Vol. 19, No. 3
INDUSTRIAL A N D ENGINEERING CHEMISTRY
372
oven-dry weight of straw and therefore ratio of chemical to straw-were maintained constant. Periods of cooking were successively lengthened in the experiments of each series in order to afford a view of the reaction as it progressed. Table I-Conditions PROPORTION OF NazS08 TO
of Tests
CONCENTRATION
\'OLlJME
OF
DRYSTRAW BY WEIGHT
OF
SOLUTION
SOLUTION
Per cent
Grams/lrler
cc.
20 40 40
40 40 80
125 250 125
I I1
I11
SERIESI-The data given in Table I1 for Series I and recorded graphically in Figure 1 show that the yield of fibrous residue, or that portion of the straw remaining undissolved at the end of the pulping period, decreases very rapidly during the first hour of cooking. Beyond that point the rate of change in yield and in chemical properties with time of cooking is relatively slow. The cellulose suffers its greatest loss during the first hour of cooking. Afterward the dilute sodium sulfite solution hydrolyzes it but slowly. This loss is not indicated in the pentosans present in the Cross and Bevan cellulose, but rather in the pentosan-free cellulose, as shown in the eighth column of Table 11. The pentosans, determined in the cellulose, remain practically constant throughout 12 hours, the maximum period of cooking. During the early stages of cooking the sodium sulfite solution attacks the material determined as lignin to a much more marked degree than it does the cellulose. Beyond the first hour the lignin removal proceeds more slowly, but even after 12 hours the total amount removed exceeds that of cellulose for the same period. The pentosans not in the Cross and Bevan cellulose, like the lignin, are removed at an exceedingly rapid rate during the first hour of cooking and also, like the lignin, are more slowly removed during the remainder of the cooking period. I n the twelfth column of Table I1 i t is of interest to note that values closely approximating 100 per cent are obtained for all the cooked samples by adding together the lignin, the pentosan-free cellulose, and the total pentosans. SERIES11-Acomparison of the data for Series I and I1 shows that the rate of cooking is considerably accelerated ~ 1 sa result of increasing the ratio of chemical to straw. It Table 11-Analytical
-
1 3 6"
8 10
12 1l/z
3 6 ll/pa
3" 6"
CELLULOSE
ADDED
Per 100 grams Concn. straw
0
3ASED O N OVEN-DRY WEIGHT OF RESIDUE
BASEDO N OVEN-DRY WEIGHTOF STRAW
2:;-NazSOa Hours
is noteworthy, however, that for a given yield the chemical properties of the insoluble residue are in all cases practically identical-a fact which is observed even when the time required to reach that yield, due to doubling the ratio of chemical to straw, has been reduced by 50 per cent. SERIES111-From a comparison of the data for Series11 and I11 it is evident that a change in concentration of the sodium sulfite from 40 grams to 80 grams per liter is practically without effect upon the rate of decomposition or upon the relation of chemical properties to yield.
