I S D U S T R I A L A N D ENGINEERI,VG CHEMISTRY
March, 1927
Table 111-Effect
of H e a t T r e a t m e n t of Fruit on Fermentation
I Uninbculated and not heated: Cherries Pineapple cubes Inoculated but not heated: Cherries Pineapple cubes Inoculated and heated to 80” C . : Cherries Pineapple cubes Inoculated and heated to boiling temperature; Cherries Pineapple cubes
3ii3
SUXBER OF PIECESBURSTAT ENDOF
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does not cause objectionable deterioration in the quality of the fruit. This maximum period \Till vary with the kind of fruit and to some extent with its condition. Observation of numerous batches of cordialized fruit-center candy showed that when invertase was added in about twice the proportion used in plain fondant candy, fermentation occurred only rarely. The use of invertase alone in this type of confectionery solves the problem to a great extent. Although no controlled experiments in which the use of invertase was combined with preliminary heat treatment of the fruit have been made, i t seems certain from the foregoing considerations that this n-ould reduce fermentation to a point of practical negligibility.
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I n the experiment reported in Table I, the standard invertase preparation was used in the proportion of practically 100 cc. to 100 pounds of fondant. It is probable that this proportion may be reduced somewhat in plain fondant and still allow a sufficient margin of safety. The action of invertase increases the proportion of liquid to solid phase and softens the fondant. This effect is usually desired. If, however, the proportion of invertase used to prevent fermentation is found in any case to render the fondant too soft, this may be corrected by increasing the stiffness of the fondant when prepared. This is accomplished by increasing the boiling temperature to which the sirup used for making the fondant is concentrated.
Gaseous Explosions’ IV-Rate of Rise of Pressure, Velocity of Flame Travel, and the Detonation Wave By Geo. Granger Brown and Geo. B. Watkins DCPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITY OB MICHIGAN, ANN .IREOR, MICH.
T
HE addition of a diluVelocity of flame travel and rate of rise of pressure v e l o c i t y of the detoiiatioii ent to any r e a c t i v e are shown to be similar and vary in the same way with wave in explosive mixtures of mixture generally dechanging initial conditions. h y d r o g e n and oxygen, are Detonating mixtures of pure liquid fuels and subplotted in Figure 1. creases the rate of the reaction. If the foreign material stantially theoretical oxygen were exploded with varying Dixon also found that the amounts of nitrogen in the constant volume bomb. detonation wave was not uniincreases the rate of the rea c t i o n or has an abnormal The amount of nitrogen necessary to reduce the informly propagated in mixeffect in decreasing the rate tensity of the detonation to an arbitrary standard was turcs of methane, oxygen, of reaction, the foreign mafound to vary directly as the rate of rise of pressure as and nitrogen in the proporreported in the previous paper. These data lead to the tion CH4 + 1.5 O2+ 2.5 Nz. terial is called a catalyst Gaseous explosions are chemconclusion that the rate of rise of pressure upon exBerthelotd found it impossible icalreactions, and are affected plosion of a fuel mixture is the major factor indicating t o i n i t i a t e the detonation by diluents and catalysts in the tendency of that fuel mixture to set up the detonawave in mixtures of carbon the same way as other chemtion wave in a progressive homogeneous reaction, and monoxide or of methane and ical reactions. that engine knock is not due to a detonation wave as air under atmospheric presIt is impossible to measure recognized in progressive homogeneous explosions. sure, and in cyanogen mixdirectly the rate of reaction in t u r e s of t h e composition any progressive gaseous explosion (one in which the flame ClN2 20 2 4 Nz. moves progressively through the explosive mixture) . 2 The Both of these investigators found that mixtures of hyeffect of diluents on the velocity of the detonation wave drogen and air propagated the detonation wave readily. was accurately determined by Dixon3 in detonating mixtures These meager results which are reported in Table I seem to containing hydrogen, methane, ethylene, acetylene, carbon indicate that the amount of nitrogen per unit volume of monoxide, and cyanogen. I n every case the addition of a reactants necessary to prevent, propagation of the detonation diluent, either oxygen or nitrogen, decreased the velocity wave varies as the velocity of the detonation wave propaof the detonation wave. The data reported by Dixon, gated in similar mixtures free from the nitrogen diluent. showing the effect of nitrogen and oxygen as diluents on the Diluents Decrease Velocity of Flame and Rise of Pressure
+
Presented under the title “Gaseous Explosions.
