Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/520842
26 May- June 2015 | www.machinerylubrication.com further account for the spectral variability induced by real samples and to align the data with the corresponding ASTM method. PLS serves only to refi ne the measurement and to ensure that the results match the ASTM reference method used in its development. A variety of mixed-mode PLS calibrations were recently devel- oped and assessed. The bulk of the samples analyzed for the PLS component of the base number calibration were in-service engine oils covering most major lubricant suppliers and representing a wide range of equipment applications (mining, transport, genera- tors, marine, etc.), with nearly 70 percent using diesel fuel and the balance natural gas. In the case of acid number, a mix of new and in-service oils covering a wide range of suppliers and grades was considered, including oils from engines, compressors, hydraulic systems, turbines, transmissions and gearboxes. Figures 2 and 3 illustrate the typical cross-validated FTIR cali- brations obtained for acid number and base number, respectively. The performance of the mixed-mode calibrations was moni- tored over a six-month period. Some 177 acid number samples and 284 base number samples were analyzed using both the FTIR method and the corresponding ASTM titration methods (D664 and D4739). Samples included a mixture of new and used oils from a wide variety of components, including hydraulic systems, gear- boxes, transmissions, engines, turbines and compressors. Figures 4 and 5 show the differences between the individual ASTM and FTIR results for acid number and base number, respec- tively. The analytical differences between the two methods are normally distributed in both cases, with each having an overall mean difference of almost zero. This indicates on-average similarity in their results, with the variability around the mean difference refl ecting the reproducibility of the ASTM reference methods. These extended production results clearly demonstrated that the FTIR acid number/base number methods are capable of delivering ASTM-identical results. OIL ANALYSIS Figure 2. A cross-validation chart of the mixed-mode calibration comparing acid number data for in-service oil samples analyzed by ASTM D664 and the FTIR acid number method Figure 4. Comparing the differences between ASTM and FTIR acid number results obtained for random operational samples Figure 5. Comparing the differences between ASTM and FTIR base number results obtained for random operational samples Figure 3. A cross-validation chart of the mixed-mode calibration comparing base number data for in-service oil samples analyzed by ASTM D4739 and the FTIR base number method 0 10 20 30 40 50 0.4 0.2 0 -0.2 -0.4 Sample Frequency Acid Number AN Difference (ASTM - FTIR); mg KOH/g 0 20 40 60 80 100 120 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 Sample Frequency BN Difference (ASTM - FTIR); mg KOH/g Base Number