Alcohol Blends

.

Carbon Monoxide in Engine Exhaust

of operation with gasoline and two alcohol-gasoline blends a t v a r i o u s air-fuel ratios; also, to determine the extent of the effect of alcohol in the alcohol blends upon the exhaust gas analysis both a t the same and comp a r a b l e a i r - f u e l ratios, and a t the maximum torque or a t other percentages of maximum-torque air-fuel ratios.

Apparatus and Fuels

Using

Alcohol Blends L. C. LICHTY AND C. W.PHELPSl Yale University, New Haven, Conn.

Tests on engines with gasoline and 10 and 20 per cent ethyl alcohol-gasoline blends show that the amount of carbon monoxide in the exhaust gases depends upon the air-fuel ratio and is practically the same for all three fuels at air-fuel ratios comparable with regard to the theoretical air requirement for the particular fuel. With all fuels, air-fuel ratios necessary for desirable engine performance result in carbon monoxide in the engine exhaust and in the blow-by gases which leak past the engine piston. Variations in carbon monoxide from individual exhaust ports indicate, for the fuels studied, that factors other than fuel characteristics are the more important in influencing distribution of air or fuel or both in the engine used. Carbon monoxide can be eliminated either with gasoline or alcohol-gasoline blends by providing more air than is required for complete combustion, but this condition results in a lowered performance that is not considered desirable.

Single-Cylinder Engine Tests

The air-fuel ratios in these tests are the results of volume measurements of both air and fuel, and are reported on the customary weight basis. The air was measured with a large gas meter w h i c h r e q u i r e d a pressure differential of less than one inch of water for the rates measured. The fuel rates were determined from the time required for the engine to consume a definite volume of fuel. A Cities S e r v i c e p o w e r prover @), which indicates the relative amount of combustibles, was connected to the exhaust line of the engine. The results of the power prover are plotted against measured air-fuel ratios in Figure 1 and indicate a straightline relation between the power-prover indication and airfuel ratio. The addition of alcohol to the gasoline decreased the air-fuel ratio corresponding to a given powerprover reading. The results of the Orsat analyses of the exhaust products are shown in Figures 2 and 3. Figure 2 shows the relation between the carbon monoxide in the exhaust and air-fuel ratio for the three fuels. The addition of alcohol to the gasoline decreases the carbon monoxide in the exhaust for a given air-fuel ratio. However, it is obvious that the carbon monoxide in the exhaust products can be decreased to zero for any of the fuels if the air-fuel ratio is increased suffi-

T

HE presence of carbon monoxide in the exhaust of an internal combustion engine using any fuel containing carbon is due primarily to a deficiency in the oxygen or air supply-i. e., to the use of what is commonly termed "rich" mixtures. Thus, if the ratio between the required air and fuel is increased, making the mixture leaner either by adjustment of flow of either or both fluids or by the changing of fuels to one requiring less air (for example, by substituting ethyl alcohol-gasoline blends for straight gasoline), there will be a decrease in the carbon monoxide content of the exhaust gases of an internal combustion engine. The object of the tests reported here was to determine the exhaust gas analysis of the products of combustion from several internal combustion engines under various conditions 1

Tests were run first on a standard C. F. R., variable-compression, constantspeed engine, at three c o m p r e s s i o n ratios and at three heat supplies to the intake m a n i f o l d . These were followed by tests on a 1935 six-cylinder Chevrolet engine at one corn reesion ratio, three speeds, and three loa$. The standard grade of commercial gasoline (known as Super Shell) distributed in the New Haven district in June, 1936, was obtained from the stocks of the New Haven distributing plant. This gasoline is a nonleaded fuel with a specific gravity of 0.738 at 60' F. The initial, 50 per cent, 90 per cent, and end points of the distillation curve of this fuel as reported by the manufacturer are No,227", 335', and 398" F., respectively. Anhydrous denatured ethyl alcohol (formula 10 and 10M) was used for the alcohol blends. Two alcohol-gasoline blends were used, one containing 10 per cent and the other 20 per cent ethyl alcohol by volume. Some comparative runs were made with pure a b s o l u t e ethyl alcohol t o determine the effect of the denaturant, if any. The specific gravity of the denatured alcohol was 0.799 at 60" F.

Present address, Connecticut State College, Storrs, Conn.

