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Corrosion Behavior of Automotive Materials with Biodiesel: A Different Approach.

Introduction

Compatibility of different fuel carrying materials with biodiesel becomes a vital area of research. Generally, fuel comes in contact with a broad variety of metallic and non-metallic materials before delivery of fuel to engine system. Ferrous materials like cast irons, steel and non-ferrous materials like copper and aluminum alloys come in contact with fuel [1, 2]. The literature reported that biodiesel is more corrosive in nature compared to petrodiesel. Limited literature is found on the material compatibility of biodiesel [3]-20]. It is found that there are only few studies available to explore the corrosion behavior of copper and aluminum in biodiesel [6]-[15]. Copper was found more vulnerable to biodiesel compared to aluminum.

Kenneth et al. [13] described that among the fuel conveying materials, copper alloy based parts like fuel pump; bearing, bushing, etc. are mostly influenced by the fuel. A static immersion test was conducted by Geller et al. [4] for fat based biodiesel. It was reported that carbon steel and stainless steel did not undergo any weight loss during corrosion tests. Among the materials studied, copper exhibited maximum weight loss followed by brass.

Biodiesel degrades through oxidation, moisture absorption, attack by microorganisms, etc. during storage or use and thereby becoming more corrosive. This fact creates a certain amount of anxiety amongst OEMs in automotive sector to issue warranty on critical engine components. Tsuchiya et al. [17] studied the corrosion of terne sheet steel by immersion in diesel and 5% fatty acid methyl ester blended diesel fuel at 80 [degrees]C. After 500 h, it was found that pitting corrosion occurred on the surface of the sample immersed in 5% blended diesel. It was observed that corrosion took place even in 2% biodiesel. According to their study, reformation of extremely corrosive fatty acids takes place from biodiesel during the oxidation process.

A static immersion test was conducted by Kaul et al. [3] for 300 days at (15-40)[degrees]C to study corrosion on piston metal and piston liner metal by using diesel and biodiesel derived from non edible oils. It was found that higher corrosion occurred in both Salvadora and Jatropha curcas biodiesel as compared with diesel. The study showed that aluminum alloy experienced more corrosion resistance in all the biodiesel tested.

Copper and copper based alloys not only get corroded with biodiesel, but also degrade fuel properties [8]. An investigation was carried out by Haseeb et al. [11] for the corrosion behavior of copper and leaded bronze in palm biodiesel. It was reported that, copper was more vulnerable to corrosion than leaded bronze. According to their work, fresh biodiesel found less corrosive than oxidized biodiesel. Also, corrosion rate was found higher at higher temperature. Corrosive effect of biodiesel on sintered bronze filter of an oil nozzle was studied by Sgroi et al. [16]. It was found that pitting corrosion occurred on bronze when the nozzle operated at 70 [degrees]C for several hours. The corrosive character of biodiesel seems to be due to its FFA elements and impurities remaining after transesterification process. Increasing biodiesel concentration in the blend increases corrosion of metals. Norouzi et al. [15] carried out static immersion test of rapeseed methyl ester (0%, 50%, 75% and 100%) at 60 [degrees]C for 600 h. Copper was more corroded compared with aluminum [12, 15]. Elements of copper and iron found responsible for the decomposition of biodiesel [12].

The corrosive nature of biodiesel also depends on its feedstock [3, 14]. The corrosion of pure aluminum in canola based biodiesel by the electrochemical technique was studied by Diaz-Ballote et al. [5]. It was observed that the corrosion rate can be decreased by decreasing the level of impurities remaining after transesterification process. Even lower blend of biodiesel corrodes copperish metals [15]. Fazal et al. [20] described that the rate of corrosion in both diesel and biodiesel for mild steel, increases with increase in temperature. Beside this, biodiesel is hygroscopic in nature and can absorb moisture from the air and thereby can increase the water content [4]. The corrosiveness of biodiesel can be reduced by using additives [17].

Although attempts have already been made by some researchers on the corrosive nature of biodiesel from palm, rapeseed etc., but limited work is available in open literature on the corrosion behavior of biodiesel derived from the vegetable oil deodorizer distillate. Moreover, in most of the reported literature fuels were not changed periodically throughout the immersion time. However, in actual practice the flow of fuel is always regular and not stored one. This is exactly what is specified in SAE standard. By considering this, fuels were replaced with fresh fuels weekly as per recommendation specified in SAE standard. Under such conditions, the present study was aimed to study the corrosion behavior of metals exposed surface in diesel and biodiesel at 45 [+ or -] 2 [degrees]C for 2880 h as per SAE J1747 standard. Comparative corrosion rates, corrosion products and changes in properties of the fuel were investigated. Surface study was carried out by digital camera, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Though the biodiesel was found comparatively more corrosive for materials compared to diesel, but not that much corrosive as reported in the literature due to replacing of fresh fuels periodically.

