Auxiliary power unit lubrication systems, APU lubricating oils, and aircraft cabin air systems

Abstract

Auxiliary power unit (APU) systems, APU lubricating oils, and aircraft cabin air systems that include APU system and lubricating oils, wherein the APU system comprises: an engine system comprising an engine compressor, combustor, and engine turbine; a load compressor; a generator; an oil pump with reservoir having an inlet and an outlet; and a flow path in fluid connection with the inlet, outlet, engine system, load compressor, and generator, wherein the flow path supplies a lubricating oil composition to one or more of the engine system, load compressor, or generator.

Description

AUXILIARY POWER UNIT LUBRICATION SYSTEMS, APU LUBRICATING OILS, AND AIRCRAFT CABIN AIR SYSTEMSTECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to an auxiliary power unit (APU) lubrication system, APU lubricating oils, and aircraft cabin air systems that include APU lubrication system and 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. Such oils typically contain pentanoic acid as a component of the base stock. The APU load compressor and propulsion engine compressor supply, inter alia, bleed air to the aircraft environmental control system (ECS), which provides air pressurization and conditioning of cabin air. The APU and propulsion engine can leak very fine droplets of oil lubricant into the bleed air from the compressors due to various design and deterioration scenarios. The result is an odor which may be perceived in the aircraft cabin due to the use of APU or propulsion engine bleed air.

[0003] Odor events reported by airlines to the FAA between 2012 and 2017 found the known causes to include predominantly the APU, but in some cases the propulsion engine. Once oil is leaked from an APU or engine, air temperature and humidity encountered during certain flight segments (take off, climb, cruise, descent, etc.) have an enormous influence on the oil that has contaminated the ECS system. Pentanoic acid released due to deterioration of the lubricating oil base stock is particularly egregious since the smell is nauseating and irritating at very low concentrations. As noted in EP3323728B1, an odor may be perceived in the bleed air where the peak concentration of pentanoic acid detected was approximately 0.5 ppb, and upon the increase in the concentration to approximately 2 ppb a “strong smell” was observed. The loss ofaircraft use due to the subsequent clean-up of the aircraft is costly both in labor and reduced asset productivity.

[0004] In addition to the discomfort and loss of value due to pentanoic acid exposure in aircraft cabin events, 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.

[0005] Accordingly, there remains a need for APU lubrication systems and aircraft cabin air systems that minimize the odors, while still maintaining or improving operation of the systems.SUMMARY

[0006] Disclosed in embodiments herein are auxiliary power unit (APU) systems for an aircraft. The APU systems comprise: an engine system comprising an engine compressor, combustor and engine turbine; a load compressor; a generator; an oil pump with reservoir having an inlet and an outlet; and a flow path in fluid connection with the inlet, outlet, engine system, load compressor, and generator, wherein the flow path supplies a lubricating oil composition to one or more of the engine system, load compressor, or generator, wherein the lubricating oil composition comprises: a. at least 80 wt.% of a lubricating oil base stock comprising 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 C7-C10linear monocarboxylic acids, wherein the lubricating oil base stock comprises less than 0.2 wt.% of C5 and C6 monocarboxylic acids; and b. from 1 wt.% to 5 wt.% of an antiwear 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.

[0007] Further disclosed in embodiments herein are lubricating oil compositions for use in an auxiliary power unit (APU) system of an aircraft. The compositions comprise a. at least 80 wt.% of a lubricating oil base stock comprising 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 C7-C10 linear monocarboxylic acids, wherein the lubricating oil base stock comprises less than 0.2 wt.% of C5 and C6 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 compositioncomprises: 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 polyol of the lubricating oil base stock is a mixture of trimethylol propane and neopentyl glycol. In one or more embodiments herein, the lubricating oil base stock comprises less than 0.1 wt.% of C7- C10 branched monocarboxylic acids.

[0009] 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 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. 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.

[0010] 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, and mixtures thereof.

[0011] Further disclosed in embodiments herein are aircraft cabin air systems. The aircraft cabin air systems comprise: the auxiliary power unit systems as described in one or more embodiments herein; a propulsion engine 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 propulsion engine lubricating oil composition to one or more of the turbine, compressor, or gearbox; and an environmental control system(ECS) comprising an air distribution system, one or more heat exchangers, and one or more air cycle machines, wherein the ECS is in pneumatic connection with the auxiliary power unit system and the propulsion engine system.

[0012] In one or more embodiments herein, the propulsion engine lubricating oil composition comprises: a. at least 80 wt.% of a base stock composition; 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.

[0013] In one or more embodiments herein, the propulsion engine 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 ester selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and 2. a mixture of 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 of 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.

[0014] 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

[0015] FIG. 1 schematically depicts an aircraft auxiliary power unit lubrication system.