495

INDUSTRIAL AND ENGINEERING CHEMISTRY

496

VOL. 29, NO. 5

alcohol blends, as indicated by the curves, appears to be about 14.4 per cent. About 0.3 per cent oxygen is found in the exhaust analysis of the single-cylinder engine when using rich mixtures. A comparison of the single-cylinder engine exhaust gas analyses with other data, using gasoline as a fuel, is made later in the paper. A comparison of the three fuels a t the same air-fuel ratios in each case results in the following tabulation of carbon monoxide values (from Figure 2): CO in Exhaust of Single-Cylinder Engine 10% alcohol 20% alcohol Gasoline blend blend

Air-Fuel Ratio

%

AIR FUEL RATIO

%

%

BYWEIGHT D R Y AIR BASIS

215. AIR-FUELRATIO IN SINGLE-CYLINDER FIGURE 1. POWER-PROVER READING ENGINBTESTS

= gasoline, o

-

These figures indicate t h e m a g n i t u d e of the decrease in carbon monoxide which results when changing from gasoline to an alcohol blend but maintaining the same air-fuel ratio by weight. Actually, the data obtained upon the C. F. R. engine show an increase in fuel flow for a &en head when changing to the alcohol blends. However, more air is induced into the engine with the alcohol blends, apparently because of lower mixture temperatures. This more than offsets the increased fuel flow, resulting in an increase in airfuel ratio of about 1 to 2 per cent for the 10 per cent blends and 2 to 3 per cent for 20 per cent blends, the higher values being applicable to the richer mixtures. Changing to an alcohol blend without carburetor adjustment will result in

10 per cent alcohol blend A = 20 per cent alcohol blend: A B alcodol blend

-

absolute

ciently to provide an amount of air slightly greater than that theoretically required for complete combustion. The use of pure absolute alcohol rather than denatured alcohol showed no difference that exceeded the experimental error involved (shown by points AB covering comparative tests, in Figures 1, 2, and 3). The corrected indicated horsepower curves for no manifold heat input and for a 5 to 1 compression ratio are also plotted on Figure 2. Mixture ratios for mixtures 5 and 10 per cent richer in fuel than the theoretically correct mixture are also indicated for each fuel. Maximum-power of a single-cylinder engine occurs a t a mix13 I I ture ratio about 10 per cent richer than the correct mixture in all cases; and 2.5 to 3.0 per cent carbon monoxide by volume will be found in t h e e x h a u s t products for all fuels a t the mixture ratio for maximum power. The use of leaner air-fuel ratios to eliminate carbon monoxide in the exhaust products of a single-cylinder engine results in a decrease in indicated power of about 0.7 to 1.1 per cent for the cases shown. Figure 3 shows the relation between both carbon dioxide and oxygen in the exhaust and air-fuel ratio for the three fuels. Here, again, the shifting of the curves to lower air-fuel ratios (for a given exhaust gas analysis) for the alcohol blends is due to the lower amount of air required for alcohol compared to gasoline. The reaction equations for the correct mixtures of fuel and air show that the dry gas analysis should result in 14.5 and 15.0 per cent carbon dioxide for octane and ethyl alcohol, respectively. Thus, 9 IO II 12 13 14 15 16 a 20 per cent blend of alcohol and gasoAIR-FUEL RATIO BY WEIGHT DRY A I R BASIS line should show a maximum of about 14.6 per cent carbon dioxide. The maxiFIGURE 2. CARBON MONOXIDE US. AIR-FUIL RATIOIN SINOLE-CYLINDER ENUINE mum percentage of carbon dioxide obTESTS tained from the gasoline and the two = gasoline, o 10 per cent blend, A 20 per cent blend; A B = absolute alcohol blend

I

E

I

I

1

MAY, 1937


497

less carbon monoxide in the exhaust than with gasoline as the fuel. However, such a change will not eliminate c a r b o n m o n o x i d e from the exhaust of an automobile engine unless the carburetor setting was previously so lean as to result in a low percentage of carbon monoxide with gasoline as a fuel.

