energies

Article Diesel-Injection Equipment Parts Deterioration after Prolonged Use of Biodiesel

Dimitrios N. Tziourtzioumis 1 and Anastassios M. Stamatelos 2,* 1 Vehicle Mechanical Engineering Dept., Alexandrion TEI of Thessaloniki, 57400 Thessaloniki, Greece; [email protected] 2 Mechanical Engineering Department, University of Thessaly, 38334 Volos, Greece * Correspondence: [email protected]; Tel.: +30-24210-74067

 Received: 27 March 2019; Accepted: 14 May 2019; Published: 22 May 2019 

Abstract: The application of biodiesel blends is known to significantly affect operation of diesel-injection equipment, especially the and fuel . This paper summarizes experience on this subject from burning fuel blends with high-percentages of biodiesel (up to 70%) on a common-rail, high-pressure-injection diesel and a conventional DI engine. Both were unable to start after running for 100 h each and staying shut off for more than two months. In order to understand the wear characteristics of the nozzle, pump , and elastomer parts (in the case of the high-pressure pump of the common-rail engine), due to the prolonged operation with high-percentage biodiesel blends, their injectors and parts were examined and compared by performing normal photography and low magnification microscopy. Additionally, the various elastomer parts of the high-pressure of the common-rail engine were examined for wear and deterioration. The results are compared with existing literature results from other researchers. The observed deterioration of diesel-injection equipment is caused by use of high-percentage biodiesel blends and subsequent engine shut down.

Keywords: ; ; biodiesel; fuel pump; fuel injectors; engine parts deterioration

1. Introduction Biodiesel is defined as the mono alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats. The term fatty acid methyl ester (FAME) [1] is often used as a generic expression for the trans-esters of these naturally occurring triglycerides, which find application as either a replacement for or a blending component for use with fossil-derived diesel. Significant variation in product quality and specification is allowed by legislation for products generally described as biodiesel. The influence of biodiesel blends on the steady-state and transient performance and emissions of various diesel engine types has been extensively reported in the literature [2–4]. The use of biodiesel blends with less than 10% biodiesel on diesel fuel is generally considered favorable mainly for the engine particulate emissions, but it is legislated for sustainability reasons.

1.1. Biodiesel Fuel Quality and Stability Problems Oxidation of biodiesel may damage fuel injection system parts and excess heating of vegetable oils may cause polymerization of the biodiesel. The extent of biodiesel oxidation depends on its fatty acid composition [4]. Experience has shown that several fuel quality, handling, storage, and vehicle operability issues need to be successfully addressed whenever high-percentage biodiesel blends are to be used in an automotive diesel vehicle fleet. This has led to numerous initiatives by fuel producers, original equipment manufacturers (OEMs), and their industry associations to publicize their issues and to lobby fuel legislators to include a number of parameters in regional biodiesel specifications.

Energies 2019, 12, 1953; doi:10.3390/en12101953 www.mdpi.com/journal/energies Energies 2019, 12, x FOR PEER REVIEW 2 of 22 Energies 2019, 12, 1953 2 of 21 their issues and to lobby fuel legislators to include a number of parameters in regional biodiesel specifications. In the United States, this has led to the firstfirst specificationspecification standard for the test methods to be employed inin thethe determination determination of of certain certain properties properties for for biodiesel, biodiesel, adopted adopted in 2002. in 2002. In its In current its current form, ASTMform, ASTM D6751-18 D6751-18 [5], this standard[5], this addressesstandard theaddres qualityses ofthe the quality pure biodiesel of the (B100)pure biodiesel component (B100) that iscomponent to be blended that tois produce to be blended biodiesel /todiesel produce fuel blends.biodiesel/diesel In regards fuel to theblends. specification In regards of biodiesel to the blends,specification the ASTM of biodiesel D975 standardblends, the for ASTM diesel D975 fuel, modifiedstandard infor 2008, diesel allows fuel, modified up to 5% in biodiesel 2008, allows to be blendedup to 5% into biodiesel the fuel, to be whereas blended ASTM into D7467-18athe fuel, wh [6ereas] covers ASTM fuel D7467-18a blend grades [6] ofcovers 6 to 20 fuel volume blend percentgrades (%)of 6 biodiesel,to 20 volume with percent the remainder (%) biodiesel, being a with light-middle the remainder or middle being distillate a light-middle diesel fuel. or middle Biodiesel distillate blends arediesel generally fuel. Biodiesel referred blends to as BX, are wheregenerally X is referred a number to whichas BX, denoteswhere X the is a volume number percent which ofdenotes biodiesel the incorporatedvolume percent in theof biodiesel finished fuel.incorporated The ASTM in the D6751 finished standard fuel. specifiesThe ASTM biodiesel D6751 asstandard long-chain specifies fatty acidbiodiesel methyl as esterslong-chain from fatty vegetable acid methyl or animal esters fats fr containingom vegetable only or the animal alcohol fats molecule containing on oneonly ester the linkage.alcohol molecule This effectively on one excludes ester linkage. raw or This unrefined effectively vegetable excludes oils, whichraw or contain unrefined three vegetable ester linkages. oils, Withinwhich contain the United three States ester and linkages. the European Within Union,the United soybean States oil and [7] andthe European rapeseed oilUnion, [8], respectively, soybean oil are[7] theand leading rapeseed source oil [8], biodiesel respectively, feedstock. are the Used leading cooking source oils are biodiesel also employed feedstock. in theUsed raw cooking oil mixture oils are [9]. Thealso Europeanemployed Committee in the raw foroil mixture Standardization [9]. The developedEuropean Committee a uniform standard, for Standardization EN14214 [10 developed], to replace a theuniform respective standard, national EN14214 standards. [10], to replace the respective national standards. The use of high-percentage biodiesel blends is known to be associated with fuel injector deposits [[11]11] and other types of injection system eeffffectsects [[12,13].12,13]. On the other hand, US and European market fuel surveys indicate that many retail biodiesel samples are out of specification, specification, which means that poor quality biodiesel is not scarcescarce [[14,15].14,15]. The most demanding issue with the use of biodieselbiodiesel is its oxidation stability, whichwhich aaffectsffects performance,performance, emissions,emissions, andand engineengine durabilitydurability (Figure(Figure1 1).). TheThe more generalgeneral termterm biodiesel biodiesel degradation degradation is is referred referred to to the the modification modification of itsof originalits original composition composition and propertiesand properties due todue aging, to aging, oxidation, oxidation, and metaland meta corrosionl corrosion during during the storage the storage process process [12,16 [12,16].].

Figure 1. EffectsEffects of biodiesel oxidation stability problems on engine operation.

The compatibility of seal and hose materials co commonlymmonly encountered in automotive fuel systems using conventionalconventional hydrocarbonhydrocarbon fuels fuels has has long long been been established established and and elastomer elastomer manufacturers manufacturers are able are toable make to make recommendations recommendations for their for use. their Specialized use. Specialized studies [17 studies,18] and [17,18] in-use experienceand in-use suggestexperience that certainsuggest seals, that ,certain seals, and hoses gaskets, may and degrade hoses under may harshdegrade operating under harsh conditions operating in contact conditions with B50 in orcontact high-percentage with B50 or blends. high-percent Elastomerage materials blends. generallyElastomer su materialsffer physical generally or chemical suffer changes physical when or inchemical contact changes with fuel. when The in extent contact of with these fuel. changes The extent depends of these on the changes tendency depends of the on material the tendency to absorb of fuelthe material or on specific to absorb compounds fuel or on to specific be dissolved compounds or extracted. to be dissolved This may or leadextracted. to swelling, This may shrinkage, lead to embrittlementswelling, shrinkage, or modifications embrittlemen of tensilet or modifications properties [19 ].of The tensile extent properties of a physical [19]. change The extent that can of bea toleratedphysical change depends that on can the specificbe tolerated application. depends For on example,the specific a material application. that swelledFor example, or softened a material after

