INDUSTRIAL AND ENGINEERING CHEMISTRY
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2133
and White, A. H., IND.ENG.CHEM.,23, 259-66
(13)
Milner, G., Spivey, E., and Cobb, J. W., J . Chem. SOC.,1943, pp.
(4) Johnstone, H. F., Chen, C. Y., Scott, D. R., I b i d . , 44, 1564-9
(14)
Neumann, B., Kroger, C., and Fjngas E., Z. anorg. u. allgem.
(3) Fox, D. A., (1931).
578-89.
(1 952).
(5) Kroger, C., Angew. Chem., 52, 129-39 (1939). (6) Kroger, C., and Knothe, H., Brennstoff-Chem., 20, 373-8,
(1921).
388-91 (1939). (7)
Chem., 197, 321 (1931). (15) Sihvonen, V., Fuel, 19,35-8 (1940). (16) Taylor, H. S., and Neville, H. A., J . Am. Chem. SOC., 43,2065-70
Kroger, C., and hilelhorn, G., Ibid., 19, 157-69 (1938).
( 8 ) Ibid., pp. 257-62. (9) Long, F. J., and Sykes, K. W., J . chim. phys., 47, 361-78 (1950). (10) Long, F. J . , and Sykes, K. W., Proc. Roy. Soc., A 193, 377-99 (1 948). (11) Ibid., A 2 1 5 , 100 (1952). (12) Marson, C. B., and Cobb, J. W., Gus. J., 175,882 (1920).
(17)
Young, D. C., Pacific District National Carbon Co. private communication, November 1952.
-4CCEPTED April 23, 1966. RECEIVED for review April 19, 1964. From a thesis submitted t o t h e faculty of t h e Cniversity of Gtah in partial fulfillment of the requirements for the degree of doctor of philosophy March 1954. Presented a t Division of Gas and Fuel Chemistry, 124th Meeting, ACS, Chicago, Ill., September 1953.
Emulsified Fuels in Compression Ignition Engines .
I. CORNET AND W. E. NERO’ University of California, Berkeley, Calg.
T
HE object of this investigation was to determine experimentally the effects of water emulsified in Diesel fuel on the performance of a Diesel engine. The use of additives to improve the cetane number of Diesel fuels has been widely investigated. Acetone peroxide and alkyl nitrates are generally considered to be the most effective (4,8, 9, 13, 22, 26), but are not completely soluble in Diesel fuel. I n classifying ignition accelerators, Bogen and Wilson (4)make the following rough generalization: “The more effective the ignition accelerator, the less soluble in Diesel fuel.” Mang watersoluble compounds which theoretically would be good additives are not soluble in Diesel fuel, but they may function as ignition accelerators. It would therefore be of interest to know how water, as a vehicle for these additives, would affect the fuel. Emulsified fuels are the subject of numerous patents ( 1 , 2, 10-12, id-19, 21, 2 5 , W )dating back over 50 years ( I d ) , but rela1
Present address, T h e Trane Co., Los Angeles, Calif.
Figure 1.
Experiment station
tively little information on such fuels has appeared in the technical literature ( 5 ) . EQUIPMENT, MATERIALS, AND PROCEDURE
Description of Apparatus. ENGINE.The engine used, shown in Figure 1, was a General Motors series 2-71 Diesel, which is a two-stroke-cycle, two-cylinder engine employing a Roots-type blower supercharger and General Motors unit injectors, injecting solid fuel directly into the cylinder chamber. I n a Diesel engine, the throttle controls the quantity of fuel injected. I n order to have full control of the throttle position, the governor unit was rendered inoperative and replaced mith the mechanical throttle control lever shown in Figure 2. Xormal injection timing (14” C. before TDS, top dead center) was used in all runs except four in TThich the effects of varying injection timing were determined. DYNAMOMETER. The engine was connected t o a Sprague dynamometer rated a t 122-pound load from 500 to 2000 r.p.m. on a torque arm of 1.3125 feet. The torque arm was connected to a balance scale, and the load read directly from the scale. The output from the dynamometer was absorbed in a series of cast-
Figure 2.
