Water in Fuel

8/12/2019 Water in Fuel

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the international journal for filtration and separation

ISSN 1479-0602

www.filtrationsolutions.co.ukVolume 10 Number 2

FILTRATION is the official journal of The Filtration Society and the American Filtration & Separations Society


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FILTRATION, 10(2), 2010

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Filtration Solutions

INTRODUCTION Advances in fuel filtration technology depend heavilyon the nature of the fuels. Diesel fuel has evolvedfrom having high sulphur content, to low and presentlyto ultralow. In the United States (US) and Europe, theincreasing desire of oil independence and greenenergy initiatives are driving the introduction ofbiodiesel from feed stocks such as vegetable oils andanimal fats. More recently research is extending toalgae and other bioprocesses for production ofbiofuels 1.

For the foreseeable future, ultra-low sulphur diesel(ULSD) and ULSD/biodiesel blends will influence thetransportation diesel fuel market. In the US, ULSD hasbeen mandated since October 2006. B2, a 2% blendof biodiesel in ULSD, was mandated in Minnesotathree years ago, and more aggressive use of biodieselblends of up to 5-15% are under way or being plannedby the state governments.

Concurrently, engine designs are evolving to meet

more stringent emission regulations, and theseengines require a much higher level of fuel cleanliness.Fuel filtration must be designed to achieve theseincreasing levels of cleanliness to protect the engineand its components from wear and damage. Thus,changes in both fuel and engine designs are bringing anew level of complexity to filtration including arequirement for finer particle filtration and the need toreduce or eliminate fine water droplets. Filtration isfurther complicated by the increase of organiccontaminants present in diesel fuels. High efficiencydiesel fuel filtration is typically achieved on a vehicle;however, with increasing cleanliness requirements and

water content, there is an emerging opportunity forbulk fuel filtration.

In light of this perspective, the diesel fuel filtrationmarket looks very promising. Today, with total dieselengine production in 2008 of 30 million engines, weestimate the diesel fuel filtration market to be about$8B. Trends show increasing use of alternative fuelsand the need for integration of more features andfunctions into fuel filtration systems. Understandingthe limitations of todays fuel filtration as well asemerging industry needs creates an opportunity foraddressing these challenges with innovativetechnology.

EMISSION REGULATIONS ARE DRIVINGCHANGES IN FUELS

Changes in emission regulations continue to drivesignificant changes in the design of past, current andfuture diesel engines. Filtration development hascentred on exhaust emissions including particulates,nitrogen oxides (NOx), hydrocarbons and carbonmonoxide. For example, particulate matter (PM) and

NOx emissions are being partially controlled throughelevated fuel injector pressures, multiple injections andcontrolled combustion temperatures. Injectorpressures have risen from 1000 bar in the 1980s up to2500 bar today and are projected to pass 3500 bar inthe next few years. These increased pressures requirereduced component clearances on the order of 2-5 m, thereby placing a higher demand on fuelcleanliness. In addition to changes in engine andinjector design, current and future emission regulationsalso require usage of catalytic control systems tomitigate NOx and PM emissions. In order to facilitatethe usage of these control systems, the sulphur

content of diesel fuel was reduced to prevent catalystpoisoning 2. Using ULSD limits the amount of sulphur

Tougher environmental regulations, a move toward energy security and sustainability and emerging greeninitiatives are significantly impacting the fuel industry. Removal of sulphur from traditional diesel fuels toproduce a cleaner burning fuel and the introduction of biofuels derived from non-fossil fuel sources are lead-ing to new challenges in particle, water and soft organic contaminants filtration. In addition, new enginedesigns developed to meet environmental concerns require higher levels of fuel cleanliness. Thus, provid-ing higher performance fuel filtration to achieve these new cleanliness standards is further exacerbated bythe complex nature of the evolving diesel fuels. An emerging challenge for filter manufacturers is designingsystems which retain filtration performance under actual operating conditions. Historically, filters wereevaluated using standard laboratory tests that do not necessarily reflect real world driving conditions wherecyclic flow and vibration are common phenomena. There is also a trend toward fuel system flexibility which

helps manufacturers integrate multiple functions into a fuel filter module. A modular design is a cost effec-tive means for providing a variety of performance features which allows individualization of the fuel filtrationsystem.