Energies 2019, 12, 1953 3 of 21 contact with a fuel may continue to acceptably act for a long time as a static seal. On the other hand, dynamic applications are more sensitive to swelling, due to increased friction and wear. Thus, a lower degree of volume change can be tolerated. The requirement to produce low and ultra-low sulfur fuels for environmental reasons, is generally met by hydro-treatment. This process destroys polar nitrogen and oxygen compounds, thus leading to a deterioration of the lubricity of diesel fuel. Fuel injection system parts deterioration after using low quality fuels is reported in analogous situations in marine engines [20]. Several researchers reported that biodiesel blending at low percentages may significantly improve the lubricating properties of low sulfur diesel fuel. Moreover, the use of biodiesel blends may reduce the concentration of metallic wear particles and increase engine durability [21]. On the other hand, the associated formation of corrosive materials (organic acids, water, methanol) may affect engine life. Additionally, thermal and oxidative instability and water separation may give rise to engine operability problems. The following problems have been identified during extensive field trials: corrosion of fuel injection system parts, seal failures and low-pressure fuel line, fuel filter blockage. High-pressure fuel system problems include fuel injector holes blockage, engine oil dilution, and polymerization. Additional problems reported include pump seizures at low temperatures. Due to the above reasons, Original Equipment Manufacturers Associations are conservative regarding the use of high-percentage biodiesel blends [22,23]. Clark et al. reported no abnormal characteristics in fuel injection system tests after 200 h of operation of a John Deere 4239 TF turbocharged diesel engine fueled with methyl and ethyl soybean esters [24]. On the other hand, Fraer et al. reported higher sludge formation on the valve deck around the rocker assemblies and more injector replacement for B20 fueled engine particularly for Mack tractor engines [25]. In the same way, the National Biodiesel Board has reported that a 1000 h durability test on an engine with B20 soybean ester blend caused serious technical problems, like failure of fuel , softening of fuel system seals, and deposits on air box covers, components, and injectors. Furthermore, truckers’ associations have complained that fuel filter plugging is increasing as animal fat- and soybean-based fuels are being introduced nationwide [26]. Based on the previous paragraphs, it is obvious that fuel system problems, including filter plugging by use of B100 fuel, have been mainly documented in the United States. According to a survey conducted by the Minnesota Trucking Association [27], 62% of 900 fleets said they had experienced fuel filter plugging. In most of the studies, the main problems were fuel filter plugging and injector coking. In this study, the impact of high (B70) and medium percentage biodiesel blends (B20 and B50) on a first generation common-rail injection system and a conventional “pump-in-line” injection system, respectively was investigated. It should be mentioned that the experiments were conducted on unmodified diesel engines. The most serious failure was that of the common-rail high-pressure fuel pump and the inline pump of the single engine. These failures repeated a second time, always after the engine stayed shut down for a period of a few months each. The details of the biodiesel impact to the injection system components are presented and discussed in this paper in an effort to motivate the scientific and technical community to further investigate these effects that damage the high reliability of the diesel powertrain.

1.2. Main Types of High-Pressure Pumps for Passenger . The high-pressure pump is the interface between a common-rail system’s low- and high-pressure stage. Its function is to keep the quantity of fuel required by the system ready at the necessary rail pressure level depending on the operation point [28–30]. The high-pressure stage of the common-rail system is divided into three sections: pressure generation, pressure storage, and fuel metering. The high-pressure assumes the function of pressure generation. Pressure storage takes place in the fuel rail to which the rail pressure sensor and the pressure-control and pressure-relief valves are fitted. The evolution of high-pressure pumps for passenger cars is presented in Figure2. Energies 2019, 12, 1953 4 of 21 Energies 2019, 12, x FOR PEER REVIEW 4 of 22

(standard),First generation CP1K (compact), common-rail and systems CP1H (reinforced). utilize high-pressure Compared pumps to CP1K/S, with eccentric CP1H shaftis designed drives and for threehigher radially-arranged pressures up to plungers.1600 bar. This There is areachieved three types by reinforcing of CP1 high-pressure the drive mechanism, pumps: CP1S modifying (standard), the CP1Kvalve (compact),units, and andintroducing CP1H (reinforced). measures to Compared increase the to CP1Kstrength/S, CP1H of the ispump designed housing. for higher pressures up toBosch 1600 bar. CP3 This is a is monoblock-housing achieved by reinforcing three-plunge the drive mechanism,r radial high-pressure modifying thepump valve with units, suction and introducingthrottle control measures and an to external increase gear the pump strength for of fuel the delivery, pump housing. which is flange-mounted directly on the pump.Bosch This CP3 construction is a monoblock-housing of housing reduces three-plunger the potential radial high-pressureof leakage in pumpthe high-pressure with suction throttlesection, controland permits and an a externalhigher delivery gear pump rate. for The fuel low-pressure delivery, which ports is flange-mounted are mainly located directly in the on thealuminum pump. Thispump construction flange, which of housing is bolted reduces with the the forged potential steel of housing. leakage in This the pump high-pressure can withstand section, pressures and permits up ato higher 1600 bar. delivery Unlike rate. the The CP1 low-pressure pump series, ports the are polygon’s mainly locatedmovement in the is aluminum not directly pump transferred flange, whichto the isplunger bolted withbut rather the forged to the steel bucket housing. This placed pump in canbetween. withstand This pressureskeeps the up lateral to 1600 forces bar. induced Unlike the by CP1friction pump away series, from the plunger polygon’s and movementconducts them is not to directlythe pump transferred housing, toimproving the plunger the butpump’s rather stability to the bucketunder load tappet [28,30]. placed in between. This keeps the lateral forces induced by friction away from plunger and conductsCP4 is the them latest to Bosch the pump common-rail housing, radial improving high-p theressure pump’s pump stability which under consists load of [28 one,30 (CP4.1)]. or two CP4(CP4.2) is the radial latest arrayed Bosch plungers common-rail and a radial drive high-pressureshaft with a double pump , which as consistsshown in of Figure one (CP4.1) 2d (1). orThe two CP4 (CP4.2) handles radial pressure arrayed levels plungers from and1800 a to drive 2700 shaft bar withand ais doubleused for cam, both as on-and shown inoff-highway Figure2d (1).applications The CP4 handlesfrom passenger pressure cars, levels light- from and 1800 medium to 2700-duty bar andvehicles is used up to for small both heavy-duty on-and off-highway vehicles. applicationsAnalogous models from passenger are produced cars, by light- Dens ando corporation, medium-duty HP2, vehicles HP3, HP4 up to [31]. small heavy-duty vehicles. AnalogousAll the models types of are high-pressure produced by pumps Denso corporation,operate in the HP2, same HP3, reciprocating HP4 [31]. mode which consists of suctionAll theand types delivery of high-pressure strokes. The pumps working operate pump in elements the same reciprocatingare the plunger, mode barrel, which suction consists and of suctiondelivery and valve. delivery The strokes.drive shaft, The workingFigure 2a pump (2), is elements mounted are in the a plunger,central bearing, barrel, suction Figure and 2a delivery(3). The valve.pumping The elements drive shaft, are arranged Figure2a radially (2), is mounted with respec in at centralto the central bearing, bearing. Figure The2a (3). polygon, The pumping Figure 2c elements(4), is fitted are to arranged drive the radially shaft which with respect forces the to the pu centralmp plunger, bearing. Figure The 2b polygon, (5), to move Figure up2c (4),and isdown. fitted to drive the shaft which forces the pump plunger, Figure2b (5), to move up and down.

FigureFigure 2.2. ComparativeComparative cross-section cross-section views views of of the the different different pump pump generations: generations: CP1 CP1 (a,b (),a,b CP3), CP3(c), CP4 (c), CP4(d). (d).