Throttle control lever
INDUSTRIAL AND ENGINEERING CHEMISTRY
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iron grids and the load on the engine was controlled by varying the number of grids connected and the field voltage of the dynamometer. All controls were located on a panel board, which was also provided with switches for connecting the dynamometer as a motor for starting the engine. The field excitation was taken from the campus direct current supply and adjusted by a variable-resistance rheostat. SPEED-MEASURING EQUIPMENT. A Strobotac stroboscopic tachometer (General Radio Co., Cambridge, Mass.) was used for all speed measurements, periodic checks being made with a tachometer, Both the Strobotac and tachometer were calibrated against a synchronous-motor-driven calibrator. To ensure accurate speed measurements, the Strobotac was calibrated against its reed, in the range of operation, approximately once an hour and rechecked against the calibrator periodically. I n all cases adjustments were made so that the Strobotac error was less than 1%.
INJECTORS -
R
F
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Figure 3.
TANK
1
System €or fuel mixing and distribution
FUEL MIXING AND DISTRIBUTIONSYSTEM. A commercial type (Waring) Blendor was used to emulsify all fuel mixtures. The blender, through appropriate copper tubing and valves, was connected to an aircraft fuel pump, a weighing tank, and a storage tank, shown in Figure 3. By proper manipulation of the valves, the fuel could be pumped from any or all of the tanks to any or all of the tanks. Thus, the mixture could be emulsified and circulated simultaneously. The weighing tank, mounted on a 1-to-1 balance scale, was used to determine the fuel rate for both the plain Diesel fuel and the emulsified fuel. Thus, a direct weight rate was obtained. Copper tubing was used for connections between the engine transfer pump, the weighing tank, and a 5-gallon Diesel fuel supply tank, and for connection between the engine return line and the weighing tank, supply tank, and a waste tank. By
V A R I A T I O N OF V I S C O S I T Y O F DIESEL F U E L DUE T O T H E A D D I T I O N OF W A T E R
Vol. 47, No. 10
proper adjustment of the valves, the fuel supply could be taken from either the weighing tank or the supply tank and the excess from the injectors discharged to the weighing tank, supply tank, or waste tank. PHYSICAL PROPERTIES OF LIQUIDSUSED. The fuel mixtures used were emulsions of a commercial high-grade Diesel fuel (California stock, cetane number 39), emulsifier (Polyethylene glycol 400, di-triricinoleate), and distilled water. Physical properties of the emulsions are shown in Figure 4. The higher heating value of the Diesel fuel was 20,150 B.t.u. per pound, as determined with an Emerson bomb calorimeter. All percentages cited are percentages of the total mixture, by weight. The emulsifier used was polyethylene glycol 400 di-triricinoleate with a specific gravity of 0.970 a t 80" F., the average mixing temperature. z.
Experimental Procedure. The engine was operated a t full throttle with plain Diesel fuel a t speeds ranging from 800 to 1450 r.p.m. in order to determine its normal operating characteristics and reproducibility of results. This speed range was chosen so as to bracket the normal governed speed of 1200 r.p.m. for stationary installations. Two thousand revolutions per minute is the normal governed speed when this engine is used for truck installations. Runs were made at full throttle and speeds ranging from 800 to 1450 r.p.m. using mixtures of Diesel fuel, emulsifier (0.20 volume yo of the mixture), and distilled water, varying from 1 volume % (1.16 weight %) of the mixture, to 20 volume % (22.5 weight %) of the mixture, and for each percentage of water used, performance data were collected. I n order to determine the effects of the emulsifier, four runs were made a t full throttle with a mixture of 0.25 volume 70 of emulsifier and 99.75 yo of Diesel fuel. For all runs with the watered fuel the engine was started and thoroughly warmed on plain Diesel fuel. During this period data were taken as a check against the normal operating characteristics to ensure that a true comparison could be made. The criterion for this check was the torque. It was felt that as long as the torque m-as in agreement and exhaust t,emperatures were reasonably close, the specific fuel consumption would be within the desired accuracy of 1%. Therefore, only spot checks of specific fuel consumption were made. A t the conclusion of each run with the watered fuel the engine was again run on plain Diesel fuel to ensure that all fuel lines were cleared of the mixed fuel. After performance data had been obtained with the watered fuel, a set of data was collected with plain Diesel fuel a t full throttle and speeds from 800 to 1450 r.p.m.; these performance curves agreed with the reference curves. Thus, it could be as-
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V A R I A T I O N OF S P E C I F I C G R A V I T Y OF D I E S E L F U E L D U E TO T H E A D D I T I O N OF W A T C R DATA O B T A I N E D B Y WESTPHAL BALANCE AT RO'F-
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2 4 6 8 1 0 1 2 1 4 PERCENT WATER IN MIXTURE-BY WEIGHT
Figure 5. Variation of specific fuel consumption with water emulsified in Diesel fuel PERCENT WATER IN MIXTURE- BY WEIGHT
Figure 4.
