AbstractWith the promotion of the laws about energy consumption of engines and the emission of pollutant in recent years, the technology of diesel engine is progressing. The use of High Pressure Common Rail, HPCR, is getting common. To protect the oil supply systems with high precision and smaller gaps, the fuel filters play a more important role. On the other hand, to reduce the use of fossil energy and the emission of greenhouse gas, every country is actively promoting the use of bio-fuel that can be regenerated. However, much research in the world all indicate that using biodiesel blend will cause problems to fuel filters, including lowering the emulsified water separation efficiency, shortening the usage life of fuel filters, and so on.

Therefore, this research used the biodiesel made completely by the transesterification of waste cooking oil with different percentage of blend and the standard testing methods of ISO 19438 and ISO 16332 to study the effects on the filtration efficiency and fuel-water separation efficiency of the fuel filters. The testing results showed that with the increase of the percentage of biodiesel, the filtration efficiency of tiny particles of the filters increased slightly while the fuel-water separation efficiency decreased.

1. IntroductionFuel may pollute because of the manufacturing process, refueling tool, refueling environment, and the cleanness of the fuel tank. However, during the operation of diesel engine, various contaminants, such as particles like dust, dirt, sand, rust, fiber, rubber, and paint fragment, worn metals or excessive additives like aluminum, copper, iron, lead, tin, silicon, sodium, zinc, barium, and phosphorous, water, sealing materials like teflon tapes, seal tapes, and seal glue, sludge, organic acid, microorganism, oxide and other erosions, might be produced due to many different reasons and cause various problems. It shows that the fuel filters play a more and more important role.

The water in the fuel can be dissolved in diesel to some degree and the rest is represented as undissolved water. [3] The water might

pollute the fuel in different ways. For example, during the transportation process of the fuel between the oil refinery and gas station, if there is water in the channel for oiling, it will cause the wear of the fuel injector to hasten the wear of the mechanics and reduce their lives. Despite the water content of the fuel is subsumed into the standard regulations, the manufactures of the fuel components, such as fuel injector and high-pressure pump, still demand the minimum filtration efficiency of the fuel-water separator. They mostly demand the separation efficiency to be over the range of 93% to 95%[1][2] to protect the components from erosion and wear.

There is a tension existed between the interface of fuel and water, which is called interfacial tension, IFT. Due to interfacial tension, the two systems always tend to decrease the contacting measure of area between the two fluids, which is to combine as big liquid drops from small liquid drops to reduce the total measure of area of small liquid drops. The bigger the interfacial tension is, the stronger the tendency gets. [3] The principle of fuel-water separation is based on the difference of interfacial tension between materials. Water is not infiltrated into some materials, which is called hydrophobicity, while fuel can be infiltrated into these materials, which is called lipophilicity. When the filter made of this kind of material filters diesel, as long as there is water in the fuel, the water will be blocked by the filter due to hydrophobicity. The blocked tiny water drops gradually aggregate as bigger water drops to increase the difference of density with the liquid of the environment. Then, based on the difference of density between water and fuel, the principle of gravity settling is used to descend the aggregated big water drops to the filter so as to reach the effects of separation of water. The aggregation of the liquid drops can be mainly divided into three steps, as shown in Figure 1-1. [4]

• Collect single liquid drop of small particle size • Combine several small liquid drops to become bigger liquid

drops • With the increase of the difference of density, the liquid drops

float and descend

Impacts of Biodiesel Blends on Fuel Filters of High Pressure Common Rail (HPCR) System

2016-01-1280

Published 04/05/2016

Ta-Wei Tang, Yong-Yuan Ku, and Chun Lin ChenAutomotive Research & Testing Center

CITATION: Tang, T., Ku, Y., and Chen, C., "Impacts of Biodiesel Blends on Fuel Filters of High Pressure Common Rail (HPCR) System," SAE Technical Paper 2016-01-1280, 2016, doi:10.4271/2016-01-1280.

Copyright © 2016 SAE International

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Figure 1-2. The Three Steps of Liquid Drops Aggregated on the Fiber[4]

To reduce the use of fossil energy and the emission of greenhouse gas, every country actively promotes the bio-fuel with the quality of regeneration. The use of bio-fuel on vehicle transportation is the focus of the development of every country. However, much research in the world all indicates that using biodiesel blend will cause problems of fuel filters, including lowering the emulsified water separation efficiency, shortening the usage life of fuel filters, and so on. The stability of the storage of biodiesel, oxidation stability and its high affinity with water can shorten the usage life of fuel filters and decrease the fuel-water filtration efficiency.

