Emulsified Fuels in Compression Ignition Engines

October 1955 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 2133

(3) Fox, D. A., and White, A. H., IND. ENG. CHEM., 23, 259-66

(4) Johnstone, H. F., Chen, C. Y., Scott, D. R., Ib id . , 44, 1564-9

(5) Kroger, C., Angew. Chem., 52, 129-39 (1939). (6) Kroger, C., and Knothe, H., Brennstoff-Chem., 20, 373-8,

(7) Kroger, C., and hilelhorn, G., Ibid. , 19, 157-69 (1938).

(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

(11) Ibid., A215, 100 (1952). (12) Marson, C. B., and Cobb, J. W., Gus. J., 175,882 (1920).

(1931).

(1 952).

388-91 (1939).

( 8 ) Ibid., pp. 257-62.

(1 948).

(13) Milner, G., Spivey, E., and Cobb, J. W., J . Chem. SOC., 1943, pp.

(14) Neumann, B., Kroger, C., and Fjngas E., Z. anorg. u. allgem.

(15) Sihvonen, V., Fuel, 19,35-8 (1940). (16) Taylor, H. S., and Neville, H. A., J . Am. Chem. SOC., 43,2065-70

(17) Young, D. C., Pacific District National Carbon Co. private

578-89.

Chem., 197, 321 (1931).

(1921).

communication, November 1952.

RECEIVED for review April 19, 1964. -4CCEPTED April 23, 1966. From a thesis submitted to the faculty of the 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.

HE object of this investigation was to determine experi- T mentally 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 water- soluble 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, 25,W) dating back over 50 years ( I d ) , but rela-

1 Present address, The Trane Co., Los Angeles, Calif.

tively little information on such fuels has appeared in the tech- nical 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. In 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 to 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 1. Experiment station Figure 2. Throttle control lever

2134 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 47, No. 10

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 cali- brated against a synchronous-motor-driven calibrator. To ensure accurate speed measurements, the Strobotac was cali- brated 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

FR-

I TANK 1

Figure 3. System €or fuel mixing and distribution

FUEL MIXING AND DISTRIBUTION SYSTEM. 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.

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

Thus, a direct weight rate was obtained.

V A R I A T I O N O F V I S C O S I T Y O F D IESEL F U E L DUE T O T H E A D D I T I O N OF W A T E R

70 6 5

; 60

5 45 ui 55 I

F 50

9 40 Lo 5 35

30

ti: I I I I 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

DUE TO T H E A D D I T I O N OF W A T C R RO'F- DATA O B T A I N E D BY WESTPHAL BALANCE AT

PERCENT WATER IN MIXTURE- BY WEIGHT

Figure 4. Properties of mixed fuels

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 LIQUIDS USED. 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.

In 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-

0 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 Witte engine, normal timing, constant load, constant

speed (6) Specific fuel consumption Diesel fuel based on hydrocarbon


0 DIESEL FUEL + 0 28% EMULSIFIES

E X H ALIST - E M P E R A T L I R E 820

700 I , T O R O b E ,

a I: 0580 a s 0 5 6 0

0 III 0 540

$ 0 500

$ 0 480

m U W a o 520

800 900 1000 1100 I 2 0 3 1300 I400 1500 SPEED- RPM

Figure 6. Performance curves General Motors Diesel engine Model 2-71, full throttle,

normal timing, plain Diesel fuel

sumed that the operation of the engine had not changed signifi- cantly 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 (0.23 weight %) emulsifier, and Diesel fuel. Perform- ance 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 (17.02 weight 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 yo water, 0.40 yo emulsifier, and 66.0 weight yo Diesel fuel and performance data were obtained.

RESULTS A N D DISCUSSION

I n this study i t was desired to lay a foundation for future in- vestigations 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 two- cylinder, 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.

0 6 2 0

0 600!-Jk-Ll -- P L A I Y D I E S E L FUEL 1 IL 0 5 8 0 I a 0 5 6 0 2 0 5 4 0

E 0 5 2 0 0 500

E a

0 z 5 0600

0 5 8 0

p 0.560

2 0 5 4 0 2 0 5 2 0

0500

W 2 0 5 8 0

2 0 5 6 0

0 5 4 0

a 0 5 2 0

0 500

W

01

0.480L I 1 I I 800 900 IO00 1100 1200 1300 1400 1500

SPEED - RPM

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.

