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 injectors and fuel pump. 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 engine and a conventional DI engine. Both engines 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 injector nozzle, pump pistons, 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 pumps parts were examined and compared by performing normal photography and low magnification microscopy. Additionally, the various elastomer parts of the high-pressure fuel pump 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: diesel engine; fuel injection; 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 gaskets,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