TYPES TYPES OF OF ADDITIVE ADDITIVE .1 Antioxidants

7 ADDITIVES USED IN AVIATION FUELS7 ADDITIVES USED IN AVIATION FUELS

7.3 TYPES TYPES OF OF ADDITIVE ADDITIVE .1 Antioxidants

7.3 TYPES TYPES OF OF ADDITIVEADDITIVE 7.3.1 Antioxidants

7.3.1 Antioxidants Antioxidants are

Antioxidants are added added to to aviation aviation fuel fuel to to prevent prevent peroxidation during peroxidation during storage. storage. Straight-runStraight-run fuels do not normally require the addition of antioxidant additive because they tend to fuels do not normally require the addition of antioxidant additive because they tend to contain naturally occurring antioxidant species. These species are removed from the fuel contain naturally occurring antioxidant species. These species are removed from the fuel during hydroprocessing, leaving the fuel vulnerable to peroxidation. Consequently, during hydroprocessing, leaving the fuel vulnerable to peroxidation. Consequently, antioxidant additives are normally added only

antioxidant additives are normally added only to hydroprocessed fuels.to hydroprocessed fuels.

Antioxidants are mandatory in

Antioxidants are mandatory in Jet A-1 Jet A-1 certified to DEF certified to DEF STAN 91-91 but STAN 91-91 but optional in Jet A/Jetoptional in Jet A/Jet A-1

A-1 certified certified to to ASTM ASTM D1655, D1655, for for fuel fuel componencomponents ts that that have have been been hydro-processhydro-processed ed (i.e.(i.e.

manufactured using a catalytic hydrogen process such as hydro-treating, hydro-fining, manufactured using a catalytic hydrogen process such as hydro-treating, hydro-fining, hydro-cracking

Antioxidants shall shall always always be be added added after after hydro-processhydro-processing ing oror synthesizing as near to the point of manufacture (at plant rundown) as synthesizing as near to the point of manufacture (at plant rundown) as possible (this is a specification requirement for Jet A-1 meeting DEF possible (this is a specification requirement for Jet A-1 meeting DEF STAN 91-91 and for synthetic components as defined in ASTM

STAN 91-91 and for synthetic components as defined in ASTM D7566),D7566), and definitely before the fuel has had a chance to meet with oxygen, and definitely before the fuel has had a chance to meet with oxygen, e.g. in the

e.g. in the componencomponent rundown tank.t rundown tank.

The purpose of this requirement is to prevent the initiation of the free

already started, is of limited effectiveness.limited effectiveness.

Where a finished fuel comprises a

Where a finished fuel comprises a blend of several different components, the requirement forblend of several different components, the requirement for mandatory addition of a qualified antioxidant at a concentration of 17.0 to 24.0 mg/L applies mandatory addition of a qualified antioxidant at a concentration of 17.0 to 24.0 mg/L applies only to the portion of the blend that ha

only to the portion of the blend that has been hydro-proces been hydro-processed. ssed. For fuel (or fuel componeFor fuel (or fuel component)nt) which has not been hydro-processed, addition is optional but shall not exceed 24.0 mg/L.

which has not been hydro-processed, addition is optional but shall not exceed 24.0 mg/L.

These concentrations do not include any solvent used to

These concentrations do not include any solvent used to dissolve the active ingredient.dissolve the active ingredient.

The antioxidants listed below are qualifie

The antioxidants listed below are qualified for use in Jet d for use in Jet A/Jet A-1:A/Jet A-1:

−

− 2,6-ditertiary-b2,6-ditertiary-butyl utyl phenol phenol [Qualification [Qualification ref: ref: RDE/A/606]RDE/A/606]

−

− 2,6-ditertiary-b2,6-ditertiary-butyl-4-methyl utyl-4-methyl phenol phenol [Qualification [Qualification ref: ref: RDE/A/607]RDE/A/607]

−

− 2,4-dimethyl-62,4-dimethyl-6-tertiary-butyl -tertiary-butyl phenol phenol [Qualification [Qualification ref: ref: RDE/A/608]RDE/A/608]

−

− 75% min75% min. 2,6-ditertiar. 2,6-ditertiary-butyl phey-butyl phenol, plus nol, plus 25% max25% max. mixed tertia. mixed tertiary and triry and tritertiary-butyltertiary-butyl phenols [Qualification ref: RDE/A/609]

phenols [Qualification ref: RDE/A/609]

−

− 55% 55% min. 2min. 2,4-dimethyl-6-tertia,4-dimethyl-6-tertiary-butyl ry-butyl phenol, phenol, plus plus 15% m15% min. 2,6-din. 2,6-ditertiary-butyl-4itertiary-butyl-4-methyl-methyl phenol; remainder as monomethyl and dimethyl tertiary-butyl phenols [Qualification ref:

phenol; remainder as monomethyl and dimethyl tertiary-butyl phenols [Qualification ref:

