September, 1924
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
trons instantly, thus preventing their advance ahead of the flame front. Attempts to produce this effect, however, were unsuccessful. Lind4 made the same attempt about twelve years ago, though the work was not published until after the writers’ work was completed, Lind was unable to show any effect on the velocity of a hydrogen-oxygen explosion in a brass tube fitted with an axial e1ect)rodecharged by means of a Wimshurst machine. The present attempt involved the explosion of an acetyleneair mixture in the ratio of 1: 7.14, which is the best ratio to give carbon monoxide gas and the most likely to detonate. Detonation in a 1-meter Pyrex tube was, in fact, very marked when this mixture was fired by an ordinary automobile spark plug, but no decrease in the detonqtion could be observed when the tube was fitted with a long axial brass electrode 4
J . P h y s . Chem., 28, 57 (1924).
893
charged to *500 volts by means of a battery of dry cells. Similarly, there was no effect when the tube was placed within a solenoid 7 inches long and containing 500 turns of copper wire with a field strength of 2000 ampere turns. Finally, with a solenoid 2.5 feet long with 1500 turns of wire and carrying 7.5 amperes, hence a field strength of 11,000 ampere turns, no effect was noted, whichever polarity was used. Neither did a strong horseshoe magnet with an iron core so placed that two poles were on opposite sides of the glass tube a t various distances from the spark plug show any effect. While these experiments were failures, it was hardly to be expected that the attainable fields would be sufficient to affect decisively the velocity or the number of electrons in the flame, especially when no exact measurements were made and the only criteria of the effect were the visual and audial judgments of the violence of detonation.
Relative Effects of Some Nitrogen Compounds upon Detonation in Engines’ By T. A. Boyd GENERALMOTORS RESEARCH CORP.,DAYTON, OHIO
quite effective for suppressITROGEX in some of Nitrogen in some of its compounds exerts a greater influence upon ing detonation, in some it its compounds exerts the character of combustion than any other element of small atomic is apparently almost neua greater influence number. The action of nitrogen is influenced in a large way by the eletral, and in some it exerts upon the character of coinments or radicals attached to it. Thus, in some of its compounds it is the remarkable effect of inbustiori than any other elequite effectivefor suppressing detonation, in some it is almost neutral, ducing detonation. For exment of small atomic numand in some it exerts the remarkable effect of inducing detonation. ample, detonation is supber.2 Unlike molecular ioFor example, detonation is suppressed by aniline, it is affected pressed by aniline, it is afdine, though, which is very very little by pyridine, and it is induced or increased by propylnitrite. fected very little by pyrieffective for influencing inThedatapresented in this paper show that in general the nitrogen comdine, and it is induced or internal combustion, molecupounds which are most effectivefor suppressing detonations are the creased by propyl nitrite. lar nitrogen has no effect for primary and the secondary amines. Of these the aryl amines or those The purpose of this paper suppressing detonation, exthat contain at least one aryl group have much the larger influence is to present in a systematic cept in so far as it slows for eliminating detonation from internal combustion engines. way the relative effects of a down ljherate of flame m o w number of the comDounds agation by diluting the’combustible mixture. But in this latter particular a similar effect of nitrogen upon detonation in internal combustion engines. is produced by other inert gases, such as carbon dioxide for WEREMADE How THE MEASUREMENTS example. I n distinction from its ineffectiveness in the molecular state, The apparatus used in determining the relative influences of nitrogen in some of its compounds exerts a large influence upon the various compounds has already been described in considerthe character of combustion. By weight nitrogen forms able detail.3 This instrument, called the “bouncing-pin about 73 per cent of a proper combustible mixture of kerosene apparatus,” consists essentially of a sensitive detecting device and air. When such a mixture is burned in an engine of 75 designed to screw into the heat of the engine cylinder, and an pounds compression, the combustion is accompanied by vio- electrolytic cell placed in an electric circuit which is arranged lent detonation. However, if there is added to the fuel an in such a way that contact points are closed intermittently amount of diphenylamine, for example, sufficient to increase whenever detonation occurs in the engine. I n the lower end the weight of nitrogen in the total fuel-air mixture only 0.026 of the cylinder element is a small piston the vertical movement per cent, or from 73,000 to 73,025 parts per 100,000, the char- of which is resisted by a stiff spiral spring. Resting on top acter of the combustion is entirely changed and the operation of the piston simply by gravity is a light steel rod or pin, the of the engine becomes very smooth and free from the distur- upper end of which touches a cantilever spring element bearbance that is called a detonation or knock. ing the lower of the two contact points. As might be expected from its low atomic weight, the acThe strength of the spiral spring above the piston is such tion of‘nitrogen is influenced in a large way by the elements or that during normal combustion the amplitude of the piston’s radicals attached to it. Thus, in some of its compounds it is vertical movement is only a few thousandths of an inch, so that the pin following the movement of the piston does not 1 Presented before the Division of Petroleum Chemistry a t the 67th close the contact points. When the violent impulse produced Meeting of the American Chemical Society, Washington, D . C., April 21 t o 26, 1924. by a detonation in the combustion chamber is applied to the 2 Other publications describing means of influencing detonation, or the lower end of the piston, however, its movement is so sudden “knock,” in automotive engines are‘ Midgley and Boyd, J. Soc. Aulomolive
N
Eng., 10, 7 (1922); Ibid., 10,451 C1922); (1922); Midgley, Ibid., 15, 421 (1923).
