Ind. Eng. Chem. Res. 1999, 38, 3543-3548
3543
Impact of Esters of Mono- and Dicarboxylic Acids on Diesel Fuel Quality Aikaterini Serdari,* Euripides Lois, and Stamoulis Stournas Laboratory of Fuel Technology and Lubricants, Department of Chemical Engineering, National Technical University of Athens, Zografou Campus, 157 73 Zografou, Athens, Greece
The objective of this work was to assess how esters of mono- and dicarboxylic acids of different structure affect diesel fuel quality, by measuring cetane numbers and cold flow properties of blends of the esters under investigation with gasoil. An increase in either the chain length of the normal alcohol used for the esterification or the chain length of the mono- or dicarboxylic acid involved in the esterification improves the cetane number. Among the fatty acid esters of the same molecular type, those having the carboxylic group close to one end of the molecule have better ignition quality, whereas those having the ester group around the middle of the molecule appear to have better cold flow performance. Oleates combine good ignition quality with adequate cold flow performance, whereas the high oxygen content of some diesters seems to be an extra advantage. 1. Introduction Anticipated changes in crude oil quality, changes in petroleum distillate demands, new requirements for modern diesel engines, and environmental pollution problems result in the necessity to enhance diesel fuel quality. In recent years, fatty acid methyl esters (FAME), commonly known as biodiesel, have successfully been used as diesel fuel substitutes or extenders.1,2 Biodiesel can be easily prepared from vegetable oil triglycerides through the transesterification reaction with methanol; it is compatible with conventional diesel fuel and already comprises a commercial fuel in Europe. In addition, biodiesel has been used in place of heating oil and in several other applications. Due to its oxygen content, biodiesel as a fuel generally results in improved combustion quality; it leads to lower HC, CO, and particulate emissions while a slight increase of NOx and aldehyde emissions is observed in some cases. Besides, it is well-known that biomass-derived fuels can help alleviate the greenhouse effect since the raw material is involved with the photosynthesis phenomenon.3-6 The common biodiesel, however, as it has a cetane number similar to the conventional diesel fuel, essentially offers no improvement in ignition quality. The objective of this work is to assess how esters of mono- and dicarboxylic acids of different structure affect diesel fuel quality, by measuring cetane numbers and cold flow properties. Cetane number is one of the most significant properties of automotive diesel fuel, and its increase usually results in reducing exhaust emissions, lowering fuel consumption, and reducing engine noise.7,8 Also, Cetane number enhancement means better engine performance and better driveability. Cold flow properties characterize the behavior of the fuel at low temperatures. Inadequate cold flow performance may cause serious problems in colder regions, especially in winter. As a consequence, it is important * Telephone: + (30-1)-7723 213. Fax: + (30-1)-7723 163. E-mail:
[email protected].
to guarantee good cold flow behavior due to either the inherently good cold flow performance of the fuel or the addition suitable cold flow improvers. One of the disadvantages of the commonly used biodiesel types is an inadequate cold flow performance during winter. The use of oxygen containing fuels, such as esters, assists in the reduction of particulate matter emissions. More generally, it has been mentioned in the literature that the oxygen-carbon ratio (O/C) of a fuel significantly affects particulate emissions; so to achieve low smoke emissions (lower than 0.5 in the Bosch range), the O/C ratio must be higher than 0.2.9 2. Experimental Procedure Some of the components that are mentioned here were commercially available, and they were used as received. Most of them had a purity of 97% or higher, except for esters of oleic acid, which were of technical grade. The acetate esters were prepared by treatment of the corresponding fatty alcohols with excess of acetic anhydride. After a reaction time