Propulsion engine systems

Abstract

Propulsion engine systems and propulsion engine lubricating oils, wherein the propulsion engine system comprises: a turbine; a compressor; a gearbox; an oil pump with reservoir having an inlet and an outlet; and a flow path in fluid connection with the inlet, outlet, turbine, compressor, and gearbox, wherein the flow path supplies a lubricating oil composition to one or more of the turbine, compressor, or gearbox, wherein the lubricating oil composition comprises: a. at least 80 wt.% of a lubricating oil base stock and b. from 1 wt.% to 5 wt.% of an anti-wear agent composition, wherein the lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate.

Description

PROPULSION ENGINE SYSTEMSTECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to propulsion engine systems, and more specifically, the lubrication of a propulsion engine system as well as propulsion engine lubricating oils.BACKGROUND

[0002] An aircraft lubrication system is often associated with an APU and one or more propulsion engines in order to dissipate heat and / or lubricate various components. The lubrication system generally involves circulating an oil that is resistant to thermal and oxidative degradation along a flow path through one or more components of the APU and propulsion engine.

[0003] There is scrutiny on certain triaryl phosphates used as antiwear additives, at a significant concentration in aviation turbine oil formulations. In many products currently used on aircraft, tricresyl phosphate (TCP) is utilized due to its excellent wear inhibition and load-carrying performance, but the compound has come under scrutiny due to known neurotoxic effects of its ortho isomers of TCP at high concentrations. Since 2005, SAE International has recommended specifications controlling the amount of mono, di, and tri-ortho cresyl isomers of TCP to be less than 0.2 wt.% in total of any TCP used in the fully formulated oil. Changes in the manufacturing and distillation processes of TCP raw ingredients (cresols) have minimized the content of these ortho isomers. An alternative triaryl phosphate used is isopropylated triphenyl phosphate (iPTPP), which possesses reduced wear inhibition and load-carrying capabilities, and unique toxicity concerns.

[0004] Accordingly, there remains a need for propulsion engine lubrication systems that maintain or improve operation of the systems.SUMMARY

[0005] Disclosed in embodiments herein are propulsion engine systems for an aircraft. The propulsion engine systems comprise: a turbine; a gearbox; an oil pump with reservoir having an inlet and an outlet; and a flow path in fluid connection with the inlet, outlet, turbine, compressor, and gearbox, wherein the flow path supplies a lubricating oil composition to one or more of the turbine, compressor, or gearbox, wherein the lubricating oil composition comprises: a. at least 80 wt.% of a lubricating oil base stock comprising: (i) a first base stock comprising the reaction product of: 1. a polyol selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and 2. a mixture C5-C10 linear or branched monocarboxylic acids; and (ii) a second base stock comprising the reaction product of: 1 . a polyol ester selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol and mixtures thereof, and 2. a mixture C5-C10 linear or branched monocarboxylic acids; and b. from 1 wt.% to 5 wt.% of an anti-wear agent composition selected from compounds of formula I:wherein Rl, R2, and R3 are independently selected from the group consisting of phenyl,3-tert-butylphenyl, and 4-tert-butylphenyl; wherein the anti-wear agent composition comprises: 1 . at least 90 mol.% of a compound of formula I wherein at least one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and4-tert-butylphenyl, and 2. from 5 to 27.5 mol.% of a compound of formula I wherein at least two of the Rl, R2, or R3 groups are selected from the group consisting of a 3-tert- butylphenyl and 4-tert-butylphenyl; and wherein the lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate.

[0006] Further disclosed in embodiments herein are lubricating oil compositions for a propulsion engine system. The lubricating oil composition comprises: a. at least 80 wt.% of a base stock composition comprising: (i) a first base stock comprising the reaction product of: 1. a polyol selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and 2. a mixture C5-C10 linear or branched monocarboxylic acids; and (ii) a second base stock comprising the reaction product of: 1. a polyol ester selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol and mixtures thereof, and 2. a mixture C5-C10 linear or branched monocarboxylic acids; and b. from 1 wt.% to 5 wt.% of an anti-wear agent composition selected from compounds of formula I:

[0007] wherein Rl, R2, and R3 are independently selected from the group consisting of phenyl, 3-tert-butylphenyl, and 4-tert-butylphenyl; wherein the anti-wear agent composition comprises: 1. at least 90 mol.% of a compound of formula I wherein at least one of the Rl, R2, or R3 groups is selected from the group consisting of a 3- tert-butylphenyl and 4-tert-butylphenyl, and 2. from 5 to 27.5 mol.% of a compound of formula I wherein at least two of the Rl, R2, or R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl; and wherein the lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate.