In the Biodiesel Handling and Use Guide published by NREL[5], it mentioned that biodiesel is a kind of tender solvent. At the early stage of using biodiesel, compared with fossil diesel, the deposits on the fuel tanks and walls of fuel pipes can be dissolved more easily to cause the early block of filters. In addition, during the process of storing or using, it might cause the deterioration of fuels, decrease of the quality, and the formation of sticky oil dusts because of oxidation, which will cause higher acid number, viscosity and the aggregation of gelatinous compounds.

The most obvious change of the characteristics of biodiesel and fossil diesel on fluid flow is viscosity. The viscosity of fossil diesel at 40°C is about 2 to 3 mm2/s, while the viscosity of the biodiesel made from soybeans is about 4 to 5 mm2/s. The difference can be two times the highest. Wilfong et al. [6] had observed the penetration rate of the impurity to the same type of filter with two fuels of different viscosity when the filter were shook. Figure 1-2[6] shows that the viscosity of MILH-5606 fuel was six times higher than that of Viscor fuel. It was found that tremble and shake would increase the penetration rate of impurities, and the particle penetration rate of fuel with lower viscosity was higher. Therefore, viscosity will affect the motion of the particles in the fluid and the filtration performance of the filters.

Figure 1-2. The Penetration Rate of Impurities of Filters with the Fuels of Different Viscosity[6]

In addition, according to the research of international filter manufacturer[3], in the surveys to the users of biodiesel, 40% of the problems were caused by water pollution, 20% were due to the growth

of microorganism, 25% were because of glycerine, 10% were due to the inappropriateness of blend and the rest 5% were caused by other factors. Therefore, the water content in the fuels and the fuel-water separation efficiency are important issues. So, the hygroscopicity of the biodiesel was studied. The testing results showed that the hygroscopicity of the fuels indeed would be affected by the amount of biodiesel contained. After being placed for two days, the water content in the biodiesel was increased with different degrees. The water content of B100 was especially higher than the regulations of 500 ppm at the end of the testing, as shown in Figure 1-3.

Figure 1-3. The Comparison of Hygroscopicity of the Biodiesel with Different Percentage[1]

The research also tested the interfacial tensions of the biodiesel with different percentage. The results showed that with the increase of the percentage of the biodiesel, the interfacial tension between fuel and water would be decreased. When the percentage of biodiesel reached 20%, the interfacial tension became stable, as shown in Figure 1-5. So at a blending ratio over 20 vol%, the biodiesel Chemical composition dominates the interfacial tension of the blend. [1] At last, the research also compared the differences of the fuel-water separation efficiency between fossil diesel and biodiesel blend. The interfacial tension of fossil diesel was 28.26 mN/ m while that of biodiesel blend was 12.98 mN/ m.

Figure 1-4. The Interfacial Tensions of the Biodiesel with Different Percentage [1]

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Sogefi Filter [2] also used clean and new filters to test the fuel-water separation efficiency of biodiesel. The testing results in Table 1-1 showed that the fuel-water separation efficiency of biodiesel and polyblend both decreased. The main reason was the water emulsifying state of biodiesel was more stable. Therefore, the initial filtration efficiency of biodiesel on filters might be different.

Table 1-1. The Impact of Biodiesel Blends on Initial Filtration Efficiency [2]

Another experiment in this research even found that when the biodiesel with higher percentage (B30) was used to conduct car endurance tests, the performance of fuel-water separation would decrease to some extent under certain mileages. After analyzed by SEM surface observation, it was found that because the large deposits produced during the oxidation process of biodiesel had attached to the surface of melt-blown fiber, the melt-blown fiber for filtering water had lost its hydrophobicity, which caused the decrease of the filtration efficiency. [2]

This was because the interfacial tension between biodiesel and water was much lower than that between fossil diesel and water, which was from 10 mN/m to 13 mN/m. The reason that biodiesel is hydrophilic is mainly because the alkyl-esters and unsaturated acids in the biodiesel have more polarity. However, there is barely any alkyl-esters and unsaturated acids in the diesel distilled from petroleum crude oil. Therefore, even if there is no surface active agentin the biodiesel, it is more hydrophilic because some compositions of biodiesel are similar with surface active agents. [7]

The dissolved water concentration of fossil diesel is usually from 30 ppm to 180 ppm, while that of biodiesel is over 300 ppm. And when biodiesel is mixed with free water to reach the fuel water saturation, its water content even increases 2.5 to 5 times. To evaluate the performance of fuel-water separation of the fossil diesel with low interfacial tension mixed with biodiesel, one research used soybean biodiesel and animal fat biodiesel with different percentage to conduct fuel-water separation test, as shown in Figure 1-6. [9] The results showed that with different source materials of biodiesel, the fuel-water separation efficiency might be the same or decrease. In conclusion, regardless of the types of filter mediums, even 5% biodiesel blend would lower the filtration efficiency of emulsified water.