Properties of mixed fuels
Witte engine, normal timing, constant load, constant speed (6) Specific fuel consumption Diesel fuel based on hydrocarbon
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2135
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1955 0
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Performance curves
General Motors Diesel engine Model 2-71, full throttle, normal timing, plain Diesel fuel
Figure 7.
sumed that the operation of the engine had not changed significantly during the course of experimentation. Following these runs, data were obtained from 800 to 1400 r.p.m. at full throttle with a mixture of 15 volume % (18.6 weight yo) of 5-V ammonium nitrate aqueous solution, 0.20 volume yo (0.23weight %) emulsifier, and Diesel fuel. Performance curves were obtained and compared with normal operating characteristics. A series of runs was made with plain Diesel fuel and with a 15 volume yo(17.02weight yo)water mixture at injection timing settings of 2.6' advanced, 1.2"advanced, 1.2"retarded, and 2.6" retarded from the normal setting of 14' before TDC, a t full throttle and speeds from 1270 to 1435 r.p.m. I n order to compare the performance of this engine on watered fuel with the equivalent plain fuel performance based on the same rate of petroleum fuel injected, runs were made a t part throttle (50 t o 90%) and speeds ranging from 850 to 1325 r.p.m. using plain Diesel fuel, To extend the range of this investigation, the engine was run at full throttle and speeds from 850 to 1370 r.p.m., using a mixture of 33.6 yowater, 0.40 yoemulsifier, and 66.0 weight yoDiesel fuel and performance data were obtained.
1
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'I RESULTS A N D DISCUSSION
I n this study i t was desired to lay a foundation for future investigations with water-soluble Diesel fuel additives, which required the establishment of the effects of water in the fuel on the performance of a Diesel engine. Figure 5 shows results obtained by Cornet and Boodberg in an earlier study (6) using a Witte Diesel engine. Aqueous emulsions, prepared as noted in the procedure, were used as the fuel, and performance data were obtained for a twocylinder, two-stroke-cycle, direct-injection, General Motors 2-71 Diesel engine. Figure 6 shows the results obtained with plain Diesel fuel at full throttle and is the basis of the comparison between plain fuel performance and watered fuel performance shown in Figures 7, 8, 9, and 10. Figure 6 also indicates that in the four runs made with a mixture of 0.28y0 emulsifier and 99.72% Diesel fuel no change in specific fuel consumption or torque was evident. Figures 7 to 21 illustrate graphically the results obtained with this Diesel engine. Figure 22 indicates the effects of a 5N ammonium nitrate solution on the performance of this engine.
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Figure 8.
900
1000 1100 SPEED
-
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Effects of water in fuel on specific fuel consumption
General Motors Diesel engine Model 2-71, full throttle
Eighty-nine per cent of all experimental points are within 1% of the curves as drawn, and 96.5% are within 1.5%. Figure 23 is taken from data obtained by Cornet and Boodberg ( 5 ) . These figures are discussed below. I n general, efficiency of operation of compression ignition engines is controlled b y many complex variables. The fuel injection system, injection pressure, drop size, spray formation, injection timing, combustion chamber design, supercharging, valve timing, and type of fuel used are all of primary importance in determining the thermal efficiency of a given engine. Of these
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 47,No. 10
22.5% water. However, as speeds increase, the increase in efficiency decreases and a t 1200 0.660 and 1300 r.p.m. the curves have shifted suffiF a ciently to cross the curves of speeds as low as 1000 r.p.m. Noting the curve of specific fuel l J 7c l0 . 6 2 0 consumption (pounds of petroleum fuel per z m 0 brake horsepower-hour) equal to plain fuel 50.500 specific fuel consumption (petroleum fuel as it --1a comes from the refiner), it is evident that the 3 m L O z 0.540 minimum percentage of water that must be 0' present to give increased economy increases E2 y 0.500 with an increase of speed. Considering the portion of the curves where v) a the specific fuel consumption is reduced, as com0.460 0 2 4 6 8 10 12 14 16 18 20 22 pared with pure fuel data a t full throttle, it was P E R C E N T WATER I N M I X T U R E BY WEIGHT assumed that the reason was more complete Figure 9. Variation of specific fuel consumption with water emulcombustion and less afterburning. Inasmuch sified in Diesel fuel as water is relatively insoluble in Diesel fuel, it may be assumed that a mixture of fuel and General Motors Diesel engine Medel2-71, full throttle, normal timing water is obtained which consists of droplets of water surrounded by oil. When this mixture is injected into the cylinder, the water flashes into steam, owing to variables, all except injection timing and type of fuel used are the high temperature, and in so doing breaks the oil into smaller design features. For a given engine the optimum setting of inparticles, increasing