EMERGING CHALLENGES OF FUEL FILTRATION

Debra Wilfong, Andrew Dallas, Chuanfang Yang ([email protected]), Philip Johnson, KarthikViswanathan, Mike Madsen, Brian Tucker and John Hacker

Donaldson Company, Minneapolis, MN 55431, USA.


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based compounds in the exhaust allowing thesecatalysts to operate efficiently over the vehicle life.

ULTRA-LOW SULPHUR DIESEL FUELSULSD is mandated by environmental regulatory bodiesin the US, Japan and the European Union (EU) since itis considered a cleaner burning fuel. ULSD, or S15, isdefined by the U.S. Environmental Protection Agency(EPA) as diesel fuel with a maximum sulphur contentof 15 ppm (parts per million). Low sulphur diesel(LSD), LS500, is defined as diesel having a sulphurcontent of less than 500 ppm. These designations areused throughout North America; however, in otherregions of the world, sulphur content can vary and mayexceed these limits. In 2006, the change from LSD to

ULSD was initiated across the U.S. Current EPAregulations require 80% of all on-road diesel fuel beULSD by 2010. For off-road vehicles, diesel fuel waslimited to LSD in 2007 and will start moving towardsULSD by 2010.

The difference between LSD and ULSD fuel lies notonly in the sulphur content, but also in the physical andphysicochemical properties. To make ULSD fromcrude oil, the refinery typically applies a hydrotreatingprocess for desulphurization. As a result, not onlysulphur is removed, but also some naturally-occurringlubricants. In addition, distillation temperature, fueloxidation stability, conductivity, and aromatics content

are lowered, while cetane number, cloud point andwax content are increased 3. These changes aredependent on refinery feed stocks and specific

operating conditions for desulphurization such astemperature, pressure and catalysts 3.

OIL DEPENDENCY INITIATIVES ARE DRIVINGDEVELOPMENT OF BIOFUELS

Worldwide production of oil is currently around 90million barrels per day. An approximate distribution ofmanufactured oil products coming out of a typicalrefinery is shown in Figure 1 4. It is noteworthy that amajority of oil production goes into liquid fuels and onlya relatively small portion of all crude oil refining findsits way into non-fuel products. Approximately 80% ofthe 90 million barrels per day is converted into fuels forcombustion engines. Of the 80%, almost 15% (500+million gallons per day) of this fuel is currently used in

diesel engines. Over the next ten years, thispercentage is expected to grow 5. Some projectionsshow more than one in four internal combustionengines made will be a diesel engine by 2020. This isan increase from one diesel engine in five in 2003 5.

Long term energy security and sustainability call forreduced dependency on fossil fuels. Initiatives toreduce dependency on fossil fuels are drivingdevelopment of biofuels derived from plant or animalbased sources. From a transportation perspective,some studies have indicated that utilization of biodieselcan reduce the amount of hydrocarbon and carbonmonoxide emissions since these fuels are typically

more oxygenated than traditional diesel fuels andconsequently cleaner burning. Similar studies haveshown that PM emissions can be reduced with usage

Figure 1: Approximate distribution of manufactured oil products from a barrel of oil.

Finished Motor Gasoline, 51%

Asphalt & Road Oil, 2%Other Refined Prod., 2%

Lubricants, 1%

Residual Fuel Oil, 3%

Liquid Refinery Gas, 3%

Distillate Fuel Oil, 15%

Jet Fuel, 13%

Still Gas, 5%

Marketable Coke, 5%

Finished Motor Gasoline, 51%

Asphalt & Road Oil, 2%Other Refined Prod., 2%

Lubricants, 1%

Residual Fuel Oil, 3%

Liquid Refinery Gas, 3%

Distillate Fuel Oil, 15%

Jet Fuel, 13%

Still Gas, 5%

Marketable Coke, 5%


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of biodiesel 6.