[0008] In one or more embodiments herein, the ratio of first base stock to second base stock is from 75:25 to 95:5. In one or more embodiments herein, the anti-wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2, and R3 groups are phenyl. In one or more embodiments herein, the antiwear agent composition comprises from 70 mol.% to 85 mol.% of a compound of formula I wherein one of the Rl, R2, or R3 groups is selected from the group consistingof a 3-tert-butylphenyl and 4-tert-butylphenyl. In one or more embodiments herein, the anti- wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2, and R3 groups are selected from the group consisting of a 3-tert- butylphenyl and 4-tert-butylphenyl. In one or more embodiments herein, the lubricating oil composition further comprises from 0.1 wt.% to 5 wt.% of one or more antioxidants selected from the group consisting of aromatic amines, aromatic amine oligomers, hindered phenols, and mixtures thereof.

[0009] Additional features and advantages of the embodiments will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein. It is to be understood that both the foregoing and the following description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 schematically depicts a propulsion engine lubrication system.DETAILED DESCRIPTION

[0011] Reference will now be made in detail to embodiments of propulsion engine systems and lubricating oil compositions for use in propulsion engine systems. The propulsion engine systems may be used in aircrafts, such as airplanes or helicopters. It is noted, however, that this is merely an illustrative implementation of the embodiments disclosed herein. The embodiments are applicable to other technologies that are susceptible to similar problems as those discussed above.Propulsion Engine System

[0012] The propulsion engine system is designed to provide the necessary thrust to propel an aircraft through the air by expelling a high-speed stream of gases. As shown in FIG. 1, the propulsion engine system (100) comprises a turbine (105); a compressor (110); a gearbox (115); an oil pump with reservoir (115) having an inlet (120) and an outlet (125); and a flow path (130, 135) in fluid connection with the inlet (120), outlet(125), turbine (105), compressor (110), and gearbox (115). Also shown is the combustor (140) and fan (145).

[0013] The flow path supplies a propulsion engine lubricating oil composition to one or more turbine (105), compressor (110), or gearbox (115), and can also include the fan (145). The turbine (105) and compressor (110) are mounted on a shaft (150) which may be dynamically supported by bearings arranged in several bearing sumps where the propulsion engine lubricating oil composition may be used to spray the bearings, and then collected and returned to the oil tank (115). The turbine (105) drives the compressor (110) via the shaft (150). The turbine (105) also drives a power takeoff gearbox which provides mechanical power to the accessory gearbox (115) via a shaft (150). The power takeoff gearbox distributes some of the mechanical power from the shaft (150) for accessories like the accessory gearbox (115) and oil pump (115). The recirculating oil flow path (130, 135) includes an oil pump that draws the oil from a reservoir (115) and supplies a filtered lubricating oil composition to one or more of the turbine (105), compressor (110), accessory gearbox (115), and can also include the fan (145), where the oil provides necessary lubrication, thermal management and debris removal.

[0014] Outside air enters through an inlet (155) and the air is compressed by the compressor (110). The compressor (110) is configured to deliver a portion of compressed bleed air to the environmental control system (ECS) whereas the majority of the compressed air is delivered to the combustor to support the combustion of jet fuel which powers the turbine. The compressor (110) may optionally include variable stator vanes, which can allow for the management of a wide range of flow and pressure ratio conditions. The compressor (110) also provides high pressure, high temperature bleed air to the aircraft ECS and other aircraft systems (e.g. engine and aircraft deicing, pressurizing aircraft fluid systems, internal engine cooling) through valves and bleed air ducts (160), as shown in FIG. 1. Bleed air is taken from low and high stage compressor sections depending on engine operating conditions. Low stage (or low pressure) is selected for most engine high power settings, such as takeoff, climb, and cruise, and high stage (or high pressure) is selected for lower engine power settings, such as descent.Lubricating Oil Composition

[0015] In embodiments herein, the lubricating oil compositions comprise a lubricating oil base stock and an anti-wear agent composition, wherein the lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate. As used herein, the term “free of’ means that tricresyl phosphate and isopropylated triphenyl phosphate are not intentionally added to the lubricating oil composition.