the dispersion in the cylinder chamber. ThuP, jection timing, for a normal fuel and a normal range of speeds, ignition is aided ( 7 ) , more complete combustion occurs, less is determined by the manufacturer. Thus, the type of fuel afterburning takes place, and the thermal efficiency is increased. used in an engine is the only major variable that would change It was noted by visual observation in this investigation that in its operating characteristics. As the rate of burning, rate of one case less smoke was present in the exhaust gases with water pressure rise, and completeness of combustion are dependent in the fuel than with pure fuel, indicating less free carbon in the on the quality of fuel used, maximum efficiency would be obcombustion gases. Van Steenbergh (9, 25) observed that when tained only with the best available fuel (90). Because of dissooil is mixed with superheated steam and subjected to contact ciation a t the high temperatures encountered and inadequate with carbon at temperatures near 1800' F., the steam is decomfuel and air dispersion, complete combustion in the cylinder is posed, resulting in the production of methane, hydrogen, and rarely obtained with any fuel. carbon monoxide. Thus, there is a possibility that the water-gas As indicated by Figure 9, which was derived from Figures 7 reaction which was promoted by the added water might have and 8, general trends may be established as to the effects of water contributed to the improved combustion efficiency and also added to Diesel fuel on the efficiency of a Diesel engine. At might tend to reduce the carbon formation in the engine. It was all speeds water up to approximately 5 weight % ' in the mixture beyond the scope of this investigation to analyze the smoke produces a deleterious effect on the engine economy. Beyond formation and carbon deposits; therefore, further experithis percpQtage the economy is increased, a t all speeds, up to mentation should be done. 0.700
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Figure 11.
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.
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October 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
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T H R O T T L E SETTING ---O-
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General Motors Diesel engine Model 2-71, normal timing, plain Diesel fuel
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Specific fuel consumption compared with fuel injection rate
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Fuel injection characteristics
General Motors Diesel engine Model 2-71, normal timing
Approximately 1300 B.t.u. per pound are required to bring the water in the fuel to exhaust conditions; thus i t would be reasonable to expect that a t the higher percentages of water this heat would become a significant factor and tend to overcome the beneficial effects of water and cause the specific fuel consumption to increase. Figure 9 shows that at all speeds the specific fuel consumption is a minimum and still decreasing a t 22.5y0 water in the mixture, indicating that the limiting conditions had not been reached and that higher percentages of water could be used advantageously. The injection pressure of this engine varies from approximately 7000 pounds per square inch at idle to approximately 40,000 at
2100 r.p.m. ( 2 4 ) . Because drop size generally decreases with increasing injection pressure and rate of injection (8), the effect of the water on drop size should become less as speed increases, and the rate of decrease of specific fuel consumption should become less. This is borne out by the changing slopes of the curves in this range. The maximum reduction of specific fuel consumption of 9.7yo occurs at 850 r.p.m. and 22,5y0water. Water in percentages less than that which gives maximum specific fuel consumption for a given speed is apparently insufficient to break up the fuel effectively. At low concentrations of water and high temperatures it is possible that the water dissolves in the oil. The predominating effect of dissolved water is to absorb heat, increasing the ignition delay and decreasing the thermal efficiency. Where the water exists as a discrete phase, the atomization of the fuel due to the rapid formation of steam becomes significant, causing an increase in combustion efficiency and therefore a decrease in specific fuel consumption. The percentage of water required for maximum specific fuel consumption and for specific fuel Consumption equal to that with-
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Torque characteristics
General Motors Diesel engine Model 2-71, normal timing
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General Motors Diesel engine Model 2-71, normal timing, plain Diesel fuel
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 47, No. 10
I70
165 I60 I55 165
160 I55
6
$ 0 520
150
3 0
a I
0540 0.520
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800 900 SPEED-
RPM
Figure 16. Specific fuel consumption with water in fuel compared with equivalent plain fuel General Motors Diesel engine Model 2-71, normal timing Equivalent means same amount of petroleum fuel injected per stroke with and without water.
