The impact of N-Methyl Aniline (NMA) octane booster on lubricating oil has previously been studied and the main findings were reported in SAE paper 2016-01-2273. Increased sludge formation had been observed in modified ACEA black sludge testing when NMA was added to the fuel but there was very limited viscosity increase, which did not corroborate the trend evidenced on modified CEC L-109 oxidation testing where significant viscosity increase was noted when NMA was added to the oil and fuel mixture.
Accordingly, modified black sludge tests have been run with and without NMA added to the oil sump at the beginning of the test to better match modified L-109 oxidation bench test conditions. Results showed the same trend in terms of viscosity increase between the modified L-109 oxidation bench test and black sludge test. However, no impact on sludge formation was noted under this configuration and, in addition, no NMA could be detected in end of test samples as opposed to what has been observed when NMA was added to the fuel. This could suggest that NMA had either evaporated or reacted with lubricating oil.
In order to better understand the interaction between NMA and lubricating oil to explain viscosity increase, two fully formulated oils evaluated in the previous study, as well as their respective base stock blends only, were run in modified L-109 oxidation tests in the presence of fuel only and fuel with NMA. In addition, individual additive components were added to base stock blends to study their interaction with NMA. End of test samples were then investigated using several analytical techniques such as Fourier Transformation Infra-Red, Gel Permeation Chromatography and Gas Chromatography with Nitrogen Chemiluminescence Detector.
When added to base stock blends only, NMA acted as an anti-oxidant, thus limiting viscosity increase. However, when added to fully formulated oils and as previously observed, significant viscosity increase occurred, confirmed by the high molecular weight species identified by various analytical techniques. Those techniques also confirmed that NMA did not evaporate at the end of test but reacted, preferentially with dispersant and detergent additives.