Biodiesel Production

Vegetable oil deodorizer distillate:

In oil refineries, the crude vegetable oil is refined before being used for edible purposes. Refining edible oil is a process where free fatty acids are volatized, condensed and recovered simultaneously with the use of vacuum in the operation of neutralization, bleaching, deodorization and decolorization. Before deodorization process, it is essential to ensure that the oil does not contain any acid oil, bleaching agents, or soaps. So a packed column, which is the distillation column to remove Free Fatty Acids (FFA) and volatile from the oil, is used. The volatile material will be recovered as the deodorizer distillate (used as a feedstock in present study) and the oil will be recovered as Refined Bleached Deodorized (RBD) oil.

In India, non edible oils such as Jatropha, Mahua, Pongamia and Neem are used for biodiesel production. According to a recent survey conducted by authors in different states of India, it was found that the price of these commonly used non edible oil feedstocks per liter is more as compared to diesel. Jatropha, Mahua, Pongamia and Neem feedstock price per liter is 1.39 times, 1.3 times, 1.49 times and 1.67 times the diesel price respectively. Since the biodiesel production cost includes about 80% feedstock price, which results in higher cost of biodiesel. However, the deodorizer distillate feedstock price per liter is only about 0.74 times the diesel price which implies cheaper production of biodiesel. In the present study, the vegetable oil deodorizer distillate was used as a viable and cheap feedstock for biodiesel production.

Materials for Biodiesel Production

The vegetable oil refinery by-product, deodorizer distillate oil, used in the present study was obtained from a nearby medium scale vegetable oil refining industry in Maharashtra state (India). This unit processes about 365000 metric tons per annum of oil and produces about approximately 0.5%, i.e. 1825 tonnes of deodorizer distillate oil per annum as a by-product. All chemicals used in the experiments such as 99.8% methanol, potassium hydroxide and 98% sulfuric acid were of analytical reagent grade and purchased from Sterling Labcare, Surat (India).

Biodiesel Production Process

The deodorizer distillate obtained from oil refinery was preheated then it was poured into the glass reactor for esterification. The acid-catalyzed esterification reaction was conducted in a laboratory-scale experiment. The alkali-catalyzed transesterification reaction was carried out using the same experimental setup as that of acid-catalyzed esterification step. The reactants, reaction temperatures and time are followed as described in Nakpong and Wootthikanokkhan [19]. The details of biodiesel production are as follows.

Preheating The deodorizer distillate oil was preheated to 120 [degrees]C temperature in an open cauldron to remove moisture. When the temperature falls to 60 [degrees]C, it is poured into the glass reactor for esterification.

Acid-Catalyzed Esterification The acid-catalyzed esterification reaction was conducted in a laboratory-scale experiment. The apparatus used for the experiment contained flat bottom reaction flask and hot plate with magnetic stirrer. The volume of the reaction flask capacity was 21 and contained three necks, one for condenser and the others for a thermometer and an inlet for the reactants. A known amount of preheated deodorizer distillate oil was poured into the reaction flask. The 0.35 v/v of methanol was added to the preheated deodorizer distillate oil and stirred for a few minutes. The sulfuric acid (0.7% v/v of oil) was then added as a catalyst to the mixture and the reaction was carried out at 60 [degrees]C for 60 min. After this reaction, the mixture was allowed to settle for 4 h in the separating funnel and the methanol-water fraction at the top layer was removed. The lower layer comprised of deodorizer distillate oil having a lower content of FFA and impurities were purified by washing gently with hot distilled water at 55 [degrees]C until the washing water had a pH value that was similar to that of distilled water. The deodorizer distillate oil layer was then dried at 110 [degrees]C by the hot air temperature oven. Finally, the acid value of the oil produced was determined by using standard test methods.

Alkali-Catalyzed Transesterification The alkali-catalyzed transesterification reaction was carried out by using the same experimental setup of acid-catalyzed esterification step. The oil product from the pretreatment step was preheated to 60 [degrees]C temperature in the reaction flask. The methanol to oil ratio of 0.4 v/v, catalyst concentration of 1.5% w/v was used at the reaction temperature of 60 [degrees]C and reaction time of 60 min. The solution of potassium hydroxide in methanol was prepared freshly in order to avoid the moisture absorbance and maintain the catalytic activity. The methanolic solution was then added to the heated oil in the reaction flask. After the reaction, the mixture was allowed to separate into two layers by settling overnight in the separating funnel. The upper layer comprised of methyl esters, whereas the lower layer contained a mixture of glycerol and impurities. Methyl ester layer was purified by washing gently with hot distilled water at the 55 [degrees]C until the washing water had a pH value that was similar to that of distilled water. The methyl ester layer was then dried at 110 [degrees]C by the hot air temperature oven. The ester conversion and fatty acid profile in the product was determined by Gas chromatography and mass spectroscopy (GCMS). Moreover, the biodiesel properties were determined by using standard test methods.