of 24 h at room temperature, the mixtures were washed with water and 5% aqueous sodium bicarbonate, dried over anhydrous sodium sulfate and vacuum-distilled to furnish the desired materials, whose properties corresponded to those reported in the literature. The methyl esters (laurate, myristate, palmitate, and stearate) were prepared through the reaction of the corresponding fatty acids with 15-fold excess of methanol, in the presence of acid catalyst [BF3‚O(C2H5)2]. The mixtures were mildly heated, under reflux, with continuous stirring for about 24 h. They then were washed with ice cold water and 5% aqueous sodium bicarbonate; the organic phases were dried over anhydrous sodium sulfate and vacuum-distilled to furnish the desired materials, whose properties corresponded to those reported in the literature. The esters of higher alcohols that were not commercially available were prepared by reacting chlorides of carboxylic acids with alcohols. The alcohols and small excesses of triethylamine were dissolved in tolouene, followed by the gradual addition of 1.2 mol equival of
10.1021/ie9900115 CCC: $18.00 © 1999 American Chemical Society Published on Web 07/22/1999
3544 Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 Table 1. Base Fuel Properties property
value
test method
density at 15 °C, kg/L viscosity at 40 °C, cSt pour point, °C cloud point, °C CFPP, °C Cetane number distillation °C: initial Boiling Point 10% v/v rec at 50% v/v rec at 90% v/v rec at final boiling point aromatics, % vol water, ppm copper corrosion 3 h at 50 °C sulfur content, wt %
0.8543 3.4 -12 -10 -10 47.7
ASTM D-1298 ASTM D-445 ASTM D-97 ASTM D-2500 IP 309 DIN 51773 ASTM D-86
174 206 284 356 382 35.5 68 1A 0.14
Table 2. Cloud Points (°C) and Pour Points (°C) of Esters of Monocarboxylic Acids type of ester tetradecyl acetate hexadecyl valerate decyl caprate ethyl laurate octyl laurate dodecyl laurate
ASTM D-1319 ASTM D-1744 ASTM D-130 IP 336
hexadecyl laurate methyl palmitate ethyl palmitate decyl palmitate
the acid chlorides (when preparing esters of dicarboxylic acids, a 0.7 mol equiv of the corresponding dichloride was used) with continuous stirring and cooling. The mixtures were stirred at room temperature for 24 h. Afterward, they were washed with ice cold water, HCl 0.01 N, and 5% aqueous sodium bicarbonate and distilled (in most cases by vacuum distillation) to receive the final products, whose properties were similar to those reported in the relevant literature. The measurements of cetane numbers (CN) were carried out by employing a standard, single-cylinder BASF diesel engine according to the DIN 51773 method,10 which gives results similar to those obtained by the standard ASTM D-613 method, as it is mentioned in the BASF engine manual;11 this has also been checked with some of our previous experiments.12 The repeatability of the method DIN 51773 is (0.5 units, and its reproducibility is (1.0 units. Cloud points (CP) and pour points (PP) were measured by the ASTM D-250013 and ASTM D-9714 methods, respectively, whereas for cold filter plugging point (CFPP) measurements, a standard automatic apparatus that operates according to the standard IP 309 method.15 was employed. The repeatability of the ASTM D-2500 and ASTM D-97 methods are 2 and 3 °C, respectively. As for IP 309, in the range between -1 and -25 °C, the repeatability is 1 °C. The properties of the base fuel used in this series of experiments are shown in Table 1, along with the standard methods that were used for their determination. 3. Results and Discussion To compare the ignition-improving effectiveness of the various esters under investigation, blending cetane numbers (BCNs) were used. The BCN is the cetane number of the substitute when blended with the base fuel, if the impact on mixture cetane number is considered to be linear. The BCN depends on both chemical structure and concentration and is evaluated according to the following relationship:
BCN ) [A - (1 - x)B]/x where A is the measured cetane number of the blend, B is the cetane number of the base fuel, and x is the concentration of the added component (w/v). The precision of BCN determinations depends on both the precision of the cetane number determination and the concentration of the added compound; in our case,