THIS JOURNAL, 14, 589,
849, 894
8
Midgley and Boyd, J. Sop. 14, 589, 894 (1922).
JOURNAI,,
.4UtOmOliUe
Eng., 10, 7 (1922); THIS
INDUSTRIAL AND ENGINEERING CHEMISTRY
894
that the pin is thrown upward and-free from the piston, thereby closing the electric circuit at the contact points and causing a generation of gas in the electrolytic cell. The elements bearing the contact points are springs; and, since the more violent the detonation the greater the impulse given to the pin, the length of time the contacts are closed is a function of the
0 I 2 3 4 J PERGENTA”r e y VOLUME IN HEROSENE FIG 1 - C O M P A R I S O N
OF PROPPLAMLNOBENZENE WITH ANILINE Propylaminobenzene Aniline 3 02 grams = 2 28 grams 0 0 2 2 4 mol = 0 0 2 4 5 mol 1 mol = 1.10 mols
intensity of detonation. The amount of gas generated in the cell, in turn, is proportional to the length of time the circuit is closed. And so the volume of gas evolved in the electrolytic cell, which is arranged to measure it automatically, is a function of the intensity of detonation. The observations reported in this paper were made on a small, single-cylinder, air-cooled engine. Kerosene was used as fuel, and in all the measurements aniline in concentrations of 1 to 3 per cent by volume in the fuel was employed as the standard of effect in suppressing detonation. I n such concentrations aniline is readily soluble in kerosene a t ordinary temperatures, so that no binding material of high solvent action was needed to carry it into solution. I n one or two cases, however, where the material whose effect was being compared with that of aniline was not sufficiently soluble in kerosene alone, a mixture of absolute alcohol and kerosene was used as fuel, and the compression of the engine was raised in order to give knocking conditions. The standard aniline was of course always dissolved in the same fuel as the compound under test. TARLE I-INPLuRNCE
COMPOUND
O F SOXE CrKOTiPS ATTACHED T O T H E ATOM O N THE ANTIKNOCKEFF’RCT OF NITROGEN Reciprocal of mols required to give antiknock effect equivalent t o 1 SOURCE OF COMmol of aniline’
FORXULA
POUND
0.09 (negatit4 NHa Ammonia CzHsNHz 0.20 Ethylamine (CzHs)zNH Diethylamine Eastman (CzHs)aN Triethylamine C 6 H s N (CzHa) z 0.24 Diethylaniline General Motors Ethyldiphenylamine CzHaN ( C c H s ) z Research (C16H613N Triphenylamine 1.5 Eastman Diphenylamine (C6Hs)zNH d u Pont 1.0 Phenylamine (aniline) C e H s N H z a Based on concentrations of aniline up t o 3 per ce,nt by volume in kerosene.