Materials and Methods

Biodiesel produced from vegetable oil deodorizer distillate was used. For comparing the effect of biodiesel on metal surfaces, diesel is used as a reference fuel in the present study. The metal samples were placed in biodiesel as well as in diesel under similar temperature and time duration. Diesel was purchased from nearby Indian oil, fuel station. Round bars of different metals were purchased from the local market.

Biodiesel Properties

The feedstock oil had the viscosity value of 29.57 [mm.sup.2]/s. The viscosity of oil feedstock was reduced from a value of 29.57 [mm.sup.2]/s to 4.83 [mm.sup.2]/s by the two-step process. It was lower than the acceptable level of the biodiesel (B100) specification; however, it was not very close to that of petroleum diesel (3 [mm.sup.2]/s). This is because biodiesel produced from triglycerides contained chiefly of higher molecular weight methyl esters, especially methyl oleate and methyl linoleate. In addition, biodiesel consisting mainly long chain fatty acids containing 19 carbon atoms, has higher viscosity value. The fatty acid profile of biodiesel product obtained by GCMS has been shown in Table 1. The physical and chemical properties of biodiesel were determined by standard test methods and the results in comparison with those of Indian biodiesel (B100) standard were shown in Table 2.

Biodiesel Characterization

Acid Value

The acid value of the esterified biodiesel after the first step and methyl ester after the second step was determined by the acid base titration technique. A standard solution of 1 mol potassium hydroxide was used.

Chromatography and Mass Spectroscopy Method

The fatty acid profile of biodiesel product was determined by Gas chromatography and mass spectroscopy (GCMS). The GCMS study was carried out at Central Salt and Marine Chemical Research Institute (CSMCRI), Bhavnagar. Gas chromatography and mass spectroscopy method is a combination of gas chromatography (GC) which separates and identifies compounds in complex mixtures; and mass spectroscopy (MS), which determines the molecular weight anionic of component of individual compounds. In this study, the biodiesel product was analyzed by GC of SHIMATZU QP 2010 that was equipped with a flame ionization detector and a capillary column (32 m X 0.2 mm diameter). The GC oven was kept at 250 [degrees]C for 5 min. The carrier gas was helium (0.5 ml/min). The analysis was carried out by injecting 1 [micro]l sample. In this method, the methanol was used as a solvent for preparing the sample solution. The ionization mode was electron impact. The methyl ester was identified by comparing their retention time to those of a standard methyl ester of fatty acids.

Properties of Deodorizer Distillate Oil and Biodiesel

The properties of deodorizer distillate oil and biodiesel were determined by standard test methods as follows; Fatty acid profile AOAC (2000); Density ASTM D 1298; Kinematic viscosity ASTM D 445; Calorific value ASTM D 5865; Flash point ASTM D93; Cloud point ASTM D2500; Pour point ASTM D90; Cetane number ASTM D613; Acid value ASTM D664; Iodine value EN 14111; Copper strip corrosion (ASTM D130); Biodiesel Rancimet EN 14112 and Ester content EN 14103.

Biodiesel Rancimet Test (EN 14112)

Fatty acid profile of biodiesel was determined by GCMS indicated that biodiesel comprised of 80% unsaturated fatty acids. It is revealed that more the unsaturated fatty acids, poorer the oxidation stability of biodiesel. Hence in this study, the biodiesel product was analyzed by Metrohm 873 biodiesel rancimet equipment. About 3 g of biodiesel sample, dissolved in solvent is used for testing. During the measurement a stream of air is passed through the Fatty Acid Methyl Ester (FAME) sample enclosed in sealed and heated reaction vessel. This treatment results in oxidation of the FAME molecules in the sample, with peroxides initially being formed as the primary oxidation products. After some time, the FAMEs begin to decompose; the secondary oxidation products formed include low-molecular organic acids along with other volatile organic compounds. These are conveyed in the stream of air to a second vessel containing distilled water. The conductivity in this vessel is noted constantly. The organic acids can be identified by the increase in conductivity. The time passed until these secondary reaction products appear is called induction time or induction period (h).