In general, efficiency of operation of compression ignition engines is controlled by 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

Figure 7. Effects of water in fuel on specific fuel consumption

General Motors engine Model 2-71, full throttle Specific fuel consumption gives pounds of hydrocarbon

fuel per brake horsepower-hour

0 600 0 580

0 560 & L 0 540

0 520

0 500 a 04130

u) n 5 0 5 8 0 0 4. 0 5 6 0

5 0 5 4 0

E 0 5 2 0

5 0.500

Z 0480 ul

0 0

d o 5130 3

0 560 0 5 4 0 'I 2 0 5 2 0

$I 0 500

0.480 0 460

800 900 1000 1100 1200 1300 1400 1500 SPEED - RPM

Figure 8. Effects of water in fuel on specific fuel consumption

General Motors Diesel engine Model 2-71, full throttle

2136 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 47, No. 10

0.700 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 suffi- F a ciently to cross the curves of speeds as low as

1000 r.p.m. Noting the curve of specific fuel consumption (pounds of petroleum fuel per

l J 7 l $ c 0 . 6 2 0 z m 0 brake horsepower-hour) equal to plain fuel

specific fuel consumption (petroleum fuel as it 50.500

3 m comes from the refiner), it is evident that the z 0.540 minimum percentage of water that must be

present to give increased economy increases 0' y 0.500 with an increase of speed. v) a Considering the portion of the curves where

the specific fuel consumption is reduced, as com- 0 2 4 6 8 10 12 14 16 18 20 22 pared with pure fuel data a t full throttle, it was

assumed that the reason was more complete Figure 9. Variation of specific fuel consumption with water emul- combustion and less afterburning. Inasmuch

as water is relatively insoluble in Diesel fuel, it may be assumed that a mixture of fuel and water is obtained which consists of droplets of

--1a

L O

E 2

. 0.460

PERCENT WATER IN MIXTURE BY WEIGHT

sified in Diesel fuel General Motors Diesel engine Medel2-71, full throttle, normal timing

-

variables, all except injection timing and type of fuel used are design features. For a given engine the optimum setting of injection timing, for a normal fuel and a normal range of speeds, is determined by the manufacturer. Thus, the type of fuel used in an engine is the only major variable that would change its operating characteristics. As the rate of burning, rate of pressure rise, and completeness of combustion are dependent on the quality of fuel used, maximum efficiency would be obtained only with the best available fuel (90). Because of disso- ciation a t the high temperatures encountered and inadequate fuel and air dispersion, complete combustion in the cylinder is rarely obtained with any fuel.

As indicated by Figure 9, which was derived from Figures 7 and 8, general trends may be established as to the effects of water added to Diesel fuel on the efficiency of a Diesel engine. At all speeds water up to approximately 5 weight '% in the mixture produces a deleterious effect on the engine economy. Beyond this percpQtage the economy is increased, a t all speeds, up to

water surrounded by oil. When this mixture is injected into the cylinder, the water flashes into steam, owing to the high temperature, and in so doing breaks the oil into smaller particles, increasing the dispersion in the cylinder chamber. ThuP, ignition is aided ( 7 ) , more complete combustion occurs, less afterburning takes place, and the thermal efficiency is increased.

It was noted by visual observation in this investigation that in one case less smoke was present in the exhaust gases with water in the fuel than with pure fuel, indicating less free carbon in the combustion gases. Van Steenbergh (9, 25) observed that when oil is mixed with superheated steam and subjected to contact with carbon at temperatures near 1800' F., the steam is decom- posed, resulting in the production of methane, hydrogen, and carbon monoxide. Thus, there is a possibility that the water-gas reaction which was promoted by the added water might have contributed to the improved combustion efficiency and also might tend to reduce the carbon formation in the engine. It was beyond the scope of this investigation to analyze the smoke formation and carbon deposits; therefore, further experimentation should be done.

I 6 5 I 6 0

I 5 5 150

145

2 160

5 I 5 5 0

150 & 145 P

2

1 160 155

o 150 k

I 6 0

I 5 5

I 5 0 145

I40

135 I30

800 900 1000 1100 1200 1300 1400 1500 SPEEO - R P M

Figure 10. Effects of water in fuel on torque General Motors Diesel engine Model 2-71, full throttle