Figure 1-6. The Changes of Filtration Efficiency of Biodiesel with Different Percentage [7]

2. Experimental MethodsThe fuels used in this research were 2% (B2), 5% (B5) and 20% (B20) of the biodiesel made from waste cooking oil mixed with fossil diesel, D100. The characteristics of the testing fuels are shown in Table 2-1. It could be found that the viscosity of biodiesel was 1.6 times higher than that of D100 and water content was about six times higher.

Table 2-1. The Characteristics of Fossil Diesel and Waste Edible Oil Biodiesel

This research had chosen the filter equipped in the vehicle with common rail system as research object. The testing filter had pleat star and made from the compound material of melt-blown and wire cutting fiber. It also had the functions of filtering impurities and fuel-water separation, as described in Table 2-2. The actual filter is shown in Figure 2-1.

Table 2-2. The Specifications of Testing Filters

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Figure 2-1. The Actual Testing Filter

ISO19438Diesel fuel and petrol filters for internal combustion engines - Filtration efficiency using particle counting and contaminant retention capacity

The performance test of filtering impurities had used the testing method of ISO 19438. The particle counter and differential pressure sensor installed before and behind the testing filters were used to measure the number of pollutant particles and difference of pressure between upstream and downstream of the filter. The difference of numbers of particles upstream and downstream of the filter was compared to calculate the filtration efficiency of the filter. During the test of filtration efficiency of filtering impurities, the impurities added were the testing dusts of A3 defined by ISO 12103-1 to ensure the consistency of the size of the pollutant particles. The particle counter used in this research can detect eight sizes of particle diameter, including Particle size greater than 4 μm, 6 μm, 14 μm, 21 μm, 25 μm, 38 μm, 50 μm and 70 μm. Every size had its own counting number. For example, 4μm represent the sum of particle size more than 4μm. Therefore, the curve line of filtration efficiency of the eight sizes could be calculated.

ISO16332Diesel engines - Fuel filters - Method for evaluating fuel/water separation efficiency

Figure 2-2. The Testing Process of Filtration Performance of Impurities and Fuel-Water Separation Efficiency

For the fuel-water separation efficiency, the testing method of ISO 16332 was used. Samples from upstream and downstream of the filter were obtained to analyze the water concentration content in the fuel. The difference of water concentration content upstream and downstream of the filter was compared to calculate the fuel-water separation efficiency. The testing period was sixty minutes and the samples were analyzed every ten minutes. The water was poured into the fuel circuit (1500ppm) through the quantity control valve and water emulsifying device. The sample fuels were analyzed by Coulometric method for water concentration. The testing process was planned as Figure 2-2.

3. Result Analysis

3.1. The Analysis of Filtration Efficiency of the Biodiesel with Different PercentageFigure 3-1 shows the average filtration efficiency of biodiesel with different percentage. It was found that the filtration rate for the impurities of the particle size over 14 μm was almost 100%, meaning there was no residue of the particles over 14μm after filtered by the filter. The filtration efficiency of size of 4 μm was between 80% to 85%, while that of size of 6 μm was almost 90%. This showed that the filtration efficiency was pretty good.

As for the average filtration efficiency of biodiesel with different percentage, the figure shows that there were two trends. The trends of filtration efficiency of D100, B2 and B5 were very similar. The filtration efficiency of the size of 4 μm was about 80%, while that of size of 6 μm was almost 90%. There was little difference among the three fuels, but it could still be found that with the increase of the percentage of biodiesel, the filtration efficiency of tiny particles also increased slightly. For B20, the phenomenon was more obvious. The filtration efficiency of B20 of the size of 4 μm was about 85%, while that of the size of 6 μm was almost 93%. Compared with B100, B2 and B5, the filtration efficiency increased.

Figure 3-1. The Average Filtration Efficiency of the Biodiesel with Different Percentage

There was no obvious difference found in the pressure difference between the upstream and downstream of the filter in different fuels, as shown in Figure 3-2. The trends of change of the four fuels were almost the same. It was mainly because the difference of viscosity of B20, 2.62 mm2/s and that of D100, 2.89mm2/s was not big. In addition, the figure also shows that the change of the pressure difference during the first thirty minutes was more leveled. However, after forty minutes, the pressure difference increased obviously. This

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indicated that with the accumulation of impurities, the blocking of porous material was not linear, but after reaching the limit, the trend of pressure difference became index change.

Figure 3-2. The Change of Pressure Difference of Biodiesel with Different Percentage during the Testing Period

The above analysis showed that the increase of the percentage of biodiesel would cause the filtration efficiency of impurities to increase. The fluid characteristics of fossil diesel and biodiesel might be the reason. The drag force imposed upon the impurities in the fuel of higher viscosity, like B20, was stronger, which made the impurity particles diffuse not easily and move with the stream of the fluid. Therefore, the particles were captured by the medium fiber more easily due to interception.