Copper Strip Corrosion Test

A polished copper strip is immersed in a specific volume of the sample being tested and heated under conditions of temperature and time that are specific to the class of material being tested. At the end of the heating period, the copper strip is removed, washed and the color and tarnish level assessed against the ASTM Copper Strip Corrosion Standard. The copper strip corrosion test covers the detection of the corrosiveness of biodiesel on copper. This test is based on the effect of the test sample on a polished copper strip. The indicators of corrosiveness namely copper strip corrosion. The corrosive nature of biodiesel is increased with the increase in presence of impurities and water. In this study, the copper strip corrosion test for biodiesel was carried out at Materials Research Lab, Automotive Research Association of India (ARAI), Pune (India).

SAE and ASTM Standards

Standard practices from SAE and the ASTM were considered to develop the specific testing procedures. The procedure developed was a combination of SAE J1747, Recommended methods for conducting corrosion tests, and ASTM G31, Standard practice for laboratory immersion corrosion testing of metals. SAE J1747 modifies ASTM G31 to make its fuel-specific testing.

Preparation of Metal Coupons

Based on the review of numerous material compatibility studies, only the base materials used in the construction of fuel system components were tested, rather than actual components. Testing raw materials permit for much broader coverage than testing actual components. This was determined to be more practical than testing each of the components separately. Also, many industry-accepted standard tests need specimens of specific dimensions that would be complex to obtain from actual components. A sample size of 25 mm in diameter and 2 mm thickness was chosen. The raw materials for the samples were obtained in bars. The test samples were cut from the bars using a horizontal band saw machine and then milled to the final dimension to ensure uniformity and accuracy. After milling, a 2 mm hole was drilled to provide a means of suspending the sample (Refer Photo 1). X-ray fluorescence analyzer (Model X-MET 5000, Oxford Instruments Analytical, Finland make), was used to determine the composition of the alloy in selected materials. An identification number was stamped on each sample to identify the material, the state in which it is to be tested, and the fuel it is to be tested on. Finally, before testing, all samples were prepared in accordance with ASTM G31, Standard practice for preparing, cleaning, and evaluating corrosion test samples. The materials included in this study are copper, aluminum, leaded bronze, brass and stainless steel.

Immersion Apparatus

The metal samples were placed in 500 ml, glass bottles for the immersion testing (Refer Photo 2). A wide mouth design was selected to allow easy access to the test samples. Each test sample was separated by using glass beads from any adjacent test sample. Precaution was taken to avoid the contact of the samples with the walls of the glass bottles (Refer Photo 3). An explosion-proof friction air oven was used to maintain the samples at 45 [+ or -] 2 [degrees]C.

Static Immersion Test

After the samples were prepared, the weights and dimensions were measured to provide a baseline for comparison. Photographs of the color and surface texture were also taken. One bottle was used for each material. Each contained three coupons of a specific material. The diesel/biodiesel was then added to each of the bottles along with the three test samples. The unsealed bottles were placed in the oven until a temperature of 45 [+ or -] 2 [degrees]C was reached. Upon temperature stabilization, the bottles were sealed. The samples were exposed to the test fluid for a period of 2880 h. The static immersion test was carried out at 45 [+ or -] 2 [degrees]C (SAE J1747 para 4.1.5.3) for 2880 h as per SAE J1747. According to standard SAE J1747 (para 4.4.5.3), the fuel (diesel and biodiesel) was changed weekly to minimize bulk solution composition changes, oxygen depletion, and to replenish ionic contaminates. Change of fuels supports the real time condition of fuel flow from tank to engine.

Comparative Data Collections

The weights and dimensions of samples were recorded before being exposed to the diesel/biodiesel. Along with weight, images were taken of each sample to provide a reference of the original color and surface texture. The color of the solution was also noted before weekly fuel change. After a sample was removed from the test fuel, it was dried and weighed to determine any mass gains or losses. The samples were cleaned by scrubbing with a bleach-free scouring powder and a soft bristle brush. This is done to remove any corrosion that occurred. After that, the metal samples were weighed again to determine any mass losses. Metteler Toledo analytical balance with resolution of 0.1 mg was used to measure the mass of the test samples.

Comparative Mass Loss

To understand the effects of the diesel/biodiesel with respect to time, the mass loss can be changed to a corrosion rate. The corrosion rate is a prediction of the amount of the material in mils per year (mpy), that a component would lose after being exposed to the diesel/biodiesel. This can be used to project the amount of time a component made of a particular material will last before failure. The data gathered from the original dimensions and weights is used along with the data collected from weighing the samples throughout the test to calculate percent mass lost or gained. If uniform corrosion had occurred, the corrosion rate is calculated in mils per year (1 mils = 0.001 inch). The mass-loss analysis involves calculating the corrosion rate from the data gathered on each sample. This data includes the time of exposure in hours, the surface area of each sample, the density of the material, and a constant to convert units. The formula for determination of corrosion rate is given in ASTM G1 Section 8.1.