Comparable Air-Fuel Ratios The reaction equations b e t w e e n fuels and air provide information regarding the correct air-fuel ratios, which contain the required amount of oxygen for the complete combustion of the fuel. Assuming gasoline to be represented by octane (CSHIS), the correct air-fuel ratio is 15.1 to 1 by weight. The correct air-fuel ratio for ethyl alcohol is 9.0 to 1 by w e i g h t . M a k i n g use of the volumetric relationship of the blends of alcohol and gasoline, as well as the specific gravities, the correct airfuel ratio for the blends is found as follows : The correct air-fuel ratio for the 10 per cent (by volume) alcohol blend is:

II 12 13 14 15 16 17 AIR-FUEL R A T 10 BY WEIGHT DRY AIR BASIS DIOXIDE AND OXYGENus. AIR-FUEL RATIOIN SINGLE-CYLINDER FIGURE3. CARBON ENGINETESTS

IO

9

= Gasoline, o

-

+

Ib. a,lcohol X 9.0 Ib. gasoline x 15.1 lb. of blend (0.18X 0.799) X 9.0 4- (0.90 X 0.738) X 15.1 = 14.4 (0.10 X 0.799)

+ (0.90 X 0.738)

In like manner the air-fuel ratio for the 20 per cent alcohol blend is found to be 13.8 to 1. These values represmt airfuel ratios containing the required air and are indicated in the following table as 100 per cent required air; the carbon monoxide content in the exhaust from the single-cylinder engine tests for these as well as other percentages of required air and for the three fuels are also given: Required Air

Richness -Air-Fuel Ratio--of Mix10% 20 ture Gasoline alcohol alco?~l

%

%

100 95 90 85 80

Correct 5.2 11.0 17.5 25.0

15.1 14.3 13.6 12.8 12.1

14.4 13.7 13.0 12.2 11.5

13.8 13.1 12.4 11.7 11.0

in Exhaust--10 20 Gasoline aloo& alco%l

-CO

%

%

%

0.1 1.6 2.9 4.0 6.5

0.1 1.3 2.7 4.6 6.6

0.3 1.8 3.2 4.8 6.8

These data show that for a given percentage of required air (i. e., a t comparable air-fuel ratios) the carbon monoxide content in the exhaust is practically the same for gasoline and a 10 per cent alcohol-gasoline blend, but is somewhat higher far the 20 per cent alcohol-gasoline blend.

10 per cent blend, A = 20 per cent blend; A B = absolute alcohol blend

cylinder tests indicated that, a t least when calibrated for a given fuel, it should give reliable indications of air-fuel ratios and of carbon monoxide in the exhaust products. Consequently, the exhaust products in the multicylinder engine tests were not analyzed with the Orsat apparatus but only with the power prover. However, the air flow was measured by means of an air box with such size of orifice that the pressure drop across the orifice did not exceed 2.5 inches of water.

a > 0 a n a

w

8 P la

K J

w

3 L

!a k

Multicylinder Tests The accelerating pump, economizer needle, and main metering orifice were removed from the Carter carburetor supplied with the Chevrolet engine. The idling jet was also made inoperative. A needle valve was inserted in the lower part of the main gasoline jet, by means of which the various air-fuel ratios were obtained. The use of the Cities Service power prover on the single-

AIR-FUEL RATIO

AIR BOX

FIQURE4. AIR-FUELRATIOSBY AIR-BOXMEABUREMENTS AND POWER-PROVER INDICATIONS Symbol 0 A

I 3

Orifice Diam., Inches 2.524 2.004 1.751

Orifice Discharge Coe5cient 0.60 0.60 0.60


498

G A S 0LINE

. .

I O PERCENT ALCOHOL

10 II 12 1 3 14 15 16 A I R - F U E L RATIO

'

rx

VOL. 29, NO. 5

9 IO I1 12 13 14 15

14

w 12 a

Z

IO

8 w 0 6

i34 z 0 2 = 0 Z 0 -

u

10 II

12 13 14 15 16

IO I 1 12 13 14 15 16 A I R - FUEL

IO I I 12 13 14 15 16

RATIO

m

u'4

96

v'2

95

a

10

94

8

93

6

92

4

91

2

90

O 1 ) I I 12 13 14 15 16

PORT N0.I

IO I I 12 13 14 15 16 A I R - FUEL R A T I O

0 PORT NO. 2

+

EX. PIPE

80

PORT NO.4 TORQUE POINTS

V PORT X

10 II 12 13 14 15 16

NO.3

MONOXIDE AND INDICATED BEAMLOADus. AIR-FUEL RATIO FOR FIGURE 5. CARBON AT 1000 R. P. M.