3.2. The Analysis of Fuel-Water Separation Performance of Biodiesel with Different PercentageFigure 3-3 shows the water content in the biodiesel with different percentage. In the fuel standard regulations, the water content of the fuel under B5 must be under 200 ppm, referred to EN 590 and ASTM D975. The water content of the fuels of B6 to B20 must be under 500 ppm, referred to ASTM D6751.

However, the figure also shows that with the increase of the percentage of biodiesel, the water content also increased nonlinearly. The water content of B20 was three times more than that of D100. This result was similar with the results of the above researches. The increase of the percentage of biodiesel would indeed increase the water content. It was mainly because biodiesel is more hygroscopic than fossil diesel. Therefore, with the increase of the percentage of biodiesel, the hygroscopicity also increased.

Figure 3-3. The Water Content of Biodiesel with Different Percentage

Figure 3-4 shows that the fuel-water separation efficiencies of D100, B2 and B5 were all over 99%, while that of B20 was about 98%. This indicated that the impact of the deterioration of fuel-water separation efficiency of B20 was not obvious.

Figure 3-4. The Momentary Water Separation Efficiency of Biodiesel with Different Percentage

Figure 3-5 shows the average filtration efficiency of the four fuels. It could still be found that with the increase of the percentage of biodiesel, the fuel-water separation efficiency decreased slightly. The difference of the filtration efficiency of D100 and B20 was about 1%. This might be related to the interfacial tension between fuel and water. The interfacial tension of biodiesel was actually lower than that of fossil diesel. The interfacial tension of fossil diesel was about 25 mN/ m to 30 mN/ m, while that of biodiesel was about 10 mN/ m to 13 mN/ m. Therefore, when fossil diesel was mixed with biodiesel, the interfacial tension had decreased, too. [1-2][7]

The decrease of the interfacial tension was mainly because some compositions of biodiesel are similar with surface active agents. The alkyl-esters and unsaturated acids in the biodiesel have more polarity. And, there is barely any alkylesters and unsaturated acids in the diesel distilled from petroleum crude oil. This makes biodiesel more hydrophilic and hygroscopic to further increase the stability of the water emulsion of the fuel to lower the fuel-water separation efficiency.

Figure 3-5. The Average Fuel-Water Separation Efficiency of Biodiesel with Different Percentage

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4. ConclusionsWith the increase of the percentage of biodiesel, the filtration efficiency of tiny particles also increased. This was mainly caused by the viscosity of the fluid. However, with the increase of the percentage of biodiesel, the impact of the pressure difference should also be taken into consideration.

The hygroscopicity of biodiesel would cause the increase of water content to different degrees with the increase of the percentage of biodiesel. However, the initial fuel-water separation efficiency of the four fuels did not decrease obviously. This explained that the applicability of fuel-water separator to the fuels under B20 is the same as that of D100. But, the long-term applicability still needs to be confirmed.

References1. Yoshino, F., Marques, G., and Ferrari, F., "Water Separation

Challenge for Brazilian Diesel Engine," SAE Technical Paper 2013-01-1693, 2013, doi:10.4271/2013-01-1693.

2. Petiteaux, M. and Monsallier, G., "Impacts of Biodiesel Blends on Fuel Filters Functions, Laboratory and Field Tests Results," SAE Technical Paper 2009-01-1876, 2009, doi:10.4271/2009-01-1876.

3. Yip's Chemical, http://www.yipslubricant.com/, 2015-07

4. Shirazi1 Mohammad Javad A., Bazgir1* Saeed, Shirazi2 Mohammad Mahdi A., “ Edible oil mill effluent; a low-cost source for economizing biodiesel production: Electrospun nanofibrous coalescing filtration approach”, Biofuel Research Journal 1 (2014) 39-42

5. “Biodiesel Handling and Use Guide Fourth Edition”, National Renewable Energy Laboratory, January (2009)

6. Wilfong Debra, Dallas Andrew, Yang Chuanfang, Johnson Philip, Viswanathan Karthik, Madsen Mike, Tucker Brian and Hacker John, “EMERGING CHALLENGES OF FUEL FILTRATION”, International Journal for Filtration and Separation, 10(2) , ISSN 1479-0602, 2010

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Contact InformationTa-Wei TangProject EngineerAutomotive Research and Testing Center, Taiwandavidtw@artc.org.tw

Yong-Yuan KuProject EngineerNational Chung-Hsing Univ.tom@artc.org.tw

Chun-Lin ChenProject EngineerAutomotive Research and Testing Center, Taiwanyeachyi1120@artc.org.tw

AcknowledgmentsThe authors would like to thank the financial support by Bureau of Energy, Ministry of Economic Affairs (R.O.C.) which has made this report successful.

The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE’s peer review process under the supervision of the session organizer. The process requires a minimum of three (3) reviews by industry experts.

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