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Many incidents associated with filter plugging have extensively been reported in microbially contaminated diesel and biodiesel fuel systems, especially under long term storage conditions. In this study a quantitative assessment of the undesirable insoluble solids produced in contaminated biodiesel fuels was carried out in order to evaluate their evolution rate during biodeterioration. For this purpose, a series of contaminated biodiesel fuel microcosms were prepared and stored for six months under stable conditions. The quantity of the particulate contaminants was monitored during storage by a multiple filtration technique which was followed at the end by a comparison with the active bioburden per ATP bioluminescence protocol. Additionally, identical microcosms were treated with a commercially available biocide in order to examine the latter’s activity both on solids formation and the microbial proliferation.

Additives that enhance properties, such as cetane number or cold flow, are introduced in diesel-biodiesel blends in order to upgrade its performance as well as to aid its handling and distribution. Furthermore, in order to protect the engine and fuel operating system equipment, diesel fuel may be treated with corrosion inhibitors and detergents. However, additives could also have an impact on other parameters beyond those that they are intended to boost. In the present study the effect of diesel fuel improvers on fuel’s microbial stability is examined. An additive-free ultra low sulfur diesel (ULSD) was blended with Soybean Fatty Acid Methyl Esters (FAME) and the resulting blend was treated separately with a series of commercially available diesel fuel additives.

FAME is the most common renewable component of conventional automotive diesel. Despite the advantages, biodiesel is more susceptible to oxidative deterioration and due to its chemical composition as well as its higher affinity to water, is considered to be a favorable substrate for microorganisms. On the other hand, apart from biodiesel, alcohols are considered to be promising substitutes to conventional diesel fuel because they can offer higher oxygen concentration leading to better combustion characteristics and lower exhaust emissions. More specifically, n-butanol is a renewable alcohol demonstrating better blending capabilities and properties when it is added to diesel fuel, as its composition is closer to conventional fuel, when compared ethanol to for example. Taking into consideration the alleged disinfectant properties of alcohols, it would be interesting to examine also the microbial stability of blends containing n-butanol in various concentrations.

The aim of this study was to investigate the effect of a variety of phenolic type antioxidant additives on the microbial stability of biodiesel and diesel/biodiesel blends. Six synthetic phenolic type antioxidant agents were added in FAME at concentrations up to 1000 ppm. Treated FAME was also blended with Ultra Low Sulfur Diesel (ULSD) fuel at a concentration of 7% v/v in order to examine the activity of the substances in the final blends. The oxidation stability in the presence of the phenolic compounds was determined by carrying out measurements under accelerated oxidation process in the Rancimat unit. The effectiveness of those antioxidant agents against microbial contamination in biodiesel fuel was studied under certain testing protocols for detecting microbiological activity in the fuel supply chain and for evaluating antimicrobials against fuel bio-deterioration.

The fuel supply chain faces challenges associated with microbial contamination symptoms. Microbial growth is an issue usually known to be associated with middle distillate fuels and biodiesel, however, incidents where microbial populations have been isolated from unleaded gasoline storage tanks have also been recently reported. Alcohols are employed as gasoline components and the use of these oxygenates is rising, especially ethanol, which can be a renewable alternative to gasoline, as well. Despite their alleged disinfectant properties, a number of field observations suggests that biodeterioration could be a potential issue in fuel systems handling ethanol-blended gasoline. For this reason, in this study, the effect of alcohols on microbial proliferation in unleaded gasoline fuel was assessed. Ethanol (EtOH), iso-propyl alcohol (IPA) and tert-butyl-alcohol (TBA) were evaluated as examples of alcohols utilized in gasoline as oxygenates.

For many years Rancimat was the only standardized method for measuring the oxidation stability of FAME and FAME/diesel blends. However this method is not applicable to pure conventional petroleum products and so the effect of FAME on diesel fuel stability could not be evaluated directly. Recently a Rapid Small Scale Oxidation Test (RSSOT) that covers the determination of the stability of biofuels and petroleum products was developed and standardized. In this study the oxidation stability of seven different types of FAMEs was assessed, either neat or blended with three types of ULSD fuel, by employing both the Rancimat and the RSSOT accelerated oxidation methods. The determinations from either test were analyzed and a comparative assessment of these two method was carried out.

According to the existing maritime regulation, the marine diesel equipment will be necessary to operate with low sulfur marine fuels. Low Sulfur Middle Gas Oils (MGOs) often have a viscosity that is lower than that of Heavy Fuel Oil (HFO). The problems in diesel engines are mainly related to high pressure fuel pumps that depend on the fuel oil for their lubrication. A solution to that problem probably will be the addition of Fatty Acid Methyl Esters (FAME) as an additive to the fuel. On the other hand, for the purposes of International Standard ISO 8217:2012 in the case of distillate fuels it is recommended that “de minimis” level of FAME is recommended. “De minimis” level is determined approximately as the 0.1% volume of the fuel. In this study, Distillate Marine Diesel Oil with good lubricity performance was used blended with FAME fuel, according to national and European Standard (ELOT EN 14214), was used as an additive.