The fuel flow was determined by the time required for the consumption of a given volume of fuel. The measured air-fuel ratios obtained from all the multicylinder engine tests with the three fuels are plotted in Figure 4 against the air-fuel ratios as determined by the power-prover indications; use is made of the relations shown in Figure 1.. Three thin-plate, sharp-edge orifices, measuring 2.524,2.004, and 1.751 inches in diameter, were used with the air box.

A

SIX-CYLINDER CHEVROLET ENGINE

An orifice coefficient of 0.60 was used in computing the airfuel ratios. Orifice coefficients of 0.64, 0.66, and 0.70 would be required to give perfect correlation as indicated by the dashed line in Figure 4. With gasoline the power prover indicates no carbon monoxide a t an air-fuel ratio slightly greater than 15 to 1, as would be expected. Using the smallest orifice, the air box indicates an air-fuel ratio for this condition of about 18 to 1, an air-fuel ratio much too rich for zero carbon mon-

MAY. 1937


oxide condition with gasoline. Hence the power-prover indications of air-fuel ratios are used rather than air-box measurements which are questionable.

Distribution The results of the multicylinder engine tests are shown in Figures 5, 6, and 7, on which are plotted the carbon monoxide values as obtained from the power-prover readings of the gases issuing from the four ports and the exhaust pipe of the six-cylinder engine. These carbon monoxide values are plotted against engine air-fuel ratios as indicated by the power-prover analysis of the gases leaving the engine. Values of the indicated dynamometer beam load are also plotted in Figures 5, 6, and 7, principally to indicate the airfuel ratio for maximum power. The indicated beam loads a t part throttle conditions have been corrected to a given absolute manifold pressure in each case of speed and part load for the three fuels; a t wide-open throttle the loads have been corrected for both barometer and humidity. Gases issuing from ports 1 and 4 indicate the richness of mixture flowing to cylinders 1 and 6, respectively; that issuing from ports 2 and 3, each of which is Siamesed, indicate the mean richness of mixture to cylinders 2 and 3 in the first case, and cylinders 4 and 5 in the latter case. At 1000r. p. m. (Figure 5) better distribution occurs a t onethird load than a t the other loads, with the exception of the two-thirds load with gasoline. This is indicated by the relative closeness of the carbon monoxide curves. I n all cases, except the run a t two-thirds load on gasoline, the gases from ports 1 and 2 indicate the leanest mixtures, while the gases from ports 3 and 4 indicate the richest mixtures. The order of richness is changed in the case noted which was run considerably after the rest of the tests a t 1000 r. p. m. At 2000 r. p. m. (Figure 6) the distribution appears to be better with the 20 per cent alcohol blend. At one-third load with the 20 per cent alcohol blend the distribution was so nearly perfect that a curve was drawn only for the carbon monoxide in the exhaust pipe. Some time later, check runs on this condition at the air-fuel ratios indicated showed a spread of 1.2 per cent carbon monoxide a t an air-fuel ratio Qf 11.5 to 1. The full-load run on the 20 per cent alcohol blend, made considerably later than the rest of the runs and prior to the two-thirds load run on gasoline a t 1000 r. p. m., showed a reversal of the order of richness of mixture in the engine similar t o that noted for gasoline a t 1000 r. p. m. At 3000 r. p. m. the best distribution occurred with gasoline a t full load. The full-load runs a t this speed show a different distribution from that of the other runs with less throttle opening. The distribution of the charge to the engine cylinders may vary with speed and load to an extent indicated by a minimum range of less than 1 per cent carbon monoxide to a maximurn range of over 6 per cent a t the maximum power air-fuel ratios. Using data from Figure 2, this indicates a variation of about 0.5 as a minimum to 2.2 air-fuel ratios as a maximum. It seems obvious that distribution is not appreciably influenced in this case by the nature of the fuel, but is more dependent upon speed, throttle position, design of carburetor, manifold. etc.