[0016] In embodiments herein, the lubricating oil composition comprises at least 80 wt.% of the lubricating oil base stock and from 1 wt.% to 5 wt.% of the anti-wear agent composition. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the lubricating oil composition comprises from 80, 85, 87.5, 90, 92.5, or 95 wt.% to 99, 97.5, 95, 92.5, or 90 wt.% of the lubricating oil base stock and / or from 1, 1.25, 1.5, 1.75, 2, or 2.25 wt.% to 5, 4.5, 4, 3.75, 3.5, 3.25, 3, 2.75, or 2.5 wt.% of the anti-wear agent composition. In other embodiments, the lubricating oil composition comprises from 87.5 or 90 wt.% to 97.5 or 95 wt.% of the propulsion engine lubricating oil base stock and / or from 2 or 2.5 wt.% to 4 or 3.5 wt.% of the anti- wear agent composition.

[0017] In one or more embodiments herein, the propulsion engine lubricating oil base stock may comprise a first base stock and a second base stock. In some embodiments herein, the ratio of first base stock to second base stock is from 75:25 to 95:5. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the ratio of first base stock to second base stock is from 77.5:22.5 to 95:5, 80:20 to 95:5, or 85:15 to 95:5.

[0018] The first base stock is the reaction product of: (1) a polyol selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and (2) a mixture of C5-C10 linear and / or branched monocarboxylic acids. In some embodiments, the first base stock is the reaction product of: (1) monopentaerythritol, and (2) a mixture of C5-C10 linear and / or branched monocarboxylic acids. In other embodiments, the first base stock is the reaction product of: (1) a polyol selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and(2) a mixture of C5-C10 linear and branched monocarboxylic acids. In further embodiments, the first base stock is the reaction product of: (1) monopentaerythritol, and (2) a mixture of C5-C10 linear and branched monocarboxylic acids. The monocarboxylic acids are reacted in proportion with synthetic alcohols, leading to a completely esterified monopentaerythritol or dipentaerythritol.

[0019] The second base stock is the reaction product of: (1) a polyol selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol, and mixtures thereof, and (2) a mixture of C5-C10 linear or branched monocarboxylic acids. In some embodiments, the second base stock is the reaction product of: (1) a polyol selected from the group consisting of trimethylol propane, neopentyl glycol, and mixtures thereof, and (2) a mixture of C7-C10 linear or branched monocarboxylic acids. In further embodiments, the lubricating oil base stock is the reaction product of: ( 1 ) a polyol is a mixture of trimethylol propane and neopentyl glycol, and (2) a mixture of C7-C10 linear or branched monocarboxylic acids. The monocarboxylic acids are reacted in proportion with synthetic alcohols, leading to a completely esterified polyol.Anti -wear Agent Composition

[0020] In embodiments herein, the anti-wear agent composition is selected from compounds of formula I:wherein Rl, R2, and R3 are independently selected from the group consisting of phenyl, 3-tert-butylphenyl, and 4-tert-butylphenyl.

[0021] The anti- wear agent composition comprises: 1. at least 90 mol.% (alternatively, at least 92.5 mol.% or 95 mol.%) of a compound of formula I wherein at least one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert- butylphenyl and 4-tert-butylphenyl, and 2. from 5 to 27.5 mol.% of a compound of formula I wherein at least two of the Rl, R2, or R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the anti- wear agent composition comprises: 1. 92 to 99 (alternatively, 94 to 99 or 96 to 99) mol.% of a compound of formula I wherein at least one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl, and 2. from 10 to 27.5 (alternatively, 15 to 27.5 or 17.5 to 27.5) mol.% of a compound of formula I wherein at least two of the Rl, R2, or R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl.

[0022] In one or more embodiments herein, the anti-wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2 and R3 groups are phenyl. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the anti- wear agent composition comprises from 0 mol.% or greater than 0 mol.% to 4.5 mol.%, 4.0 mol.%, or 3.5 mol.% of a compound of formula I wherein the Rl, R2 and R3 groups are phenyl. Alternatively, the anti- wear agent composition comprises greater than 0 mol.% to 4.0 or 3.5 mol.% of triphenyl phosphate.