RDE/A/610]

−

− 72% min. 72% min. 2,4-dimethyl-62,4-dimethyl-6-tertiary-butyl p-tertiary-butyl phenol, 28% henol, 28% max. monomemax. monomethyl and dthyl and dimethyl- imethyl-tertiary-butyl phenols [Qualification ref:

tertiary-butyl phenols [Qualification ref: RDE/A/611]RDE/A/611]

Antioxidants hav

Antioxidants have no known side e no known side effects that adverseeffects that adversely affect fuel propertily affect fuel properties.es.

7.3.2 Static dis sipater addit ive (SDA)

Static Dissipater Additive (SDA), also known as antistatic additive or conductivity improver additive, is used to increase the electrical conductivity of the fuel, which enables rapid dissipation of electrostatic charge generated during fuel movement.

The use of SDA is mandatory to meet the electrical conductivity requirements of Jet A-1 certified to DEF STAN 91-91 (and the Joint Fuelling System Checklist) at point and temperature of delivery to the aircraft. SDA may be used by agreement in Jet A/Jet A-1 certified to ASTM D1655.

Historically, it was always recommended that SDA should be added in refineries during production. More recently, problems with excessive conductivity loss (especially on ships fitted with inert gas systems) and the need to meet MSEP requirements, have highlighted the benefit of dosing the additive further downstream (see Annex H). Refineries may, with the agreement of the receiving company, supply product without SDA but the RCQ shall clearly state that ‘this product meets the specification for all properties except conductivity’.

Only one SDA is approved for use in Jet A/Jet A-1: Stadis® 450 [Qualification ref:

RDE/A/621] manufactured by Innospec LLC. Note: another SDA is currently undergoing the industry approval process. If approved and a new RDE/A/ number has been allocated to it, it will be equally suitable for use.

SDA may be added at a maximum initial concentration of 3.0 mg/L, up to a cumulative maximum of 5.0 mg/L. When SDA is used, it is recommended that the initial amount added does not exceed 1.0 mg/L, which should result in a fuel conductivity meeting the specification limits of 50 – 600 pS/m.

When doping product with SDA, refineries should take into account normal depletion of conductivity that may occur as the product passes through the distribution system from the refinery to the airport. It is recommended that refineries aim for a conductivity in the range 250 to 300 pS/m (or higher, depending on the mode and duration of transfer to the airport terminal) at the point of batching of the tank and at the delivery temperature of the product at the refinery. The level targeted should ensure Jet A-1 at entry into airport storage is >100 (or

>150 pS/m depending on the layout of the airport, e.g. hydrant or refueller) and therefore reaches the aircraft above the 50 pS/m minimum required by the specification.

In certain circumstances, it may be necessary to make further additions of SDA to Jet A-1 at intermediate supply installations or terminals. For details on how this is controlled, refer to 7.9. For further information see Annex H.

Conductivity normally increases with temperature. Consideration of the temperature effect should be given to the question of whether the delivery temperature is likely to be significantly different from the sample storage/testing temperature. In cases of dispute, the conductivity measurement taken in situ in the storage tank shall prevail.

SDA is a surfactant and overdosing may degrade the water separation characteristics of the jet fuel. Although at normal dosage rates experience shows that filter/coalescers are not

disarmed, low MSEP values may indicate problems. However, it is acknowledged that the ASTM D3948 test method is oversensitive to Stadis 450 and low MSEP values could predict problems where they may not exist; guidance on how to deal with such situations can be found in JIG Bulletin No.14 MSEP protocol.

The surface-active nature of SDA may also clean up distribution systems by dispersing dirt or rust previously attached to the pipework. In this way high levels of finely dispersed rust can be produced which can cause filtration problems downstream.

It should also be noted that maximum loading velocities into road and rail tankers for aviation fuels, both with and without SDA, should be in accordance with the constraints laid down in the EI Model Code of Safe Practice Part 21 Guidelines for the control of hazards arising from static electricity, or API RP 2003 Protection against ignitions arising out of static, lightning, and stray currents to avoid hazards related to electrostatic charging.

7.3.3 Metal deactiv ator addit ive (MDA)

Metal Deactivator Additive (MDA) [Qualification ref: RDE/A/650] may be added to jet fuel where dissolved trace catalytic metals, notably copper, have caused the fuel to fail the ASTM D3241 Standard test method for thermal oxidation stability of aviation turbine fuels (often referred to as the Jet Fuel Thermal Oxidation Test). MDA comprises N,N’-disalicylidine-1,2-propanediamine, a chelating molecule that wraps itself around trace metal atoms in the fuel and thus shields the fuel from their catalytic propensity.