[0016] FIG. 2 schematically depicts a propulsion engine lubrication system.

[0017] FIG. 3 schematically depicts an environmental control system.DETAILED DESCRIPTION

[0018] Reference will now be made in detail to embodiments of APU systems and lubricating oil compositions for use in APU systems, as well as aircraft cabin air systems. The APU and aircraft cabin air 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.APU System

[0019] As shown in FIG. 1, the APU system (100) comprises an engine system (105); a load compressor (110); a generator (115); an oil pump with reservoir (120) having an inlet (125) and an outlet (130); and a flow path (135, 140) in fluid connection with the inlet (125), outlet (130), engine system (105), load compressor (110), and generator (115). The engine system (105) is configured to power various systems, such as the load compressor (110) and generator (115), and comprises an engine compressor, combustor and engine turbine. The engine system (105) drives the load compressor (110) via a shaft (155) and a gearbox (115) for various accessories such as a generator (115) and oil pump (120).

[0020] The load compressor (110) is configured to deliver compressed air to the ECS as well as pneumatic power for the aircraft main engine start capability. Outside air enters through an inlet (145) and the air is compressed by the load compressor (110). The load compressor (110) may optionally include variable inlet guide vanes and / or a variable diffuser, which can allow for the management of a wide range of flow and pressure ratio conditions. The air from the load compressor (110) is directed through a bleed duct (150) to be circulated through an air conditioning system to drop its temperature prior to being used for fresh, pressurized air to maintain aircraft cabin and flight deck habitability and comfort.

[0021] The generator (115) is configured to provide ground and emergency in-flight electrical power needs. The engine system (105) drives a gearbox which provides mechanical power to the generator (115) via a shaft (155). The gearbox distributes someof the mechanical power from the shaft (115) for accessories like the generator (115) and oil pump (120). The recirculating oil flow path (135) includes an oil pump that draws the oil from a reservoir (120) and supplies a filtered lubricating oil composition to one or more of the engine system (105), load compressor (110), or generator (115), where the oil provides necessary lubrication, thermal management and debris removal.Lubricating Oil Composition

[0022] 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.

[0023] 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 90 or 92.5 wt.% to 99 or 97.5 wt.% of the lubricating oil base stock and / or from 1.5 wt.% to 2.75 or 2.5 wt.% of the anti-wear agent composition.

[0024] In embodiments herein, the lubricating oil 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 C7-C10 linear monocarboxylic acids. In some embodiments, the lubricating oil 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 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 monocarboxylic acids. The C7 to CIO linear monocarboxylic acids include heptanoic acid, caprylic acid, pelargonic acid, capric acid and combinations thereof.

[0025] In embodiments herein, the lubricating oil 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 C7-C10 linear monocarboxylic acids, and comprises less than 0.2 wt.% of C5 and C6 monocarboxylic acids. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the lubricating oil base stock comprises less than 0.15, 0.125, or 0.1 wt.% of C5 and C6 monocarboxylic acids. In further embodiments, the lubricating oil 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 C7- C10 linear monocarboxylic acids, and C5 and C6 monocarboxylic acids are not intentionally added to the lubricating oil base stock.

[0026] In one or more embodiments herein, the lubricating oil 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 C7-C10 linear monocarboxylic acids, and comprises less than 0.1 wt.% of C7-C10 branched monocarboxylic acids. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the lubricating oil base stock comprises less than 0.1, 0.08, or 0.07 wt.% of C7-C10 branched monocarboxylic acids. In further embodiments, the lubricating oil 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 C7-C10 linear monocarboxylic acids, and C7-C10 branched monocarboxylic acids are not intentionally added to the lubricating oil base stock.Anti -wear Agent Composition

[0027] 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.

[0028] 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 l ' l .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.

[0029] 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 acompound 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.

[0030] 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.

[0031] 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

[0032] 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, 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 from0.1, 0.5, 1.0, 1.5, or 2.0 wt.% to 5, 4.5, 4.0, 3.5, or 3.0 wt.% of one or more antioxidants selected from the group consisting of aromatic amines, aromatic amine oligomers, and mixtures thereof.

[0033] 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 phenothiazine, 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. In some embodiments herein, the lubricating oil composition further comprises from 0.1 wt.% to 5 wt.% of one or more aromatic amines. Other antioxidants such as hindered phenols can be added to the lubricant as a monomeric antioxidant or in addition to the aromatic amine antioxidant.