Comparative Data Analysis

Two methods of determining the effects of the biodiesel (B100) were incorporated into this study. The first was a visual examination of the samples for pitting, surface texture change and discoloration. The test fuels were examined for color change and loose by-products each week. The second was the mass loss analysis as described in ASTM G1. After that, metal surface exposed in biodiesel/diesel was studied by SEM and XRD.

Results and Discussion

The following section describes the results obtained from the corrosion study of metal surface exposed to biodiesel/diesel for 2880 h at 45 [degrees]C. The first method of determining the effects of the test fuels is through a visual examination of each sample.

Comparative Visual Inspections

An overall appearance of the exposed metal surfaces before and after 2880 h of immersion time is presented in Appendix A. Only oxide formation on some metal samples was observed as shown in Appendix A. On aluminum and stainless steel, no sign of oxide formation were observed. Copper forms a black corrosion product on the surface, this black corrosion could be an oxide layer on its surface in B100, as a consequence of higher dissolved oxygen in biodiesel. As shown in the Appendix A, only some part of the sample shows dark black layers on the surface. It was noted that the layer formed on copper surface in diesel is comparatively thinner than the copper in biodiesel. Compared to copper sample in biodiesel, copper sample in diesel showed light black corrosion product on the surface after 2880 h of immersion at 45 [degrees]C. On leaded bronze biodiesel exposed surface, brown color layers of oxide were observed. However, no extensive corrosion is generally observed for aluminum, brass and stainless steel surfaces exposed both in diesel and biodiesel. Further, an investigation was carried out for weight loss and corrosion rate of metal samples.

Comparative Corrosion Rate

Figure 1 shows the corrosion rates of all tested metals. It can be observed that the corrosion rates for copper is 0.11 mpy and 0.0393 mpy in biodiesel and diesel respectively whereas for aluminum, 0.055 mpy and 0.007 mpy in biodiesel and diesel respectively. Similarly for leaded bronze, corrosion rates of 0.089 mpy and 0.045 mpy were obtained in biodiesel and diesel, respectively. These results show that for copper, aluminum and leaded bronze, the corrosion rates are much higher in biodiesel than in diesel. This may be due to the presence of unsaturated fatty acids as shown in Table 1 (linoleate, 50.9% and oleate, 30%) in biodiesel, determined by GCMS. Moreover, biodiesel used in the present study, showed only 2.1 h induction period, determined by Rancimat apparatus. As per standard (EN 14214), biodiesel should have minimum 6 h induction period. The lower induction period indicates poor oxidation stability of biodiesel.

From the data presented in literature and the results of present study, it can be stated that biodiesel is more corrosive than diesel. The corrosive nature of biodiesel seems to be attributed to its FFA elements and impurities remaining after conversion processing. According to Kaul et al. [3] and Maru et al. [14] corrosive nature of biodiesel also depends on its feedstock. Even a lower blend of biodiesel corrodes copperish metals [12]. Table 3 shows the summary of reported results on corrosion rates for copper and aluminum in different biodiesel. It can be stated that the corrosion rate increases with an increase in temperature and storage time. Upon exposure to palm biodiesel for 2880 h and at room temperature, Fazal et al. [8] reported the corrosion rate of copper is 0.3927 mpy and for aluminum 0.1730 mpy. In present study, the static immersion test was carried out at 45 [+ or -] 2 [degrees]C (SAE J1747 para 4.1.5.3) for 2880 hours as per SAE J1747. According to standard SAE J1747 (para 4.4.5.3), the fuel (diesel and biodiesel) was changed weekly to minimize bulk solution composition changes, oxygen depletion, and to replenish ionic contaminates. The corrosion rates obtained for copper are 0.11 mpy and for aluminum 0.0393 mpy which is much less than that reported in the literature (Refer Table 3). The corrosion rates obtained for leaded bronze is 0.089 mpy and for brass is 0.0236 mpy.

Figure 2 shows the corrosion rate for Cu and Al in biodiesel (B100) in comparison with data presented in literature for similar operating conditions and duration. Present study reported less corrosion rate for materials tested. Fazal et al. [8] reported the corrosion rate for copper is 0.3927 mpy and for aluminum 0.1730 mpy when metal coupons exposed to palm biodiesel (B100) for 2880 h and at room temperature. Upon exposure to rapeseed biodiesel (B100) for 600 h and at 80 [degrees]C, Nourouzi et al. [15] reported the corrosion rate of copper is 0.92 mpy and for aluminum 0.35 mpy. According to Fazal et al. [21], with increase in storage temperature the corrosion rate increases. In another study by Hu et al. [12], upon exposure to rapeseed biodiesel (B100) for 1400 h and at 43 [degrees]C, the corrosion rate of copper is 0.918 mpy and for aluminum 0.133 mpy, which is about 9 times higher than present study. The literature results on corrosion rate are quite higher. This is mainly due to continued storage of fuels during immersion, which results in an increase in acid value and oxidation. Increase in acid value and oxidation leads to more corrosion level. However, the lower corrosion rate for metals and alloys in the present study can be attributed to the change of fuels weekly as per SAE standard.