The use of MDA is optional and experience has shown that a dosage rate of 1.0 mg/L or less (active ingredient) is usually sufficient to recover thermal stability – successive higher treat rates can be used as necessary, but shall not exceed 2.0 mg/L. Cumulative addition of MDA shall not exceed 5.7 mg/L active ingredient.

Where the thermal stability fails the specification limit, the refinery should determine whether the cause is due to metal contamination by analysing the fuel for trace levels of Copper, Cadmium, Iron, Cobalt and Zinc. Where metallic contamination is unproven, i.e. below 10 ppb, it is NOT recommended to use MDA to recover the thermal stability unless a clear explanation is found for the failure. However, MDA may be used to recover thermal stability provided that the Thermal Oxidation Test is determined before and after MDA addition and reported on the test certificate. Prior to MDA addition, a laboratory blend of the fuel with the proposed level of MDA should be made and a Thermal Oxidation Test carried out to confirm the effectiveness of this addition.

7.3.4 Lubric ity impro ver additive (LIA)

The use of Lubricity Improver Additive (LIA), formerly known as Corrosion Inhibitor/Lubricity Improver (CI/LI), is optional in commercial jet fuel to improve the lubricity of severely hydroprocessed fuel components. However, it may not be a practical solution to inject LIA in the refinery to correct poor lubricity because the additive may be depleted from the fuel by adsorption onto tanks and pipeline walls in the downstream distribution system before it reaches the aircraft. A preferable solution, where necessary, is to improve the lubricity of severely hydroprocessed fuel by blending in the refinery with other, higher lubricity, components such as Merox processed or other straight-run kerosine.

Lubricity improver additives are controlled by MIL-PRF-25017 and DEF STAN 68-251. Both of these specifications have an associated Qualified Products List (QPL).

The use of LIA is mandatory in military grades of fuel covered by specifications MIL-DTL-83133, MIL-DTL-5624, DEF STAN 91-87 and DEF STAN 91-86.

Jet Fuel Lubricity

Aircraft and engine fuel system components and fuel control units rely on the fuel to lubricate their moving parts. The effectiveness of a jet fuel as a boundary lubricant in such equipment is referred to as its lubricity. Differences in fuel system component design and materials result in varying degrees of equipment sensitivity to fuel lubricity. Similarly, jet fuels vary in their level of lubricity. In-service problems experienced have ranged in severity from reductions in flow to unexpected mechanical failure leading to in-flight engine shutdown.

Because of the chemical and physical properties of jet fuel, it is a relatively poor lubricating material under high temperature and high load conditions.

Severe hydro-processing removes trace components resulting in fuels which tend to have lower lubricity than other fuels, such as straight-run, wet-treated, or mildly hydrogen treated fuels. Certain additives, for example corrosion inhibitors, can improve the lubricity and are widely used in military fuels. They have occasionally been used in civil jet fuel to overcome aircraft problems but only as a temporary remedy while improvements to the fuel system components or changes to fuels were achieved. Because of their polar nature, these additives can have adverse effects on ground based filtration systems and on fuel water separation characteristics. Filter/water separator elements qualified to EI 1581 5^th edition are more resistant to the surface active effect of the LIA.

Some modern aircraft fuel system components have been designed to operate on low lubricity fuel. Other aircraft may have fuel system components which are sensitive to fuel lubricity. In these cases the manufacturer can advise precautionary measures, such as use of an approved lubricity additive to enhance the lubricity of a particular fuel. Problems are most likely to occur when aircraft operations are confined to a single refinery source where fuel is severely hydro-processed and where there is no co-mingling with fuels from other sources during distribution between refinery and aircraft.

ASTM Test Method D5001 (BOCLE) is a test for assessing fuel lubricity and is used for in service troubleshooting, lubricity additive evaluation and in the monitoring of low lubricity test fluid during endurance testing of equipment.

However, because the BOCLE may not accurately model all types of wear which cause in-service problems other methods may be developed to better simulate the type of wear most commonly found in the field.

LIA may be blended into Jet A-1 in accordance with DEF STAN 91-91 without prior customer notification to correct a lubricity problem, but use of these additives in Jet A/Jet A-1 in accordance with ASTM D1655 is by agreement of the purchaser.

The lubricity improver additives cited here are qualified for use in Jet A-1*. This qualified product list shows concentrations for each additive that provide acceptable lubricity properties while minimizing effects on water separation properties.