BIODIESELBiodiesel is a fuel produced from renewable resourcessuch as soybean or rapeseed oils. The burgeoningbiodiesel industry is associated with renewable energydevelopment efforts. Despite the debate on non-sustainable food-to-energy, biodiesel is emerging asan alternative to ULSD or as a blend with ULSD. Feedstocks in addition to soybean or rapeseed are beinginvestigated. In the US, soybean oils and animal fatsare major sources for large scale biodiesel production.For soybean oil, a transesterification process isemployed where the oil is converted to a methyl esterby reacting with methanol using NaOH or KOH as the

catalyst.Use of biodiesel or its blends with fossil fuel baseddiesels reduces overall dependency on crude oil.However, biodiesel is less stable and morehygroscopic than ULSD. It is also known to have ahigher cloud point and more unsaturated hydrocarboncontent which can lead to earlier wax precipitation andincreased intensity of fuel oxidation causing prematurefuel filter plugging. However, biodiesel blended withfossil fuel based diesel can improve its performancewith diesel engines. These blends can improvelubrication properties, provide higher cetane numberand reduce emissions relative to ULSD 7.

In addition to efforts directed toward biodiesel, there isalso ongoing activity in Brazil blending ethanol withdiesel fuels. Vegetable oil has also been blendeddirectly with diesel fuels.

CONTAMINANTS IN FUELSThere are many opportunities for contaminant ingressin fuels from production to point of use. Filtration ofdiesel fuel on mobile vehicles dates back to theearliest installations of diesel engines. An earlyparagraph written on diesel system care came out of a1931 Caterpillar owners manual. It states that 90% ofdiesel problems are due to dirt or water in the fuel 8.

Although emission standards have led to removal ofsulphur from todays diesel fuels, dirt, water and softorganic contaminants still remain.

Common rail fuel injection systems utilized on modernlow emission engines have critical filtrationrequirements due to their ever increasing operatingpressures and correspondingly tighter clearancesrequired for both injectors and pumps. On-vehiclefiltration is the last line of defence for an engine tofunction efficiently over long service intervals. For thefiltration industry this represents emerging challengesfor developing next generation fuel filter technology formanaging 1) particles, 2) water, and 3) soft organics.

Particles in FuelParticulate contaminants include road dusts, enginerust or wear particles, and any other hard particles that

can cause engine damage. These particles aretypically rigid in nature and can cause severe wear to afuel injection system. The extent of damage realizeddepends on particle size, shape, rigidity, concentrationand sometimes on chemical composition.

Particle contamination makes its way into vehicle fuelsystems through multiple paths. One source is thediesel fuel itself. Diesel fuel cleanliness varies fromgas pump to gas pump. Typical fuel cleanliness levelscoming out of the pump are ISO rated at 22/21/18.(ISO cleanliness code of 22/21/18 translates to aparticle count of 20,000 to 40,000 per ml for particlesof 4 m and greater; 10,000 to 20,000 per ml for

particles of 6 m and greater; and 1300 to 2500 per mlfor particles of 14 m and greater).

A second source of ingress is through the tank vent. As the fuel tank is drawn down ambient air is drawninto the tank. Furthermore, wear debris from fuelsystem components provide yet another source ofparticles.

One measure of relative injector wear is the ability toflow more fuel through the injector orifice. Fuel injectornozzle orifice wear is shown to increase as a functionof particle contaminant concentration in Figure 2 9.Erosion of a nozzle orifice can adversely affect the

atomization process thus negatively impactingemissions. Consequently, clean fuel minimizes fuelsystem wear and engine exhaust emissions.

Diesel fuel pump manufacturers are already requiringfuel with ISO cleanliness counts of 13/9/6 or better atthe injector; with typical fuel cleanliness levels comingout of the gas pump at 22/21/18, this represents athousand fold reduction in contaminant required by thetime the fuel reaches the fuel injector system 10.

1E+3 1E+4 1E+5 1E+6 1E+7 1E+80

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Figure 2: Fuel injector nozzle wear represented by increasein fuel flow as a function of particle concentration.

Assumption 2 ppm fuel.


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In terms of particle filtration efficiency, beta ratio is stilla quantitative way to define filter medium effectivenessto keep fuel relatively free of damaging wear particles.

Beta ratios, defined as the ratio of the number ofparticles upstream to the number of particlesdownstream at a specific particle size, are ofteninadequate measures of fuel filter performance. Betaratios are derived from standardized multi-pass fuelfilter tests while on-vehicle fuel filtration generallyoccurs in a single pass. ISO cleanliness level at thefuel injector may well be an improved method formeasuring a filters performance 10.

In addition, standard laboratory tests generally usesilica ISO dusts (see Figure 3A) to quantify a filtersdust capacity and dust filtration efficiency. However, itis well known that ISO dusts do not necessarilyrepresent real-world contaminants as shown in Figure3B, and therefore do not provide an adequaterepresentation of actual filter performance.