Energies 2019, 12, 1953 5 of 21

1.3. Plunger Manufacturing Process High-pressure fuel pumps are manufactured with extremely close tolerances, especially between plunger and barrel (about 10 µm [32]). It is important to understand the manufacturing process for these parts, which is summarized below. The fuel pump plunger pushes the fuel through a positive displacement pump by reciprocating through a chamber. This reciprocating action enables the pump to attain high-pressures. The plunger’s pumping motion guides the fuel in the cavity from the high- to low-pressure side. The plunger first creates suction, drawing the fuel into the chamber. It then moves the opposite direction to build pressure, forcing the fuel to the discharge port. Plunger manufacturing consists of the following phases:

Preheating: To prepare for coating, the plunger barrel is mounted on a coating lathe. A spray gun • preheats it by means of a flame. The barrel is heated to 200–220 ◦C, for a duration that depends on plunger’s size. Coating: Once the plunger reaches a prescribed temperature, a hopper loaded with a mixture of • tungsten carbide powder is mounted on the gun. The gun then deposits a layer of the powder to the plunger barrel’s surface. Fusing: As soon as the barrel is completely coated, the powder hopper is removed. Subsequently, • the plunger barrel is heated to 700–750 ◦C. This results in the fusion of tungsten carbide powder to the barrel’s surface. Then, the plunger is cooled at room temperature. Grinding: The plunger’s diameter is measured to check uniformity of coating. Then, the coated, • semi-finished plunger is mounted on a CNC (computer numerical control) grinder. The surface is finished to a prescribed RMS (root mean square) roughness. Finishing: The plunger is checked for surface roughness, concentricity, and uniformity. If it is • found to meet the specifications, it is mounted to a CNC lathe for finishing.

1.4. Elastomer Parts Compatibility Biodiesel, a mixture of fatty acid methyl esters (FAME), is a renewable fuel produced from the homogeneous catalytic transesterification of vegetable oils, like rapeseed oil, soybean oil, and animal fats using basic hydroxides as catalysts. In a standard process of biodiesel production from rapeseed oil there are the following process steps: esterification of oil (vegetable, rapeseed, soybean, canola), separation of esterification products, methanol distillation, and purification of ester. Glycerol (glycerin) is the main formed by-product of oil esterification process. In this process, soaps and fatty acids are also created. FKM (Fluorocarbon-Based Elastomer), NBR (Nitrile Butadiene Rubber), and HNBR (Hydrogenated NBR) are also chemically compatible with both of them. Glycerin is a by-product of the biodiesel production process and is related to amounts of unconverted or partially-converted fats and oils left from the manufacturing process. If the amount of glycerin is too high, it can lead to storage tank and fuel system filter plugging. Table1 summarizes the compatibility properties of various commercial elastomer parts when exposed to different types of biodiesel components, raw materials, and by-products [33], according to the manufacturers [34]. On the other hand, a review of reported effects of liquid biofuels on the deterioration of automotive rubbers [19] concluded that the physical and mechanical properties of NBR decreased after exposure to almost all the commercially-available biofuels. In regards to FKM, the main weakness of FKM rubbers towards biofuel attack was the metal oxides and hydroxides in their curing systems. Energies 2019, 12, 1953 6 of 21

Energies 2019, 12, x FOR PEER REVIEW 6 of 22 Table 1. Elastomer materials compatibility with different types of biodiesel raw materials, components, and by-products.Soybean oil very good very good very good

AnimalRaw Materials, fats Biodiesel veryNitrile good Butadiene HNBR very (Hydrogenatedgood Fluorocarbon-Based very good Components,Animal oil and By-Products veryRubber good (NBR) very goodNBR) Elastomer very (FKM) good VegetableRapeseed oil oil very good good * very good good * very very good good ** Soybean oil very good very good very good Glycerin (glycerol)Animal fats very verygood good very very good good very very good good SoapsAnimal oil very verygood good very very good good very very good good Vegetable oil very good very good very good FattyGlycerin acids (glycerol) good very good good very good very very good good * Good suitability:Soaps Some effects from exposure very good with some loss very of good physical properties. very Some good chemical Fatty acids good good very good swelling. ** Very good suitability: Elastomer shows little or no effect from exposure. Little effect on * Good suitability: Some effects from exposure with some loss of physical properties. Some chemical swelling. **performance Very good suitability: and physical Elastomer properti showses. little Very or nogood effect resistance. from exposure. [34]. Little effect on performance and physical properties. Very good resistance. [34]. 2. Materials and Methods 2. Materials and Methods In this section, the specific fuel injection systems of the two engines tested, the periods and detailsIn thisof operation section, the points specific tested, fuel injectionthe fuels systemsemploy ofed thein twothe tests, engines the tested, experimental the periods apparatus and details for surfaceof operation analysis points and tested, the cleaning the fuels and employed disassembl in they procedures tests, the experimental applied for apparatusthe injection for surfacesystem componentsanalysis and are the presented. cleaning and disassembly procedures applied for the injection system components are presented. 2.1. Technical Data of the Engines Studied 2.1. Technical Data of the Engines Studied Two different engines were employed in the tests with high-percentage biodiesel blends in the LaboratoryTwo di offferent Thermodynamics engines were and employed Thermal in Engines: the tests (a) with a PSA high-percentage DW10 ATED biodiesel2.0 L, four blends , in four the cylinder,Laboratory turbocharged, of Thermodynamics equipped and with Thermal Bosch Engines:first generation (a) a PSA common-rail, DW10 ATED ECU 2.0 (Electronic L, four stroke, Control four Unit)-controlledcylinder, turbocharged, injection equipped system (Figure with Bosch 3a, Table first generation 2); and (b) common-rail, a Ruggerini ECURF91 (Electronic0.5 L, four Controlstroke, singleUnit)-controlled cylinder, naturally injection systemaspirated, (Figure equipped3a, Table with2); anda pump-in-line (b) a Ruggerini injection RF91 system 0.5 L, four (Figure stroke, 3b, single Table 3).cylinder, naturally aspirated, equipped with a pump-in-line injection system (Figure3b, Table3).

(a) (b)

Figure 3. Engine test beds: ( (aa)) PSA PSA DW10 DW10 ATED, ATED, ( b) Ruggerini RF91.

Table 2. PSA DW10 ATED engine specifications. Table 2. PSA DW10 ATED engine specifications.

Engine EngineType Type HSDI HSDI Turbocharged Turbocharged Diesel EngineDiesel Engine NumberNumber of cylinders of cylinders 4 in line 4 in line stroke 85 88 mm Bore × stroke× × 85 × 88 mm Rated power 80 kW, 4000 rpm Rated powerRated torque 250 Nm, 80 2000 kW, rpm 4000 rpm RatedCompression torque ratio 250 18:1 Nm, 2000 rpm CompressionElectronic control ratio unit version Bosch EDC 15C2 18:1 HDI version Bosch EDC 15C2 HDI

Table 3. Ruggerini RF91 engine specifications.

Engine Type DI 4-Stroke Naturally-Aspirated Diesel Engine

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Table 3. Ruggerini RF91 engine specifications.

Engine Type DI 4-Stroke Naturally-Aspirated Diesel Engine Number of cylinders 1 Bore stroke 90 75 mm × × Rated power 8.1 kW, 3600 rpm Rated torque 25 Nm, 2500 rpm 18.5:1

2.2. Fuel Injection Systems of the Engines Studied Bosch high-pressure pump, CP1S, can provide a 1350 bar maximum rail pressure. On the other hand, the New Diesel conventional inline pump can increase the injection pressure up to 210 bar. Technical specifications of the tested pumps, New Diesel and Bosch, are presented in Tables4 and5, respectively.

Table 4. PSA DW10 ATED injection system specifications.

Fuel Injection Pump Type Bosch, CP1S3/R65/10-16S, OEM PN: 0 445 010 010 Pump displacement 0.69 cc/rev Architecture 3-plunger Pump plunger diameter 6.5 mm Nominal max pressure 1350 bar Injectors type Bosch 0445110076 Number/diameter of nozzle holes 5 0.123 mm ×

Table 5. Ruggerini RF91engine injection system specifications.

Fuel Injection Pump Type New Diesel, OEM PN: NPFR 1K60-1685 Injector needle diameter 4 mm Number/diameter of nozzle holes 4 0.24 mm × Nozzle hole length 0.6 mm Pin height 0.125–0.175 mm volume 0.36 mm3 Injector opening pressure 210 bar Pump plunger diameter 7 mm

2.3. Properties of Fuels Employed The fuels under investigation were three volume-based blends of biodiesel in diesel fuel, 20%, 50%, and 70%. The tested fuels were denoted as B20, B50, and B70, respectively. Diesel fuel conforms to European standard EN 590. The biodiesel employed in the experiments was a fatty acid methyl ester produced by 40% rapeseed oil, 30% soybean oil, and 30% recycled cooking oils. It was supplied by ELIN Biofuels SA (Volos Greece) and conforms to EN14214-2012 [35]. The main specifications of the fuels are summarized in Table6[36,37].