The method of making the measurements can best be described by giving a specific example. A comparison of the effect of propylaminobenzene with that of aniline may be used for this purpose. First, it was roughly determined that about 3 parts of propylaminobenzene and 97 parts kero-
Vol. 16, No.,??
sene by volume gave about the proper amount of detonation in the engine-that is, it gave a knock of such intensity that somewhat less than 1.26 cc. of gas was generated in electrolytic cell in 1 minute. This value was known t between that for 2 parts and that for 3 parts of aniline, which was the compound used as a standard of effect, in the same fuel. A number of 1-minute runs were then made, the fuel being successively 3 parts aniline and 97 parts kerosene by volume, 3.02 grams propylaminobenzene in 100 cc. total mixture with kerosene, and 2 parts aniline and 98 parts kerosene. For each run the volume of gas generated and the power output of the engine were recorded, the latter simply as a check on the engine operation. This set of runs was then repeated in the reverse order. All the values for the volumes of gas generated in the electrolytic cell during the runs on each fuel were then averaged and the data so obtained were plotted on coordinate paper in the manner illustrated in Fig. 1 in which the results of two determinations like that described are shown. . The amount of aniline to which 3.02 grams of propylaminobenzene are equivalent was obtained simply by projecting its value in gas generated horizontally to the corresponding aniline curve and vertically to the abscissa scale, where the aniline equivalent was read directly. These numbers were then averaged and converted to the molecular basis, as is shown by the tabulation under Fig. 1.
RESULTS The results of the determinations, or the data on which this paper is based, are tabulated in Tables I and 11, and shown graphically in Figs. 2 and 3. The most striking thing about these charts is the way in which the curves of effect rise and fall with the different elements or radicals attached to the nitrogen atom.
FIG 2-INFLUCNCI:
OF THE GROUPSATT.4CHED TO T 4 E ATOMO N THE ANTIKNOCKEFFECT O F NITROGEN
These interesting facts may be noted about the data in Fig. 2: (1) The curve has minimum points when the atoms or radicals attached to the nitrogen atom are all alike. Thus, minimum effects on detonation are shown by NH3, (C2Hs)sN,and (CeH5)3N. ( 2 ) The curve has maximum points a t d i e t h y l a ~ m eand a t diphenylamine, both secondary amines, the intermediate maximum point being a t ethyldiphenylamine, a tertiary amine. The superior effect of the phenyl radical for influencing the antiknock action of nitrogen is illustrated by the values for diethylamine and diphenylamine, the latter being three times as great as the former. (3) Two of the intermediate points on the curve are a t primary amjnes, ethylamine and aniline, the other being a t the tertiary amine, phenyldiethylamine (diethylaniline). The compound a t this last intermediate point differs from that a t the adjacent maximum point by having two alkyl groups and one aryl group, instead of two aryl groups and one alkyl group. The greater effect of the aryl than the alkyl radicals for influencing the antiknock value of nitrogen is illustrated here also in the relative values for ethylamine and aniline, the latter of which is much more effective than the former.
Further data on the influence of the atoms or radicals attached to nitrogen on its effect upon detonating combustion
.
September, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
are plotted in Fig. 3, which shows the relative antiknock values of a number of derivatives of aniline. Although the diagram is self-explanatory, mention may be made of the following points: Replacing one of the hydrogen atoms of the amine group by an organic radical increases the effectiveness in the cases of the methyl, ethyl, and phenyl radicals. Thus, methylaniline is 40 per cent more effective molecularly than aniline, and diphenylamine is 10 per cent more effective than methylaniline; but when an alkyl radical larger than ethyl is substituted in the amine group the antiknock effect is lowered.
895
nitrogen is only about one-eighteenth as effective molecularly as diethyl telluride and only about one-eightieth as effective as tetraethyl lead.
NEARLYNEUTRALNITROGENCOMPOUNDS AND THOSE THAT INDUCE DETONATION
Some organic nitrogen compounds have very little effect upon the character of combustion. Thus, such materials as pyridine, quinoline, piperidine, phenylhydrazine, acetamide, and organic cyanides have little importance because, relatively speaking, the influence they exert upon detonation is extremely small. But when nitrogen is bonded into organic TABLE II--EFFECTSON THE ANTIKNOCK VALUEOF ANILINE OF SUBSTITUTING
VARIOUSORGANIC RADICALS FOR HYDROGEN IN THE RING AND IN THE AMINE GROUP Reciprocal of mols required t o give anti-knock effect equivalent t o 1 SOURCE OF COMCOMPOUNI) FORMULAniol of anilinea POUND Aniline CeHsNHi 1.0 du Pont CHaCsH4NHz Toluidine Eastman (CI1a)zCsHaNHz ??-Xylidine du Pont Cumldine (CHs)aCaHzNHz Ethvlaminobenzene CzHsCeH4NHz n-P;op ylaminobenzene' C ~ H T C S H I N H Z General Motors n- Butylaminobenzene C ~ H B C ~ H ~ N H Z Research Amylaminobenzene CsHiiCxHaNHz Aminodiphenyl CeHsCaHaNHi 1.14 J Monomethylaniline Eastman CoHsNHCHs 1.4 Monoethylaniline du Pont CeHsNHCzHs 1.02 Mono-n-propylaniline CeHjNHC3H7 Eastman Mono-n-butylaniline CsHsNHCaHe Mono-iso-amylaniline CeHaNHCsHu General Motors 0.248 Research Eastman Diphenylamine CsHsNHCsHs 1.6 0.21 Baker Dimethylaniline CsHsN(CHdz 0.24 Dieth ylaniline CsHsN(CzH6)z Eastman Di- n-propyldniline CeHsN (CsH7) z 0.27 a Based on concentrations ot aniline up t o 3 per cent by volume in kerosene. b Average of 0 , rn, and p values.
