2002-09- sin 2.4 Evaluation of New Fuel Oil for Internal Combustion Engine (Showa Shell Sekiyu K.K) Chief researcher Shunichi Koide Masahiko Shibuya, Tsuyoshi Kashio, Junichi Hosoya, Yuji Akimoto, Kensaku Miyahara 1. R&D Objectives Atmospheric and environmental deterioration due to large consumption of fossil fuels has become an environmental problem taken up on a global scale. Resolving this problem, together with global warming by CO 2, has become one of the foremost issues in modern society. In recent years, in particular, attention has focused on diesel vehicle emissions as a major cause of atmospheric deterioration. Policies are being advanced to reduce the burden on the atmosphere and the environment both in terms of fuel and in terms of fuel-burning equipment. As to fuel, improvement in quality of fuel is advanced, especially for diesel engines. It has been resolved that sulfur content in gas oil should be reduced to 50 ppm or less, and ways to lower sulfur still more in the future are being discussed. Against this background, as one solution in terms of fuel, there are strong demands for the development of technology for consuming new fuel oils in a manner harmonious with the environment. Attention has focused on the characteristics of environment-friendly fuels such as fuels of low sulfur and aroma content. GTL gas oil, recycle oil and biofuel are expected to be introduced as new fuels. Thus far, however, systematic investigations of such fuels in terms of reduced load on the environment and applicability as internal combustion engine fuels have not been adequate. To have these new fuels disseminated in the future, systematic technological evaluations of their applicability as fuels is imperative. Accordingly, the objectives of the present R&D are: 1) to evaluate the characteristics of vegetable oil methyl ester and GTL gas oil, beginning with their properties and emissions constituents, since plans already call for partial introduction of these new fuel oils into European and American markets; 2) to evaluate the feasibility of these fuels as petroleum product applications; and 3) to collect technological data essential for standards preparation and reforming technology so that an environment can be established for standardization and new types of environment-friendly fuels can be used. 2. R&D Contents Implementation of the present R&D began in JFY 2000. In that year, various types of vegetable oil methyl ester fuels were taken up as new fuels, their properties were measured, and their characteristics, including oxidation stability and materials compatibility, were evaluated. In addition, emissions of these fuels from practical diesel engines were measured, and those emissions were compared with the emission characteristics of gas oil. The results of evaluation of the characteristics of vegetable oil methyl ester are summarized as follows. 1
Vegetable oil methyl ester is an oxygen-containing fuel with unsaturated fatty acid methyl ester as its main component. It has potential as an alternative diesel fuel, since it is equivalent to gas oil in cetane value, and contains no sulfur and aromatics. Nevertheless, it has higher density, kinematic viscosity and residual carbon than gas oil and it is feared that it will lead to deterioration of spray formation in the combustion chamber and to the production of engine deposits. The results of evaluation of the characteristics of vegetable oil methyl ester fuel are summarized in Table 1. Table 1: Oxidation stability Oxidation stability Hydrolysis stability Results of Characteristics Evaluation Tests (JFY2000) Item Test method Comparison with gas oil performance Metal compatibility JIS K2267 Remarks ASTM D2274 - Greater precipitation volume after test than with gas oil. ASTM D2619 No problem with hydrolysis stability, but precipitants believed to be impurities are produced. JIS K2513 Slight corrosion observed on copper and brass but not considered problematic. Lubricity (wear) JPI-5S-50-98 Lubricity is superior to gas oil. Lubrication (anti seizure) Elastomer compatibility ASTM D5000 Anti seizure is superior to gas oil. JIS K6258 Big influence on NBR. For FKM, equivalent to gas oil. Storage stability ASTM D4625 Equivalent to gas oil with no precipitants produced. Rust-preventing JIS K2510 Although rust is produced, it is not problematic, being the same as with gas oil. Water reaction JIS K2276 Water separability JIS K2520 : Superior to gas oil, : Equivalent to gas oil : Difference by ester or material, : Inferior to gas oil For nearly all items, compatibility and characteristics equivalent to those of gas oil were exhibited, but in elastomer compatibility test, big influence on the rates of change in elongation and in tensile strength were manifested with NBR as compared to gas oil. For FKM, applicability was equivalent to that of gas oil. 2