Table 6. Comparison of the main fuel properties, between biodiesel and diesel fuel.

Specifications/Ranges Biodiesel (FAME) Diesel 3 Density (15 ◦C) [kg/m ] 865 825 Viscosity (40 ◦C) [cSt] 4.7 2.5 Cetane number 55 50 Cold filter plugging point [ C] 3 12 ◦ − − Gross heating value [MJ/kg] (measured) 40.3 46.1 Lower heating value [MJ/kg] (calculated) 37.7 43.3 Water content [mg/kg] 330 - Acid number [mg KOH/g] 0.16 - Sulfur content [ppm] - 50 Iodine number g iodine/100 g 117 - Energies 2019, 12, 1953 8 of 21

High-percentage biodiesel blend, B70, was employed in the engine tests with the PSA DW10 ATED HDi (common-rail, high-pressure injection) engine. On the other hand, medium- and low-percentage biodiesel blends, B20 and B50, were employed in the engine tests with the Ruggerini RF91 DI diesel engine (low-pressure injection).

2.4. Period of Operation with Biodiesel Fuels Both engines are regularly employed in student laboratory exercises, and also for research and development projects of the Lab. In the case of DW10, the engine was subjected to steady-state and transient testing with the B70 fuel for a total of 100 h in the period 2008–2010 (Table7)[ 36,37]. The testing time was uniformly distributed among the operation points listed in Table8. This prolonged use led to the failure of the high-pressure pump and the wear of the injector’s moving parts. After replacing with a new fuel pump and injector, the engine was regularly employed in student lab exercises with regular diesel fuel (EN590 specifications, which contains about 7% biodiesel in Greece). The lab exercises comprise short-term engine tests (typical steady-state operation points) with normal fuel, not significantly adding to engine parts deterioration. The engine was run again on-low percentage biodiesel blend (B20) for a further 50 h in 2016, in the frame of diesel filter loading and regeneration tests. After a six-month stand still of the engine, it failed to start again for the student lab testing exercises in March 2017. This time, the fuel pump was dismantled and the components were inspected for deposits, wear, and surface texture. Photographs of the components were taken in order to confirm the effect of biodiesel fuel. The results are presented in this section.

Table 7. Use of the two engines in tests and experiments in the period 2008–2017.

DW10 DW10 RF91 RF91 Engine Year Engine Duration Engine Duration Duration Engine Duration Tests Tests Tests Tests Engine Laboratory Laboratory 2008–2009 cycles w. 55 h exercises 5 h - - exercises 2 h B70 vs B0 (students) (students) Engine Laboratory Laboratory 2009–2010 cycles w. 35 h exercises 5 h - - exercises 2 h B70 (students) (students) Laboratory Laboratory 2010–2011 -- exercises 2 h - - exercises 2 h (students) (students) Laboratory Diesel Laboratory 2011–2012 -- exercises 2 h Particulate filter 50 h exercises 2 h (students) loading B20–50 (students) Laboratory Diesel Laboratory 2012–2013 -- exercises 2 h Particulate filter 50 h exercises 2 h (students) loading B20–50 (students) Laboratory Laboratory 2013–2014 -- exercises 2 h - - exercises 2 h (students) (students) Laboratory Laboratory 2014–2015 -- exercises 2 h - - exercises 2 h (students) (students) Diesel Laboratory Laboratory filter 2015–2016 50 h exercises 2 h - - exercises 2 h loading (students) (students) B20 Laboratory Diesel Laboratory 2016–2017 -- exercises - Particulate filter 10 h exercises 4 h (students) loading B20 (students) Energies 2019, 12, x FOR PEER REVIEW 9 of 22

loading Energies 2019, 12, 1953 B20 9 of 21

Table 8. DW10 engine operation points tested with B70 fuel (see Table 7). Table 8. DW10 engine operation points tested with B70 fuel (see Table7). Engine Speed [rpm] 900 1260 1500 1760 2020 2400 2520 2800 Engine Speed [rpm] 900 1260 1500 1760 2020 2400 2520 2800 bmep [bar] 0 0.8 6.7 2.3 9.3 11.5 4.5 13.7 bmep [bar] 0 0.8 6.7 2.3 9.3 11.5 4.5 13.7 bmep [bar] 2.3 9.3 4.5 11.5 13.7 6.7 15.1 bmep [bar] 2.3 9.3 4.5 11.5 13.7 6.7 15.1 On the other hand, RF91 was subjected to steady-state testing with B20 and B50 fuels for a total of 50On and the 50 other h, respectively, hand, RF91 in was diesel subjected filter toload steady-stateing and regeneration testing with tests, B20 and in the B50 period fuels for December a total of 502011 and to 50January h, respectively, 2013 (Table in diesel7) [38–40]. filter loadingThe diesel and particulate regeneration filter tests, loading in the was period mainly December carried 2011 out toat January3250 rpm 2013 and (Table 16.2 N-m7)[ 38 RF91–40]. engine The diesel operation particulate point. filter Regeneration loading was of the mainly diesel carried particulate out at filter 3250 rpmwas andcarried 16.2 out N-m at RF91the 3250 engine rpm operation and 22.2 point. Nm engine Regeneration operation of thepoint, diesel with particulate a total duration filter was of carriedabout 4 out h. atAfter the shut 3250 rpmoff of and the 22.2 engine Nm and engine staying operation still for point, 4 months, with a total it failed duration to start of about again. 4 h.The After mechanical shut off ofpump the engineand injector and staying were disassembled still for 4 months, in order it failed to id toentify start the again. cause The of mechanicalthe failure. After pump cleaning and injector and werereplacing disassembled of the pump in order on the to identifyengine, thethe causeengine of was the failure.routinely After employed cleaning in and student replacing laboratory of the pumpexercises on thein engine,the period the engine 2014–2017. was routinely After being employed employed in student in laboratory10 h diesel-filter exercises loading in the period and 2014–2017.regeneration After testing being in employed summer in2017 10 h(Table diesel-filter 7), the loading engine and failed regeneration to start testingagain for in summer the student 2017 (Tablelaboratory7), the tests engine in 2018. failed Again, to start the again pump for plunge the studentr was stuck laboratory and cleaning tests in and 2018. replacing Again, thethe pumppump plungeron the engine was stuck was necessary. and cleaning and replacing the pump on the engine was necessary.

2.5. Cleaning and Optical Microscopy Procedure The cleaning procedure consisted of three phases: (i) The injectors and both of the high-pressure pumps were dismantled in accordanceaccordance with manufacturermanufacturer technical instructions, and the metal components were thoroughly cleanedcleaned using diesel fuel in order to remove dirt and gummy deposits; (ii) InIn thethe secondsecond phase,phase, thethe componentscomponents were brushedbrushed using isopropanol alcohol; (iii) In the third phase, the components were put inin anan ultrasonicultrasonic bathbath forfor 4545 min.min. Surface analysis was performed using optical microscopy [[41]41] at 1010× magnification.magnification. × 2.6. Disassembly Procedure of the Injection Systems The common-rail injector consists of two parts: injector body and nozzle body. The most easily aaffectedffected parts, besides the nozzle holes, are the injector’s moving components, like like needle, needle, plunger, plunger, and spring. An exploded view of this injector is presented in Figure4 4..

c b a

e d

f

Figure 4.4. Common-railCommon-rail injectorinjector components. components. From From right right to to left: left: (a) ( Injectora) Injector body body including including supply supply and returnand return fuel line,fuel line, (b) spring, (b) spring, (c) plunger (c) plunger and nozzleand nozzle body body including including (d) needle, (d) needle, (e) nozzle (e) nozzle house, house, and (andf) washer. (f) washer.