out water tends to increase with increasing speeds, again indicating that water is more effective when the drop size is relatively large. Thus, low pressure injection units might derive even more benefit from water mixed with the fuel than is evident in this Diesel engine. Data obtained by Cornet and Boodberg (6) (Figure 5) show that for a Witte Diesel engine, which has a low pressure (1350 pounds per square inch) injection system, the specific fuel consumption was 8.4% lower than that with plain fuel and still decreasing a t 13.6% water in the fuel mixture, for a constant load test. The general shape of the curves in Figure 9 and Figure 5 is similar. The increase of specific fuel consumption at low concentrations of water is much more pronounced in the General Motors engine than in the Witte engine, and the percentage of water required to obtain an increase in efficiency is higher. Thus, the type of combustion chamber, type of injectors, injection pressure, and general engine design must be influencing factors on the performance of a Diesel engine with water added to the petroleum fuel. The curves of Figure 10 indicate that in most cases the torque and hence, the output of the engine, are reduced with increased percentages of water. However, in all cases above approximately 5y0water, the reduction of torque is less than the corresponding reduction of Diesel fuel. Therefore, the addition of water not only increases the efficiency of the engine but also increases the output-Le., for a given weight of fuel injected the specific fuel consumption would be lower and the torque higher if water above 5% were added to the fuel than if plain Diesel fuel were used. The reduction of output with water in the fuel is due to the reduction of fuel per charge and is an advantage in that, for a given engine output, the injectors would be larger, making the metering and construction problems easier. While the preceding discussion might satisfactorily explain the general trends of the curves, the magnitude of the improvnient (up to 9.7%) seemed too great to have been caused by water in the fuel. As shown by data obtained by Cornet and Boodberg
1000 1100 SPEED
1200
- RPM
1300
1400 150C
Figure 17. Torque with water in fuel compared with equivalent torque with plain fuel General Motors Diesel engine Model 2-71, norrhal timing
( 5 ) , (Figure 23), the cetane number of Diesel fuel was materially reduced with increased percentages of water in the mixture. This fact would indicate a reduced efficiency with water in the fuel. It has been found (9) that when water is sprayed into the air-gas mixture of a spark-ignition engine, concentrations up to equal weights of water and gasoline can be used without appreciably affecting the economy, and that the water has no effect on the amount of gasoline required t o carry a given load. If this idea were carried over to a Diesel engine, the anticipated result of using water in Diesel fuel would, a t best, be unchanged efficiency. I n order to explain satisfactorily the results originally obtained, performance data were obtained with plain Diesel fuel a t varying throttle settings through the range of speeds. The results are shown in Figures 11 to 15 and indicate that possibly the only effect of water is to reduce the throttle setting. Thus, a true comparison between plain fuel and watered fuel performance must be based on the same rate of fuel injection. Figure 12 shows the fuel injection rates for various throttle settings and varying amounts of water in the mixture. For a given speed and a given fuel injection rate the engine has a fixed specific fuel consumption, torque, and exhaust temperature (Figures 13, 14, and 15). By determining the rate of fuel injection and speed for the watered fuel runs from Figure 12 and taking the equivalent plain fuel performance from Figures 13, 14, and 15 and comparing the resulting curves with watered fuel performance, a true evaluation of the effects of water can be made. Figure 16 indicates t h a t in all cases the water caused an increased specific fuel consumption and, correspondingly, a reduced torque (Figure 17). T h e exhaust temperature (Figure 18) does not follow so simple a pattern and indicates a possible beneficial effect due to the water. The results of using 33.6y0 water by weight in the fuel mixture are shown in Figure 19. The equivalent plain fuel curves-i.e., curves based on a throttle setting which gives the same rate of petroleum fuel injected as that with water in the fuel mixture-
2139
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1955
a' 800
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Figure 19.