[0023] In one or more embodiments herein, the anti-wear agent composition comprises from 70 mol.% to 85 mol.% of a compound of formula I wherein one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl. For example, in some embodiments, the anti-wear agent composition comprises from 70, 72.5, or 75 mol.% to 85, 82.5, 80, or 77.5 mol.% of a compound of formula I wherein one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl. Alternatively, the antiwear agent composition comprises from 70, 72.5, or 75 mol.% to 85, 82.5, 80, or 77.5 mol. % of diphenyl t-butylphenyl phosphate.

[0024] In one or more embodiments herein, the anti-wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2 and R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert- butylphenyl. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the anti-wear agent composition comprises greater than 0 mol.% to 4 mol.%, 3 mol.%, 2.5 mol.%, or 2 mol.% of a compound of formula I wherein the Rl, R2 and R3 groups are selected from the group consisting of a 3-tert- butylphenyl and 4-tert-butylphenyl. Alternatively, the anti-wear agent composition comprises greater than 0 mol.% to 4 mol.%, 3 mol.%, 2.5 mol.%, or 2 mol.% of tri(t- butylphenyl) phosphate.Other Components

[0025] In one or more embodiments herein, the propulsion engine lubricating oil composition further comprises from 0.1 wt.% to 5 wt.% of one or more antioxidants selected from the group consisting of aromatic amines, aromatic amine oligomers, hindered phenols and mixtures thereof. Antioxidants may be used to reduce the tendency of lubricating oils to deteriorate in service. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the lubricating oil composition further comprises from 0.1, 1.0, 2.0, 2.5, 3.0, or 3.5 wt.% to 5, 4.9, 4.8, or 4.75 wt.% of one or more antioxidants selected from the group consisting of aromatic amines, aromatic amine oligomers, hindered phenols, and mixtures thereof.

[0026] Exemplary aromatic amines may include, but are not limited to, diphenyl amine, alkylated diphenyl amines, styrenated diphenyl amines, phenyl-N-napthyl amine, alkylated phenyl-N-naphthyl amines, styrenated phenyl-N-napthyl amines, phenothiazine, alkylated pheno thiazine, and styrenated phenothiazine. Exemplary aromatic amine oligomers may include the polymerized reaction product of one of more diphenyl amines, one or more phenyl naphthyl amines, or both one or more diphenyl amines with one or more phenyl naphthyl amines. Exemplary hindered phenols may include, but are not limited to, 6-di-tert-butylphenol; 2-tert-butyl-4-methoxyphenol; 3- tert-butyl-4-methoxyphenol; 2-tert-butyl-4,6-dimethylphenyl; 2,6-di-tert-butyl-4-ethylphenol; 2,6-di-tert-butyl-4-n-butylphenol; 2,6-di-tert-butyl-4-i-butylphenol; 2,6- di-tert-butyl-methylphenol; 2,6-di-cyclopentyl-4-methylphenol; 2-(a- methylcyclohexyl)-4,6-dimethylphenol; 2,6-di-octadecyl-4-methylphenol; 2,4,6-tri- cyclohexylphenol; 2,6-di-tert-butyl-4-methoxymethylphenol; 2,6-Di-tert-butyl-4- methoxyphenol; 2-tert-butylhydroquinone; 2,5-di-tert-butylhydroquinone; 2,5-di-tert- amylhydroquinone; 2,6-diphenyl-4-octadecyloxyphenol; 2-tert-butyl- 1,4- benzoquinone; tri-methyl-di-hydroquinoline.

[0027] In one or more embodiments herein, the lubricating oil composition further comprises from 0.1 wt.% to 5 wt.% of one or more other components, such as metal rust inhibitors, corrosion inhibitors, hydrolytic stabilizers, other oxidation inhibitors, friction modifiers, anti-foaming agents, and rust inhibitors.TEST METHODSFour-Ball Wear

[0028] The Four-Ball Wear test is used to evaluate the relative wear preventative properties of lubricating fluids in sliding contact under a static load. The efficacy of lubricants is determined by comparing the average size of scar diameters work on the three lower balls, with a lower diameter corresponding to improved wear resistance. The test equipment and procedure are employed in duplicate according to ASTM D4172, with the average results reported in Table 3.Wear Performance - WAM