Data o n Flax Straw Hydrolyzed with Sodium Sulfite-Effect of Concentration, Ratio of Chemical t o Straw, a n d Time of Cooking o n Yield and Chemical Properties
I
SAMPLE
SERIES I 371 388 386 384 383 382 385 I1 393 392 394 111 391 389 390
Figure 1
Grams Grams per liter
Yield of pulp
%
Lignin
%
Total
Pentosanfree
%
70
urn of pencellulose, osan-fiee Copper
PENTOSANS
Total
%
In cellulose
%
A-ot in cellulose
70
Solub1e
Consumption of chemical
ignin, and number total pentosans
70
~ A S E DO N CHEMI CAI. ADDED
70
Grams
Yo
33.73 10.45 7.75 10.52 8.17 8.23 8.72
None 2.86 3.07 4.31 4.17 3.96 4.13
None 56.9 61.0 84.9 82.1 78.0 82.1
None 40 40 40 40 40 40
100 68.36 65.59 64.36 62.97 61.95 61.37
23.28 13.75 11.70 11.10 10.45 9.45 9.80
53.80 51.15 51.15 50.15 50.80 50.40 49.50
46.75 44.30 43.60 43.35 43.40 43.00 42.50
17.10 10.32 10.23 10.11 9.50 9.57 9.45
7.06 6..84 7.58 6.78 7.40 7.44 6.97
10.05 3.48 2.65 3.33 2.10 2.13 2.48
87.13 99.98 99.84 100.21 100.50 100.05 100.54
7.97 5.17 3.64 5.10 4.36 4.62 3.99
40 40 40
40 40 40
65.26 64.19 62.01
12.10 11.81 10.16
51.00 50.00 49.15
43.60 42.83 42.38
9.87 10.02 9.58
7.43 7.12 6.73
2.44 2.90 2.85
100.40 100.75 100.20
3.00 3.35 3.68
7.29 8.13 9.81
3.00 2.85 2.71
29.85 28.40 26.90
40 40 40
80
67.74 64.79 61.94
13.16 11.50 9.95
51.80 49.60 48.85
43.95 42.75 42.15
11.00
80 80
7.85 6.87 6.73
3.15 3.58 3.17
100.51 99.80 100.02
3.31 4.94 5.38
8.56 11.29 11.75
3.04 3.60 4.43
30.1 35.5 43.7
None 20 20 20 20 20 20
Resulting pulp was filtered with difficulty.
10.45 9.90
March, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
373
Studies of Combustion in the Gasoline Engine' I-Determination of Rate of Burning by Chemical Analysis By Wheeler G. Lovell and John D. Coleman, with T. A. Boyd RESEARCH LABORAT~SRIES, GENERALMOTORS CORP.,DETROIT, MICA.
T
The Burning as a Whole HIS investigation was made in an effort to follow the progress of combustion in the gasoline engine from a The composition of the exhaust gas, or the final product of chemical point of view. Its object was to obtain some data upon the rates and the physical nature of combustion as combustion, gives some valuable information upon what has it occurs in the automobile engine, and, if possible, some in- happened chemically during the combustion of the fuel in formation, also, upon the actual course of chemical reactions an engine. The examination of this gas is a simple and direct that take place there between the fuel and the air. More matter which can be carried out merely by running an engine intimate knowledge of the nature of the combustion, and of under various conditions, and making analyses of the gases the reactions which occur during it, are of importance not only passing through the exhaust pipe. Numerous studies of in engine design, operation, and economy, but also in the ef- this kind have been made under a wide variety of operating c o n d i t i o n s ,-n o t a b l y by fort to explain detonation in Fieldner, Straub, a n d engines, and the action of Jones,3 and the results have antiknock compounds, such As a departure from the usual methods of investigatbeen subjected to analysis as tetraethyl lead. ing combustion in gasoline engines, a study has been particularly in terms of mixPurely physical measuremade of the burning during its progress, from a chemiture ratio. Some of these ments made upon the gases cal point of view. The ordinary method of examining r e s u l t s were further anain the engine cylindercombustion by means of the engine exhaust1is subject lyzed in a previous paper, i n d i c a t o r cards, for exto the disadvantages that combustion occurs so long in which an apparent equiample-give little informabefore the exhaust stroke that the final products do librium condition from the tion upon what chemical not give definite information as to how it has proceeded. standpoint of the water-gas reactions take place there. I t is important, therefore, to sample gases from the reaction was shown to exist T h e d a t a of the spectrocylinder during the actual explosion period. For this in the products of comscope, an instrument which purpose, a special quick-acting, water-cooled sampling bustion of gasoline engines. has been used to some exvalve has been devised, which makes it possible to follow It may be noted that most tent as a means of finding the progress of combustion. of the analyses of engine exout what happens in the This new experimental method yields data particuhaust available in the literc y l i n d e r during combuslarly adapted for determining the rate of combustion. ature have been made on the tion,2 are difficult to transThe knock is accompanied by an increase in the rate of gases from multi-cylinder late into terms of chemical burning of gasoline, whether the detonation is caused engines. From the standsubstances and reactions. by addition of kerosene, or by the presence of a chemipoint of a careful study of Investigation of combuscal knock inducer. In the presence of tetraethyl lead combustion, these are subtion in the gasoline engine gasoline burns a t about its normal rate. ject to an apparent disadfrom a chemical standpoint vantage in that the exhaust has been based almost enconsists of a mixture of gases tirelv. " , in the Dast. uDon the examination of the final products-that is, upon analysis from the different cylinders. Consequently, on account of of the exhaust gas. The gas obtained by sampling the ex- inequalities of fuel distribution in the intake manifold, the haust has the composition