An exploded view of the inline pump of the RF91 engine is shown in Figure5 5.. ThereThere isis onlyonly oneone pump element (single cylinder engine) and thethe componentscomponents areare arrangedarranged inline.inline. The most critical components of the high-pressure pump are the plunger,plunger, FigureFigure5 5a,a, and and the the barrel, barrel, Figure Figure5 b.5b. The The plunger is driven by the pump and reset by the plunger spring, and the plunger stroke is constant. The plunger compresses fuel as it movesmoves upward and delivers it to the nozzle.

Energies 2019, 12, 1953 10 of 21 Energies 2019, 12, x FOR PEER REVIEW 10 of 2223

b a

Figure 5. Exploded view of New Diesel pump. ( (aa)) plunger; plunger; ( (bb)) barrel; barrel.

The disassemblydisassembly procedureprocedure of of each each pumping pumping cylinder cylinder of the of CP1Sthe CP1S pump pump consisted consisted of three of stages,three stages,as shown as shown in Figure in 6Figure. At the 6. At beginning, the beginning, the four the overhead four overhead torx screwstorx screws are removed, are removed, allowing allowing the theremoval removal of the of castthe steelcast steel pump pump valve valve head, head, as presented as presented in Figure in Figure6a,b. In 6a,b. the secondIn the second stage, as stage, shown as shownin Figure in6 c,Figure the steel 6c, valvethe steel plate, valve which plate, includes which suction includes and suction delivery and valves, delivery is removed. valves, is Finally, removed. the Finally,pumping the element pumping is removed, element is which removed, consists which of plunger, consists barrel,of plunger, and spring. barrel, and spring.

(a) head removal (b) valve plate on top

(c) valve plate removal (d) pumping element removal

Figure 6. Disassembly steps of the common-rail high-pressure pump: removal removal of of head, head, valve valve plate, plate, and pumping element.

An exploded view of the dismantled pump is pres presentedented in Figure7 7.. TheThe pumppump consistsconsists ofof threethree pumping cylinders, as described below.

Energies 2019, 12, 1953 11 of 21 Energies 2019, 12, x FOR PEER REVIEW 11 of 2322

Cylinder 3 Cylinder 1 Cylinder 2

Figure 7. Disassembly view of the Bosch CP1S high-pressure pump, showing components assessed Figure 7. Disassembly view of the Bosch CP1S high-pressure pump, showing components assessed for wear.

3. Inspection Inspection Results and Discussion In this section, the impact of high- and low-percentage biodiesel blends on the fuel system components’ durability, ofof modernmodern andand conventionalconventional dieseldiesel engines,engines, isis presented.presented. Biodiesel isis characterizedcharacterized by by poor poor oxidation oxidation stability stability that that causes causes the the fuel fuel to biodegrade to biodegrade over time.over Thistime. processThis process is amplified is amplified due to due improper to improper storage storage and handling and handling along along the retail the distributionretail distribution chain. Thechain. results The ofresults oxidation of oxidation include bacterialinclude growthbacterial in growth tanks and in pluggingtanks and of fuelplugging filters, of injectors, fuel filters, and injectors,high-pressure and high-pressure pumps [33]. pumps [33]. 3.1. Plugging 3.1. Fuel FilterFilter Plugging Plugging Following the fuel line, the first component of the injection system is the fuel filter, which consists Following the fuel line, the first component of the injection system is the fuel filter, which of the box and the filter. Figure8 illustrates fuel filter’s condition after 150 h operation with B70 blend. consists of the box and the filter. Figure 8 illustrates fuel filter’s condition after 150 h operation with It is obvious that the filter was totally plugged by sticky slurry, causing problems in the fuel flow from B70 blend. It is obvious that the filter was totally plugged by sticky slurry, causing problems in the the filter to the high-pressure pump. A significant quantity of brown dense slurry was also found at fuel flow from the filter to the high-pressure pump. A significant quantity of brown dense slurry was the bottom of the filter box. This finding is in accordance with the reported results of other researchers also found at the bottom of the filter box. This finding is in accordance with the reported results of and associations [42]. other researchers and associations [42].

Figure 8. Fuel filter holder (left) and the filter cartridge (right) of the DW10 engine after 100 h operation withFigure B70 8. andFuel 50 filter h operation holder with(left) B20and (see the Table filter7 ).cartridge (right) of the DW10 engine after 100 h operation with B70 and 50 h operation with B20 (see Table 7).

Energies 2019, 12, 1953x FOR PEER REVIEW 1212 of of 23 21 Energies 2019, 12, x FOR PEER REVIEW 12 of 22 3.2. Common-Rail Injector Wear 3.2.3.2. Common-Rail InjectorInjector WearWear The next affected component of the injection system is the injectors. The effect of biodiesel fuel on theTheThe long-term nextnext aaffectedffected durability componentcomponent of fuel of ofpumps thethe injectioninjection or injectors systemsystem is anisis the theimportant injectors.injectors. subject TheThe eeffect ffforect all ofof biodiesel biodieselbiodiesel fleet fuelfuel users,onon thethe since long-termlong-term fuel injectors durabilitydurability and ofof especially fuelfuel pumpspumps high-pre oror injectorsinjectorsssure ispumpsis anan importantimportant are costly subjectsubject parts. forforA new allall biodieselbiodiesel set of DW10 fleetfleet common-railusers,users, sincesince fuelfuel injectors injectorsinjectors is shown andand especiallyespecially in Figure high-pressure9.high-pre ssure pumpspumps areare costlycostly parts.parts. AA newnew setset ofof DW10DW10 common-railcommon-rail injectorsinjectors isis shownshown inin FigureFigure9 .9.

Figure 9. NewNew set set of common-rail injectors ( leftleft)) and injector nozzle ( right). Figure 9. New set of common-rail injectors (left) and injector nozzle (right). On the other hand, Figure 10 presents the condit conditionion of injectors after the prolonged testing with B70 fuel. On theIt It is is other obvious obvious hand, that Figure the nozzle 10 presents body andthe conditthe holes ion were of injectors totally after covered the prolonged by a dense testing slurry. with B70 fuel. It is obvious that the nozzle body and the holes were totally covered by a dense slurry.

Figure 10. Used common-rail injectors (left) and closer view of the deposits (right). Figure 10. Used common-rail injectors (left) and closer view of the deposits (right). In orderFigure to better 10. Used understand common-rail the impact injectors of (left biodiesel,) and closer each view injector of the wasdeposits analyzed (right).by means of low magnificationIn order to better optical understand microscopy. the impact Several of photos, biodiesel, magnification each injector 10 was, of theanalyzed nozzle by body, means tip of × lowthe nozzle,magnificationIn order and to the better optical nozzle understand microscopy. holes area the were Severalimpact taken. ofphotos, Figurebiodiesel, magnification 11 shows each injector heavy 10×, oily was of depositsthe analyzed nozzle on bybody, the means injector tip ofof thenozzlelow nozzle, magnification that and disturbed the nozzleoptical the flow holesmicroscopy. pattern area were of Several the taken. injected photos, Figure fuel. magnification11 Nozzleshows heavy holes 10×, wereoily of deposits the totally nozzle covered on body,the injector except tip of nozzleforthe thenozzle, that first disturbedand injector, the nozzle whereby the flow holes the pattern area holes were of remained the taken. injected Fi open.gure fuel. Based11 Nozzle shows on theseheavyholes figures,were oily depositstotally the third covered on andthe injectorexcept fourth forinjectorsnozzle the firstthat seem injector,disturbed to have whereby the serious flow the operation pattern holes ofremained problems. the inje ctedopen. fuel. Based Nozzle on these holes figures, were totally the third covered and fourthexcept injectorsfor theThe first seem next injector, stepto have was whereby serious to disassemble operationthe holes and remainedproblems. clean the open. injectors Based according on these tofigures, the offi thecial third repair and manual, fourth asinjectors shown seem in Figure to have4. The serious cleaning operation process problems. included the removal of the brownish lacquer deposit via an ultrasonic bath in an aggressive detergent, at temperature of 60 ◦C. After the cleaning procedure, the surfaces of each part were carefully investigated for wear by means of the optical microscope. Figure 12 presents photos of the clean nozzle plungers. It was obvious that the prolonged operation with biodiesel led to further corrosion of the plungers, as indicated by the red circles.