− HITEC 580 [Qualification ref: RDE/A/661]: Dosage rate: 15 – 23 mg/L

− Innospec DCI-4A [Qualification ref: RDE/A/662]: Dosage rate: 9 – 23 mg/L

− Innospec DCI-6A [Qualification ref: RDE/A/663]: Dosage rate: 9 – 15 mg/L

− Nalco 5403 [Qualification ref: RDE/A/664]: Dosage rate: 12 – 23 mg/L

− Tolad 4410 [Qualification ref: RDE/A/665]: Dosage rate: 9 – 23 mg/L

− Tolad 351 [Qualification ref: RDE/A/666]: Dosage rate: 9 – 23 mg/L

− Unicor J [Qualification ref: RDE/A/667]: Dosage rate: 9 – 23 mg/L

− Nalco 5405 [Qualification ref: RDE/A/668]: Dosage rate: 11 – 23 mg/L

− SPEC AID 8Q22 [Qualification ref: RDE/A/669]: Dosage rate: 9 – 23 mg/L (For the latest listing of approved LIAs, refer to the appropriate specification’s QPL)

*For Jet A and Jet A-1 meeting ASTM D1655, only three of the above additives – Hitec E580, DCI-4A and Nalco 5403 – are currently listed as approved.

For aviation gasolines, these same additives can be used as corrosion inhibitors to provide protection for avgas storage facilities and for aircraft fuel system components during the sometimes long periods of idleness between flights.

7.3.5 Fuel system ici ng inhibi tor (FSII)

FSII is used to prevent aircraft fuel system blockage by ice formation from water precipitated from fuels during flight. As most commercial aircraft are, with minor exceptions, provided with fuel filter heaters, they have no requirement for the anti-icing properties of this additive, although some operators may use the additive for its biostatic properties.

FSII is mandatory only for military grades of jet fuel covered by specifications MIL-DTL-83133, MIL-DTL-5624, DEF STAN 91-87 and DEF STAN 91-86, and for certain business jets.

The only approved FSII for Jet A and Jet A-1 is diethylene glycol monomethyl ether (di-EGME) [Qualification ref: RDE/A/630] meeting the appropriate additive specification, such as Type III requirements of ASTM D4171 Specification for fuel system icing inhibitors, MIL-DTL-85470B or DEF STAN 68-252. Where FSII is required, the concentration shall be between 0.10 and 0.15 volume percent.

FSII is only sparingly soluble in jet fuel so effective injection/mixing facilities are essential to ensure complete mixing. Undissolved FSII can damage elastomers, tank coatings and other materials in aircraft. Good mixing with fuel requires that the additive has low acid and dissolved water content. FSII is removed from the fuel by free water so it is imperative that fuel storage tanks are effectively drained of water prior to FSII addition and kept free of water thereafter.

If a refinery is required to supply fuel containing FSII, it is recommended that any FSII is added using an additive injection system during delivery of the fuel into the transportation system rather than into bulk storage (see 7.9.3.2).

The concentration of di-EGME in fuel can be determined using ASTM D5006. This method is suitable for field use.

7.3.6 Biocides

Biocides are not approved by DEF STAN 91-91 (or AFQRJOS Check List) and are primarily intended for strictly controlled use in aircraft fuel tanks. If used within a refinery or supply installation, the fuel shall be down-graded to non-aviation use. If microbiological growth is found in refinery or supply installation storage tanks, the preferred approach is to steam clean and/or pressure water wash the tank rather than treat it with biocide (see EI Guidelines for the investigation of the microbiological content of petroleum fuel and for the implementation of avoidance and remedial strategies).

Biocidal additives are available for use under strictly controlled conditions, usually by the aircraft operator - they are not to be used for preventative maintenance purposes.

ASTM D1655 lists biocides as an acceptable additive class; however they are not cited as acceptable additives in DEF STAN 91-91. Biocides are used to kill microbiological growth in hydrocarbon fuels. Owing to the time required for treatment to be effective, biocides are normally used when the aircraft is left standing filled or partially filled with treated fuel, such as during scheduled maintenance. The fuel may then be used by the operator in accordance with both airframe and engine manufacturer’s requirements. In most cases, any treatment other than in the aircraft itself will render the fuel unfit for use and require downgrading or disposal.

Two biocide additives have been approved for use – Biobor JF and Kathon FP 1.5.

Turbine engine and airframe manufacturers’ service manuals shall be consulted for specific details on approved products and permitted conditions for use. In addition, any restrictions or prohibitions due to local laws and regulations shall be understood before biocide use is considered.

As noted in 7.3.5, DiEGME has been found to have biostatic effects in some situations.

7.4 RECEIPT PROCEDURES FOR ADDITIVES

In document Jig Standard 1530 Manual (Page 56-61)