Generally, particle filtration media include, but are notlimited to, cellulose, glass, blends of cellulose andglass, melt blown/cellulose composites and spunbondpolyester. Particles capable of causing wear in todayscommon rail fuel systems are significantly smaller thanthe primary wear contributors twenty years ago.Today, particles significantly smaller than four micronsare now potential wear contributors. These smallerparticle sizes challenge the limits of our measurementcapabilities.

These fine particulate contaminants will require bothnew filtration technology and a corresponding systemsapproach to successfully remove them from dieselfuels; with current filtration technology it may be nolonger practical to rely solely on on-vehicle filtrationsystems to control fine particles. Filtration of fuels ateach transfer point, from production to the gas stationpump, may be necessary as performancerequirements for particle filtration become morestringent.

Water in FuelWater found in diesel fuels can cause engine partcorrosion and erosion, fuel lubricity deterioration, fuel

pump cavitation, fuel injector deposit build-up and fuelfilter plugging. It can also promote fuel instability andat the fuel/water interface provide an environmentwhere bacteria can grow. Water can be found withinfuel as free water, dissolved water and emulsifiedwater.

Dissolved water is dispersed in fuel molecule-by-molecule. Once the amount of water exceeds themaximum level for it to remain dissolved, water will fallout of the fuel, forming a water-in-fuel emulsion withsmall water droplets suspended in the fuel. Whenmore water is unavoidably introduced in the fuel duringfuel storage, shipping, pumping and through

condensation, free water can be found at the bottom ofstorage or fuel tanks due to the difference in densitybetween fuel and water. Free and emulsified watermust be effectively removed from fuel and a significantamount of dissolved water can also be a potentialthreat to the engine. World Fuel Chartersrecommends a maximum water content to be less than200 ppm 10.

Water contamination is introduced to the fuel systemthrough the same basic paths as particlecontamination. On road vehicles fuelling at truck stopsand service stations draw fuel from relatively controlledsources, and pumps have point of use filters to helpcontrol free and emulsified water contamination.However, water can also be transferred into thevehicles fuel tank as the level of dissolved water in thefuel equilibrates with the relative humidity of theoutside surroundings. Therefore, at a minimum, somewater will always be brought into the vehicles fuelsystem when fuelling. For remote off road sites suchas mines, controlling fuel storage and dispensingconditions are more challenging and the chance ofintroducing substantially larger quantities of water are

Figure 3: Scanning Electron Micrographs (SEMs) of: A) ISO fine dust; B) a used diesel fuel filter.

AA BB


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much greater.

Water also enters the fuel systems through fuel tankvents, but unlike particle contamination, water is notnecessarily driven by the level of fuel in the tank butrather by fluctuations in environmental conditions, i.e.changes in temperature and relative humidity.

Typical water saturation vs. temperature values fordiesel fuel are not readily available since they fluctuatewidely from batch to batch and from refinery torefinery. Laboratory testing at Donaldson Companyindicates that it is not unusual for a ULSD fuel to havea 50 ppm water saturation limit at around 50F andclose to a 200 ppm saturation limit at 100F. Usingthese two values, a 50 degree temperature swing from50F to 100F at 100% RH increases the dissolvedwater concentration of the fuel from 50 ppm to 200ppm. This amounts to 1.7 ounces of water for every100 gallons of fuel. When fuel in the tank and airspace above it cools to 50F the dissolved waterholding capacity of the fuel is reduced to its startingvalue and the calculated amount of water is droppedout of solution and into the fuel tank as free oremulsified water.

In ULSD, loss of naturally occurring lubricants must becompensated with lubricity additives to protect themoving components of the engine that rely on fuel astheir lubricant. These lubricity additives increase fuelsurfactancy, which in turn has the unintended effect of

increasing stability of water droplets in the fuel.Filtration of this emulsified water is more challengingthan removal of the larger droplets found in LSD.

For water in fuel, interfacial tension (IFT) is a measureof the affinity between water and fuel. A lower value ofIFT represents a higher affinity where water is moredifficult to separate from fuel. Water droplet size infuels with different interfacial tensions (IFT) as afunction of water concentration is shown in Figure 4 11 .