Carbon Monoxide in Total Exhaust Gases The analysis of the gases in the exhaust pipe indicated a carbon monoxide value which is about the weighted average of the carbon monoxide values for the gases issuing from the various ports, in all cases except wide-open throttle and

499

3000 r. p. m. I n this case burning apparently continues after the gases leave the exhaust ports and mix in the exhaust pipe. At maximum power conditions the carbon monoxide in the exhaust line averages 3.9, 3.8, and 3.6 per cent for the gasoline, the 10 per cent alcohol blend, and the 20 per cent alcohol blend, respectively. In view of the difficulty of determining maximum power air-fuel ratios and the experimental error involved, it can be concluded that practically the same carbon monoxide content (3.8 per cent) was found in the exhaust gases for all three fuels with maximum power air-fuel ratios. This value (3.8 per cent) compares with an average of about 2.7 per cent for maximum power air-fuel ratios with the single-cylinder engine tests. The average maximum power air-fuel ratios were 13.0, 12.5, and 12.2 to 1 for the gasoline, 10 per cent alcohol blend, and 20 per cent alcohol blend, respectively. Maximum power was attained with mixtures about 10 per cent rich in the case of all three fuels in the single-cylinder engine tests and with mixtures about 16, 15, and 13 per cent richer, respectively, than the theoretically correct mixture in the multicylinder engine tests. The difference in carbon monoxide, air-fuel ratios, and richness of mixture for maximum power in the singleand multicylinder engine tests are due, at least partly, to the effects of mixture distribution in the multicylinder engine. The extrapolation of the curves for the ports indicating the highest carbon monoxide content in the multicylinder engine tests gives an indication of the engine air-fuel ratio at which no, or only traces of, carbon monoxide might be found in the exhaust gases. The average of all these extrapolated values is 15.3, 14.8, and 14.3 to 1 for the gasoline, the 10 per cent alcohol blend, and the 20 per cent alcohol blend, respectively. These values compare with 15.1, 14.5, and 14.0 to 1 for the single-cylinder tests, indicating that mixture distribution in the multicylinder engine requires an increase of about 0.3 of an air-fuel ratio, compared to the single-cylinder tests, to eliminate carbon monoxide from the exhaust.

Carburetor Characteristics Tice (10) called attention to the various conditions of operation imposed on the automobile engine which necessitate the use of different air-fuel ratios to obtain the desirable performance. Under idling conditions a very rich mixture is required to offset the effect of dilution of the small quantity of idling mixture with the exhaust products left in the engine clearance space from the previous cycle. The effect of dilution becomes less as the throttle is opened and more mixture is admitted to the cylinder. Hence, a t part throttle operation (about one-fourth to three-fourths load) carburetors are designed to provide leaner mixtures. Maximum power is desired a t wide-open throttle, and as this condition is approached the mixture is made richer. Most carburetors are provided with accelerating devices which introduce extra fuel into the engine intake manifold and thus enrich the mixture when the throttle is opened for accelerating the car. Therefore, only at part throttle (about one-fourth to three-fourths load) and a t constant speed is there a possibility of no carbon monoxide in the exhaust of an automobile engine, regardless of fuel used; under idling, accelerating, and wide-open throttle conditions, carbon monoxide will be found in the exhaust regardless of which of the three fuels is used, if standard carburetor practice is followed. Since air-fuel ratios of less than 10 to 1 are encountered under idling conditions (I), 10 per cent or more carbon


500

GA S 0 LINE

14

I-

VOL. 29, NO. 5

20 PERCENT ALCOHOS9

12

40

IO

8

47 46

6

45

4

44

2

43

z o LI

u

IO I I 12, 13 14 15 16

IO I I 12 13 14-15 16 AIR-FUEL RATIO

9 IO II 12 13 14 15

10 II I2 13 14 15 16 AIR-FUEL RATIO

9 IO I I 12 13 14 15

9 8 !?

42

D

$14 a12

210 E0 g 6 2 4 0

2 2 n z

'U

1 '0

I I 12 13 14 15 16

m

5 I4 * 12

I02

IO

IO I

8

too

6

99

4

98

2 n -10 II 12 13 14 15 16

97

I 10 II 12 13 14 15 16 AIR-FUEL RATIO

9

PORT NO. I 0 P O R T N 0 . 2 V PORT N0.3

IO I I 12 13 14 15

96

P O R T NO. 4

+

EXH. P I P E X TORQUE POINTS MONOXIDE AND INDICATED BEAM LOADUS. AIR-FUELRATIOFOR A SIX-CYLINDER CHEVROLET ENGINE FIGURE 6. CARBON AT 2000 R. P. M. monoxide in the exhaust may be expected with either gasoline or alcohol blends under this condition; obviously, therefore, it is extremely dangerous to operate an automobile engine with either gasoline or alcohol blends under any condition in a closed room or garage if any of the exhaust is discharged into the room, since the breathing of an atmosphere with as low as 0.03 per cent carbon monoxide by volume will eventually produce severe symptoms of carbon monoxide poisoning, as indicated by the work of Henderson et al. (9).

