INVESTIGATION OF SUCCINIMIDE DISPERSANTS AND THEIR INTERACTIONS USING REDUCED TOTAL OIL VOLUME LUBRICANT DEGRADATION
Reduced Total Oil Volume RTOV sampling was developed from reduced sump sampling. The technique involves alterations to an engine enabling the total volume of lubricant within the engine to be reduced, without altering the basic function or operation of the engine. Critical regions where large volumes were removed were the use of a smaller oil filter and the elimination of the standard oil cooler by an internal sump oil cooler. The alterations to the engine allowed the operating volume to be reduced to over 75% of the original standard operating volume. This reduction enabled discriminatory oil degradation engine runs to be performed in only 6 hours. Operating the engine on minimal volume gave rise to oil additions being made as oil was consumed within the engine. The effect of addition of fresh oil on the used oil analysis was corrected for mathematically. A model was derived which accounted for combustion losses and also the relative volatility of the oil. Five oils were investigated, four similar in all respects apart from the dispersant; a tris-succinimide. a bissuceinimide and a mono-succinimide with the same molecular weight polyisobutylene (RIB) backbone, and a second bis-succinimide with a lower molecular weight PIB backbone. The fifth oil had the lower molecular weight PIB bis-succinimide, but had a secondary ZDDP molecule, whereas all the others had a primary ZDDP molecule. Using the R'l'OV technique on a VW 1.6 turbocharged diesel CY Series engine, a mid range and a high range speed-load point were used for each oil. Lach oil was repeated al the speed load points in triplicate. One oil was also used at 4 other speed-load points to more fully map the effect of increasing speed and load on the oil. again each point being repeated in triplicate. The maximum speed and load point also had an extended engine run of 24 hours rather than the standard 6 hours, to investigate the effect of a continuously severe environment on the oil. The oil analysis consisted of standard condition monitoring techniques. Soot concentration, total base number, viscosity al 40°C. viscosity at 100°C, volatility and FTIR. The functional groups C=O. N=O. P=S. P-0, 0-H were till measured. These parameters, along with temperatures and pressures monitored whilst the engine was operating were analysed using principal component analysis, The correlations and trends highlighted enable the condition of the oil Io be monitored using a reduced number of variables. At the mid range speed-load point the dispersants were able to be discriminated. The tris-succiniinide gave the highest performance, whilst the mono-succinimide was the worst. There was also a significant difference observed between the primary tuiil secondary ZDDP groups. This is understood to be due to the interaction between the ZDDP group and the succinimide dispersant. At the high speed-load point the clear discrimination was not evident. The tris-sueeinimide did not perform as well tis expected, and in some of the analyses performed significantly worse than the bis-succininiides. In the multivariate analysis the best performing oil was the low molecular weight bis-succiniinide with the primary ZDDP group, and whilst this did not perform as well at the midrange point, it gave the best all round performance. Other analyses of the samples concentrated on the soot contamination, and assessing the role of the dispersant in terms of maintaining the soot in suspension. Particle Size Distribution (PSD) analysis determined the centre of the distribution to be ().()7pin. which was then confirmed by Scanning Electron Microscopy (SEM). The PSD investigation also determined the growth of larger particles at the higher speed-load conditions, which are attributed to a loss in dispersant functionality. Use of an environmental SI:M identified the generation of calcium, sulphur anil oxygen containing particles on the walls of the combustion chamber. A dispersancy test was developed using a spotting technique onto 'Phin Layer Chromatography (TLC) plates. Variation in the inas.s of oil deposited was accounted for, and increased accuracy attained by measuring the surface area of the generated spots. Analysis highlighted difference's in the dispersancy of the oils, particularly at the mid range speed-load points. Recommendations are made to develop this technique further, to turn it into a realistic tool for oil condition monitoring.
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