The present study agrees with the reported results that the rate of corrosion in biodiesel is more than diesel. Here, the intention of present study is not to criticize the reported results or to support the presented results in the present article but to highlight the difference in the results obtained with the different methodology.

Comparative XRD Pattern

X-ray diffraction (XRD) study was carried out to investigate the diesel and biodiesel exposed surface after 2880 h at 45 [degrees]C. XRD peaks of metal surface exposed to diesel and biodiesel are shown in Appendix B. It was observed that the diesel exposed copper surface showed the least amount of presence of copper oxide compared to biodiesel exposed copper surface. The diesel and biodiesel exposed aluminum surface did not show any compound formed. It was noticed that the diesel exposed copper surface showed the existence of copper oxide (CuO) and a small amount of cuprous or dicopper oxide ([Cu.sub.2]O) with base metal. Copper oxide was black, brown in color and cuprous oxide was brownish red in color. Biodiesel exposed copper surface showed the presence of CuO, [Cu.sub.2]O and less amount of copper hydroxide [Cu(O[H.sub.2])]. It was seen that for copper surface exposed to biodiesel, copper oxide of red black color is the main compound appeared while on diesel exposed surface cuprite oxide of red color is appeared. Biodiesel exposed leaded bronze surface showed the presence of CuO, [Cu.sub.2]O. The diesel and biodiesel exposed brass and stainless steel surfaces did not show any compound formed. As shown in Appendix A, biodiesel exposed sample showed the more, black layer near the hanging hole and on the opposite side of the hanging hole while diesel exposed copper coupon showed red color layers on the surface. For further study of metal surface degradation, these coupons were cleaned and then scanning electron microscopy (SEM) images were taken.

Comparative Surface Characteristics

The exposed metal coupons were cleaned and SEM micrograms were taken for further study. The copper and leaded bronze in B100 showed some pits on surface than that in a diesel. However, no extensive corrosion damage or pitting was observed from aluminum, brass and stainless steel (SS) surfaces exposed to diesel and biodiesel as shown in Appendix C. The SEM images of copper surface exposed to diesel did not show any significant surface damage except the formation of the oxide layer. However, copper exposed to B100 at 45 [degrees]C showed few pits on the surface. Although these pits were very small in size and was unable to trace without microscopy, they indicated the initiation of pitting corrosion on the surface. This also indicated that at higher temperature and when exposed to stored fuels, copper may be susceptible to pitting corrosion in biodiesel. According to Blanc et al., [21] and Mankowski et al. [22] oxygen and active oxygen in B100 lead to the formation of metal oxides (CuO, [Cu.sub.2]O and CuC[O.sub.3]) layer. As biodiesel is an oxygenated fuel, pits are formed by replacing oxygen ion from cuprite oxide through the damage of copper oxide layer from exposed copper surface. The lower pitting corrosion of copper is observed in the present study. This can be attributed to the change of fuels weekly as well as lower immersion temperature. The change of fuels weekly reduces the effect of oxidation and as described earlier, at the higher temperature copper may be prone to more pitting corrosion in biodiesel. However, these results showed that the vegetable oil deodorizer distillate biodiesel seems to be less pitting corrosive to the exposed copper surface.

Hu et al. [12] described that copper is simply oxidized and chemical reaction took place on metal oxides. Conversely, aluminum is conductive to the formation of metal oxide, which prevents metal from the oxidation and indicates the lowest corrosion rate. The films of metal oxide not only prevent the oxygen from contacting with the surface of metals, but also prevent the biodiesel/diesel from contacting with the metal surface. Hence their corrosion rates are lower. Similarly, the pitting corrosion rates of exposed copper and aluminum sample are lower in diesel due to the chemical stability of diesel composed of saturated hydrocarbons.

Comparative Fuel Properties

Appendices D and E presents average acid value and the variation of kinematic viscosity for 2880 h (i.e. 17 weeks). There were five bottles for 5 different samples. The kinematic viscosity and acid value were shown in the Appendices D and E and indicated as fuel (Cu), fuel (Al), fuel (bronze), fuel (Brass) and fuel (SS). In addition, fuels (biodiesel and diesel) were stored (without metal samples) for same period i.e. 2880 h. Kinematic viscosity and acid value were measured during the same period weekly. These stored fuels (biodiesel and diesel) were not replaced or changed throughout immersion time. The kinematic viscosity and acid value of this stored fuel were shown in the last two columns (Refer Appendices D and E) indicated as 'stored fuel'.