corresponding to the scavenging exhaust is a composite of the gases issuing from a number of stroke of the piston, which portion of the cycle (in. the usual cylinders, each of which may be operating with a different four-cycle engine) begins a t the end of the explosion or power mixture ratio. For this reason, the investigation covered stroke, after the expansion of the burned or burning gases has in this paper was begun by analyzing the exhaust from singletaken place. Thus, some of the exhaust gas may issue from cylinder engines operating under a wide range of conditions, the exhaust valve a t a full 360 degrees after ignition, or after in order to serve as an additional check upon the determinations made by others. the initiation of the combustion reactions. For this reason, it is evident that the exhaust gases repreThe results obtained in this study of the exhausts of singlesent the combustion reactions only in an indirect way, and any cylinder engines were in substantial agreement with those of information obtained about combustion from them must other investigators, to which reference has already been be projected backward over a period of time. I n order made. For all conditions, with the possible exception of t o obtain more direct information as to the rate of com- those prevailing during extremely high speeds, the fuel is bustion, or as to the chemical reactions occurring during completely burned, so far as the amount of air available will combustion, it is necessary to examine the gases during the permit. I n the case of a fuel composed of carbon and hytime of the burning. I n order to do this, it became necessary drogen, the exhausted products consist of carbon dioxide, and to devise a method of sampling the gases in the cylinder dur- water. When insufficient air for complete combustion is ing the actual period of the combustion. Such a method has present, as is nearly always true in practice, the exhaust been devised, and is described herein. contains, in addition to these, carbon monoxide and hydrogen. But the oxygen is always completely used up-except a trace 1 Presented before the Division of Petroleum Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 which persists possibly as a result of a chemical equilibrium ~
to 11, 1926.
9 Midgley and Gilkey, J. Sac. Automotive Eng , 10, 218 (1922); Clark and Thee, THISJOURNAL, 18, 528 (1926).
8
THISJOURNAL, 13, 51 (1921). and Boyd, I b d , 17, 1216 (1925).
' Lovell
I S D U S T R I A L A-YD E,VGISEERIAVG CHEMISTRY
March. 1927 Results
The results shown graphically in Figure 3, in which the composition of the gases obtained from the engine cylinder a t different times are plotted against time, are typical of the data which were secured. These data were obtained from a n air-cooled Delco-Light engine operating on gasoline a t 1200 r. p. m. a t a mixture ratio of about 7 5 per cent of the air required for complete combustion, or a t approximately the mixture ratio for maximum power. The horizontal dottpd lines represent the composition of the exhaust, which was sampled a t the same time as the gases in the cylinder. The constancy of the exhaust composition serves as a check upon the operation of the engine, and in particular shows that the fuel-air ratio was unchanged during the series of experi-
375
zero time after ignition show some products of combustion. This is due to the fact that since scavenging of the burned gases is never complete, a part of the new charge consists of exhaust gas from the previous explosion. It is possible to estimate the efficiency of the scavenging of the previous charge from these data. The form of the curves in Figure 3 indicates that the mixture in the combustion chamber is probably almost homogeneous. There is no abrupt break in the curve, such as might be expected to be present if there were a narrow zone of flame moving progressively across the cylinder, within which the combustion reaction completed itself, so far as the air present permitted. This does not mean a t all that a "flame" did not proceed through the chamber, as there must have been a spread of something through the charge that marked the beginning of combustion. But the data do seem to show that the combustion reaction was of considerable duration, and that during this period it was apparently going on substantially throughout the combustion chamber. This is n matter that n-ill be taken up more comprehensively in a subsequent paper of this series; but here attention may be called to the fact that the data presented in these papers were obtained from the gasoline engine, so that they are probably not strictly comparable t o those secured under the itatic conditions that prevail in a bomb. While the particular data in Figure 3 were being collected. the sampling \alve was located in the top of the cylinder a t one side, opposite and about 2.5 inches from the spark plug, which was inserted from the side of the cylinder. I t was found experimentally that when the location of the valve was changed from this position 2.5 inches away from the point of ignition to another which was only 0.25 inch away. samples taken from the two points a t corresponding times differed slightly in composition or in the amount of burning which had taken place. This difference is relatively small,
" " i I l l
D
5
30
23-
m
.a-
I
l
l
90
s3-
9-0
I 93-
5u
J 55
7/42? cax7t;p ZWZ'Z??@XGPZZS ' aCP&MRmW)