As IFT is lowered, the mean water droplet sizebecomes smaller and smaller, and consequently moredifficult to remove. At higher IFT, the droplet sizeincreases with increasing water concentration;however, this trend does not persist below an IFT of 10mN/m. At IFTs below 10 mN/m, the emulsion is stableenough to prevent further coalescence of waterdroplets; this is true even at elevated waterconcentrations.

These stable water-in-fuel emulsions render traditionalfuel/water separation media, such as water-repellentcellulose and melt blown/cellulose composites,ineffective. These media are typically designed forrelatively high IFT fuel and coarse water filtrationwhere emulsion stability is not an issue.

Biodiesel is inherently more hygroscopic than ULSD

due to its polar fatty acid and methyl ester compositionand its residual glycerin by-products created during the

transesterification process. In addition, emulsifiedwater in biodiesel is believed to have a finer dropletdistribution due to the surfactant nature inherent in the

fatty acids and the role of glycerin in stabilizing theemulsion. Consequently, when biodiesel is blendedwith ULSD, emulsified water removal becomes evenmore challenging.

Regardless of these technical challenges, the fuelfiltration industry is facing a test standard issue. Forexample, the current US emulsified water filtration teststandard, SAE J1488, is no longer representative oftodays fuels. ULSD and its biodiesel blends canexhibit a range of interfacial tension from about 3 to 30mN/m. The current standard specifies fuel with aninterfacial tension of 25-30 mN/m. Consequently, afuel/water separator that passes this standard test withover 95% efficiency may not work for real world fuelshaving low interfacial tension. ISO/TC 16332 wasdeveloped to tackle this problem but is beingchallenged by participating members. The issues arehow to select a standard fuel for water/fuel separationtests, and how to generate a water-in-fuel emulsionmore representative of real world fuels.

Organic Contaminants in FuelOrganic contaminants can be soft, sticky or slimy innature. They can occur naturally or as a result of fueldegradation. These contaminants are not well defined,however, they can be naturally occurring compounds,end products of fuel oxidation through thermalstressing, by-products of fuel additives interacting withfuel constituents, apple jelly types of materials thathave something to do with water contamination, or amix of all of these phenomena.

Filters plugged with diesel fuel organic contaminantsare shown in Figure 5. A typical ULSD fuel filter afteruse is shown in Figure 5A and similarly after use withbiodiesel in Figure 5B. It can readily be seen that thefuel type has a dramatic impact on the morphology andstructure of the organic contaminants. Note thedifferences between the organic contaminant formed

Figure 4: Mean droplet size as a function water concentrationand IFT.

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from ULSD as compared to that from biodiesel inFigures 5C and 5D respectively.

The complexity and variety of fuel contaminants arerevealed in Figure 6. Diesel fuels contain long chainparaffinic molecules. These higher carbon contentmolecules generally have higher cetane level forimproved combustion during compression ignition.Reduction of aromatics in ULSD lowers wax solubilityand promotes wax precipitation when temperature islowered. This can lead to premature plugging of fuelfilters.

ULSD organic contaminants can also damageelastomeric fuel filter seals and consequently shortenfilter life. In this case, the organic contaminants arethe result of free radical reactions. These reactionsare accelerated for ULSD due to the removal ofnaturally occurring antioxidants from the refineryshydrotreating process. As a result a large number ofhydrocarbon peroxides are generated. Theseperoxides promote oxidation and polymerization ofunsaturated fuel molecules, and have a damagingeffect on elastomeric seals used in vehicle fuelsystems. When fuel temperature is raised and incontact with metal surfaces, oxidation becomesincreasingly problematic forming organic acids thatmay cause engine corrosion. With further oxidation,organic sediments can also be formed. As a result,fuel filters may be clogged prematurely and fuelinjectors may be fouled or plugged. To prevent this,fuel stabilizers are typically used. However, under fuel

thermal stress conditions, other fuel contaminants cancoexist as oxidation sources and reduce theeffectiveness of antioxidant additives.

For biodiesel, fuel oxidation is related to the rate ofreaction of fuel molecules with oxygen through a free-radical initiated mechanism. This is important becausethe end products of oxidation may contain soft stickyparticles that can adhere to fuel filters and enginecomponents. The induction period of oxidation is usedas a standard to quantify fuel oxidation stability. Thelonger the induction period, the more resistant the fuelis to oxidation when exposed to oxygen or air. Whenbiodiesel is blended with ULSD the induction perioddecreases as the blend ratio increases as is shown inFigure 7 12.

