Continued from page 27
The needs of the aviation industry Jet engines run hotter and hotter, as a result of the quest for ever increasing energy efficiency (figure 3). In order to cope with harsher operating conditions and more stringent requirements on jet engine oils, specific anti-oxidant systems were developed, based on oligomers of traditional anti-oxidant compounds.
- Thermal Stability and Corrosivity, a test method assessing the thermal stability and corrosivity of the oil without air or moisture (274°C, 96 h). Oligomer technology shows much lower viscosity and acid number increase (figure 5).
Figure 5
- ERDCO high temperature bearing deposition test (max 260°C). Here again the bearing demerit is much lower, even for a 200 h test duration, with oligomer technology (figure 6).
Figure 3: turbine inlet temperatures over time
Anti-oxidants usually show very good responses in esters. Nevertheless, such oligomeric compounds show improved durability as they are less volatile; they also show increased thermal resistance and more efficient free radical stabilisation.
The combination of high performance neopolyol esters and dedicated anti-oxidant systems have proven to show superior performance in terms of resistance to thermo-oxidation and engine cleanliness – a technology that allows formulators to pass the requirements of “High Performance Capability (HPC)” jet engine oils of the SAE AS 5780 performance standard.
In particular, such a technology has demonstrated excellent results in the following tests: - Hot Liquid Process Simulator. This test evaluates the coking propensity of the oil under single phase flow conditions found in certain parts of gas turbine engines, by circulating the oil in a heated tube (375°C) for 20 or 40 hours. The amount of generated deposit is significantly lower using oligomer anti-oxidant technology (HPC), even if test duration is doubled (figure 4).
Figure 6
- Vapour Phase Coking Test (260°C). This in-house test apparatus evaluates deposits on metal surfaces not directly in contact with the oil. Visually, oligomer technology reduces the amount of deposits in vapour phase too (figure 7).
Figure 7 Figure 4
Extreme conditions may be found in industrial applications too In industrial turbines, furnace conveyors, engine turbochargers or in foundry equipment, for instance, very high temperatures may be encountered, sometimes exceeding 300°C. Quite logically, the technology developed for the aviation industry may also be used to improve performance on such applications.
28 LUBE MAGAZINE NO.154 DECEMBER 2019
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