 10 to 30% of total hydrocarbons being related to the absorption/desorption process.

A novel lubricant additive has been formulated for the purpose of reducing the quantity of fuel which is absorbed into the bore lubricant film, and hence the quantity of fuel subsequently desorbed. This paper describes a programme to evaluate the effect that this lubricant additive can have on engine-out emissions from a single cylinder research engine, together with results from current technology, low-emitting US and European vehicles, tested over FTP and ECE drive cycles.