1500
-
1200 1300 RPM
1400
I500
Performance curves
General Motors Diesel engine Model 2-71, full throttle, normal timing, 33.6 weight % water in fuel mixture
Figure 18. Exhaust temperature with water in fuel compared with plain fuel General Motors Diesel engine Model 2-71, normal timing
6 4
beyond 1150 r.p.m. are extrapolated and appear to be accurate to within 301,. Figure 20 shows the effects of water on the specific fuel consumption and exhaust temperature of this engine based on the equivalent plain fuel performance. The spread in values a t different speeds is indicated by the distance between the curves and, up to 22.5y0 water in the mixture, is less than 1%. Figure 21 presents an average over-all summary of data obtained in this investigation, and therefore, a generalized evaluation of results. Noting the specific fuel consumption curve, a definite similarity to Figure 9 is evident. At concentrations of water between 0 and 7%, the effect of the water is to increase the specific fuel consumption, by a maximum of 5% over that obtained with plain fuel. This corresponds to the 0 to 5% range of Figure 9, wherein the average maximum increase is 5.6%. In the range from 7 to 33.6% water, the specific fuel consumption is increased by an average of 1% over that obtained with plain fuel, which is approximately the same as the probable experimental error. Therefore, in this range, the effect of water on the efficiency of the engine is negligible. Considering the portion of the curve below 7yowater, some factor or factors must be present which cause the increase in specific fuel consumption. Figure 21 shows that in this range the exhaust temperature is higher than with plain Diesel fuel and Figure 23 shows that the cetane number is slightly lower than that of plain fuel. The higher exhaust temperature would indicate more afterburning was taking place or that the peak pressure was higher or occurred later in the cycle. This would imply a longer ignition delay, as would the lower cetane number. At 3'% water the maximum increase in specific fuel consumption occurs. With increased water content, breaking up of the fuel droplets by the explosive vaporization of the water may cause an increased combustion efficiency which would tend to overcome the losses due to increased ignition delay. As the concentration of water is increased, the increase in combustion efficiency is great enough to overcome the effects of the lower cetane number and the effects of the increased ignition delay, and a t approximately 7% water the specific fuel consumption is practically t>hesame as that with plain Diesel fuel. At this same point the
2 0
u
0
4 8 12 16 20 24 28 32 PERCENT WATER IN FUEL M I X T U R E - BY WEIGHT
36
Figure 20. Change in specific fuel consumption and exhaust temperature due to water i n fuel mixture General Motors Diesel engine Model 2-71, normal timing
exhaust temperature increase is a t a maximum. Between 7 and 18% water content the specific fuel consumption remains unchanged but the increase in exhaust temperature drops to zero. Thus, in this range, the combustion efficiency was increased sufficiently t o account for the vaporization and heating of the water and to prevent the increased ignition delay, due to the lower cetane number, from causing a higher specific fuel consumption. Beyond 18% water the increase in combustion efficiency and the losses due to increased ignition delay (lower cetane number) are essentially equal, with the heat required to vaporize and heat the water being abstracted from the exhaust gases. As it x a s necessary to convert the water in the fuel into steam at exhaust conditions, it could be assumed that this amount of heat was taken from the fuel, making it possible to lower the specific fuel consumption curve by this amount of energy. Inasmuch as the heat required to establish the exhaust temperature must also come from the fuel, a further adjustment could be made to account for the heat required to cause the temperature changes shown in Figure 21. Up to approximately 18% water, the exhaust temperature is higher than the plain fuel temperature;
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
r z:.“ -20
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24
28
32
36
P E R C E N T WATER I N F U E L M I X T U R E - BY WEIGHT
Figure 21. Average change in specific fuel consumption and exhaust temperature due to water in fuel mixture Normal timing, General Motors Diesel engine Model 2-71
d I0.580 a 20.560
.
~~
E Q U I V A L E N T P L A I N FUEL CURVES
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I
I
I
I
1
50.540 a 0.520 70.500 20.480 m
I
I
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,
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145 140
135
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720 680 640 600
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1000 1100 1200 I300 SPEED RPM
Figure 22.