It was observed that a fuels oxidation stability doesnot necessarily correlate to formation of the solidcontaminants that causes filter plugging; however,improved oxidation stability prevents deposits andincreases both reliability and working life in enginesand filters 13.

FUEL FILTRATION SYSTEMSFuel filters are as widely varied as the vehicles onwhich they are used. A range of products aimed at themore traditional fuel markets is shown in Figure 8.Spin on filters are most commonly utilized in the fuelmarket world wide; however, new global demands arechanging the configurations desired for vehicles in

Figure 5: A) plugged ULSD fuel filter, B) plugged biodiesel fuel filter, C) SEM of ULSD formed organic contaminants, and D) SEMof biodiesel formed organic contaminants.

CBCBAAAA

BCBC DDDD


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these markets.

New demands in smaller vehicle markets centrearound application flexibility which help manufacturersintegrate multiple functions into the fuel filter module.Examples of modular designs which areenvironmentally responsible and offered to meet theserequirements are shown in Figures 9 and 10.

There are two shifts in fuel filter system design andconfiguration. The first centres on replacement filtersin the vehicle markets. Typically, replacement filters

have been either a spin-on style with a metal housingand thread plate or a cartridge style element asdepicted in Figure 9. Some markets are nowdemanding cartridge style elements due to regionaldifferences in used filter element disposal. Thesecond evolution is the modular filter which offersflexibility in design allowing the fuel filter system tosatisfy a variety of performance needs. Figure 10shows an example of a typical remote mount fuel filterassembly that has the ability to incorporate a numberof performance features such as a water sensor,electrical heater, visual water bowl, manual primingpump, life indicator or a Donaldson Twist&Drainvalve. The demand for these features depends on enduser preferences and filter location in the fuel system.

Effective fuel filtration for modern engines generallyconsist of two sequentially placed filters, a primaryfilter and a secondary filter. The location of thesefilters is shown in Figure 11.

The PowerCore fuel processor, Figure 12, is oneexample of how we are anticipating the future. Onapplications where the two separate filters are required(a primary filter on the suction side of the transferpump and a secondary filter on the pressure side),Donaldson Company developed a fuel filter systemwhich integrates both these filters into a single unit,

Figure 6: Field contaminants extracted from a plugged fuel filter.

Plugged field filter

Field filtercontaminant-1

Field filtercontaminant-2

Materialextraction

Filtermedia

SEM of carbon-basedparticles

Carbon-basedparticles

Figure 7: Induction time vs. soybean biodiesel/ULSD blendratio.

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thereby reducing overall replacement element cost, aswell as maintenance time servicing the filters. Inaddition, an electrically driven transfer pump can nowbe added to this system allowing more flexibility inmounting this unit in an already crowded enginecompartment.

Additional features can be added as needed includinga water sensor, automatic or manual drain valve,

primer pump (if electric transfer pump is not used),pressure sensor, and filter life indicator.

FUEL FILTRATIONPrimary filters are most commonly utilized on thesuction side of the fuel transfer pump (Figure 11). Thisplacement allows for protection of the pump whilesimultaneously taking advantage of easier fuel waterseparation conditions before the pump emulsifies thefuel/water mixture. Typical micron ratings for suctionside primary filters vary over a wide range. Dependingon vehicle, engine and operating environment primary

filters usually have efficiency ratings from 7 m to over25 m. This is typically achieved using cellulose

media or, for higher dirt capacity, meltblown cellulosecomposite media.

Water is generally removed from fuel by using either astripping or coalescing mechanism. A filter mediumthat removes water in front of it is referred to as awater stripper. It is normally either naturally waterrepellent or hydrophobically treated with chemicalagents; commercially available media such asmeltblown polyester on cellulose and siliconeimpregnated cellulose are examples.

A coalescer is a filter that separates water by allowingit to pass into the media where droplets are capturedand combine to form larger droplets and are thenfinally released on the downstream side. Coalescerstypically consist of small size fibre glass with surfaceproperties aiding efficient water droplet capture, growthand release. Multi-layered coalescing media are notuncommon. As water droplets in low interfacialtension fuels form more stable emulsions, bothstrippers and coalescers can become ineffective andnot achieve the required water filtration efficiency.