It is feared that vegetable oil methyl ester is inferior to gas oil in oxidation stability. Nevertheless, because there are no standards in gas oil oxidation stability, more data will have to be collected, and the positioning of vegetable oil methyl ester will have to be clarified. The result of an evaluation in JFY2000 of emissions characteristics of vegetable oil methyl ester are presented below. In the DI engine, together with an increase in the percentage mixture of vegetable oil methyl ester in gas oil, SOF increased at lowload, and dry soot and black smoke decreased at high load. The trend toward increase of SOF at low load was especially pronounced. For DI engine, countermeasures such as the installation of oxidation catalyst are considered necessary. In the IDI engine, together with an increase in the percentage mixture of vegetable oil methyl ester, although SOF increased slightly irrespective of load, PM decreased due to a reduction in dry soot. It was also confirmed that oxidation catalyst reduces SOF and that virtually none of the sulfates originating from sulfur compounds in fuel are emitted. These results suggest that a combination of ester with oxidation catalyst is effective in reducing loads on the environment. The aforesaid trends in emissions observed in both DI and IDI engines were the same with each ester, irrespective of the kind of vegetable oil methyl ester, such as rape seed, soy bean or waste recycle oil. Concerning unregulated emissions, in the DI engine, emissions of benzenes and aldehydes were generally greater in volume from esters than from gas oil. Nevertheless, more data will have to be collected before any definitive conclusions of unregulated emissions. Based on the results obtained in JFY2000, a survey was conducted in JFY2001 for improving characteristics, with attention focused on oxidation stability as the characteristic of vegetable oil methyl ester. In order to clarify the positioning of vegetable oil methyl ester in reducing environmental load, the influences of waste recycle oil and of soybean oil methyl ester on emission were investigated. In addition, the influence of waste recycle oil on engine detergency was investigated. In the investigation in JFY2001, GTL gas oil was taken up as a new fuel; its applicability as a petroleum product and as a fuel oil base was examined. An investigation was also made for improving the characteristics of GTL gas oil as a fuel oil base. Specific survey items are given in Table 2. 3
Table 2: Survey Items in JFY2001 New fuel Target item Outline Vegetable oil methyl ester GTL gas oil Improvement of oxidation stability Evaluation of engine detergency Emissions characteristics Properties Characteristics evaluation Effect of oxidation inhibitor Evaluation by JASO engine detergency test Survey of recycle oil emissions after removing impurities Influence of carbon number comprising methyl ester Measurement of unregulated emissions Measurement of density, distillation, cetane number, etc. Compatibility with metals and elastomer Effect of cold flow improver 3. R&D Results 3.1 Vegetable oil methyl ester 3.1.1 Improvement in Oxidation Stability In JFY2000, oxidation stability was evaluated with respect to rape seed oil methyl ester, soybean oil methyl ester and waste recycle oil. These methyl esters were inferior in comparison to gas oil, irrespective of the kind of vegetable oil, oxidation stability of waste recycle oil was investigated. Figure 1 shows the results of an evaluation, by the JIS method, of the effect of adding oxidation inhibitor. Figure 2 gives the same results by the ASTM method. Induction time (min) Volume of oxidation inhibitor (%) Precipitation weight (mg/100 ml) Volume of oxidation inhibitor (%) Figure 1: Effect of Adding Oxidation Inhibitor (JIS method) Figure 2: Effect of Adding Oxidation Inhibitor (ASTM method) 4