methyl stearate ethyl stearate methyl oleate ethyl oleate octyl oleate decyl oleate
concn in the base fuel (% w/v)
cloud point (°C)
pour point (°C)
10 20 10 10 10 20 5 5 10 5 5 7 5 10 5 10 5 10 5 10 10 20 10 5 20 5 7
-4 +2 -7 -10 -10 -10 -8 -6 -1 +4 -3 -1 -3 -3 -2 +2 -3 +10 -3 +1 -9 -10 -10 -8 -10 -7 -8
-6 0 -9 -12 -14 -17 -12 -12 -14 -3 -9 -6 -6 -6 -12 -3 -9 0 -6 -3 -12 -12 -12 -12 -12 -12 -12
Table 3. Cold Filter Plugging Point (CFPP, °C) of Esters of Monocarboxylic Acids type of ester
concn in the base fuel (% w/v)
CFPP (°C)
hexadecyl acetate
10 20 10 10 10 5 7 10 10 10 10 20 7
-10 -6 -11 -10 -2 -3 +6 -8 -1 +7 -4 -10 -10
hexadecyl valerate decyl caprate dodecyl laurate hexadecyl laurate methyl palmitate ethyl palmitate decyl palmitate methyl stearate ethyl stearate octyl oleate decyl oleate
for a constant concentration of 5% (w/v) and a CN repeatability of (0.5 units, the BCN precision is about (10 units, whereas for a concentration of 7% (w/v) the BCN precision is about (7 units. The BCNs mentioned in next tables constitute the mean value of three individual measurements. 3.1. Esters of Monocarboxylic Acids. 3.1.1. Cold Flow Performance of Esters of Monocarboxylic Acids. Table 2 presents cloud point and pour point measurements, and Table 3 presents cold filter plugging point measurements at various concentrations. Obviously, esters with high melting points cause cold flow problems. Such esters are methyl palmitate (melting point 30-30.5 °C), methyl stearate (melting point 37-39.5 °C), and hexadecyl laurate (melting point 38.5-39 °C). Among the saturated esters of the same molecular type, those having the ester group around the middle of the molecule appear to have better cold flow performance. For example, if one compares the CP and PP values of ethyl stearate, decyl caprate, and octyl laurate that have the same molecular type (C20H40O2), it is observed that although decyl caprate and octyl laurate seem to have equal performance, ethyl stearate causes a notable increase of CP and PP even when added in
Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 3545 Table 4. Blending Cetane Numbers (BCN) of Esters of Monocarboxylic Acids acetate methyl ethyl propyl butyl hexyl octyl decyl dodecyl tetradecyl hexadecyl octadecyl
valerate
caprate
laurate
myristate
palmitate
stearate
oleate
70 73 71 73 74 84 84 85
72 72 71 73 72 71 72 74
80 80 83 87 87 107 91
81 86
71 72 72 102 102 131 134
60 64 63 64 62 77 81 86 90
49 61 67 68 70
81
Figure 1. Impact of the concentration of ethyl laurate on blending cetane number.
the low concentration of 5%. Moreover, if one compares the cold flow performance of ethyl palmitate and hexadecyl acetate (both of which have molecular type C18H36O2 and the carboxylic group near an end of the molecule), it is obvious that both give almost the same results. With respect to oleates, due to their unsaturated nature (one double bond), even the oleates of higher molecular weight appeared to have very good cold flow performance. On the contrary, the corresponding palmitates and stearates had a negative effect (caused an increase) on the cold flow properties of the base fuel. 3.1.2. Ignition Quality of Esters of Monocarboxylic Acids. In Figures 1-3, the impact of concentration (230% w/v) on BCN is illustrated, for specific types of esters (ethyl laurate, methyl palmitate, and methyl oleate, respectively). Considering the poor precision of BCN measurement (which is displayed by error bars), BCN values appear to be constant and rather independent of the quantity of ester added to the base fuel. In Table 4, the blending cetane numbers of simple esters of monocarboxylic acids are depicted. In all cases, the ester were added in the base fuel in the concentration of 7% w/v. Regarding esters derived from the same monocarboxylic acid, an increase in the chain length of the normal alcohol used for the esterification reaction results in higher BCN values; conversely, if the chain length of the alcohol is kept constant, an increase in the chain length of the acid used also increases the BCN.
88
Figure 2. Impact of the concentration of methyl palmitate on blending cetane number.
Figure 3. Impact of the concentration of methyl oleate on blending cetane number.