IV--Rate
of Rise
of Pressure and the Detonation Wave” before the Division of Gas and F u e l
Chemistry a t the 72nd Meeting of the American Chemical Society, Philadelptia, PA.,September 5 to 11, 1926. 2 Brown, Tam JOURNAL, 17, 1229 (1925). j TYans R o y . Soc. London, 184A, 97 (1893).
+
Since the Classic work of Dixon. manv investigators have studied the effect of diluents on flame iropagatiin and rate of rise of pressure in gaseous explosions. 1
Cornpt. r e n d , 93, 18,145 (1881).
INDUflTRIAL A N D ENGINEERING CHEMISTRY
364 Table I-Efiect
of Nitrogen
Dixon M./sec. 2821 Presumably not propagated 2322
++ + 7 + 2 Oz ++ 21.502 + 7.5 ++ 1.5 0 2 + 2.5 iY2 2 ++ 2On0%+ 4 + + 4 NZ 0 2
N2
0 2
Initiation of Detonation Wave
VELOCITY
FUEL MIXTURES
2 H2 2 H2 CH4 CHI CHI CH4 CzNa CnNz 2 co 2 co
0x1
N 2
2470 Went out sometimes 2321
0 2
0 2
n.2
1930 extrapolated
0 2
Berthelot
M./sec. 2810
Not propagated
S o t propagated 1940 calculated Not propagated
Mason and Wheeler,6 and later Payman,6found that when nitrogen was added to explosive mixtures of methane and oxygen it decreased the velocity of flame propagation before the detonation wave was i n i t i a t e d , a s D i x o n f o u n d that nitrogen d e c r e a s e d the velocity of flame n *2 propagation in the dex w tonation wave. Some -n of these data are givei X.1 in Table 11. Similar results were obtained by C a m p b e l l a n d Ellis,’ who found that 2900 27W 2500 2300 2100 lW0 17W the addition Of nitroM e t e r s per Second gen to explosive mixFigure 1-Effect of Excess Oxygen and t u r e s of m e t h a n e , Nitrogen on t h e Velocity of Detonation ethylene, and carbon in Electrolytic Gas ( 2 +~ oz) ~ (Dixon) disulfide d e c r e a s e d the velocity of flame travel. of Nitrocen on Velocity of Flame Travel
Table 11-Effect ~
FUEL MIXTURE
++ 22 + 1.3 N2 + 2 ++ 222 OO02zz + + 6 N2 + 7.5 Nz (air) ++ 22 ++ 7.74 Nz 8.62 Nz + 2 + 9.34 + + 11.3 Nz + 22 + 12.6 Nz ++ Oz + 2.175 Nz + + 3.55
CH4 CH4 CH4 C H4 CH4 CH4 CH4 CH4 CHI CH4 2 co 2 CO 2 co
0 2 0 2
N2
0 2 0 2
0 2
N2
0 2
0 2
0 2
0 2
N2
VELOCITYOP
FLAME TRAVEL Cm./sec. 5502.0 1822.0 967.0 232.0 93.0 87.0 66.0 55.0 36.0 21.9 350 199 107
REFERENCE
Payman Payman Payman Payman Mason and Wheeler Mason and Wheeler Mason and Wheeler Mason and Wheeler Mason and Wheeler Payman Crowe and Newey Crowe and Newey Crowe and Newey
Crowe and Neweyg found that nitrogen decreased the velocity of flame travel in explosive mixtures of carbon monoxide and oxygen a t an initial pressure of two atmospheres, as given in Table 11. Crowe and Nem-ey also studied the effect of mixture strength on the rate of flame travel and maximum pressure developed. They found (Figure 2 ) that the maximum velocity of flame travel and maximum pressure were always obtained with rich mixtures of the same composition. The maxima of both curves occur a t about 40 per cent, while the theoretical mixture contains 30 per cent of carbon monoxide. Bone, Newitt, and Townsendg studied the effect of nitrogen activation in carbon monoxide-air mixtures a t high pressures by photographing pressure-time curves of explosions. Their J . Chem. SOC.(London). 111, 1044 (1917). Ibid., 117, 48 (1920). I b i d . , 125, 1957 (1924). 8 Phil. M a g . , 49, 1112 (1925). 0 Proc. Roy. SOC.London, 103A, 205 (1923); 1 0 5 8 , 4 0 6 (1924); and 1088, 393 (1925). 6
VOl. 19, No. 3
data (Table 111) clearly show that nitrogen and argon, when acting as diluents, decrease the rate of rise of pressure in gaseous explosions of carbon monoxide mixtures. Table 111-Effect
of Inert Gas on t h e Rate of Rise of Pressure, a s Determined b y Bone
FL-EL MIXTURE
INITIAL MAX. PRES- PRESSURE SURE
+ +
2 co 0 2 2CO+Oz+4A 2 c0 0 2 t 4 Nz
Atntos. 4.3 3.0 3.0
TIME .FOR
Av. MAX. RATEOF R I S E
RECORDED PRESSURE
Atmos. 43 25.5 21.4
Sec.