Energies 2019, 12, x FOR PEER REVIEW 13 of 23

Energies 2019, 12, 1953 13 of 21 Energies 2019, 12, x FOR PEER REVIEW 13 of 22

Figure 11. Common-rail injectors magnified view (10×) after 100 h operation with B70 fuel.

The next step was to disassemble and clean the injectors according to the official repair manual, as shown in Figure 4. The cleaning process included the removal of the brownish lacquer deposit via an ultrasonic bath in an aggressive detergent, at temperature of 60 °C. After the cleaning procedure, the surfaces of each part were carefully investigated for wear by means of the optical microscope. Figure 12 presents photos of the clean nozzle plungers. It was obvious that the prolonged operation with biodieselFigure led 11. toCommon-rail further corrosion injectors of magnifiedmagnified the plungers, view (10(10×)as indicated) after 100 byh operation the red circles.with B70 fuel. × The next step was to disassemble and clean the injectors according to the official repair manual, as shown in Figure 4. The cleaning process included the removal of the brownish lacquer deposit via an ultrasonic bath in an aggressive detergent, at temperature of 60 °C. After the cleaning procedure, the surfaces of each part were carefully investigated for wear by means of the optical microscope. Figure 12 presents photos of the clean nozzle plungers. It was obvious that the prolonged operation with biodiesel led to further corrosion of the plungers, as indicated by the red circles.

Figure 12.12. MagnifiedMagnified view (10(10×)) of the injector plungers. × Even though biodiesel provides better lubricity than diesel, corrosive wear and friction increase due to absorbing moisture. Biodiesel Biodiesel is is more more hygroscopic than than diesel diesel fuel fuel and it attracts moisture, causing hydrolysis and the formationformation ofof organicorganic acidsacids andand bacteria.bacteria.

3.3. Standard Mechanical Injector Wear 3.3. Standard Mechanical Injector Wear Taking into account the previous findings, the same procedure was applied to the RF91 mechanical Figure 12. Magnified view (10×) of the injector plungers. injector. Figure 13 presents a comparative view of the injector after 100 h operation with biodiesel blends.Even The though nozzle biodiesel holes area provides and the better nozzle lubricity body were than covered diesel, corrosive by oily deposits wear and and friction white additiveincrease ash,due influencingto absorbing injection moisture. and Biodiesel combustion is more efficiency. hygroscopic than diesel fuel and it attracts moisture, causing hydrolysis and the formation of organic acids and bacteria.

3.3. Standard Mechanical Injector Wear

Energies 2019, 12, x FOR PEER REVIEW 14 of 2322

Taking into account the previous findings, the same procedure was applied to the RF91 mechanical injector. Figure 13 presents a comparative view of the injector after 100 h operation with Energiesbiodiesel2019 blends., 12, 1953 The nozzle holes area and the nozzle body were covered by oily deposits and 14white of 21 additive ash, influencing injection and combustion efficiency.

(a) (b) (a) (b) Figure 13. RF91 nozzle tip magnified (a) after 100 h operation with B20 and B50, including 50 ppm Figurecerium-doped 13. RF91 fuel nozzle additive; tip magnifiedmagnified and (b) after (a) afterultrasonic 100 h cleaning. operationoperation with B20 and B50, including 50 ppm cerium-doped fuel additive; and (b)) afterafter ultrasonicultrasonic cleaning.cleaning. 3.4. Common-Rail High-pressure Pump Disassembly 3.4. Common-Rail High-pressure High-pressure Pump Pump Disassembly Disassembly As reported above, the critical failure was that of the high-pressure pump. A summary of the diagnosisAs reported procedure above, is presented the critical below. failure As was reported thatthat ofof in thethe [43], high-pressurehigh-pressure in October 2010, pump.pump. after A repeated summary failures of the diagnosisto start, a procedureprocedurethorough isinspectionis presentedpresented of below. below.the fuel As As lines reported reported and ininjection in [43 [43],], in in Octobersystem October was 2010, 2010, carried after after repeated out. repeated The failures findings failures to start,towere start, apresented thorough a thorough above. inspection inspection Starting of the offrom fuelthe the fuel lines fuel lines and filter, and injection a significantinjection system system quantity was carriedwas of carried dense out. slurryTheout. findingsThe rich findings in werefatty presentedwereesters presented was above. observed. above. Starting After Starting from cleaning thefrom fuel thethe filter, fuelfuel afilter,filter significant ,a thesignificant fuel quantity injectors quantity of densewere of dense slurryremoved. slurry rich The in rich fatty injector’s in esters fatty wasestersnozzle observed. was and observed.holes After were cleaning After found cleaning covered the fuel filter,theby heavy,fuel the filter fuel oily, injectors carbonthe fuel deposits. were injectors removed. Proceeding were Theremoved. injector’s with disassemblingThe nozzle injector’s and holesnozzlethe set were andof injectors, foundholes were covered a certainfound by covered heavy,quantity oily by of heavy, carbonthe same oi deposits.ly oilycarbon deposit Proceeding deposits. was Proceedingfound with disassemblingin the with needle disassembling tip. the setAfter of injectors,theinstalling set of a ainjectors, certain new set quantity a of certain fuel of injectors, thequantity same oilytheof the engine deposit same still was oily could found deposit not in thewas start needle found and tip. thein After theindication needle installing tip.from aAfter newthe setinstallingETAS-INCA of fuel injectors,a new [44] setinterface the of engine fuel was injectors, still zero could rail the not pressure. engine start and stillInspection the could indication notcontinued start from and the with ETAS-INCA the the indication high-pressure [44 ]from interface fuelthe wasETAS-INCAlines zero and railthe [44] pressure.common-rail interface Inspection was without zero continued railany pressure.important with Inspection the findings. high-pressure continuedFinally, fuel the with lineshigh-pressure the and high-pressure the common-rail fuel pump fuel withoutlineswas examinedand any the important common-rail and it findings.was withoutfound Finally, that any theall important fuel high-pressure was fidivertedndings. fuel Finally, pumpto the was returnthe examined high-pressure line. Dismantled and it fuel was pump founddirty thatwascomponents allexamined fuel was of and divertedCP1S it pumpwas to thefound are return presented that line. all Dismantled fuelin Figu wasres diverted dirty14–17. components Examinationto the return of CP1S ofline. the pump Dismantledfuel are pump presented partsdirty incomponentsrevealed Figures a 14 thin –of17 .brownishCP1S Examination pump lacquer are of thepresented coating fuel pump on in the Figures parts barrel revealed 14 and–17. the aExamination thin internal brownish cavities of lacquerthe of fuel the coating pumpvalve on head.parts the barrelrevealedThe lacquer and a thethin was internal brownish hard, cavities dry, lacquer and of could the coating valve be removed head.on the The barrel by lacquer way and of wasthe an internalhard, ultrasonic dry, cavities and bath. could ofIn theaddition, be removedvalve head.there by wayThewere lacquer of sticky an ultrasonic darkwas brownhard, bath. dry, and In andblack addition, could particles therebe removed on were the sticky barrel, by way dark spring, of brown an and ultrasonic and valve black chamber, bath. particles In asaddition, onindicated the barrel, there by spring,werethe red sticky andcircles valvedark in Figuresbrown chamber, and 14 asand black indicated 16, particles respectively. by theon the red barrel, circles spring, in Figures and 14 valve and 16chamber,, respectively. as indicated by the red circles in Figures 14 and 16, respectively.

Figure 14. Pumping elements of the CP1S pump cylinders (barrel, plunger, spring). Two out of the three elements were stuck in the Top Dead Center position (end of delivery stroke). Energies 2019, 12, x FOR PEER REVIEW 15 of 23

Energies 2019, 12, x FOR PEER REVIEW 15 of 22

Energies 2019Figure, 12 ,14. 1953 Pumping elements of the CP1S pump cylinders (barrel, plunger, spring). Two out of the 15 of 21 Figurethree elements 14. Pumping were elements stuck in ofthe the Top CP1S Dead pump Center cylinders position (barrel, (end plunger,of delivery spri stroke).ng). Two out of the three elements were stuck in the Top Dead Center position (end of delivery stroke).