Due to their unsaturated bond, the oleic esters appear to have slightly lower BCN values than the corresponding stearates of the same chain length. However, as mentioned above, the cold flow properties of oleates are clearly superior to those of the corresponding saturated
3546 Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 Table 5. Cold Flow Properties of Diesters of Dicarboxylic Acids
type of ester
concn in the base fuel (% w/v)
cloud point (°C)
pour point (°C)
CFPP (°C)
5.0 10.0 5.0 10.0 5.0 10.0 5.0 10.0 10.0
-7 +12 -4 -4 -8 +8 -8 -8 -11
-12 -12 -12 -12 -12 -12 -12 -12 -12
-10
diethyl oxalate diethyl succinate diethyl adipate diethyl azelate dihexyl azelate Figure 4. Blending cetane numbers of acetates and the corresponding fatty ethyl esters of the same molecular type.
Table 6. Blending Cetane Numbers of Esters of Dicarboxylic Acids dimethyl phthalate oxalate malonate succinate adipate azelate sebacate a
Figure 5. Blending cetane numbers of methyl and ethyl esters of the same fatty acids.
esters (stearates). Therefore, oleates comprise an attractive category of fatty acid esters relating to their use as substitute diesel fuels, since they combine good ignition quality and adequate cold flow performance. Another interesting conclusion derives from the comparison of esters of the same molecular type. Among esters of the same molecular type, those having the carboxylic group close to one end of the molecule appear to have better BCNs. In other words, among esters of the same molecular weight, those derived from either a carboxylic acid with a very short chain length and an alcohol with a large chain length or from an alcohol with a very small chain length and a carboxylic acid of a large chain length have the best antiknock performance. When the ester group is around the middle of the molecule, the compound appears to have a lower BCN. For example, methyl laurate has a higher BCN than that of octyl valerate (molecular type C13H26O2); tetradecyl acetate has a better BCN than that of butyl laurate, which has a better BCN than that of hexyl caprate (all three compounds have the same molecular type C16H32O2); methyl palmitate has a higher BCN than that of dodecyl valerate (molecular type C17H34O2); octyl palmitate has a higher BCN value than that of dodecyl laurate (molecular type C24H48O2), and so on. According to the above observations, the acetic esters and the corresponding fatty ethyl esters should have almost the same cetane rating. In Figure 4, the BCN values of acetates and the corresponding ethyl esters of fatty acids are presented. Taking into account the wide precision limits of BCN determination, the corresponding acetates and fatty ethyl esters appear to have practically the same cetane performance. Figure 5 illustrates BCNs of methyl and ethyl esters of the same carboxylic acid. It is obvious that there are no significant differences between BCNs of methyl and
diethyl
19 15 5 24
dibutyl
dihexyl
38
48
81 83
99
dioctyl
21 15 14 47 47
89 70a
Bis(2-ethyl-hexyl) sebacate.
ethyl esters of the same acid, although in some cases, the ethyl esters show a slight increase due to the extra methylene group they contain. This remark, along with the fact that the corresponding methyl and ethyl esters appear to have similar cold flow behavior (in fact, ethyl esters perform a little better), raises the question whether biodiesel should be produced by using ethanol instead of methanol. Ethanol is produced from renewable raw material to a clearly larger extend than methanol; however, the price of ethanol could be a serious constraint to such a development. 