Blow-By Gases Further, the gases which escape from the combustion chamber and blow by the piston and rings, and which eventually leave the crankcase by way of the breather pipe, contain carbon monoxide as shown by the work of Cutter (S) in a study of blow-by. The following table shows the results of Orsat analysis of blow-by and exhaust gases from a 1931 Chevrolet six-cylinder engine run at various speeds at wideopen throttle : Cutter (8) concluded that about 30 per cent of the blow-by


MAY, 1937

10 PERCENT ALCOHOL

GASOLINE

14

20 PERCENT ALCOHOL

51 50 49

12 IO

6

48 47

4

46

2 0

45

8

IO II 12 13 14 15 16

IO II 12 13 1 4 15 16

AIR-FUEL

9

r3

1

70 69 68

IO

67 66

65 64 10 II 12 13 14 15 16 AIR-FUEL RATIO

IO II 12 13 14 15 16

9 IO II 12 13 14 1

5

14 12

94

IO 8

92 91

6

90

4

89 88

~

93

2

0

s

IO II 12 13 14

12

8 6 4 2 0

9

RATIO

14 Z -

50 1

IO II 12 13 14 15 16

10 II 12 13 14 15 16 AIR-FUEL RATIO

PORT NO.I 0 PORT N 0 . 2

V PORT NO. 3

9 IO I I 12 13 14is8' I 3 PORT NO. 4

+

EXH. PIPE X TORQUE POINTS MONOXIDE AND INDICATED BEAMLOADus. AIR-FUELRATIOFOR A SIX-CYLINDER CHEVROLET ENGINE FIGURE 7. CARBON AT 3000 R. P. M. Engine Speed

-Blow-By COz Oz

R.p.w1.%

3.0 1000 2.4 1500 2000 2.7 2500 3.2 a By difference

%

GasCO

%

N2"

%

----Exhaust Gas ---02 CO GO2

%

%

7%

Nz

%

1.7 81.3 9.5 4.8 84.0 14.0 1.7 15.3 1.2 81.1 5.3 83.9 10.2 0.6 1.3 81.3 5.0 84.0 10.0 1.0 14.7 4.6 84.2 1.3 81.0 10.7 0.5 14.5 between 100 per cent and the sum of the other dry gaeea.

in this case consisted of products of combustion. Hence, the carbon monoxide in the blow-by gases issuing from the breather pipe of an automobile engine presents a health hazard if the automobile is in a closed room or garage.

Comparison of Data with Work of Others The data obtained with gasoline in the single-cylinder engine were plotted with data obtained from the work of Graf, Gleason, and Paul a t the Oregon State Agricultural College (8), of Fieldner and Jones (6),and Fieldner, Straub, and Jones (6) a t the U. S. Bureau of Mines, of Gerrish and Tessmann of N. A. C. A. (7),and of D'Alleva and Love11 a t the General Motors Research Corporation (4). Figure 8 shows the relation between carbon dioxide and oxygen. The Oregon State line represents the trend of data obtained from

~

’


502

16

I4

I2

15

i IO

14

2 0

13

B

i j I-

512 V

5

IO

i 12

Y 6

9

a

z

w n

z

ON8 V

6

VOL. 29, NO. 5

0

2

4

6 0 1 0 1 0, IN PER CENT BY VOL.

2

211

4

5

Y IO

$2

a W n.