As diesel/biodiesel was changed weekly, and bottles were refilled with fresh fuels, the observation in the color was noted. It was seen that fresh biodiesel was red-black in color while diesel was colorless. Every week, after exposure of copper and aluminum at 45 [degrees]C, no change in color was observed for diesel and biodiesel. It showed no significant compositional change in the fuel properties. Moreover, after every week, changes in acid value and kinematic viscosity of diesel and biodiesel were noted before replacement with fresh fuels. It was noticed that very little change in acid value and kinematic viscosity is observed for biodiesel and diesel exposed to copper and aluminum. However, significant increases in acid value and kinematic viscosity of biodiesel (without metal samples) were observed when stored for the same period (2880 h) at 45 [degrees]C.

According to Fazal et al. [6], little increment in kinematic viscosity and significant increment in acid value were observed for copper and aluminum exposed biodiesel for 1200 h at 80 [degrees]C. Kaul et al. [3] described that, after 300 days of immersion period acid value increases, which indicated the oxidation of biodiesel. In the present study, little changes in acid value and kinematic viscosity were observed because the exposed fuels were changed weekly. The time of metal exposure to fuels and storage temperature was less. In this duration, biodiesel could not get oxidized which results into unalteration of biodiesel colour, acid value and kinematic viscosity. On the other hand, diesel fuel is chemically stable and does not cause change in acid value, viscosity when exposed to metal and alloy samples at 45 [degrees]C.

Though the properties of fresh biodiesel (B00) meet the given standards, but many properties change from the standard once the biodiesel gets oxidized or degraded. It is also found that exposure to copper, leaded bronze and brass showed increase in acid value and kinematic viscosity (when checked weekly) of biodiesel compared to other metal exposed biodiesel. In addition, 'stored biodiesel' for 2880 h at 45 [degrees]C showed higher acid value and kinematic viscosity because of the effect of higher temperature, oxidation and biodegradation [23, 24]. Both stainless steel and aluminum have shown to be compatible with biodiesel over a storage period of 120 days since biodiesel properties such as acid value and kinematic viscosity were not affected [25, 26].

Conclusions

The present study (conducted as per SAE J1747) on corrosive characteristics of metals exposed to diesel and vegetable oil deodorizer distillate based biodiesel at 45 [degrees]C for 2880 h summarizes following conclusions:

1. As suggested by SAE standard, biodiesel/diesel was changed weekly during immersion time. However, in actual practice the flow of fuel is always regular and not stored one. Compared to literature report in which biodiesel was not changed throughout immersion without specific mention of any standard, this study shows the least amount of weight loss, corrosion rate and pits on metal surfaces exposed in biodiesel and diesel as compared to the values reported in the literature for similar operating conditions.

2. The present study agrees with the reported results that the rate of corrosion rate in biodiesel is more than diesel. Here, the intention of present study is not to criticize the reported results or to support the results presented in the current article but to highlight the difference in the obtained results with the different methodology.

3. Even though, biodiesel was changed weekly during the immersion period, it was slightly more corrosive to copper and leaded bronze compared to diesel as shown by weight loss, corrosion rate and pits on SEM images. The corrosion rate obtained for copper is 0.11 mpy and for aluminum is 0.0393 mpy which is much less than that reported in the literature.

4. Aluminum, brass and stainless steel exposed surface didn't show any significant change in the context of corrosion in diesel and biodiesel.

5. Biodiesel and diesel properties do not change much as seen by acid value and kinematic viscosity measurement. However, steep increase was observed while stored continuously (as shown in the last two columns of Appendices D and E.

6. The literature reported results on corrosion of metal surfaces exposed to biodiesel are very high as an effect of not changing the fuel periodically. This higher corrosion rate creates a certain amount of anxiety in automotive sector, researchers and biodiesel industries. The same is likely to be mitigated by this study which is conducted as per SAE standard.

Acknowledgment

The authors would like to acknowledge the financial support provided by Gujarat Council on Science and Technology under the minor research project Grant No.: GUJCOST/MRP/2014-15/393. The authors would like to thank CSMCRI, Bhavnagar and ARAI, Pune for providing certain testing facilities.

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Appendix A

An overall appearance of the exposed metal surfaces before and after 2880 h of immersion time.

Appendix B

(a-c) XRD pattern of metal surface exposed in diesel and biodiesel.

(d-g) XRD pattern of metal surface exposed in diesel and biodiesel.