3.2. Esters of Dicarboxylic Acids. Table 5 presents results regarding the cold flow performance, whereas results from cetane number measurements of diesters of dicarboxylic acids at a concentration of 5% (w/v) are cited in Table 6. For diesters derived from the same dicarboxylic acid, an increase of the chain length of the alcohol involved in the esterification reaction leads to higher BCN values; conversely, if the chain length of the alcohol is kept constant, an increase in dicarboxylic acid chain length also increases the BCN. As expected, due to their aromatic nature,16-19 the phthalates have lower BCN values. However, even in this case, when the chain length of the alcohol involved in the esterification reaction increases, the BCN improves. Among the diesters tested, dihexyl azelate appeared to have the best antiknock performance. As with most of the diesters tested in this series of experiments, dihexyl azelate also had very good cold flow performance. This compound did not cause any change in the base fuel cold flow properties, even when it was added to the base fuel at a relatively high concentration (10% w/v, Table 5). The good antiknock performance of the linear diesters of higher molecular weight observed here agrees with the results of another reported experiment, according to which the addition of 1% (weight fraction) dibutyl oxalate to a diesel fuel no. 2 caused a cetane number increase of 1.9 units.20 Due to their high oxygen content, many diesters of dicarboxylic acids offer the additional advantage of reducing particulate emissions. In literature, it has been
Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999 3547 Table 7. Chemical Formulas of Esters name of ester decyl acetate dodecyl acetate tetradecyl acetate hexadecyl acetate octadecyl acetate octyl valerate decyl valerate dodecyl valerate tetradecyl valerate hexadecyl valerate ethyl caprate propyl caprate butyl caprate hexyl caprate decyl caprate ethyl laurate propyl laurate butyl laurate hexyl laurate octyl laurate decyl laurate dodecyl laurate hexadecyl laurate methyl myristate ethyl myristate propyl myristate butyl myristate hexyl myristate octyl myristate decyl myristate dodecyl myristate methyl palmitate ethyl palmitate propyl palmitate butyl palmitate hexyl palmitate octyl palmitate decyl palmitate methyl stearate ethyl stearate methyl oleate ethyl oleate propyl oleate butyl oleate hexyl oleate octyl oleate decyl oleate dimethyl phthalate
chemical formula CH3COOCH2(CH2)8CH3 CH3COOCH2(CH2)10CH3 CH3COOCH2(CH2)12CH3 CH3COOCH2(CH2)14CH3 CH3COOCH2(CH2)16CH3 CH3(CH2)3COOCH2(CH2)6CH3 CH3(CH2)3COOCH2(CH2)8CH3 CH3(CH2)3COOCH2(CH2)10CH3 CH3(CH2)3COOCH2(CH2)12CH3 CH3(CH2)3COOCH2(CH2)14CH3 CH3(CH2)8COOCH2CH3 CH3(CH2)8COOCH2CH2CH3 CH3(CH2)8COOCH2(CH2)2CH3 CH3(CH2)8COOCH2(CH2)4CH3 CH3(CH2)8COOCH2(CH2)8CH3 CH3(CH2)10COOCH2CH3 CH3(CH2)10COOCH2CH2CH3 CH3(CH2)10COOCH2(CH2)2CH3 CH3(CH2)10COOCH2(CH2)4CH3 CH3(CH2)10COOCH2(CH2)6CH3 CH3(CH2)10COOCH2(CH2)8CH3 CH3(CH2)10COOCH2(CH2)10CH3 CH3(CH2)10COOCH2(CH2)14CH3 CH3(CH2)12COOCH3 CH3(CH2)12COOCH2CH3 CH3(CH2)12COOCH2CH2CH3 CH3(CH2)12COOCH2(CH2)2CH3 CH3(CH2)12COOCH2(CH2)4CH3 CH3(CH2)12COOCH2(CH2)6CH3 CH3(CH2)12COOCH2(CH2)8CH3 CH3(CH2)12COOCH2(CH2)10CH3 CH3(CH2)14COOCH3 CH3(CH2)14COOCH2CH3 CH3(CH2)14COOCH2CH2CH3 CH3(CH2)14COOCH2(CH2)2CH3 CH3(CH2)14COOCH2(CH2)4CH3 CH3(CH2)14COOCH2(CH2)6CH3 CH3(CH2)14COOCH2(CH2)8CH3 CH3(CH2)16COOCH3 CH3(CH2)16COOCH2CH3 CH3(CH2)7CHdCH(CH2)7COOCH3 CH3(CH2)7CHdCH(CH2)7COOCH2CH3 CH3(CH2)7CHdCH(CH2)7COOCH2CH2CH3 CH3(CH2)7CHdCH(CH2)7COOCH2(CH2)2CH3 CH3(CH2)7CHdCH(CH2)7COOCH2(CH2)4CH3 CH3(CH2)7CHdCH(CH2)7COOCH2(CH2)6CH3 CH3(CH2)7CHdCH(CH2)7COOCH2(CH2)8CH3
dibutyl phthalate dihexyl phthalate diethyl oxalate dimethyl malonate diethyl malonate diethyl succinate dimethyl adipate dibutyl adipate dioctyl adipate dimethyl azelate diethyl azelate dibutyl azelate dihexyl azelate diethyl sebacate bis(2-ethyl-hexyl) sebacate