0.0125 0.035 0.070
O F PRZSSURE
Almos./sec. 3440 728 306
The last column was calculated by dividing the maximum observed pressure by the time in seconds required for the attainment of maximum pressure. These values clearly show that nitrogen or argon, when acting as diluents, greatly decrease the rate of rise of pressure in gaseous explosions of carbon monoxide. These conclusions are further supported by results of work carried out in a constant volume bomb similar to that described in the previous paper.10 on the effect of nitrogen as an added dihent on the rate of rise of pressure in explosions of hexane-oxygen mixtures as shown in Figure 3. Velocity of Flame Similar to Rate of Rise of Pressure
The fact that nitrogen used as a diluent in explosive mixtures decreases the velocity of flame travel and decreases the rate of rise of pressure in all types of gaseous explosions indicates that the velocity of flame travel and rate of rise of pressure are sirnilarly affected by diluents. The similarity between the rate of rise of pressure and the velocity of flame propagation is also evident in comparison of the work of Stevens” and the present authors’ earlier work.’* Stevens found that the velocity of flame travel varied directly as the velocity of chemical reaction, if pressure and initial temperature remained constant. The same relationship between rate of rise of pressure and rate of chemical reaction was used to explain the effect of initial temperature.12 T h e similarity be- Morlmum Fiame tween velocity of flame ~r~~~~~ veloc8u travel and rate of rise Lbs/s91n cm/se‘ of pressure persists even in the detonation wave. l a Woodbury, Lewis, and 260 CanbyI3 state that de2.40 tonation is most easily initiated in a mixture 220 of acetylene and oxygen in the proportion to 2.90 give carbon monoxide. ,BO The experimental data reported indicate that 160 detonation was most easily initiated in mix‘O 20 30 4C SO 60 70 Rr Cent CO A i r M t x t u r e tures containing 4ghtIy more oxygen than just Figure 2-Effect of Misture S t r e n g t h necessary to form car- o n Velocity of Flame Travel a n d Maximum Pressure bon monoxide and hydrogen. This fact is in agreement with the data given by Dixon3 on the detonation wave propagated in explosive mixtures of ethylene and oxygen, plotted in Figure 4 and given in Table IV. These data on ethylene-oxygen mixtures are the only ones available which include a sufficient number of determinations to indicate whether or not the velocity of the
D
0
7
“Gaseous Explosions-111,” THISJ O U R N A L , 19, 280 (1927). J . Am. Chem. Soc., 48, 1896 (1926). 11 THIS J O U R N A L , 17, 397 (1925). 1s J . SOL.Automolioe Eng., 8, 215 (1921).
10
11
March, 1927
INDUSTRIAL A N D EhTGINEERING CHEMISTRY
365
0 0
D!