Induction time (min) Volume of oxidation inhibitor (%) Figure 3: Influence on Oxidation Stability by Mixing Gas Oil In the evaluation of oxidation stability by the JIS method, oxidation stability was improved, with the induction time becoming longer in proportion to the amount of oxidation inhibitor added. In the evaluation by ASTM method as well, oxidation stability was improved, with the magnitude of precipitation declining in accordance with the amount of oxidation inhibitor added. The level of gas oil oxidation stability was 1440 minutes or more with the JIS method and 1.4 mg/100 ml with the ASTM method. It was found that in order for the oxidation stability of waste recycle oil methyl ester raise to that of gas oil, oxidation inhibitor must be added at 0.3-0.5 mass%. In general, the amount of oxidation inhibitor added to fuel oil is about several 10 ppm at most. In view of this fact, it is believed that a relatively large amount of oxidation inhibitor must be added to achieve the level of gas oil oxidation stability. What is more, this amount is not considered practical when used as fuel oil. Therefore, it was investigated how much oxidation stability can be improved by mixing more gas oil with waste recycle oil to which oxidation inhibitor had been added. Figure 3 shows the changes in oxidation stability when gas oil was mixed 50 vol% to 70 vol% to recycle oil. When the amount of gas oil mixture has been increased, the induction time becomes longer and oxidation stability is improved to some extent. In order to reach an induction time of 1440 minutes or more, comparable to that of gas oil, it can be estimated from Figure 3 that at least 0.2 mass% of additive, that is 2000 ppm or more, is required even when 70 vol% of gas oil has been mixed. Thus the oxidation stability of waste recycle oil is improved somewhat by adding oxidation inhibitor and by mixing with gas oil, but it was recognized that improving oxidation stability to the level of gas oil is still difficult. The changes in oxidation stability produced by adding oxidation inhibitor to vegetable oil methyl ester were evaluated by the JIS method and ASTM method, but the effect of oxidation inhibitor was extremely low in comparison to that of hydrocarbon fuels. It is conceivable that oxidation stability was evaluated at low levels with the JIS method and ASTM method because vegetable oil methyl esters differ from hydrocarbon fuels in structure, composition and properties. A method of testing oxidation stability must be modified so that when vegetable oil methyl esters serve as fuel oil, the influences on elastomer compatibility or metal corrosion can be directly evaluated. 5
3.1.2 Evaluation of Engine Detergency Compared with gas oil, an engine internal contamination after running for a long time using vegetable oil methyl ester was evaluated. Detergency test method (JASOM336-98) regulated by JASO was carried out using recycle oil methyl ester, and compared to with gas oil in terms of engine internal contamination. In the evaluation of detergent property, a 2.5L diesel engine with vortex-chamber was operated at full load for 200 hours, thereafter engine internal parts were evaluated. The results of this evaluation are presented in Table 3. No. 1 ring groove carbon clogging (TGF) is expressed as the percentage area (%) of carbon accumulated on ring groove; the smaller the figure, the lower the contamination. TGF of 60% or more is failing by standard. For other items, the extent of contamination is expressed as a score; the higher the score, the lower the degree of contamination. In a comparison of gas oil and recycle oil, the detergency of recycle oil was found to be equivalent to that of gas oil. Recycle oil has a large amount of residual carbon; its boiling point range is high in comparison to gas oil, and its oxidation stability is inferior. Given these facts, it was anticipated that detergency would be poor, but it was at the same level as gas oil. Under this test conditions, the engine is run at full load for a long time, and the combustion chamber interior is believed to reach a high temperature. In emissions tests carried out separately, there were few unburnt substances in recycle oil having high boiling point in the high load operation. It was also confirmed that black smoke was less than with gas oil, so recycle oil can be considered favorable in terms of detergent property. Table 3: Evaluation of Detergent Property of Engine Parts Engine parts Gas oil Evaluation Recycle oil No. 1 ring groove carbon clogging (TGF) 24.5 24.1 Cylinder head top surface 9.5 9.8 Rocker cover 9.5 9.8 Gear case cover 9.5 9.7 Oil strainer top surface 9.4 9.8 Oil strainer 9.5 10.0 Oil pan 9.6 9.7 Valve, exhaust valve 9.0 9.5 Valve, intake valve 9.1 8.3 Evaluation: (1) TGF denotes percentage area of accumulation in No. 1 ring groove. (2) For other items, the higher the score, the lower the contamination. 6