$gb }
::E 'I ::E 1
E 1
1
The low values for the dialkyl anilines are worthy of note; but, as may be seen from Fig. 2, the dialkylanilines are more effective than triethylamine, or even than triphenylamine, compounds in which the nitrogen atom is bonded to only one type of organic radical. The alkylaminobenzenes exhibit a peculiar type of function. The curve shows not only the dropping off from the maximum a t methylaminobenzene (toluidine) that characterizes the monoalkylanilines, but also a later increase in molecular effectiveness as the size of the alkyl radical attached to the ring becomes larger. The alkylaminobenzenes from the ethyl to the amyl were prepared by nitrating and reducing the corresponding alkylbenzenes. The compounds so obtained, and which theoretically should consist largely of the para isomer, were used in determining the values shown. I n this fact may lie the explanation for the peculiar shape of the alkylaminobenzene curve, because p-toluidine is about onesixth more effective for eliminating detonation than o-toluidine or m-toluidine, both of which are of about equal effectiveness. So it appears that the relative percentages of the para isomer present in the various alkylaminobenzenes used would exert it considerable influence on the shape of the curve.
7
8
Q
10
NUMBER OF CARBON ATOMS IN THE
I1 12 MOLECULE
3-INFLUENCE O N ANTIKNOCKEFFECT OF ANILINEO F SUBSTITUTVARIOUS ORGANIC RADICALS FOR HYDROGEN I N THE RING AND I N THE AMINEGROUP FIG.
ING
compounds with oxygen, such as nitrates and nitrites, the resulting materials are inducers of detonation, the former being more effective than the latter. The alkyl compounds of this class exert a much greater disturbing influence upon combustion than the corresponding aryl compounds. For example, isopropyl nitrite is very much more effective than nitrobenzene for inducing detonation. One mol of isopropyl nitrite is equivalent in effect upon combustion to the inverse of the detonation-suppressing influence of TABLE 111-NITROGEN COMPARED WITII SOMEOTHERELEMENTS IN EFFECT over 10 mols of aniline, but the detonation-inducing effect of UPON COMBUSTION nitrobenzene is very small. Nitric acid, and even some inorReciprocal of mols required t o give an antiknock effect equivalent t o ganic nitrates, can also cause detonation in internal combusELEMENT COMPOUND 1 mol of aniline tion engines. Nitrogen (CzHdaN 0.14 (CsHdzNH 1.5 Naturally, the compounds that have a desirable influence Selenium (CzHdzSe 6.9 upon the combustion are those which eliminate or suppress the Tellurium (CZHJ2Te 26.8 Lead (C2HdrPb 120.0 detonation characterizing the burning of most petroleum COMPARISON OF NITROGEN WITH SOMEOTHER ELEMENTShydrocarbons when the initial compression to which the fuelair mixture is subjected is an economical one. The data The effects of nitrogen compounds for suppressing detona- presented in this paper show that in general the nitrogen comtion are small in comparison with those of similar compounds pounds which are most effective for this purpose are the of some of the elements described in previous publication^.^ primary and the secondary amines; and of these the aryl Some comparative values illuktrating this point are tabulated amines, or those that contain a t least one aryl group, have in Table 111. From these data it may be seen that, even in di- much the larger influence for eliminating detonation from phenylamine, one of the best of its compounds reported, internal combustion engines.