CH3CH2OOCCOOCH2CH3 CH3OOCCH2COOCH3 CH3CH2OOCCH2COOCH2CH3 CH3CH2OOCCH2CH2COOCH2CH3 CH3OOCCH2(CH2)2CH2COOCH3 CH3(CH2)2CH2OOCCH2(CH2)2CH2COOCH2(CH2)2CH3 CH3(CH2)6CH2OOCCH2(CH2)2CH2COOCH2(CH2)6CH3 CH3OOCCH2(CH2)5CH2COOCH3 CH3CH2OOCCH2(CH2)5CH2COOCH2CH3 CH3(CH2)2CH2OOCCH2(CH2)5CH2COOCH2(CH2)2CH3 CH3(CH2)4CH2OOCCH2(CH2)5CH2COOCH2(CH2)4CH3 CH3CH2OOCCH2(CH2)6CH2COOCH2CH3 CH3(CH2)3C(C2H5)HCH2OOCCH2(CH2)6CH2COOCH2C(C2H5)H(CH2)3CH3
mentioned that even dibutyl phthalate,21 which according to our measurements has poor cetane quality, has been successfully used for diminishing particulate emissions from a diesel engine. Except for the high oxygen content, some of the diesters examined here offer the extra advantage of enhancing cetane quality. Nevertheless, of paramount importance is the fact that the simple esters of fatty acids can be prepared from renewable raw materials through simple production procedures; mix-
tures of esters of fatty acids can easily be produced directly from vegetable oils or undesirable animal fats (biomass), which may prove an attractive way to substitute diesel fuel. 4. Conclusions The following conclusions can be drawn from this study:
3548 Ind. Eng. Chem. Res., Vol. 38, No. 9, 1999
Among the saturated esters of the same molecular type, those having the ester group around the middle of the molecule appear to have better cold flow performance. Due to the oleic double bond, even the high-molecularweight oleates have very good cold flow performance. Regarding esters derived from the same monocarboxylic acid, an increase in the chain length of the normal alcohol used for the esterification results in higher BCN values; conversely, if the chain length of the alcohol is kept constant, an increase in the chain length of the acid involved in the esterification also increases the BCN. Due to their unsaturated bond, the oleic esters appear to have slightly lower BCN values than the corresponding stearates. Oleates comprise an outstanding category of fatty acid esters, because they combine good ignition quality with adequate cold flow performance. BCN values appear to be about constant and rather independent of the quantity of ester of fatty acid added to the base fuel. Among the esters of fatty acids that have the same molecular type, those having the carboxylic group close to one end of the molecule appear to have better BCN values. For diesters derived from the same dicarboxylic acid, an increase in the chain length of the alcohol involved in the esterification reaction leads to higher BCN values; conversely, if the chain length of the alcohol is kept constant, an increase in dicarboxylic acid chain length also increases the BCN. The diesters tested in this series of experiments had satisfactory cold flow performance. Due to their high oxygen content, many diesters of dicarboxylic acids offer the additional advantage of reducing particulate emissions. However, it is important to recall that simple esters of fatty acids can be prepared from renewable raw materials (vegetable oils and animal fats), through simple procedures. Nomenclature BCN ) blending cetane number CFFPP ) cold filter plugging point CN ) cetane number CP ) Cloud Point PP ) Pour Point
Acknowledgment We thank Hellenic Aspropyrgos Refinery for allowing us to use their standard BASF engine and the automatic CFPP apparatus for carrying out CN and CFPP measurements, respectively. In addition, the Hellenic Aspropyrgos Refinery supplied us with the diesel fuel that was used in all experiments. Appendix Chemical formulas of the compounds in this study are presented in Table 7. Literature Cited (1) Koerbitz, W. Recent Developments in Biodiesel. Symposium LIPIDEX ‘97; Antwerp, Belgium, 21 March 1997.