Secondary fuel filters are placed between the transferand high pressure injection pump. These filters protectthe high pressure fuel pump and sensitive fuel injectioncomponents from particles that can cause wear anderosion damage. Typical ratings for secondary filtersin high pressure common rail fuel systems are in the 4-5 m efficiency range.

Fuel Filter Performance Under Unsteady FlowConditions

An emerging challenge for filter manufacturers isdesigning systems which retain filtration performanceunder actual operating conditions. Historically, filterswere evaluated using standard laboratory tests that donot necessarily reflect real world driving conditions,where cyclic flow and vibration are commonphenomena. These conditions can degrade a filter'sperformance causing particle penetration through thefilter and recontamination of the fuel before it isinjected. The extent of particle penetration dependson cyclic flow frequency, type of filter media and

number of particles already loaded onto the filtermedia as is shown in Figure 13 14.

A significant effect on particle penetration wasobserved under vibration condition using media B withtwo different test fluids. Particle penetration is plottedagainst particle size for these two different fluids, MIL-H-5606 hydraulic fluid and Viscor, a surrogate fordiesel fuel in Figure 14. The most noticeabledifference between these two fluids is the viscosity;MIL-H-5606 is about 6 times more viscous than Viscor.Comparisons are made under two vibration conditions,no vibration and at an acceleration of 4G. Note thathigh penetration occurs for Viscor under vibration at4G acceleration. In addition, particle penetration

Figure 8: Typical fuel filters.

Figure 9: Example of metal spin-on ( left ) and replaceablefilter element cartridge ( right ).

Traditional metalspin-on filter

Reusable plastichousing with non-

metal filter cartridge


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during vibration and cyclic flow is more severe forsmaller particles (Figures 13 and 14).

Therefore, a robust filter should be designed formaximum engine protection under these operating

conditions. This alone presents another challenge aspointed out by Verdegan 15.

Figure 10: Remote mount fuel filtration assembly with optional features and functions.

IntegratedHeater

Connector

Head with upto 4 ports

Air Relief Valve

Spin-onFuel Filter

Spin-onFuel Filter

WaterSeparator

Drain Option 1:Clear Water

Collection Bowl

Drain Option 2:Twist&Drain TM

Water Sensor


Manual Priming Pump

Pressure Sensor

Visual Service Indicator

IntegratedHeater

Connector

Head with upto 4 ports

Air Relief Valve

Spin-onFuel Filter

Spin-onFuel Filter

WaterSeparator

Drain Option 1:Clear Water

Collection Bowl


Water Sensor


Manual Priming Pump

Pressure Sensor

Visual Service Indicator

Figure 11: A typical fuel systems with both primary andsecondary fuel filters.

Injection Pump

TransferPump

FuelTank

Injectors

SecondaryFuel Filter

PrimaryFuel Filter

Figure 12: Donaldson PowerCore TM fuel processor.


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BULK FUEL FILTRATIONFor many years it has been recognized that a rootcause of contamination in engines is dirty fuels.

Todays fuels are required to meet ISO cleanlinesslevels of 22/21/18. Figure 15 demonstrates theapproximate amounts of dust required to contaminate100 gallons, 1000 gallons and 10,000 gallons of dieselfuel to this ISO cleanliness level. It should berecognized that not all particles in real fuel representhard dirt, nor is ISO medium test dust necessarilysimilar to the ambient dusts that is found in fuels.However, this picture does illustrate the potentialmagnitude of the filtration challenge to clean largequantities of fuels either on the vehicle or prior to use,especially given the harsh demands of higher pressurecommon rail fuel systems. Given the potential amount

of contamination involved, this raises the interestingquestion of how big do filters really need to be in the

future to successfully capture fuel particulatecontamination.

From a practical standpoint, removing the majority ofdirt contamination prior to vehicle fuelling is aseemingly suitable solution. Currently, this is onlyhappening where an entity owns both the equipmentand the fuel delivery equipment, for example, at minesites or with major fleets such as metropolitan buses.Therefore, an opportunity exists in achieving higherlevels of fuel cleanliness by considering bulk filtrationas prelude to vehicle filtration.