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1‘400 1500
Performance curves
General Motors Diesel engine Model 2-71, full throttle, normal timing, 18.6 weight % 5Nammonium nitrate solution in fuel mixture
Vol. 47,No. 10
therefore, the resulting curve is lower in this region. Between 18 and 33.6y0 water the exhaust temperature is lower than that with plain fuel, indicating that the heat required to vaporize and heat the water has reduced the heat available to the exhaust gases. The resulting curve of per cent change of “specific fuel consimption” adjusted for the heat required to vaporize and heat the water and to prevent a change in exhaust temperature is shown in Figure 21, and indicates the effects of water on the combustion efficiency of this engine. However, as this is a generalized and averaged curve and a complete heat balance was not an objective of this investigation, no specific trends can be established. In general, a t low concentrations (less than 7y0),water produces a deleterious effect on engine performance when emulsified in Diesel fuel. Beyond this percentage the effects are insignificant. While this shows that no direct benefits can be obtained with water in the fuel in this engine, it also indicates that indirect benefits may be possible through the addition of water-soluble additives. A complete evaluation of the apparent redistribution of energy indicated in Figure 21 was beyond the scope of this investigation; thus further experimentation should be done. Such investigations could include pressure-time diagrams, complete heat balance, and analysis of exhaust gas. Figure 22 shows graphically the result of using 18.6 weight % of 5N aqueous ammonium nitrate solution emulsified in Diesel fuel. The specific fuel consumption was 1.4y0lower than that of equivalent plain fuel a t 1100 r.p.m. Taking into consideration the heat required to vaporize and heat the water and t o increase the exhaust temperature, the combustion efficiency was increased by approximately 2.5y0. Inasmuch as the exhaust temperature was higher at all speeds with the ammonium nitrate solution than with plain fuel, it may be possible to obtain a higher thermal efficiency from the mixture by advancing the injection timing. While ammonium nitrate contains a small amount of chemical energy, the percentage in this solution was so low that it would not affect the results shown. During the runs smoothness of engine operation was noted, indicating the ammonium nitrate is an effective ignition accelerator. This is also borne out by the results obtained by Cornet and Boodberg ( 5 ) (Figure 23), which show that for a mixture of 18.670 by weight of 5N aqueous ammonium nitrate solution and Diesel fuel, an increase of approximately one cetane number is obtained over that of the plain fuel. Although only a limited number of runs were made with variable injection timing, the results, compared with equivalent data on plain fuel, indicate that 17.02 weight yowater in the fuel mixture has essentially no effect on the thermal efficiency of this engine, with injection timing settings from 2.6% retarded to 2.6% advanced from normal. T o evaluate the effects of injection timing on the performance of a Diesel engine with water emulsified in Diesel oil, a complete investigation should be made. CONCLUSIONS
0
2
4
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8
IO
12
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P E R C E N T N H 4 N O s SOLUTION IN M I X T U R E
Figure 23.
16 18 WEIGHT
- BY
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Effect of water and ammonium nitrate on cetane number of Diesel fuel (5)
Water has been emulsified in Diesel fuel up to 33.6 weight % ’ of the total mixture, and the ease with which this emulsion was made indicates that higher percentages of water may be used. A General Motors Model 2-71 Diesel engine will operate satisfactorily on an emulsion of water in Diesel oil. Less than 7 weight yo of water emulsified in Diesel fuel causes the specific fuel consumption and the exhaust temperature of this Diesel engine to increase, compared with the values obtained with plain Diesel fuel. Between 7 and 18 weight % of water emulsified in Diesel fuel causes no change in the specific fuel consumption of this Diesel engine and causes the exhaust temperature to increase, compared with values obtained with plain Diesel fuel. Between 18 and 33.6 weight yo of water emulsified in Diesel fuel causes no effect on the specific fuel consumption of this Diesel
October 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
engine and causes the exhaust temperature to decrease, compared with values obtained with plain Diesel fuel. The effects of water on the performance of a Diesel engine depend on the type of engine, combustion chamber design, injection pressure, and speed of operation. A water-soluble compound may be used as a Diesel fuel additive by emulsifying the aqueous solution in Diesel fuel. A 5N solution of 18.6 weight % aqueous ammoniumnitratesolution emulsified in Diesel fuel increases the thermal efficiency of a General Motors 2-71 Diesel engine between 1000 and 1250 r.p.m., and increases the exhaust temperature, compared with values obtained with plain Diesel fuel. Water emulsified in Diesel fuel may reduce the amount of smoke in the exhaust and the amount of carbon deposit in a Diesel engine. Injection timing affects the performance of a Diesel engine with water or water-soluble additives emulsified in the fuel.
Bogen, J. S., and Wilson, G. C., Petroleum Refiner, 23, 118-52 (July 1944). (5) Cornet, I., and Boodberg, A., IND.ENG. CHEM.,45, 1033-5
(4)
(1953).