FigureFigureFigure 15. 15. TopTop Top view viewview of of ofpumping pumpingpumping elements elements covered covered covered by gummy by by gummy gummy deposits. deposits. deposits.

Energies 2019, 12,Figure x FOR 16.PEER Affected REVIEW valve heads. Black sticky particles were observed in two of them. 16 of 23 FigureFigure 16. 16.A Affectedffected valve valve heads.heads. Black sticky particles particles were were observed observed in in two two of ofthem. them.

(a()a ) (b(b) ) Figure 17. High-pressure delivery tube (a) and delivery valve (b) of the third cylinder, which were Figure 17. High-pressure delivery delivery tube tube ( (aa)) and and delivery delivery valve valve ( (bb)) of of the the third third cylinder, cylinder, which were totally covered by sticky deposits. totallytotally covered by sticky deposits. It should be noted that in this type of pump (CP1S) the plunger is not subjected to a purely axial It should should be noted noted that that in in this this type type of of pump pump (CP1S) (CP1S) the the plunger plunger is is not not subjected subjected to to a a purely purely axial axial load. Thus, a certain degree of surface wear may be present, which is enhanced by the presence of load. Thus, a certain degree of surface wear may be present, which is enhanced by the presence of load.biofuel, Thus, as a showncertain in degree Figure of 18. surface The most wear import may antbe present,parameter which when is one enhanced deals with by thefuel-injection presence of biofuel, as shown in Figure 18. The most important parameter when one deals with fuel-injection biofuel,system as parts shown is the in Figuresurface 18.roughness The most of theimport high-pantressure parameter mating when components. one deals Itwith is important fuel-injection to systeminvestigate parts ifis any the deterioration surface roughness is present. of thethe The high-pressurehigh-p surfaceressure areas mating matingpositioned components.components. close to the It It bottomis important of the to investigateinvestigatepump plungers ifif anyany deterioration anddeterioration to the top is ofis present. barrelspresent. were The The surface examined surface areas areaswith positioned optical positioned microscopy. close close to the to bottom the bottom of the of pump the pumpplungers plungers and to and the topto the of barrelstop of barrels were examined were examined with optical with optical microscopy. microscopy.

Figure 18. Magnified view (10×) of the clean pump plungers.

It can be clearly seen that first plunger (to the left) was found in the worst condition. Only the third one (Figure 18, right) shows the characteristic bright appearance of the chromium plating (20 μm). Furthermore, the wear on barrels was localized in the fuel flow line and appeared in the form of brown imprints that should be attributed to the corrosive behavior of biodiesel, as presented in Figure 19.

Energies 2019, 12, 1953 16 of 21 Energies 2019, 12, x FOR PEER REVIEW 16 of 22

FigureFigure 18. 18.Magnified Magnified view (10×) (10 ) of of the the clean clean pump pump plungers. plungers. × ItIt can can be be clearly clearly seen seen that that first first plungerplunger (to(to the left) was was found found in in the the worst worst condition. condition. Only Only the the thirdthird one one (Figure (Figure 18 ,18, right) right) shows shows the the characteristic characteristic bright bright appearance appearance of of the the chromium chromium plating plating (20 (20µm). Furthermore,μm). Furthermore, the wear the on wear barrels on barrels was localized was localized in the fuelin the flow fuel line flow and line appeared and appeared in the formin the of form brown of brown imprints that should be attributed to the corrosive behavior of biodiesel, as presented in imprintsEnergies 2019 that, 12 should, x FOR PEER be attributed REVIEW to the corrosive behavior of biodiesel, as presented in Figure17 of 1923. Figure 19.

Figure 19. Magnified top view (10×) of the clean pump barrels. FigureFigure 19. 19.Magnified Magnified toptop view (10×) (10 ) of of the the clean clean pump pump barrels. barrels. × As shown in Figure 19, the first pump barrel was, again, in the worst condition in regards to AsAs shown shown in in Figure Figure 19 19,, thethe firstfirst pumppump barrel was, again, again, in in the the worst worst condition condition in inregards regards to to surface corrosion, and the third one was in the best condition. surfacesurface corrosion, corrosion, and and the the third third one onewas was inin thethe bestbest condition.

3.5.3.5. Gasket O-Rings O-Rings O-Rings and and and Seal Seal Seal ConditionCondition Condition After careful inspection of the pump head gaskets, delivery ports gaskets, teflon washers, AfterAfter careful careful inspection inspection of theof pumpthe pump head head gaskets, gask deliveryets, delivery ports gaskets,ports gaskets, teflon washers,teflon washers, camshaft camshaft housing, O-rings, and the drive shaft seal, it was concluded that no significant wear from housing,camshaft O-rings, housing, and O-rings, the drive and shaft the drive seal, itshaft was seal, concluded it was concluded that no significant that no significant wear from wear oxidation from or oxidation or swelling were present, and no visible leaks were observed (Figure 20a,b). swellingoxidation were or swelling present, andwere no present, visible and leaks no werevisible observed leaks were (Figure observed 20a,b). (Figure 20a,b). Gaskets and O-rings are made by Nitrile and Fluorocarbon elastomer compounds, which are compatibleGaskets andwith O-rings biodiesel. are Taking made byinto Nitrile account and the Fluorocarbon seal manufacturer’s elastomer technical compounds, notes which[45], it are compatiblecompatible with with biodiesel. biodiesel. Taking Taking into into account account the sealthe manufacturer’sseal manufacturer’s technical technical notes notes [45], it[45], becomes it becomes obvious that their sealing compound is fluorocarbon. The drive shaft seal type is indicated obvious that their sealing compound is fluorocarbon. The drive shaft seal type is indicated with with red boxes. According to the specialized literature [19,46], these compounds would be expected red boxes. According to the specialized literature [19,46], these compounds would be expected to to deteriorate after prolonged use and/or high-percentage biodiesel blends. However, in our case, no deteriorate after prolonged use and/or high-percentage biodiesel blends. However, in our case, no significant deterioration or swelling was observed, which is expected due to the limited hours of significant deterioration or swelling was observed, which is expected due to the limited hours of testing. Thus, the main damage to the pump remains the sticking of two out of the three unit-pump testing.plungers Thus, on their the main barrels, damage close to to their the pump TDC positions, remains theand stickingthe additional of two sticking out of theof the three suction unit-pump and plungersdelivery on valves their for barrels, all three close pump to their units. TDC positions, and the additional sticking of the suction and deliveryBased valves on forthe allabove three findings, pump units. which agree with experience from other researchers [27,47,48], it wouldBased not on be thewise above to exploit findings, the full which range agree of biod withiesel experience blending with from these other types researchers of engines [27 until,47 ,the48], it wouldrequired not befuel wise system to exploit modifications the full are range decided of biodiesel by the manufacturers. blending with A these maximum types of blending engines of until 20% the requiredon average fuel systemwould be modifications a more conservative are decided approach. by the manufacturers. A maximum blending of 20% on average would be a more conservative approach.

(a) (b)

Energies 2019, 12, 1953 17 of 21

Energies 2019, 12, x FOR PEER REVIEW 18 of 23

Energies 2019, 12, x FOR PEER REVIEW 18 of 23

(a) (b)

((cc))

FigureFigureFigure 20.20. Elastomer Elastomer20. Elastomer partsparts parts ofof of CP1SCP1S CP1S pumppump pump (gaskets, (gaskets,(gaskets, O-rings, O-rings, washers, washers,washers, and andand seal). seal).seal). (a) pump ((a)a) pumppump gaskets gasketsgaskets and andand o-rings;o-rings;o-rings; ( b(b)) pump pump(b) pump drive drive drive shaft shaft shaft seal; seal; seal; ( c( )c(c) materials) materials materials employed employedemployed in in diesel in diesel diesel fuel fuel pumpfuel pump pump shaft shaft sealsshaft seals [ 44seals [44].]. [44].

3.6.3.6. StandardStandard3.6. Standard Pump-In-Line Pump-In-Line Pump-In-Line Disassembly Disassembly Disassembly The design and principle of the operation of the pump-in-line system employed in the RF91 TheThe designdesign and and principle principle of of the the operation operation of the of pump-in-linethe pump-in-line system system employed employed in the in RF91 the single RF91 single cylinder engine is shown in Figure 21. cylindersingle cylinder engine engine is shown is shown in Figure in 21Figure. 21.