SUMMARYChanges in diesel fuels due to tougher environmentalregulations, a move toward energy security as well as

sustainability and emerging green initiatives arecreating new challenges in fuel filtration. In addition,

Figure 14: Effect of vibration on particle penetration.

Viscor

Viscor

MIL-H-5606

MIL-H-5606

2gal/min None

4G

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* Acceleration

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Figure 13: Effect of cyclic flow on particle penetration.

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evolving engine designs require a much higher level offuel cleanliness. For the filtration industry thisrepresents emerging challenges for developing nextgeneration fuel filter technology for improvedmanagement of particles, water and soft organics. Inaddition, filter manufacturers are challenged to designfiltration systems which retain filtration performanceunder actual operating conditions of vibration andcyclic flow. As we look into the future we see anincreasing need for integration of more features andfunctions into fuel filtration systems. Understandingthe limitations of todays fuel filtration and emerging

industry needs provides an opportunity to addressthese challenges with innovative technology.

REFERENCES1. http://m.cnn.com/cnn/ne/tech/detail/928532. W.A. Majewski, 2005, Diesel Progress (North

American Edition), 71 (12), 18-19.3. Infineum Insight, 2006, Finding Another Way - The

Challenges of Producing Winter Grade ULSD in

North America, 30 ,1-3.4. http://tonto.eia.doe.gov/ask/crudeoil_faqs.asp5. Diesel Engine Production for NAFTA markets,

presented to the Association of Diesel Specialists, Aug 19 th 2004, Rhein Associates.

6. www.epa.gov/OMS/models/analysis/biodsl/p02001.pdf

7. www.nrel.gov/docs/fy05osti/37136.pdf8. R. Douglas, 2002, Improving fuel system durability,

5 th International Filtration Conference , pp.59-67.9. M.A. Barris, 1995, Total filtration: The influence of

filter selection on engine wear, emissions andperformance, SAE Technical Paper Series#952557, SAE Fuels and Lubricants Meeting andExposition , October 16-19.

10. www.naams a.co.za/un leaded/WWFC%2 04%20Sep%202006.pdf, page 50.

11. C. Yang, S. Larsen, and S. Wagner, 2007,Understanding emulsified water filtration fromdiesel fuels, 8 th International Filtration Conference ,2007, 5 pages.

12. C. Yang, L. Senne, S. Larsen and M. Madsen,2008, ULSD/biodiesel blend and its effect on fuel/water separation, American Filtration andSeparation Society Annual Conference , Paper 3-2-3, 12 pages, May 19-22, Valley Forge, USA.

13. G. Kenreck, 2007, Improving biodiesel stability withfuel additives, Biodiesel Magazine , February 2007,134-140.

14. G. LaVallee and P. Johnson, 2003, How flow andvibration affect filtration performance-Inside andoutside the laboratory, Machinery LubricationMagazine , May .

15. B. Verdegan, A. True-Dahl, W. Haberkamp, N.Blizard, D. Genter and E. Quillen, 2008, Filtrationsolutions for high pressure common rail fuelsystems, American Filtration and SeparationSociety Annual Conference , Paper 1-5-1, 9 pages,May 19-22, Valley Forge, USA.

Figure 15: Amount of ISO medium laboratory test dust re-quired to contaminate fuel to an ISO cleanliness of 22/21/18,

or alternatively which must be filtered out of the given fuelvolume.

A NEW METHOD OF MEASURING PORE SIZE DISTRIBUTIONS USING MULTI-MODAL PARTICLE SIZE STANDARDS

Graham R. Rideal 1 ([email protected]), Jamie Storey 1 and Bernd Schied 2 1Whitehouse Scientific, Chester, CH3 7PB, UK.

2 BS-Partikel, Wiesbaden, D-65205, Germany.

Porometry has been the traditional method for pore size distribution measurements. However, it has twomajor limitations: it is not traceable to the Standard Meter and instrument-to-instrument comparisons havebeen poor. Although challenge testing using traceable reference microspheres fulfils both these criteria, ithas hitherto only been able to measure maximum pore sizes. A new Multistandard of 10 non-overlappingpeaks from 0.1 to 1.5 m now enables pore size distributions to be made by analysing the relative depletion

of the peaks after passing a filter. The technique is only possible because of a high resolution, sub-micronparticle size analyser.

Documents

Water in Fuel