The lubricating efficiency is an important property of diesel fuel since several diesel engine parts, such as pumps and injectors, are lubricated by the fuel itself only. The evolution of oxidation products during oxidative deterioration may as well affect the lubricating properties of the biodiesel fuel blends and thus the proper functioning of a diesel engine. In this study Fatty Acid Methyl Esters were produced from various types of feedstock that significantly differentiate in their fatty acid profile. Each methyl ester was blended with an Ultra Low Sulphur Automotive Diesel (ULSD) at a concentration of 7% v/v which is currently the maximum acceptable FAME content according to the European Standard EN590. The B7 biodiesel blends were evaluated regarding fundamental physicochemical properties as well as their lubricating efficiency. Oxidation stability was examined on a Rancimat apparatus according to EN 15751 standard.

The diesel fuel supply chain faces new challenges associated with microbial contamination symptoms in biodiesel fuel. FAME's (Fatty Acid Methyl Esters) chemical composition along with its hygroscopic nature makes it more “biologically active” and as a result the final blends could be more prone to microbiological contamination. Survey of in-field incidents and facts in the Greek supply chain indicate that biodiesel is more prone to microbial growth. Furthermore, several experimental studies which demonstrate the susceptibility of biodiesel fuel for microbial growth have been conducted in the laboratory. The influence of FAME has been evaluated as well as the effect of microbial proliferation on the quality of the blend. Different types of biodiesel have been blended with Ultra Low Sulphur Diesel at various concentrations, and the resulting blends were mixed with bottom-water of known viable microbial colonies and stored.

This study investigates the effectiveness of seven phenolic compounds, including pyrogallol (PY), butylated hydroxytoluene (BHT), 2,5-di-tert-butylhydroquinone (DTBHQ), 4-tert-Butylcatechol (TBC), 2,5-bis(dimethylaminomethyl) hydroquinone, 2,5-bis(piperidinomethyl) hydroquinone and 2,5-bis(morpholinomethyl) hydroquinone on the oxidation stability of sunflower and soybean oil methyl esters. The seven phenolic compounds were dissolved in the base fuels at the same concentration levels, i.e., 200, 600, 800, 1000 and 1200 ppm. The oxidation stability measurements were carried out by employing a Rancimat accelerated oxidation unit according to EN 14214. Additionally, the antioxidant activity of the above mentioned compounds was also determined in a RSSOT apparatus (Rapid Small Scale Oxidation Test) according to ASTM D7545.

The ability of a catalyst to enhance the performance of synthesized biobased lubricant basestock was investigated in this study. Pomace olive oil, cottonseed oil, used frying oil and methyl oleate were utilized as starting materials for the production of the biobased lubricants and a two stages transesterification methodology was followed. Initially the oils were converted to their corresponding fatty acid methyl esters via methanolysis. The resulting methylesters were subsequently transesterified with TMP producing the desired oleochemical ester. These syntheses were carried out in the presence of either sodium methoxide or Ca/TEA alkoxide as catalysts. Following the purification phase, the synthesized esters were evaluated as potential biolubricants regarding their physicochemical properties such as viscosity index, pour point and acid value.

The aim of this study was to synthesize environmentally adapted Trimethylolpropane (TMP) esters from cottonseed and soybean oils and to examine their quality parameters and tribological properties as potential lubricant basestocks. A two stage production process was followed. At first the above mentioned vegetable oils were transformed to the corresponding methyl esters via methanolysis in the presence of sodium methoxide. The desired TMP esters were finally synthesized by alkaline transesterification of the previously produced methylesters with TMP using sodium methoxide as catalyst. Following the purification phase the physicochemical characteristics of the synthesized TMP esters were examined. The tribological properties were evaluated by employing a Four-Ball apparatus. An additive-free mineral oil base oil was used as a reference lubricating fluid.

Air pollution caused by diesel emissions, especially NOx, particulate matter, carbon monoxide and unburned hydrocarbons, has been a noteworthy matter. In Europe and the United States, legislative efforts towards improving air quality not only lead manufacturers to develop and introduce further improved emission control systems, but also the trigger demanding requirements on the oil industry towards producing advanced fuels. Therefore, much work on the effects of fuel properties on the emissions and engine performance has been performed worldwide. The fuels produced by the refineries usually comply with the existing specifications. However, alterations in the fuel properties may occur through the supply chain to the service stations due to failures of the distribution system or adulteration with lower value and taxation fuels (heating oil, marine diesel or industrial solvents).

The introduction to the European market of higher levels of biodiesel blends focuses the research interest on the compatibility problems of the diesel fuel distribution system. The influence of metals in the oxidation stability and lubricity of two different types of commercially available FAMEs (without antioxidant additive) was investigated. Zinc (Zn), Copper (Cu) and Tin (Sn), were added in the form of solid metals (heterogeneous catalysis in liquid phase oxidation) and examined for their impact on the oxidation stability of biodiesel fuel. Oxidation stability was determined by Rancimat accelerated oxidation method, according to European Standard EN14214. Additionally, in order to examine the effect of the above mentioned metals in the presence of antioxidant additive, BHT was added in both biodiesel samples and oxidation stability determinations were carried out, as well.