FigureFigure 21.21. DesignDesign andand functionalfunctional principleprinciple ofof thethe inlineinline pumppump injectioninjection system.system.

Analogous findings with the previous case were observed in the unit pump of the single cylinder engine. The pump plunger was stuck at the top dead center position (see Figure 22, view from the top, and Figure 23, right, after the dismantling of the plunger). Deposits were found also on the inside of the pump housing (Figure 23). Signs of wear were also visible on the pump cylinder (Figure 24) and the plunger’s surface (Figure 25).

Energies 2019, 12, 1953 18 of 21

Analogous findings with the previous case were observed in the unit pump of the single cylinder engine. The pump plunger was stuck at the top dead center position (see Figure 22, view from the top, and Figure 23, right, after the dismantling of the plunger). Deposits were found also on the inside of the pump housing (Figure 23). Signs of wear were also visible on the pump cylinder (Figure 24) and the plunger’s surface (Figure 25). As reported above, the surface quality of precision assemblies in the injection pump has a large impact on the proper operation of the engine. Both the plunger and the barrel of the pumping section are adjusted, so that the gap between the side surface of the plunger and the inner surface of the barrel is approximately 2–5 µm. This clearance provides sufficient lubrication of the side surfaces of the plungerEnergies and 2019 barrel,, 12, x FOR while PEER stillREVIEW providing enough sealing to maintain the high-pressure of18 fuel.of 22 The penetration of slurry deposits between the surface of the plunger and the barrel can cause the sticking of the pumpingAnalogous elements, findings as waswith the the case previous with thecase reported were observed findings. in The the stickingunit pump of pumping of the single elements cylinder engine. The pump plunger was stuck at the top dead center position (see Figure 22, view was repeatedly observed after operation with high-percentage biodiesel blends and the shutdown of from the top, and Figure 23, right, after the dismantling of the plunger). Deposits were found also on the enginesEnergies 2019 for, 12 a, periodx FOR PEER of twoREVIEW months or more. Moreover, this damage happened in two19 fuel of 23 pumps the inside of the pump housing (Figure 23). Signs of wear were also visible on the pump cylinder of diff(Figureerent technologies24) and the plunger’s and injection surface pressures.(Figure 25).

Energies 2019, 12, x FOR PEER REVIEW 19 of 23

Figure 22. Closer view of the New Diesel pump’s stuck plunger.

FigureFigureFigure 22. 22.Closer 22. Closer Closer view view view ofof of the the New Diesel Diesel Diesel pump’s pump’s pump’s stuck stuck stuckplunger. plunger. plunger.

FigureFigureFigure 23. 23.Inside 23.Inside Inside view view view of of of thethe the pumppump pump housinhousin housing.g.g. Gummy Gummy Gummy deposits deposits deposits are arepresent. arepresent. present. Figure 23. Inside view of the pump housing. Gummy deposits are present.

Figure 24. Details of wear on the pump cylinder.

FigureFigure 24. 24.Details Details of wear wear on on the the pump pump cylinder. cylinder. Figure 24. Details of wear on the pump cylinder.

Energies 2019, 12, 1953 19 of 21 Energies 2019, 12, x FOR PEER REVIEW 19 of 22

FigureFigure 25. 25. DetailsDetails of of wear wear on on the the plunger. plunger.

4. ConclusionsAs reported above, the surface quality of precision assemblies in the injection pump has a large impact on the proper operation of the engine. Both the plunger and the barrel of the pumping This paper summarizes experience on the deterioration of diesel-injection equipment parts from section are adjusted, so that the gap between the side surface of the plunger and the inner surface of the usethe ofbarrel fuel is blends approximately with high-percentages 2–5 μm. This clearance of biodiesel provides (up sufficient to 70%) lubrication on a common-rail, of the side high-pressure surfaces injectionof the diesel plunger engine and barrel, and a while single still cylinder providing diesel enough engine. sealing to maintain the high-pressure of fuel. TheIn regards penetration to theof slurry high-pressure deposits between fuel pump the su ofrface the of common-rail the plunger and engine, the barrel it was can found cause the that the mainsticking mode ofof failurethe pumping was sticking elements, of as the was pump the pistonscase with near the theirreported TDC findings. positions, The due sticking to oxidation of of theirpumping sleeves elements at this was position. repeatedly The observed same mode after of operation failure waswith foundhigh-percentage with the biodiesel inline fuel blends pump of the singleand the cylinder shutdown engine. of the This engines type for of failurea period is of not two fatal months for the or pumpmore. Moreover, and can be this repaired damage by the disassemblyhappened and in two cleaning fuel pumps of the of pump.different However, technologies successive and injection repairs pressures. lead to increased wear on the plunger-cylinder surfaces, and oxidation proceeds with prolonged use of high-percentage biodiesel 4. Conclusions blends. The condition of the various gaskets and O-rings in the high-pressure pump of the common-rail system wasThis found paper to summarizes be normal withoutexperience any on signs the ofdeteri deterioration.oration of diesel-injection This should be equipment expected parts due to the from the use of fuel blends with high-percentages of biodiesel (up to 70%) on a common-rail, short operation time with biodiesel blends. However, this relatively short operating time, of the order high-pressure injection diesel engine and a single cylinder diesel engine. of 100 h, was sufficient to cause damage to the pumps. In regards to the high-pressure fuel pump of the common-rail engine, it was found that the mainAs a mode general of failure remark, was the sticking use of of biodiesel the pump blends pistons higher near their than TDC B20 positions, must be combineddue to oxidation with of engine- and fuel-injectiontheir sleeves at systemthis position. protection The same measures mode andof failure these was engines found should with the not inline stay fuel shut pump down of forthe more thansingle one month cylinder in suchengine. cases, This in type order of tofailure avoid is stickingnot fatal of for the the fuel pump pump and plungers. can be repaired The most by probablethe reasondisassembly that such and instances cleaning are of notthe reportedpump. However, in the specialized successive repairs literature lead is to that increased the durability wear on the tests are acceleratedplunger-cylinder tests, which surfaces, do not and normally oxidation include proceeds large with periods prolonged of intermediateuse of high-percentage engine shut biodiesel down. blends. The condition of the various gaskets and O-rings in the high-pressure pump of the Authorcommon-rail Contributions: systemConceptualization, was found to be A.M.S.; normal Methodology, without any A.M.S.; signs D.N.T.;of deterioration. Investigation, This D.N.T.; should Resources, be A.M.S.;expected D.N.T.; due Writing—Original to the short operat Draftion Preparation, time with D.N.T.; biodiesel Writing—Review blends. However, & Editing, this relatively A.M.S.; Visualization, short D.N.T.; Supervision, A.M.S.; Project Administration, D.N.T. operating time, of the order of 100 h, was sufficient to cause damage to the pumps. Funding: AsThis a researchgeneral receivedremark, nothe external use of funding.biodiesel blends higher than B20 must be combined with Acknowledgments:engine- and fuel-injectionThe authors system would protection like to thankmeasur theires and former these Mechanicalengines should Engineering not stay shut students down Nikos Sakalidisfor more and Manosthan one Papadopetrakis month in such for cases, their in assistance order toin avoid the tests sticking and disassemblyof the fuel pump of the plungers. RF91 engine, The in the framemost of their probable Diploma reason Thesis that in thesuch Laboratory instances of are Thermodynamics not reported in and the Thermalspecialized Engines, literature University is that of the Thessaly. Additionally,durability special tests thanksare accelerated are due to te personnelsts, which from do not the companynormally Sielmaninclude SA,large Volos periods Greece, of intermediate for their assistance with the disassembly and photographing of the Bosch CP1S common-rail fuel pump. engine shut down. Conflicts of Interest: The authors declare no conflict of interest. Author Contributions: Conceptualization, A.S.; Methodology, A.S.; D.T.; Investigation, D.T.; Resources, A.S.; D.T.; Writing—Original Draft Preparation, D.T.; Writing—Review & Editing, A.S.; Visualization, D.T.; ReferencesSupervision, A.S.; Project Administration, D.T.

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