3.1.3 Characteristics of Vegetable Oil Methyl Ester Emissions (1) Influence of carbon number comprising fatty acid methyl esters Vegetable oil methyl esters are comprised of fatty acid methyl esters ranging from about 10 to 18 in carbon number. Here, pure substances of fatty acid methyl esters were used to investigate the influences of carbon number. The methyl esters employed were saturated fatty acids of carbon 12 (C12: lauric acid methyl ester), carbon 14 (C14: myristic acid methyl ester) and unsaturated fatty acid of carbon 18 (C18: oleic acid methyl ester). From the results of emissions tests at D13 mode using these three fatty acid methyl esters, it was learned that the emissions from fatty acid methyl esters vary by carbon number. The main properties of the three kinds of fatty acid methyl esters used in the tests are given in Table 4. Table 4: Properties of Fatty Acid Methyl Ester Test Sample C12 C14 C18= Density, g/cm 3 0.869 0.869 0.874 Boiling point, 141 (15 mmhg) 157 (7 mmhg) 213 (15 mmhg) Carbon content, wt% 72.9 74.4 77.0 Hydrogen content, wt% 12.1 12.4 12.2 Oxygen content, wt% 15.0 13.2 10.8 The density of each ester was about the same, but the boiling point increased together with the carbon number. These differences in boiling point can be considered as one major factor behind the differences in emissions. Moreover, while the oxygen content increases with a gain in molecular weight, the oxygen assisting in combustion tends to decline, and the influence of this compositional percentage of molecules can also be considered. What is more, lauric acid and myristic acid are saturated fatty acids, but oleic acid is an unsaturated fatty acid, so the differences between saturated and unsaturated molecular structure might also have an impact on emissions. Determining whether or not the influences of physical properties such as boiling point or of molecular structure are major factors will be an issue in the future. (2) Measurements of Unregulated Emissions Figure 4 gives the results with unregulated emissions at D13 mode in relation to gas oil, soybean oil methyl ester (SME), a 50 vol%/50% mixture of gas oil and soybean oil methyl ester (SEM50), and vegetable oil/recycle oil methyl ester. Measurement targets were the following four unregulated substances: benzene, 1, 3 butadiene, formaldehyde and acetaldehyde. Different range in two repeated tests are plotted on the graph. At the D13 mode, a difference in each fuel can be noted with formaldehyde. With gas oil, emissions tend to increase in the sequence: light oil < SME50 < SME < recycle oil. Figure 5 presents the relationship between THC emissions volume, measured under D13 mode and under every other constant operation mode, and emissions volumes of unregulated substances. Generally, the total emissions volume of these four unregulated substances tends to increase together with an increase in THC emissions. 7
Unregulated emissions (mg/kwh) Gas oil Recycle oil D13 mode Figure 4: Influence of Gas Oil, Soybean Oil and Recycle Oil Methyl Esters on Unregulated Emissions Total of 4 unregulated emissions (mg/kwh) Figure 5: THC vs Unregulated Substance Emissions Volume 3.2 GTL, Gas Oil 3.2.1 General Properties GTL gas oil is colorless. Since it is comprised mainly of straight chain paraffin hydrocarbons, GTL gas oil is lower in density than gas oil and its cetane number is extremely high. In its composition, it contains no sulfur and aromatics, but has a large percentage of hydrogen. GTL gas oil thus has the following four main characteristics. (1) Density is low (0.784 g/cm 3 ). (2) Cetane number is high (82.6). (3) There is no sulfur (less than 1 ppm). (4) There are no aromatics (0.0 vol%). Given these characteristics, when GTL gas oil is used in diesel engine, direct emissions from the engine are reduced. It is also amply compatible with a post-treatment unit, so it can be expected to reduce engine emissions. Distillation of GTL gas oil are roughly the same as that of conventional gas oil. Initial boiling point is somewhat high (189 C) but the final point tends to be low (346 C). Straight chain paraffin hydrocarbons are characterized by high melting points. In GTL gas oil, cloud point (0 C), cold filter plugging point (0 C) and pour point (0 C) were all high in comparison to gas oil. This suggests that low-temperature flowability is inferior. 8
