Investigating the Impact of Ethanol on the Lubricity of Gasoline and on the Lubricity Improvers Efficiency

As it is the case for Diesel engines, the Gasoline Direct Injection engines are using higher and higher injection pressures. The state of the art gasoline Direct Injection (GDI) engines are currently using injection pressures as high as 500 bar. A lot of work is also currently ongoing on Gasoline Compression Ignition (GCI) engines which use even higher injection pressures (above 1 000 bar). A high injection pressure means that a high pressure pump has to be used and so, proper lubricity has to be brought by the fuel. In the mean time the use of biofuels is increasing and several studies have shown the positive impact of ethanol on the energy consumption of gasoline engines mainly thru an octane number effect. For all these reasons, it seems important to evaluate the impact of ethanol on the lubricity of gasoline as well as on the response of lubricity additives that may be required in a medium-term future to provide gasoline enough lubricity to ensure the operability of these new engines. This paper determines how ethanol affects the lubricity (verified thru a modified version of the standard High Frequency Reciprocating Rig test procedure) of various formulations of gasoline using either a high amount of aromatics (typical of a refinery with reforming capacities) or a low amount of aromatics (typical of a refinery equipped with alkylation capacities). It also focuses on how the main lubricity improvers (acid-type or ester-based) used for treating Diesel fuels can help to increase the lubricity of such formulations of gasoline. The main outcomes show that the ethanol tends to enhance the lubricity of the fuel. But at the same time it also decreases the ability of lubricity additives to improve the lubricity. In addition, these effects seem linked to the composition of the gasoline with possibly a lower impact when large amount of aromatics are present.