‘10

II

12 13 14 AIR-FUEL RATIO

15

FIGURE10 (Above). C A R B O N MONOXIDEvs. AIR-FUELRATIO FIGURE11 (Right). CARBON DIOXIDEus. AIR-FUEL RATIO n

z

s

eN8 7 ‘10

II

12

13

14

AIRF U ~ LRATIO

15

16

17

2 4

8 2

numerous sources, m o s t of w h i c h 0 were obtained on 6 8 IO 12 14 IS COP IN PER CENT BY WL. multi-cylinder FIGURE 8 (Above). CARBON DIOXIDE e n g i n e s . The 218. OXYOEN VALUES single-cylinder reFIQURE 9 B d o W ) . CARBON MONsuits approach the OXIDE us. ARBON DIOXIDE VALUES t h e o r e t i c a l line more closely than do those from t h e multicylinder engine tests, as would be expected. Figure 9 shows the relation between carbon monoxide and carbon dioxide. The authors’ results are almost identical with those obtained by the General Motors Research Laboratory, as shown by a line thought to represent their data. The General Motors results were obtained on multicylinder engine tests. Figure 10 shows the relation between carbon monoxide and air-fuel ratio. Here again a line has been drawn to represent the actual data obtained by the General Motors Research Laboratory along with their theoretical line. The authors’ data almost coincide with this theoretical line, departing from it a t the higher air-fuel ratios. Figure 11 shows the relation between carbon dioxide and air-fuel ratio. The authors’ results follow closely the curve of the Bureau of Mines, departing from it a t the higher airfuel ratios. The authors’ curve rises to a higher value of carbon dioxide as would be expected of a single-cylinder engine test compared to that of multicylinder engines with mixture distribution difficulties.

b

3. No appreciable amount of carbon monoxide will be found in the engine exhaust, using any of the fuels tested, if more than the amount of air theoretically required for complete combustion is delivered to the engine, assuming reasonably good mixture distribution. 4. No appreciable difference appears in the mixture distribution characteristics of the three fuels; distribution is apparently more dependent upon other factors such as speed, load, and method of introducing both the air and fuel for a given engine design. 5. The reduction or elimination of carbon monoxide from the engine exhaust by use of leaner mixtures, obtained either by restricting the fuel flow or by substituting a fuel (such as alcohol-gasoline blends) requiring less air, results in an appreciable loss of power; for all fuels tested, this loss averages about 6 per cent, based on maximum power output a t wide-open throttle with the multicylinder engine. 6. The percentage reduction in carbon monoxide by using an alcohol blend containing 10 per cent or less of alcohol instead of gasoline will be relatively small under idling, accelerating, or wide-open throttle conditions. 7. Under conditions in which a health hazard from carbon monoxide does exist from the operation of automobile engines on gasoline, the substitution for gasoline of gasolinealcohol blends containing 10 to 20 per cent alcohol would not eliminate or sensibly reduce this hazard. Obviously, therefore, it is dangerous to operate an automobile engine in a closed room or garage because of the carbon monoxide in both the exhaust and blow-by gasew, regardless of whether gasoline or alcohol blends are used as fuels.

Conclusions

Literature Cited

1. The relations between the exhaust products and airfuel ratios for both the gasoline and the alcohol blends are practically identical, except that the values for the alcohol blends occur a t lower air-fuel ratios, as would be expected from the different air requirements for combustion of alcohol and gasoline. 2. The carbon monoxide present in exhaust gases will be practically the same for both gasoline and alcohol blends if comparable air-fuel ratios are used. At maximum power air-fuel ratios, about 2.7 and 3.8 per cent carbon monoxide is found in the exhaust of a single- and a multicylinder engine, respectively, regardless of the fuels used. In other words, at the same richness of mixture the carbon monoxide will be practically the same for all the fuels used.

(1) Anonymous, Bus Transportation, 10,294(1931). (2) Cities Service Co., “Cities Service Power Prover,” 1936. (3) Cutter, D. C.,thesis, Yale Univ., 1933. (4) D’Alleva and Lovell, S. A. E. Journal, 38,90(1936). (5) Fieldner and Jones, J. IND.ENQ.CHEM.,14,594(1922). (6) Fieldner, Straub, and Jones, Ibid., 13,51(1921). (7) Gerrish and Tessmann, Natl. Advisory Comm. Aeronaut., Rept. 476 (1933). (8) Graf, Gleason, and Paul, Oreg. State ColI., Eng. E r p t . Sta. Bull. 4 (1934). (9) Henderson, Haggard, Teague, Prince, and Wunderlich, R e p t . N. Y.State Bridge and Tunnel Comm., pp. 141-220 (1921). (10) Tioe, AutomotiveInd., 53,53 (1925). RECEIVED December 14, 1936. The tests reported here were run in 1936 at Mason Laboratory and form part of the graduate work of C. W. Phelps in the Mechanical Engineering Department of the School of Engineering, Yale University.

._

,

Alcohol Blends

Recommend Documents