Measurements of the properties of GTL gas oil element, except for cold flow performance, all satisfied the standards for JIS No. 2 gas oil. In terms of low-temperature flowability, GTL gas oil falls under the category of special No. 1 gas oil. 3.2.2 Characteristics Evaluation Table 5 presents the results of an evaluation of GTL gas oil in terms of oxidation stability, metal compatibility, lubricity and elastomer compatibility, all of concern because of the properties and composition of GTL gas oil. In all items, material compatibility and characteristics equivalent to those of gas oil were manifested. In the evaluation of elastomer compatibility, when NBR or H-NBR is used as the sealing material in a fuel system designed on the assumption of swelling, it have to be considered that the rates of change in the cubic volumes of NBR and H-NBR are extremely low. Table 5: Results of Characteristics Evaluation Tests for GTL Gas Oil Item Test method Comparison of performance with gas oil Remarks Oxidation stability JIS K2267 Induction time is 1440 minutes or more. Oxidation stability ASTM D2274 More precipitation volume after test than with gas oil. Metal compatibility Lubricity (abrasion) Elastomer compatibility JIS K2513 Slight impact observed on copper and brass but not considered problematic. JPI-5S-50-98 Can be dealt with using additive. JIS K6258 Concern about fuel leakage because NBR is not swollen. Storage stability ASTM D4625 Equivalent to gas oil with no precipitants produced. : Superior to gas oil, : Equivalent to gas oil, : Inferior to gas oil 3.2.3 Assurance of Cold Flow Performance The cold filter plugging point and pour point of GTL gas oil are both at 0 C, and this is a high temperature in comparison to the CFPP (-5 C) and PP (-7.5 C) of JIS No. 2 gas oil. Assuming that GTL light oil is to be used as gas oil, it must be improved so that its cold flow performance is comparable to that of No. 2 gas oil. The cold flow performance of GTL gas oil, achieved by adding cold flow improver (hereinafter CFI) and by mixing in gas oil, was evaluated. 9
When CFI was added at 250 ppm and 500 ppm which roughly equivalent to those normally added to gas oil the change in cold flow performance was as indicated in Figure 7 with respect to cold filter plugging point and in Figure 6 with respect to pour point. Cold filter plugging point and pour point are lowered and improved in accordance with the amount of additive added, and the amount of gas oil mixed in, to GTL gas oil. It was thus found that a cold filter plugging point of 5 C and a pour point of 7.5 C, the JIS standard values for No. 2 gas oil, could be satisfied by adding CFI and mixing gas oil into GTL gas oil. In Figure 7, the effect of CFI addition on the cold filter plugging point of GTL gas oil is virtually nil, and by mixing in gas oil at 50%wt or less, the cold filter plugging point is hardly improved at all. On the other hand, the effect of CFI addition in GTL gas oil can be recognized in Figure 6, and the pour point drops in accordance with the amount of gas oil mixed in. Pour point ( C) Cold filter plugging point ( C) Mixture percentage of GTL gas oil in gas oil (vol%) Mixture percentage of GTL gas oil in gas oil Figure 6: Change in Pour Point Due to Addition of CFI to GTL Gas Oil and to Gas Oil Mixture Figure 7: Change in Cold Filter Plugging Point Due to Addition of CFI to GTL Gas Oil and to Gas Oil Mixture Cold filter plugging point and pour point are determined by the amount and the carbon number of wax precipitation. The CFI used in this is an EVA (ethylene vinyl acetate compound). Using EVA type CFI, cold flow performance is improved by refinement and dispersion of precipitating wax. Those effects depend upon the distribution in carbon number of straight-chain paraffin in the fuel. In Figure 7, the reason that no benefit was gained from adding CFI is that, because the distribution in straight-chain paraffin carbon number in GTL gas oil is extremely narrow in comparison to gas oil, precipitating wax cannot be refined and dispersed by CFI, therefore, the wax grows large in size. Moreover, even if gas oil has been mixed in, the distribution in carbon number does not expand when the percentage of gas oil mixture is not more than 50%wt, and the benefit of CFI is not manifested. It is believed that the effect of adding CFI on pour point in GTL gas oil element was recognized because the precipitated wax sank to the very bottom (wax settling phenomenon), so that cold flow performance at the top surface was obtained. 10