[0029] The Wedeven Associates Machine (WAM) is a required test for qualification of a propulsion engine oil per SAE AS5780. The WAM test employs a ball-on-disk machine that undergoes a progressive loading until macroscuffing failure occurs in the lubricated contact zone, with the performance determined by the load stage at which this failure occurs. The test equipment and procedure, which are employed and followed in conduction and following examples, are described in SAE Aerospace Recommended Practice ARP6156. The tests are run in triplicate and the average results are reported in Table 3.Load-Carrying Performance - Ryder Gear

[0030] The Ryder Gear Rig is also a required test for qualification of a propulsion engine oil per SAE AS5780 and is the aviation industry standard for assessing loadcarrying capacity. The Ryder Gear equipment and test procedure are described in Federal Test Method Standard 791C Test Method 6508. The Ryder Gear test consists of incremental increases in the pressure between spur gears to measure the resultant scuffing average of all test gear faces until a failure limit is exceeded. The oil performance is scored on a percentage basis relative to a 4 cSt polyol ester basestock reference oil, Hercolube A. For qualification purposes, new oils undergo six replicates of the Ryder Gear test protocol and the average is reported. The average results of those compositions containing pentaerythritol (Basestock A or Basestock C) are reported in Table 3.Surface Micro-Pitting

[0031] The impact of antiwear additive selection on surface -initiated fatigue wear and micro-pitting is evaluated using a Micro-Pitting Rig, where three rings are rotated against a rotating central roller. Resistance to micro-pitting and surface damage is determined by the radius loss during extended contact cycles and has been shown to correlate to gear and bearing reliability. The test equipment and procedure are described in Aerospace Recommended Practice ARP6991 from the Society of Automotive Engineers. The results are reported in Table 4.EXAMPLES

[0032] The following specific examples are given to illustrate the process and performance properties associated with the inventions described herein. The inventive and comparative examples are provided below with the details of the formulations and results are provided in the tables below.Table 1 - Raw Materials

[0033] The lubricating oil compositions Fluid A, Fluid B, and Fluid C were purchased from Boeing Distribution Services. The lubricating oil compositions Fluid 1 and Fluid D are prepared by blending one or more basestocks with the antiwear, antioxidant(s), and other additives, such as metal rust inhibitors, corrosion inhibitors, hydrolytic stabilizers, other oxidation inhibitors, friction modifiers, other dispersants, anti-foaming agents, or rust inhibitors. Details of each composition are shown in Table 2. In the case of Fluid 1 and Fluid D, the compositions are essentially identical with the exception of the selected antiwear additive.Table 2 - Lubricating Oil Compositions

[0034] The fluids are measured for 4 ball wear, WAM load failure stage, and Ryder Gear, and the results are reported in Table 3. The fluids are also measured for surface micropitting and the results are reported in Table 4.Table 3 - Results

[0035] The 4 ball wear results demonstrate that the composition which contained a tBTPP mixture (Fluid 1) had a greater resistance relative to those with TCP at a similar phosphorous content (Fluid A, Fluid B, and Fluid D). Fluid 1 and D differ only by their selection of antiwear compound, suggesting an unexpected improvement in performance of the lubricant while having the same amount of the phosphorous.

[0036] The WAM failure load results demonstrate that the composition which contained the tBTPP mixture (Fluid 1) at a similar P treat rate exhibited a greater resistance to macroscuffing than those containing TCP or the iPTPP mixture (Fluid A, Fluid B, Fluid C, and Fluid D). Comparing the fluids with identical basestocks and other additives, incorporating the tBTPP mixture yielded an unexpected 9% improvement for Fluid 1, compared to those using TCP (Fluid D).

[0037] The Ryder Gear results indicate that the tBTPP mixture achieves an unexpected improvement in load-carrying capability compared to TCP and the iPTPP mixture. Fluid B, Fluid C, Fluid 1, and Fluid D contain approximately the same P content and yet Fluid 1 achieves a 5% improvement in performance, especiallynoteworthy when compared to Fluid D which contains an otherwise identical formulation.Table 4 - Surface Micropitting Results

[0038] The surface micro-pitting results show a novel benefit towards surface- initiated fatigue damage for compositions using the tBTPP mixture. Fluid 1 demonstrated the least surface damage loss at both testing durations, achieving a remarkable 38% improvement after the test completion compared to Fluid D, which uses TCP at an identical effective treat rate and an otherwise identical composition.