a"n
400
&
o
:
d
.04
5
Figure 3-Effect
C",++
8Or
TIME; IN S E C O N D S
89'G~ae A r ISO'C
20 Nr
R a t i o s a n d Velocity of D e t o n a t i o n Wave a n d of Pressure Rise
VELOCITY OF 1 FLAMETRAVEL
TIXE TO Av. RATE MAX. DEVELOP OF RISE FUELMIXTURE PRES- N A X . OF DETONATION SURE PRESPRESWAVE STlRE STTRE
BUEL
I S THE
"IXTURE
+ 2 Oz + +3
CZHI CzHa CZHI C~HI
0 2
+ 4 Oz 0 2
M./sec. 2507 2581 2368 2247
01
03
04
C , f 1 1 4 + l Z O ~ * f O N ~ 85*GAaeAi 147%
of Nitrogen a s a n Added D i l u e n t on t h e R a t e of R i s e of Pressure in Explosions of Hexane-Oxygen Mixtures of C o n s t a n t C o n c e n t r a t i o n
detonation wave is a maximum in mixtures containing slightly more oxygen than just sufficient to form carbon monoxide and hydrogen. If rate of flame travel and rate of rise of pressure are related as closely as is indicated by the data reported above, it should be possible to show a maximum rate or rise of pressure in detonation waves in explosive mixtures containing slightly more oxygen than is necessary t o form carbon monoxide and hydrogen. A series of experiments were undertaken using an apparatus similar to that described in the previous paper, in which isohexane-oxygen mixtures were exploded under conditions of constant initial temperature and pressure. The data obtained are given ill Table IV and plotted in Figurci 4. These results in determining the rate of rise of pressure 111 detonating explosions of isohexane and less than theoretical oxygen are very similar to Dixon's results on the velority of the detonation wave in ethylene-oxygen mixtures. They are of importance in indicating that the mixtures having the maximum velocity of flame propagation and the maximum rate of rise of pressure in detonation waves set up in mixtures of hydrocarbons in oxygen contain slightly more oxygen than just necessary to form carbon monoxide and hydrogen. These results are evidence in support of the conclusion that the rate of rise of pressure in gaseous explosions is influenced in the same way and by the same variables as the velocity of flame travel. Table IV-Mixture
6
1
Lbs./
++ 4.0 3.5 Oz CsHir + 5.35 Oz CsHia CsHir
CaHid
0 2
+ 6.09 Oz
sg. zn.
Sec.
400 780 630 610
0.004 0.0018 0.0022 0.0025
Lbs./sp.
in./sec.
100,000 433,000 288,000 244,000
Further evidence of the similarity betlveen rate of flame travel and rate of rise of pressure was given in a previous paperti? in which it was shown that the velocity of flame travel and the rate of rise of pressure in homogeneous explosions varied the in same way with changes in initial temperature.
Tendency to Initiate Detonation Wave Measured by Rate of Rise of Pressure
As was suggested above, the results of Dixon and Berthelot's studies reported in Table I seem to indicate that the amount of nitrogen, added as a diluent to an explosive mixture, necessary to prevent propagation of the detonation wave varies directly as the velocity of flame travel in explosive mixtures of that fuel free from nitrogen. As the rate of rise of pressure varies in the same way as the velocity of flame travel, it seems probable that the amount of diluent nitrogen required t o prevent propagation of the detonation xave varies directly as the rate of rise of pressure of the explosive mixture determined under identical initial conditions. It was impossible to verify this conclusion because no adequate data on the rate of rise of pressure of different fuel mixtures were available until the research reported in the previous paperlo was completed and the tendency of these fuels to initiate the detonation was determined. T a b l e V-Nitrogen Necessary to Reduce Intensity of D e t o n a t i o n t o Arbltrary Srandard, e n d t h e M a x i m u m R a t e of Rise of Pressure for T h a t Fuel FUEL
n-Hexane n-Heptane n-Octane Benzene Toluene Xylene Methanol Ethyl alcohol
M A X . RATEOF RISEOF PARTIAL PRESSURE PRESSURE A S DETD.I N NON-DETOS.ATISG EXPLOSIONS O N SITROCEN
Lbs./sp. in./sec.
Lbs./sq. in.