Cornet, I., and Boodberg, A., unpublished data. Dunstan, A. E., Nash, A . W., Brooks, B. T., and Tizard, H. T., “Science of Petroleum,” vol. IV, pp. 2900-1, Oxford University Press, London, 1938. (8) Elliott, M. A., “Combustion of Diesel Fuel Oils,” A.S.M.E. 19th Kational Oil and Gas Power Conference, Cleveland, Ohio,
(6) (7)
May 20, 1947. (9) (10) (11) (12) (13) (14) (15) (16) (17)
(18) ACKNOWLEDGMENT
The authors express their appreciation of Joseph DeCosta for aid in installation and adjustment of the equipment. They also pay tribute to the late Alexander Boodberg, who gave much encouragement and many helpful suggestions. LITERATURE CITED
Belknap, C. B., U. S. Patent 1,498,340 (June 17, 1924). (2) Ihid., 1,533,158 (April 14, 1925). (3) Biles, >I, B., N1.S. thesis, University of California, 1948. (1)
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(19) (20) (21) (22) (23) (24) (25) (26) (27)
Ellis, Carleton, “Gasoline and Other Motor Fuels,” Van Nostrand, New York, pp. 343, 553, 1921. Fish, G. L., U.S. Patent 1,611,429 (Dec. 21, 1926). Hannum, J. A., I h i d . , 2,538,516 (Jan. 16, 1951). Hayes, A., Ihid., 688,245 (Dec. 3, 1901). Hubner, W. H., and Egloff, G., A’ational Petroleum News, 28, NO. 32, 28-30 (1936). Kirschbraun, L., U. S. Patent 1,614,560 (Jan. 18, 1927). Ibid., 1,692,176 (Nov. 20, 1928). Zhid., 1,701,620 (Feb. 12, 1929). Ihid., 1,707,019 (March 26, 1929). Kokatnur, V. R., Zhid., 2,111,100 (March 15, 19381, Ibid., 2,152,196 (March 28, 1939). Maxwell, C. R., S A E Journal, 58, KO. 7,48-51 (1950). Nourse, I. C., U. S. Patent 2,055,503 (Sept. 29, 1936). Nygaard, E. M., Crandall, G. S., and Berger, H. G., J. Inst. Petroleum, 27, 348-68 (October 1941). Roberts, A. A,, U. S. Patent 2,090,393 (Aug. 17, 1937). Truxell, C. W., Jr., Diesel Power,22, 806-8 (1944). Van Steenbergh, B., U. 5.Patent 1,124,364 (Jan, 12, 1915). Whitman, W. G., IND. ENG.CHEM.,33, 865-6 (1941). Wiczer, C. B., and Kokatnur, V. R., U. S. Patent 2,461,580 (Feb. 15, 1949).
RECEIVED for review January 3, 1955.
ACCEPTED June 6, 1955.
Mechanism of Aromatic Amine Antiknock Action JEROME E. BROWN, FR.4NCIS X. MARKLEY, AND HYMIN SHAPIRO Ethyl Corporation Research Laboratories, 1600 West Eight Mile Road, Detroit 20, Mich.
S
I N C E the discovery in 1919 that certain organic amines have antiknock properties, more than 100 patents have been issued and more than 200 papers have appeared on amines as antiknock@. Of the published work, probably the most outstanding was reported in 1924 b y Boyd (6) who compared the antiknock action of ammonia and its alkyl, aryl, and alkylaryl derivatives with the activity of aniline. His values are in good agreement with presently accepted values. Other than the early Boyd publication, no systematic investigation has been reported concerning the effect on antiknock quality-with comparable motor fuels and under comparable engine conditions-of alkyl substitution on the nitrogen atom and on the ring. Little information is available in the literat,ure on the effect of aromatic amines on the antiknock properties of modern fuels, which have greater proportions of olefinic and arcmatic hydrocarbons, as well as increased sulfur contents and higher octane numbers, than fuels used at the time of the Boyd work. Furthermore, the effect of aromatic amines on fuel antiknock quality has not been evaluated under the more precise rating procedures available today. Our reinvestigation of the amines as antiknocks was undertaken to observe the response of amines in modern automotive fuels, t o correlate the change in antiknock effectiveness with change in structure, and t o determine the mechanism by which the effective amines function.
EXPERIMENTAL PROCEDURES
Test Fuel. Initial experiments established that the relative effectiveness of aniline, N-methylaniline, and mixed xylidines was essentially independent of base fuel composition. Therefore, for our single-cylinder engine ratings, it was possible to use a synthetic fuel consisting of 40 volume % of n-heptane and 20 volume yo each of diisobutylenes, toluene, and isooctane. This fuel can be easily reproduced, has a moderate octane number response to additions of antiknock agents, has an octane number range allowing easy rating in a Cooperative Fuels Research (CFR) engine by both Motor and Research methods, and has an olefinic and aromatic hydrocarbon content which is reasonabIy close to that of present commercial fuels. The responses of this fuel to the addition of N-methylaniline and tetraethyllead are shown in Figures 1 and 2, respectively. Test Compounds. The test compounds used in this study were of the highest purity available in quantity. I n general, compounds of Eastman White Label grade or those obtained elsewhere which had equally precise melting or boiling points were used without further purification. Compounds which were discolored or showed a broad melting or boiling point range were purified b y fractional distillation or recrystallization. Compounds which were prepared or purified in our laboratory are indicated in Table I.