0620 0 600

& 0 5 8 0

,,, 0 5 6 0

2 0 5 4 0

E 0 5 2 0

0 5 0 0

I

a

0 z 3 2 0 5 4 0

$ 0 5 2 0

E 0 5 0 0 a I

z 0 5 2 0

s 0 5 0 0 -1 0 4 8 0

I 1 I I ",

n-c! A- 7 0 7- 0 5 0 0 -er

0 480 , .. _ _ 800 900 1000 1100 1200 1300 1400 1500

SPEED - RPM

Figure 11. Specific fuel consumption General Motors Diesel engine Model 2-71, normal

timing, plain Diesel fuel

October 1955

2 580 w

I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 2137

1 I I I I I I 800 900 1000 1100 1200 1300 1400 1500

S P E E D - R P M I

T H R O T T L E SETTING ---O- F U L L --+--- 9 5 % -x- 8 5 %

* 0 I

y 2 8

5 2 2

VI 2 o

2 6 5 2 4 Q

0 z 3 0

z 2 8 0 ; 26 Y 2 4

z 2.2 2.0

? I R

-J

- . t ' +...-I8 6 % ",NO3 SOLUTION

800 900 1000 1100 1200 1300 1400 1500 S P E E D - R P M

Figure 12. 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 rea- sonable 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

VI

z 2 0

+ 0 0 U

I

W 3 0

0 e

n

a

a

SPEED - R P M I80

I70 I60

I50 140 I 3 0

8 5 0 - 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 900-28 2 7 2 6 2 5 2 4 2 3 2 2 2 I 2 0

2 1000- 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 a 1100- 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 I 2 0 a 1200 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0

1300 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0

F U E L I N J E C T E D - POUNDS PER STROKE x 1 0 4

Figure 14. Torque characteristics General Motors Diesel engine Model 2-71, normal

timing

0.4601 I I I 1 I I I I I I 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8

FUEL INJECTION RATE POUNDS PER STROKE x I O 4

Figure 13. Specific fuel consumption compared with fuel injection rate

General Motors Diesel engine Model 2-71, normal timing, plain Diesel fuel

2100 r.p.m. (24 ) . 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 22,5y0 water.

Water in percentages less than that which gives maximum specific fuel consumption for a given speed is apparently insuffi- cient 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-

780 740 700

3 660 2 6 2 0

U

IY

+

760 740

2 720 5 700

6 80 6 60

+ k

I 1 I I I I I 1 I I I V h l 1 I 850-27 2 6 2 5 2 4 2 3 2 2 2 1 2 0

5 300-28 2 7 2 6 2 5 2 4 2 3 2 2 2.1 2 0 b 1000-2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 I 20 - a IIOO- 2 8 2 7 2 6 2 5 2 4 2 5 I 2 21 2 0

I 2 0 0 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 1300 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0

FUEL I N J E C T E D - POUNDS PER STROKE lo4

Figure 15. Variation of exhaust temperature General Motors Diesel engine Model 2-71, normal timing,

plain Diesel fuel

2138 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

$ 0 520

a 3 0

I 0 5 4 0

0.520

E 0.500

$ 0 520

a 3 0

I 0 5 4 0

0.520

E 0.500

SPEED- R P M

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 Fig- ure 9 and Figure 5 is similar. The increase of specific fuel consumption at low concentrations of water is much more pro- nounced 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 5y0 water, 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 improv- nient (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

I 7 0

165

I 6 0

I 5 5

1 6 5 160

I 5 5 6 150

800 900 1000 1100 1200 1300 1400 150C SPEED - RPM

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 appre- ciably affecting the economy, and that the water has no effect on the amount of gasoline required to 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.

In 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 tha t in all cases the water caused an increased specific fuel consumption and, correspondingly, a reduced torque (Figure 17). The 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-


800

7 8 0

7 60 LL 740

' 760

740

2 720 3

4 720

W 700

680

660

620

600 I 1 1 1 1 I

800 900 do00 1100 1200 1300 1400 1500 SPEED - RPM

Figure 18. Exhaust temperature with water in fuel compared with plain fuel

General Motors Diesel engine Model 2-71, normal timing

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 7yo water, 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>he same as that with plain Diesel fuel. At this same point the

a' 0.580

a 0.560

8 0.540

0.520 m T' 0.500

a

9 130 120

2 110

g 100 0 k

o: 620

!$ 6 0 0

5 5 8 0

5 560 a

5 40

b- 520

3

z _ _ _

800 900 1000 1100 1200 1300 1400 I500 SPEED - R P M

Figure 19. Performance curves General Motors Diesel engine Model 2-71, full throttle, normal timing, 33.6 weight % water in fuel mixture

6

4

2

0

u 0 4 8 12 16 20 2 4 28 3 2 36 PERCENT WATER IN FUEL MIXTURE- BY WEIGHT

Figure 20. Change in specific fuel consumption and exhaust temperature due to water in fuel mix-

ture 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 to 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;