[0039] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

[0040] Every document cited herein, if any, including any cross- referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

[0041] While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

What is claimed is:

1. A propulsion engine system for an aircraft, the system comprising: a turbine; a compressor; a gearbox; an oil pump with reservoir having an inlet and an outlet; and a flow path in fluid connection with the inlet, outlet, turbine, compressor, and gearbox, wherein the flow path supplies a lubricating oil composition to one or more of the turbine, compressor, or gearbox, wherein the lubricating oil composition comprises: a. at least 80 wt.% of a lubricating oil base stock comprising:(i) a first base stock comprising the reaction product of:

1. a polyol ester selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and2. a mixture C5-C10 linear or branched monocarboxylic acids; and(ii) a second base stock comprising the reaction product of:

1. a polyol ester selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol and mixtures thereof, and2. a mixture C5-C10 linear or branched monocarboxylic acids; and b. from 1 wt.% to 5 wt.% of an anti- wear agent composition selected from compounds of formula Iwherein Rl, R2, and R3 are independently selected from the group consisting of phenyl, 3-tert-butylphenyl, and 4-tert-butylphenyl; wherein the anti-wear agent composition comprises:

1. at least 90 mol.% of a compound of formula I wherein at least one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl, and2. from 5 to 27.5 mol.% of a compound of formula I wherein at least two of the Rl, R2, or R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl; and wherein the lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate.

2. The system of claim 1, wherein the ratio of first base stock to second base stock is from 75:25 to 95:5.

3. The system of claims 1 or 2, wherein the anti- wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2, and R3 groups are phenyl.

4. The system of claims 1-3, wherein the anti-wear agent composition comprises from 70 mol.% to 85 mol.% of a compound of formula I wherein one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and 4-tert- butylphenyl.

5. The system of claims 1-4, wherein the anti-wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2, and R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl.

6. The system of claims 1-5, wherein the lubricating oil composition further comprises from 0.1 wt.% to 5 wt.% of one or more antioxidants selected from the group consisting of aromatic amines, aromatic amine oligomers, hindered phenols, and mixtures thereof.

7. A lubricating oil composition for a propulsion engine system, the composition comprising: a. at least 80 wt.% of a base stock composition comprising:(i) a first base stock comprising the reaction product of:

1. a polyol ester selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and2. a mixture C5-C10 linear or branched monocarboxylic acids; and(ii) a second base stock comprising the reaction product of:

1. a polyol ester selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol and mixtures thereof, and2. a mixture C5-C10 linear or branched monocarboxylic acids; and b. from 1 wt.% to 5 wt.% of an anti-wear agent composition comprising a mixture of compounds having the formula Iwherein Rl, R2, and R3 are independently selected from the group consisting of phenyl, 3-tert-butylphenyl, and 4-tert-butylphenyl; wherein the anti-wear agent composition comprises:

1. at least 90 mol.% of a compound of formula I wherein at least one of the Rl, R2, or R3 groups is selected from the group consisting of a 3- tert-butylphenyl and 4-tert-butylphenyl, and2. from 5 to 27.5 mol.% of a compound of formula I wherein at least two of the Rl, R2, or R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl; and wherein the lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate.

8. The composition of claim 7, wherein the ratio of first base stock to second base stock is from 75:25 to 95:5.

9. The composition of claims 7 or 8, wherein the anti- wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2 and R3 groups are phenyl.

10. The composition of claims 7-9, wherein the anti -wear agent composition comprises from 70 mol.% to 85 mol.% of a compound of formula I wherein one of the Rl, R2, or R3 groups is selected from the group consisting of a 3-tert-butylphenyl and 4-tert-butylphenyl.

11. The composition of claims 7-10, wherein the anti-wear agent composition comprises less than 5 mol.% of a compound of formula I wherein the Rl, R2 and R3 groups are selected from the group consisting of a 3-tert-butylphenyl and 4-tert- butylphenyl.

12. The composition of claims 7-11, wherein the lubricating oil composition further comprises from 0.1 wt.% to 5 wt.% of one or more antioxidants selected from the group consisting of aromatic amines, aromatic amine oligomers, and mixtures thereof.

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