Figure 3-Composition of Gases from Engine Cylinder a t Various Times after Ignition Full lines, cylinder gases Dotted lines exhaust gases, sampled simultaneoiisly Delco light engine-1200 r p. m. 5 0 1 compression ratio Gasoline fuel-75 per cent of theoretlcdl air
ments. The solid-line curves in Figure 3 show how the gas taken from the burning mixture a t various points in the cycle gradually changes its composition from that present before ignition to that corresponding to the regular exhaust, or to complete combustion so far as the oxygen present permits. In interpreting these data, it is recognized, first of all, that they m a y not reprebent exactly the composition of the gases in the combustion chamber a t the instant of sampling; for it is probably not possible to stop the combusticin reaction by the method used, so far as any individual molecule is concerned, except a t certain stages or equilibrium conditions. But from the results presented in Figure 3, i t is apparent that it is possible to obtain a gas consisting of partially burned fuel in various stages of combustion, as is shown by the presence of oxygen, together with some of the products of combustion-or, in other words, a sample which represents the charge when only partially burned. It is apparent, also, that the sampling valve operates rapidly enough to yield a sample which, although taken from a burning mixture, is cooled quickly enough to arrest, in part a t least, the combustion in progress a t the instant. The reaction is stopped, or greatly retarded, in different ways. The gases are cooled by contact with the cold walls of the sampling valve chamber, and this cooling may be increased to some extent by expansion through the valve. The reaction is also interrupted by the considerable decrease in the density of the gas as its pressure is reduced from that of the combustion chamber t o that of the outside atmosphere. It may be seen from Figure 3 that the points representing
Bo
s3
* h ,
"
$ &
@ . !
8
0
nfl€ AFT;CA IGNl7roNflK&GQ€E9 LV XEVOLV7fON) Figure 4-Amount of Fuel Burned a t Various Times after Ignition For normal combustion and for knocking combustion caused by different means Delco light engine--1200 r p m. 7 5 per cent of theoretical alr
and is t o be expected since there must be some spread of reaction from the point of ignition outwards. Quantitatively, with gasoline under average conditions this time lag of one point in the cylinder behind that of another may amount to as much as 10 to 20 degrees of revolution (or about 0.002 second a t 1200 r . p . m . ) ; for example, a t a given time the mixture a t one point may be 80 per cent burned and a t another 30 per cent burned. Rate of Burning and the Effect of Detonation upon It
Another important observation is that from the curves of Figure 3 it is possible to estimate the rate at which the burning is progressing. This measurement of rate may be
Vol. 19, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY
376
made directly; for from the curves information may be obtained, (1) as to what percentage of the oxygen has been consumed a t any given time, and (2) as to how much of the products of combustion have been formed at the same time. It is possible, therefore, to plot a curve showing the portion of the fuel which has been burned a t various times during the combustion stroke. This is especially valuable when dealing with gaseous fuels, which appear directly in the analysis. On this basis, the curves shown in Figure 4 have been drawn. In these the percentage of the fuel charge that has burned up to a given time is plotted against the time after ignition. It should be pointed out, with respect to these curves, that since there was an excess of fuel present, in all of these experiments, 100 per cent burned means 100 per cent reacted, or burned so far as the amount of air permitted. Measurements of the rates of burning, such as these, have an important application to the study of knock in engines and of the action of antiknock compounds, such as tetraethyl lead. Thus, in Figure 4 the normal rate of burning of gasoline is compared with that of a gasoline-kerosene mixture, with that of gasoline in the presence of a knock inducer (which in this case was a small amount of isopropyl nitrite), and with that of gasoline run under the knocking conditions
just described, but with the presence of enough tetraethyl lead to eliminate detonation. The data shown represent averages of different determinations. The relative rates under these various conditions are apparent from the chart. It is seen that when the engine knocks, whether the detonation is .caused by the presence of kerosene in the gasoline or by a chemical knock inducer, the gasoline burns at a rate more rapid than normal. It may be seen, also, that the presence of tetraethyl lead in a knocking combustion brings the rate of burning back to normal, within the probable limit of error. Inasmuch as it gives direct information upon the rate a t which fuels burn, it would seem that there is here available a powerful tool for investigating the course of combustion in the gasoline engine. The method gives, also, a measure of what the conditions are just before ignition, or the amount of the charge carried over from the previous cycle; and, in the case of gaseous fuels, of the composition of the new charge. Finally, the method gives information as to the nature of the chemical reactions occurring in the combustion chamber, for as will be seen from Part I1 of this series, it is possible to have two simple fuels in a n engine burning a t different rates.
