Turbine oil, and method for using turbine oil

A method comprising lubricating a turbine of a jet engine with a turbine oil,

• the turbine oil comprising:
• a base oil (A) comprising a polyol ester (A1);
• an antioxidant (B) comprising an amine-based antioxidant (B1);
• a polymethacrylate (C) having a weight average molecular weight of from 150,000 to 500,000;
• and
• an alkyl aromatic compound (D),
• wherein
• a content of the polyol ester (A1) in the base oil (A) is from 80 to 100% by mass based on a total amount of the base oil (A),
• a content of the base oil (A) is from 70 to 90% by mass based on a total amount of the turbine oil,
• a content of the amine-based antioxidant (B1) in the antioxidant (B) is from 70 to 100% by mass based on a total amount of the antioxidant (B),
• a content of the antioxidant (B) is from 0.1 to 5% by mass based on the total amount of the turbine oil,
• a content of the polymethacrylate (C) in terms of resin content is from 0.5 to 5.0% by mass based on the total amount of the turbine oil, and
• a content of the alkyl aromatic compound (D) is 2=54 from 110 parts by mass to 800 parts by mass per 100 parts by mass, based on a total resin content of the polymethacrylate (C),
• the polyol ester (A1) is an ester of a hindered polyol represented by the following formula (a-1′) with an aliphatic monocarboxylic acid:
• wherein RA each independently represent a monovalent hydrocarbon group having 1 to 6 carbon atoms or a methylol group (—CH2OH),
• the amine-based antioxidant (B1) consists of a combination of a naphthylamine (B11) and a diphenylamine (B12),
• a content ratio of the naphthylamine (B11) and the diphenylamine (B12), ((B11)/(B12)), by mass is from 55/45 to 80/20,
• the polymethacrylate (C) has a molecular weight distribution, Mw/Mn, of 3.7 or less,
• the alkyl aromatic compound (D) consists of an alkylbenzene, an alkylnaphthalene, or a combination thereof, and
• wherein the turbine oil satisfies the following conditions (1) and (2):
• (1):
• a viscosity index is 140 or more;
• and
• (2):
• a coking amount is 80 mg or less after continuously performing a panel coking test for 6 hours according to Fed. Test Method Std. 791-3462 under a condition of a panel temperature of 320° C. and an oil temperature of 130° C., and in a cycle of a splash time of 15 seconds and a suspend time of 30 seconds,
• wherein a Brookfield viscosity (BF) of the turbine oil at −40° C. is from 9,000 to 25,000 mPa·s.