2140

d I0.580 a 20.560

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

. ~~

E Q U I V A L E N T PLAIN FUEL CURVES --I

I I 1 I I I

Vol. 47, No. 10

r z:.“ -20 z -40 . 5 -80

..- --u -60-

z f - - O 4 8 12 16 20 24 28 32 36

PERCENT 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

50.540 a 0.520

70.500 20.480 m

I I I , , , i 155 150

145 2 140 a

E

g 135

L L

’A 720 3 680 2 640 2 600 I I- BOO 900 1000 1100 1200 I300 1‘400 1500

K

I-

w

SPEED - R P M

Figure 22. Performance curves General Motors Diesel engine Model 2-71, full throttle, normal timing, 18.6 weight % 5Nammonium

nitrate solution in fuel mixture

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 consimp- tion” 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 insignifi- cant. While this shows that no direct benefits can be obtained with water in the fuel in this engine, i t 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 investiga- tions 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 1.4y0 lower than that of equivalent plain fuel a t 1100 r.p.m. Taking into consid- eration the heat required to vaporize and heat the water and to 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 yo water 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. To 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.

0 2 4 6 8 I O 12 14 16 18 20 PERCENT NH4NOs SOLUTION IN MIXTURE - BY WEIGHT

Figure 23. Effect of water and ammonium nitrate on cetane number of Diesel fuel (5)

CONCLUSIONS

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


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 ammoniumnitratesolu- tion 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.

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

(1) Belknap, C. B., U. S. Patent 1,498,340 (June 17, 1924). (2) Ih id . , 1,533,158 (April 14, 1925). (3) Biles, >I, B., N1.S. thesis, University of California, 1948.

(4) Bogen, J. S., and Wilson, G. C., Petroleum Refiner, 23, 118-52

(5) Cornet, I., and Boodberg, A., IND. ENG. CHEM., 45, 1033-5

(6) Cornet, I., and Boodberg, A., unpublished data. (7) Dunstan, A. E., Nash, A . W., Brooks, B. T., and Tizard, H. T.,

“Science of Petroleum,” vol. IV, pp. 2900-1, Oxford Uni- versity 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,

(July 1944).

(1953).

May 20, 1947.

Nostrand, New York, pp. 343, 553, 1921. (9) Ellis, Carleton, “Gasoline and Other Motor Fuels,” Van

(10) Fish, G. L., U. S. Patent 1,611,429 (Dec. 21, 1926). (11) Hannum, J. A., I h i d . , 2,538,516 (Jan. 16, 1951). (12) Hayes, A., Ih id . , 688,245 (Dec. 3, 1901). (13) Hubner, W. H., and Egloff, G., A’ational Petroleum News, 28,

(14) Kirschbraun, L., U. S. Patent 1,614,560 (Jan. 18, 1927). (15) Ib id . , 1,692,176 (Nov. 20, 1928). (16) Zhid., 1,701,620 (Feb. 12, 1929). (17) Ih id . , 1,707,019 (March 26, 1929). (18) Kokatnur, V. R., Zhid., 2,111,100 (March 15, 19381, (19) Ib id . , 2,152,196 (March 28, 1939). (20) Maxwell, C. R., SAE Journal, 58, KO. 7,48-51 (1950). (21) Nourse, I. C., U. S. Patent 2,055,503 (Sept. 29, 1936). (22) Nygaard, E. M., Crandall, G. S., and Berger, H. G., J. Inst.

(23) Roberts, A. A,, U. S. Patent 2,090,393 (Aug. 17, 1937). (24) Truxell, C. W., Jr., Diesel Power, 22, 806-8 (1944). (25) Van Steenbergh, B., U. 5. Patent 1,124,364 (Jan, 12, 1915). (26) Whitman, W. G., IND. ENG. CHEM., 33, 865-6 (1941). (27) Wiczer, C. B., and Kokatnur, V. R., U. S. Patent 2,461,580

NO. 32, 28-30 (1936).

Petroleum, 27, 348-68 (October 1941).

(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.

INCE the discovery in 1919 that certain organic amines S 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 outstand- ing was reported in 1924 by Boyd (6) who compared the antiknock action of ammonia and its alkyl, aryl, and alkylaryl de- rivatives 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 arc- matic 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 under- taken to observe the response of amines in modern automotive fuels, t o correlate the change in antiknock effectiveness with change in structure, and to 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 reason- abIy 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.

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 else- where which had equally precise melting or boiling points were used without further purification. Compounds which were dis- colored or showed a broad melting or boiling point range were purified by fractional distillation or recrystallization. Com- pounds which were prepared or purified in our laboratory are indicated in Table I.

Test Compounds.

Documents

Emulsified Fuels in Compression Ignition Engines