(2) European Commission DG XVII. Draft Mandate to CEN for Biodiesel Standardization. Doc. 29/96 EN, M/245. Brussels, 11 June 1996. (3) Scharmer, K.; Gosse, G.; Gabrielle, B.; Golbs, G.; Lambert, L.; Poschmann, Th.; Rodenbrock, A.; Zimalla, K. Energy Balance, Ecological Impact and Economics of Biodiesel Production in Europe. Altener Programme 4.1030/E/94-002-1; Part II, December 1996. (4) The Use of Vegetable Oils or Their Byproducts in Diesel Engines; Technical Guide; Ademe: Paris, February 1994, No. 1723. (5) Proposal for a Council Directive Concerning the Specifications for Vegetable Oil Methylesters (Biodiesel) as a Motor Fuel. Presented by the Commission, EEC, Brussels, May 1993. (6) Francese, D.; Gamba, G.; Aroldi, C.; Rocchietta, C. In Environmental Effects and Economic Viability of Alternative Diesel Fuels from Vegetable Oils. Proceedings of the Ninth International Symposium on Alcohol Fuels, ISAF-Firenze, 1991; pp. 984-987. (7) Weidmann, K.; Menrad, H.; Reders, K.; Hutcheson, R. C. Diesel Fuel Quality Effects on Exhaust Emissions. SAE Paper 881649, 1988. (8) Kagami, M.; Akasaka, Y.; Date, K.; Maeda, T. The Influence of Fuel Properties on the Performance of Japanese Automotive Diesels. SAE Paper 841082, 1984. (9) Hashimoto, T.; Akasaka, Y. Evaluation of Oxygenated Fuels Using Conventional and a New Type of Diesel Engines. Proceedings of the Ninth International Symposium on Alcohol Fuels, ISAFFirenze, 1991; pp 336-341. (10) Bestimmung der Zundwilligkeit von Dieselkraftstoffen. DIN 51773, DIN Taschenbuch 57, Mineralole und Brennstoffe 3, Beuth 1980. (11) Testing-Diesel-Unit-BASF, for Rating Diesel Fuels. Kruger Prufmaschinenbau, D-6839 Oberhausen 2, West Germany, 1990. (12) Stournas, S.; Lois, E.; Serdari, A. The Effects of Fatty Acid Derivatives on the Ignition Quality and Cold Flow of Diesel Fuel. J. Am. Oil Chem. Soc., 1995, 72, 433-437. (13) ASTM D-2500. Annu. Book of ASTM Stand. 1988; Section 5, Vol. 02. (14) ASTM D-97. Annu. Book of ASTM Stand. 1988, Section 5, Vol. 01. (15) IP 309, IP Standards for Petroleum and Its Products, Part 1, Methods for Analysis and Testing, 38th ed.; 1979; Vol. 2. (16) Slodowske, W. J.; Sienicki, E. J.; Jass, R. E.; McCarthy, C. I. Diesel Fuel Property Effects on Exhaust Emissions from a Heavy Duty Diesel Engine That Meets 1994 Emissions Requirements. SAE Paper 922267, 1992. (17) Ullman, T. L.; Mason, R. L.; Montalvo, D. A. Study of Fuel Cetane Number and Aromatic Content Effects on Regulated Emissions from a Heavy-Duty Diesel Engine. Chem. Abstr. 1992, 116, 132472d. (18) Diesel Fuel, A Study of the Effects of the Aromatic Content of Diesel Fuel on Atmospheric Emissions. Concave Rev. 1992, 1 (1) April, 10-11. (19) Virk, K. S.; Lachowicz, D. R.; Mitcell, E. Diesel Fuel Cetane Number, Aromatic Content and Exhaust Emissions. Prepr. Pap.s Am. Chem. Soc. Div. Petrol. Chem. San Francisco, 1992; pp 701703. (20) Dillon, D. M.; Jessup, P. J. Composition for Cetane Improvement of Diesel Fuels. U. S. Patent 4,740,215, 1988. (21) Kyowa Hakko Kogyo Co, Ltd. Diesel Fuel Compositions. Japan Patent 59,207, 988, 1985.
Received for review January 11, 1999 Revised manuscript received June 7, 1999 Accepted June 11, 1999 IE9900115