[0034] 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.Aircraft Cabin Air System

[0035] Also disclosed in embodiments herein are aircraft cabin air systems. The aircraft cabin air systems provide air conditioning with temperature, pressure, and humidity control capabilities which distribute air to the various sections of the aircraft, such as the passenger cabin, flight deck, or cargo hold. As previously noted, the aircraft cabin air system comprises the APU system as described herein, a propulsion engine system, and an ECS. The ECS is in pneumatic connection with the APU system and propulsion engine system. The propulsion 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. 2, the propulsion engine system (200) comprises a turbine (205); a compressor (210); a gearbox (215); an oil pump with reservoir (215) having an inlet (220) and an outlet (225); and a flow path (230, 235) in fluid connection with the inlet(220), outlet (225), turbine (205), compressor (210), and gearbox (215). Also shown is the combustor (240) and fan (245). The flow path supplies a propulsion engine lubricating oil composition to one or more turbine (205), compressor (210), or gearbox (215), and can also include the fan (245). The turbine (205) and compressor (210) are mounted on a shaft (250) 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 (215). The turbine (205) drives the compressor (210) via the shaft (250).

[0036] Outside air enters through an inlet (255) and the air is compressed by the compressor (210). The compressor (210) is configured to deliver a portion of compressed bleed air to the 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 (210) may optionally include variable stator vanes, which can allow for the management of a wide range of flow and pressure ratio conditions. The compressor (210) 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 (260), as shown in FIG. 2. 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.

[0037] As shown in FIG. 3, the engine bleed duct (260A, 260B) and the APU bleed duct (150) provide air into the environmental control system (300) through air supply duct (330). That is, the environmental control system (300) is in pneumatic connection with the auxiliary power unit system (100) and the propulsion engine system (200). The environmental control system (300) comprises one or more heat exchangers (305) and one or more air cycle machines (305). In addition, the environmental control system (300) may also comprise an ozone converter (310), hot air manifold (315), filters (320), and / or an air mixing unit (325). Air returned from the aircraft cabin is through an air return duct (335). The environmental control system (300) converts high pressure, high temperature air from the auxiliary power unit system (100) and the propulsion enginesystem (200) to the sections of the aircraft such as the passenger cabin, flight deck and cargo hold in order to maintain a pressurized cabin that is habitable and comfortable.

[0038] As described herein, the flow path (230) in the propulsion engine system (200) supplies a propulsion engine lubricating oil composition to one or more turbines (205), compressor (210), or gearbox (215), and can also include the fan (245). The propulsion engine lubricating oil composition comprises a propulsion engine lubricating oil base stock and an anti-wear agent composition, wherein the propulsion engine lubricating oil composition is free of tricresyl phosphate and isopropylated triphenyl phosphate.

[0039] In embodiments herein, the propulsion engine lubricating oil composition comprises at least 80 wt.% of the propulsion engine 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 propulsion engine 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 propulsion engine lubricating oil base stock and / or from 1, 1.25, 1.5, 1.75, 2, 2.25, or 2.5 wt.% to 5, 4.5, 4, 3.75, or 3.5 wt.% of the anti-wear agent composition. In other embodiments, the propulsion engine 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.

[0040] 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.

[0041] 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 someembodiments, 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.

[0042] 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.

[0043] In embodiments herein, the anti-wear agent composition used in the propulsion engine lubricating oil composition is the same as previously described herein for the anti- wear agent composition used in APU lubricating oil composition and is incorporated herein to this paragraph by reference.

[0044] 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, thelubricating 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.

[0045] 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 phenothiazine, 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.

[0046] 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.

[0047] Without being bound by theory, Applicants have surprisingly found that through using distinct lubricating oil compositions in the APU and propulsion engine system, the cabin air quality can be improved through reduced odor as well as improving the operations and reliability of the system.TEST METHODSOdor Susceptibility - HS-GC / MS

[0048] Headspace Gas Chromatography coupled to a Mass Spectrometer (HS- GC / MS) is utilized to assess the in-situ odor susceptibility of turbine oil products in the presence of heat and water. Several propulsion engine and APU lubricating oil compositions (Table 2) are mixed with 1 wt.% of water into a 20-mL headspace (HS) vial with an air environment. Duplicate HS sample vials are prepared and analyzed for each oil. The oil and water mixtures are heated for 5 hours at 180°C in order to generate characteristic fatty acids. The prepared sample-HS vials then have 1.0-mL of vapor injected to the GC inlet for chromatographic separation and mass spectral detection. Concentrations of fatty acids in the vapor are determined using m / z=60 integrated peak areas and a calibration prepared against acetone-fatty acid standard solutions.Four-Ball Wear

[0049] 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 4.Wear Performance - WAM

[0050] 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 4.EXAMPLES

[0051] 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

[0052] The lubricating oil compositions Fluid A and Fluid B were purchased from Boeing Distribution Services. The lubricating oil compositions Fluid 1 and Fluid C are prepared by blending a basestock with the anti wear, antioxidant(s), and other additives, such as metal rust inhibitors, corrosion inhibitors, hydrolytic stabilizers, other oxidation inhibitors, friction modifiers, anti-foaming agents, and rust inhibitors. Details of each composition are shown in Table 2. In the case of Fluid 1 and Fluid C, the compositions are essentially identical with the exception of the selected antiwear additive.Table 2 - Lubricating Oil Compositions