(h-j) XRD pattern of metal surface exposed in diesel and biodiesel.

Appendix C

SEM photographs for the metals and alloy surface sample after exposing to diesel and biodiesel at 45 [degrees]C for 2880 h.

Appendix D

Average acid value of diesel and biodiesel during static immersion test of 2880 h measured when fuels changed weekly and acid value of stored fuels for same period.

Appendix E

Average kinematic viscosity of diesel and biodiesel during static immersion test of 2880 h, measured when fuels changed weekly and kinematic viscosity of stored fuels for same period.

Kamalesh A. Sorate and Purnanand V. Bhale, Sardar Vallabhbhai National Institute of Technology

History

Received: 18 Aug 2017

Revised: 11 Oct 2017

Accepted: 20 Oct 2017

e-Available: 07 May 2018

Keywords

Vegetable oil deodorizer

distillate, Biodiesel,

Acid value, Corrosion,

Metals, SAE J 1747

Citation

Sorate, K. and Bhale, P., "Corrosion Behavior of Automotive Materials with Biodiesel: A Different Approach," SAE Int. J. Fuels Lubr. 11(2):147-162, 2018, doi:10.4271/04-11-02-0007.
TABLE 1 Fatty acid profile of produced biodiesel determined
by GCMS.

Fatty acid  Formula                        Structure  Wt.%

Palmitate   [C.sub.17][H.sub.34][O.sub.2]  17:0       14.90
Stearate    [C.sub.19][H.sub.38][O.sub.2]  19:0        2.50
Oleate      [C.sub.19][H.sub.36][O.sub.2]  19:1       30.00
Linoleate   [C.sub.19][H.sub.34][O.sub.2]  19:2       50.93

[c] SAE International

(*) Remaining are the mono-, di-, triglycerides and FFA.

TABLE 2 Measured properties of biodiesel in the present
study compared with biodiesel (B100) standards.

                                Indian                   Results of
                                standard (IS             present
Properties                      15607:2005)   Limit      study

FAME content                    EN 14103      Min. 96.5   98.33
Density, kg/[m.sup.3]           EN ISO 12185  860-900    890
Kinematic viscosity at          EN ISO 3104   2.5-6.0      4.83
40 [degrees]C, [mm.sup.2]/s
Acid value, mg KOH/g            EN 14104      Max. 0.5     0.38
Calorific value, MJ/kg          Report        Report      43.5
Flash point, [degrees]C         ISO/CD 3679   >101       174
Cloud point, [degrees]C         Report        Report       1
Pour point, [degrees]C          Report        Report       4
Cetane number                   ASTM D-613    Min. 51     49
Oxidation stability at          EN ISO 14112  Min. 6       2.1
110 [degrees]C, h
Iodine value g [I.sub.2]/100 g  EN 14103      Max. 120    37
Copper strip corrosion          ASTM D130     Max. 1       1

TABLE 3 Summary of obtained results and literature reported results on
the corrosion rates for metals in different biodiesel.


Biodiesel                 Material       Immersion period (h)

Palm                      Copper          840
                                         2640
                          Leaded bronze
Palm                      Copper          600
                          Aluminum
Rapeseed                  Copper         1440
                          Aluminum       1440
Rapeseed                  Copper          600
                          Aluminum        600
Palm                      Copper         2880
                          Aluminum
                          Brass
                          C.I.
Vegetable oil deodorizer  Copper         2880
distillate (*)
                          Aluminum
                          Brass
                          Leaded bronze
                          SS
                                              Corrosion
Biodiesel                 Temp. ([degrees]C)  rate (mpy)

Palm                      Room temp.          0.042
                          60                  0.053
                                              0.025
Palm                      80                  0.586
                                              0.202
Rapeseed                  43                  0.918
                          43                  0.133
Rapeseed                  80                  0.92
                          80                  0.35
Palm                      Room temp.          0.3927
                                              0.1730
                                              0.2098
                                              0.1122
Vegetable oil deodorizer  45                  0.11
distillate (*)
                                              0.0393
                                              0.02362
                                              0.089
                                              0.00748

                          Reference and
Biodiesel                 present study

Palm                      Haseeb et al. [11]
Palm                      Fazal et al. [6]
Rapeseed                  Hu et al. [12]
Rapeseed                  Norouzi et al. [15]
Palm                      Fazal et al. [8]

Vegetable oil deodorizer  Present study
distillate (*)

(*) Fuels were changed weekly as per SAE standard.
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Author:Sorate, Kamalesh A.; Bhale, Purnanand V.
Publication:SAE International Journal of Fuels and Lubricants
Article Type:Technical report
Date:May 1, 2018
Words:7667
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