Studies of Combustion in the Gasoline Engine’ 11-The Burning of Hydrogen and Carbon Monoxide By Wheeler G . Love11 and John D. Coleman, with T. A. Boyd RESEARCH LABORATORIES, GENERAL MOTORS CORP.,DETROIT, MICH.
I
N THE preceding paper
The results of experiments described in this paper
Experimental Method
of this series2 there was indicate that the simultaneous burning of carbon The apparatus used was a described a method of monoxide and hydrogen in a gasoline engine probably single-cylinder, air-cooled enobtaining gas samples durtakes place according to the reactions: gine equipped with the speing the explosion period in a 2Hz 0 2 cial sampling valve previ2co o*gasoline engine, by means of ously described. Different where the ratio of the velocity constants which it is possible to find the compression ratios were emk ~ p : k c o= 2.3 rate a t which the fuel burns in ployed, but the engine speed Neither these reactions nor their relative rates are the cylinder. The results of was held constant at 1200 changed by a small increase in the compression ratio, experiments upon the comr. p..m. The fuel consisted of or by.the presence of a knock inducer or a knock bustion of hydrogen and cara mixture of carbon monoxide suppressor, as long as detonation does not occur. The bon monoxide in a gasoline and hydrogen. The hydrogen simultaneous combustion of two individual fuels in an engine, presented herewith, was the commercial prodengine at rates widely different for each does not appear were obtained by the method, uct prepared by electrolyto be in agreement with the concept of a narrow zone sis and the carbon monoxthe investigation having been of flame advancing across the cylinder, within which ide, compressed into cylinconducted in order to obtain combustion is completed. ders, was obtained through information upon the physithe courtesv of F. C. Zeisbera cal nature and mechanism of E. I. du Pont de Semours and Company: of combustion of these simpler gases. The fuel gases were metered to the engine in substantially I n an engine fueled with gasoline, hydrogen and carbon monoxide are products of combustion for mixtures in which equivalent proportions by means of calibrated flow meters. the fuel is in excess. On this account, an actual engine Uniform admixture with air upon admission to the cylinder study of the burning of these two simple gases themselves is was assured by a gas-mixing valve of considerable capacity of considerable practical importance, for information as to located between the throttle and the intake valve. The ratio how these fuels burn should be useful in helping to solve the of fuel to air was substantially that of a perfect mixture, problem of the mechanism of the combustion of gasoline. with neither fuel nor air in excess. This mixture ratio was Also, data upon the behavior of these gases in the presence of used as a matter of simplification, since there was then no tetraethyl lead may have application to the general problem complication from incomplete combustion, and the fuel of the action of antiknock compounds. gases were burned completely to water and carbon dioxide. 1 Presented before t h e Division of Petroleum Chemistry a t the T2nd Samples of the gases from the engine cylinder were collected Meeting of the American Chemical Society, Philadelphia, Pa., September in the manner described in Part I, and were analyzed in 5 t o 11, 1926. a Burrell precision gas analysis apparatus. 2 Page 373, this issue.
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