[0053] The fluids are measured pre- and post-hydrolysis for odor susceptibility, and the results are reported in Table 3. The fluids are also measured for 4 ball wear and WAM load failure stage, and the results are reported in Table 4.Table 3

[0054] The results demonstrate that for the oils containing both pentanoic, hexanoic, and heptanoic acids, among others, in the basestock, the components were measured in the headspace vapors following hydrolytic degradation. Fluid 1, which was formulated to be free of pentanoic and hexanoic acids, had neither species detected in the headspace vapor. The typical olfactory thresholds for human sense of hexanoic acid and heptanoic acid are 13 ppb and 28 ppb, respectively, and for pentanoic acid odors were detected at concentrations as low as 0.5 ppb and described as having a strong smell at 2 ppb. Relative to the measured concentrations of pentanoic, hexanoic, and heptanoic acids in the headspace from Table 3, it can be inferred that the degradation of Fluid A and Fluid B would be detectible in bleed air due to offensive pentanoic acid odors. Fluid1, however, would not possess this characteristic and nauseating odor as its fatty acid content is an order of magnitude less than the reported threshold for heptanoic acid.Table 4

[0055] The 4 ball wear results demonstrate that the compositions 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). The WAM failure load results demonstrate that the compositions which contained the tBTPP mixture (Fluid 1) at a similar P treat rate exhibited a greater resistance to macroscuffing than those containing TCP (Fluid A, Fluid B, and Fluid C). Comparing the model formulations with identical basestocks and other additives, incorporating the tBTPP mixture yielded an unexpected ~6% improvement for Fluid 1, respectively, compared to Fluid C.

[0056] 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.”

[0057] 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 thatany 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.

[0058] 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. An auxiliary power unit (APU) system for an aircraft, the system comprising: an engine system comprising an engine compressor, combustor, and engine turbine; a load compressor; a generator; an oil pump with reservoir having an inlet and an outlet; and a flow path in fluid connection with the inlet, outlet, engine system, load compressor, and generator, wherein the flow path supplies a lubricating oil composition to one or more of the engine system, load compressor, or generator, wherein the lubricating oil composition comprises: a. at least 80 wt.% of a lubricating oil base stock comprising the reaction product of:

1. a polyol selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol, and mixtures thereof, and2. a mixture of C7-C10 linear monocarboxylic acids, wherein the lubricating oil base stock comprises less than 0.2 wt.% of C5 and C6 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 polyol is a mixture of trimethylol propane and neopentyl glycol.

3. The system of claims 1 and 2, wherein the lubricating oil base stock comprises less than 0.1 wt.% of C7-C10 branched monocarboxylic acids.

4. The system of claims 1-3, 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.

5. The system of claims 1-4, 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.

6. The system of claims 1-5, 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.

7. The system of claims 1-6, 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.

8. An aircraft cabin air system comprising: the auxiliary power unit system of claims 1-7; a propulsion engine 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 propulsion engine lubricating oil composition to one or more of the turbine, compressor, or gearbox; and an environmental control system (ECS) comprising an air distribution system, one or more heat exchangers, and one or more air cycle machines, wherein the environmental control system is in pneumatic connection with the auxiliary power unit system and the propulsion engine system.

9. The aircraft cabin air system of claim 8, wherein the propulsion engine lubricating oil composition comprises: at least 80 wt.% of a base stock composition, and 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.

10. The aircraft cabin air system of claim 8, wherein the propulsion engine 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 ester selected from the group consisting of monopentaerythritol, dipentaerythritol, and mixtures thereof, and2. a mixture of 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 of 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.

11. A lubricating oil composition for use in an auxiliary power unit (APU) system of an aircraft, the composition comprising:a. at least 80 wt.% of a lubricating oil base stock comprising the reaction product of:

1. a polyol selected from the group consisting of trimethylol methane, trimethylol ethane, trimethylol propane, trimethylol butane, neopentyl glycol, and mixtures thereof, and2. a mixture of C7-C10 linear monocarboxylic acids, wherein the lubricating oil base stock comprises less than 0.2 wt.% of C5 and C6 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.

12. The composition of claim 11, wherein the polyol is mixture of trimethylol propane and neopentyl glycol.

13. The composition of claims 11 and 12, wherein the lubricating oil base stock comprises less than 0.1 wt.% of C7-C10 branched monocarboxylic acids.

14. The composition of claims 11-13, 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.

15. The composition of claims 11-14, 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.

16. The composition of claims 11-15, 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.

17. The composition of claims 11-16, 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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