4. Synopsis 4.1 Vegetable Oil Methyl Ester The oxidation stability of vegetable oil methyl ester is improved by adding oxidation inhibitor and by mixing with gas oil. To reach the level of oxidation stability in gas oil, however, several 10 to 100 times the amount of oxidation inhibitor normally added to fuel oil is required, and adding such amounts is problematic. Test methods must be investigated so that the degree of impact on practical performance with fuel oil base material can be directly evaluated. When glycerin and water impurities in waste recycle oil, and water have been removed through distillation, the light components are also removed, causing the fuel oil to be made heavy, and the amounts of CO and PM in emissions to increase. Since it was found that the process of making fuel heavy has a more influence on emissions than does the removing impurities, it can be concluded that the influence of impurities on emissions is small. It was learned that the composition of emissions varies with the carbon number of fatty acid ester, which makes up vegetable oil methyl ester. With an increase in carbon number, there was a conspicuous increase especially in PM emissions. To determine whether this is due to physical properties such as boiling point, or to molecular structure, emissions tests with various types of fatty acid esters are required. As for unregulated substances in the emissions of vegetable oil methyl ester, the emission levels of benzene, 1,3-butadiene and acetaldehyde were roughly the same as in gas oil, but formaldehyde tended to increase. There is a correlation between HC emissions and formaldehyde, but no other correlations were recognized respecting other unregulated substances. Further data must be collected to ascertain impacts.. With respect to engine part contamination and lubricant oil deterioration, levels were roughly the same between waste recycle oil and gas oil. It was recognized, however, that there are no problems with the engine detergent property of waste recycle oil, which is of concern because of the properties and characteristics of such oil. 4.2 GTL Gas Oil Properties, Characteristics GTL gas oil is a fuel comprised mostly of straight-chain paraffin hydrocarbons. The density of GTL gas oil is lower, and the cetane number is higher, than that of gas oil. GTL gas oil also contains no sulfur and aromatic components. Thus it is believed to have high potential as an alternative diesel fuel oil. Nevertheless, it is inferior to gas oil in cold flow performance, and it is feared that as a diesel fuel, GTL gas oil would have an adverse effect on low-temperature startup. Oxidation stability, metal compatibility, lubricity and elastomer compatibility of GTL gas oil were evaluated, all of which are of special concern because of GTL gas oil s properties and composition. In all items, material compatibility and characteristics equivalent to those of gas oil were manifested. In the evaluation of elastomer compatibility, when NBR or H-NBR is used as the sealing material in a fuel system designed on the assumption of swelling, special consideration is required because the rates of change in the volumes of NBR and H-NBR are extremely low. 11
By adding CFI and mixing in gas oil, the cold flow performance of GTL gas oil satisfies the standards for cold flow performance in JIS No. 2 gas oil. In order to secure cold flow performance of GTL gas oil, countermeasures must be taken, such as increasing the percentage of isoparaffin at the production. 4.3 Future Issues From the results of investigation and research carried out in JFY2001, the following two points can be cited as future issues. (1) Characteristics evaluation In the JIS method and the ASTM method, the oxidation stability of vegetable oil methyl ester is inferior to that of gas oil, and it was recognized that improvements cannot be made by mixing with gas oil or by adding oxidation inhibitor. It was also learned that there are no problems with the engine detergent performance of waste recycle oil. Given these facts, tests of oxidation stability in vegetable oil methyl esters must be investigated so that its impact can be directly evaluated in practical terms. (2) Emissions evaluation In year, unregulated substances in the emissions of vegetable oil methyl ester were studied. As a new issue, attention has focused on PM in terms of its impact on the human body, considering not only PM weight but also emissions volume by PM size. The influence on PM size when vegetable oil methyl ester has been used as the fuel will have to be determined. Copyright 2002 Petroleum Energy Center. All rights reserved. 12