47,500 61,500 83,700 63,000 56,500 47,000 52,000 39,500
16.0 18.5 20.0 19.0 18.0 16.0 16.5 14.0
Accordingly, detonating theoretical mixtures of the same fuels, normal hexane, normal heptane, normal octane: benzene, toluene, xylene, methyl alcohol, and absolute ethyl alcohol, were exploded under constant initial conditions of temperature and constant density of charge as described in the previous paper,1° but with varying amounts of nitrogen added as a diluent to the explosive mixtures t o eliminate the detonation wave or to reduce the intensity of the pressure rise in the detonation wave to an arbitrary standard. The results of these experiments are given in Table V, and in Figure 5 are plotted against the maximum rate of rise of pressure in slow burning mixtures ignited under constant initial conditions, as reported in the previous paper.1°
366
I S D r S T R I A L i l Y D ENGILVEERING CHEJIISTRY
As the amount of nitrogen added to the explosive mixtures was determined by means of its partial pressure indicated on a Bourdon type of gage such as is used for measuring steam pressures, these determinations do not possess a degree of accuracy equal to the determinations of the rate of rise of pressure reported in the p r e v i o u s paper.’O d ; slightly different slope 0 of the straight line in Figure 5 may be suggested for the different 400000 t y p e s of f u e l s , b u t within the limits of exp e r i m e n t a l error a straight-line r e l a t i o n e x i s t s b e t w e e n the amount of nitrogen required to eliminate the 2 0 0 0 ~ detonation wave and the rate of rise of pressure of non-detonating ,ooooo explosive mixtures deFigure 4-Effect of Mixture R a t i o o n t e r m i n e d under conVelocity of Detonation a n d R a t e of Rise stant initial conditions, of Pressure as shown in Figure 5. Sitrogen added as a diluent has been shown to decrease the velocity of flame travel and of rate of rise of pressure. Therefore the effect of the greater amount of diluent required to prevent detonation of fuel mixtures having a higher velocity of flame travel or rate of rise of pressure is simply to decrease this higher rate of rise of pressure. The results given in Table V and Figure 5 indicate that the rate of rise of pressure of an explosion is the major factor determining the tendency of the explosive mixtures to initiate the detonation wave, and when theoretical explosive mixtures of different fuels having the same density of oxygen and nitrogen are exploded under the same initial conditions, as described in the previ-
Vol. 19, No. 3
ous paper, the rate of rise of pressure so determined seems to be the major criterion of the tendency of that fuel to initiate the detonation wave. The detonation wave is evident as a well-defined type of flame propagation developed directly from the flame initiated by the spark and practically independent of the surfaces of the combustion tube. Accordingly it is a homogeneous reaction because it is entirely confined to the gas phase, and a progressive homogeneous reaction because it is a homogeneous reaction which has progressed directly from the flame initiated by the spark.2 The data presented in this paper indicate that the rate of rise of pressure as measured in non-detonating theoretical explosive mixtures varies directly as the tendency of a fuel to initiate the detonation wave in a progressive homogeneous reaction, as described. But it is we:l known that the aromatic h y d r o c a r b o n s have much less tendency to knock in in- 5 1 9 ternal combustion en- $ gines than the normal 1 1 8 paraffin hydrocarbons having similar rates of 217 rise of pressure. The relative tendency of the 6 16 n o r m a l paraffin and 2 aromatic hydrocarbons a 15 to initiate the detonatioii wave is entirely 0 different from the relaMulmumRote ~ R I ofpressure X - Lbs/sqmn/sec tive tendency of the Figure +partial Pressure of Nitrogen same fuels to knock in Required to Eliminate the Detonation Wave as a F u n c t i o n of t h e R a t e of Rise internal c o m b u s t i o n of Pressure D e t e r m i n e d u n d e r C o n s t a n t engines. Therefore the Initial Conditions detonation wave, as is recognized in progressive homogeneous reactions, is not the cause of “detonation” (fuel knock) in internal combustion eugines.
2
Gaseous Explosions‘ V-The Probable Mechanism Causing “Detonation” in the Internal Combustion Engine By Geo. Granger Brown and Geo. B. Watkins DEPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITY OF MICHIGAN, AXK ARBOR,MICH.
IXCE 1905 the demand for gasoline has increased faster than the increase in production of petroleum. The petroleum refiners have therefore resorted to the most obvious means of supplying this increasing demand for their most volatile product, that of including less volatile material in the gasoline fraction. The continuation of this practice has led to poorer engine performance and particularly to a very unpleasant “knock” in the more efficient engines of higher compression ratio. This knock is metallic in sound, but is not due to mechanical impacts, as was first suggested. It was then found that retarding the spark largely eliminated this objectionable noise and the suggestion was made that the knock was due to preignition. Further experience showed that the removal of carbon from the surfaces of the combustion chamber made i t unnecessary to
S
1 Presented before the Divisions of Gas and Fuel Chemistry and Petroleum Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa , September 5 to 11, 1926
retard the spark to eliminate this objectionable sound, which was then referred to as a “carbon knock.” During the war an intensive study was made to find more and better fuel suitable for use in the high-compression airplane engines. It was then found that some fuels would knock more readily than other fuels under the same conditions, and the “carbon knock” was rechristened the “fuel knock,” as it is now known. The knock is characterized by an intense pressure of extremely short duration and a marked decrease in the power output of the engine. The reason for this decrease in power may be explained by analogy. If it is desired to push a car or other load up a hill, the applicat.ion of a steady pressure or push is more effective in moving the load than a series of impacts, such as blows from a sledge, in which the pressure developed is many times that exerted by the steady pressure, but of such short duration that no work is accomplished. Similarly with the explosion in an internal combustion en-
