gaseous combustion at high pressures, part xiv....

57

Gaseous Combustion at High Pressures, Part XIV. Explosions of Hydrogen-Air and Carbonic Oxide-Air Mixtures at Initial Pressures up to 1000 Atmospheres.

By W illiam A. B one, D.Sc., F.R.S., D. M. N ewitt, D.Sc., and D. T. A. Townend, D.Sc.

(Received August 19, 1932.)

Introduction.

In the previous papers of this series have been described explosions of theoretical hydrogen-air, carbonic oxide-air, etc., mixtures in spherical steel enclosures at initial pressures up to 175 atmospheres ; and in 1929 our collected researches on the subject were published in a separate volume entitled “ Gaseous Combustion at High Pressures,” in which their theoretical implications were fully considered in the light of the experimental evidence as a whole.

Without recapitulating all the many points of interest established during the work, there was one of outstanding importance which should now be recalled, namely, the discovery, attested by an overwhelming mass of cumulative evidence, which is set forth in Chapters IX to X III (pp. 120 to 208) of our book, of N2-activation in C 0 -0 2-N 2 explosions at high initial pressures due to an absorption by N2-molecules of the radiation emitted by the burning carbonic oxide. In theoretical CO-air explosions this was marked by (i) a continuously increasing “ lag ” in the time taken for the attainment of maximum pressure, as the density of the medium was increased from P t- = 10 to Pt- = 175 atmospheres, and (ii) a strong exothermic effect during the subsequent “ cooling period ” ( without there having been any corresponding suppression of Jcinetic energy during the explosion itself), as the activated N2 molecules slowly reverted to their normal condition. Moreover in explosions of C 0 -0 2-N 2 mixtures containing oxygen in excess of tha t required for the complete combustion of the carbonic oxide, the so-activated nitrogen reacted with the excess of oxygen with the production of large quantities of nitric oxide.

From careful comparative measurements made on the various pressure-time records obtained during explosions of 2CO -f- 0 2 + 4R (where R = N2, CO or 0 2) mixtures at initial pressures between 3 and 150 atmospheres, as well as from data obtained from explosions of 2CO -j- 302 + 2N2 mixtures at initial pressures between 3 and 75 atmospheres, it was deduced that

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58 W. A. Bone, D. M. Newitt and D. T. A. Townend.

(i) while the N2-activation effect in a theoretical CO-air explosion increased with the density of the medium up to a steady maximum value with = 150 atmospheres, its intensity relative either to the density of the medium or to the total kinetic energy developed on explosion reached a maximum at P i = 75 to 100 atmospheres when it was equivalent to as much as nearly 25 per cent, of the total energy developed, (ii) that in 2CO -f- 3 0 2 + 2N2 explosions at P f — 75 atmospheres the nitric oxide surviving in the cold products (namely 3 per cent.) was about half the maximum amount actually formed during the explosion itself.*

In view of the theoretical interest of such deductions and their obvious bearing upon technical problems of nitrogen-fixation, it was decided to carry out further experiments upon (i) explosions of theoretical H 2-air and CO-air, etc., mixtures at much higher initial pressures than hitherto attempted, (ii) nitric oxide formation in 2CO -j- 3 0 2 -j- 2N2 explosions at Pf = 50 to 90 atmospheres under conditions such as would ensure a much more rapid cooling, and therefore a greater NO-survival, than in our former experiments, and (iii) nitric oxide formation in continuous CO-flames maintained at controlled steady high pressures in various 0 2-N2 atmospheres.

For the achievement of these objectives it was necessary to design and install in our laboratories new high-pressure vessels and ancillary appliances at considerable expense ; but thanks to the generosity of Imperial Chemical Industries, Ltd., we were enabled to do so in 1928, since which time the work has steadily progressed. And in this and the following two papers are described the principal new results obtained up to date.

E xperimental.

A.—The New Bomb to withstand Explosion Pressures up to 10,000 Atmospheres.

For the experiments contemplated under (i), it was necessary to design a new bomb (No. 5 of those used in these researches) capable of withstanding maximum explosion pressures up to 10,000 atmospheres (= 6 5 -6 tons per square inch). And after consultation with Sir George Hadcock, F.R.S., who kindly helped us with his great experience of gun-design, it was decided to employ a cylindrical explosion chamber 7-5 cm. long by 3-75 cm. diameter (capacity = 116 c.c.) closed at either end by screwed fittings, the one carrying the necessary inlet valve with ignition device and the other a Petavel mano-

* The evidence for this is set forth in Table X X X , p. 162 and pp. 161-173 of our book (q.v.).



Gaseous Combustion at High Pressures. 59

meter. At 10,000 atmospheres pressure, the walls would then have to withstand a load of 917 tons, and each end plug one of 115*5 tons. And in order to ensure a relatively uniform distribution of stress in the walls, it was decided to have a comparatively thin walled inner barrel suitably reinforced by wirewinding as in naval gun construction. The bomb was subsequently constructed for us by Messrs. Armstrong, Whitworth & Co., a t their Elswick Works, Newcastle-on-Tyne.

The Bomb Body (fig. 1).—The cylindrical barrel (A) of the bomb, machined out of a forging of nickel-chromium molybdenum steel (C = 0*32, Ni = 2*50,

1:5"—

Fig. 1.

Cr = 0• 58, Mo = 0*65, Mn = 0*55, Si = 0*16, S = 0*032, and P = 0*02 per cent.) was 18*1 inches long by 8 inches external diameter, with a cylindrical explosion chamber 3 inches long by 1^ inches diameter. Each of the end plugs was 6*45 inches long, with 4 threads per inch and tapered from 2*3 inches at the inner to 2*784 inches at the outer end. I t was calculated that an explosion pressure of 10,000 atmospheres in the chamber would subject the thread to a shearing stress of 2 • 7 tons per square inch.

A nickel-steel collar (B) was shrunk on to each end of the barrel A, and 95 layers of steel wire of section 0*25 inch by 0*04 inch were wound round its middle section as shown at C., this winding being protected by a nickel- steel jacket D, of thickness 1*03 inches. The whole bomb with its end plugs




was mounted on ball bearings in a massive cast-iron stand, bolted to a concrete foundation, in such wise that it could be readily rotated about its axis.

The Inlet Valve with Ignition Device.—In order to avoid drilling a separate hole into the explosion vessel for an ignition plug, a combined inlet valve and ignition device (fig. 2) was designed. The ignition device consisted of a steel rod A terminating in a conical boss insulated from the main body of the plug by a thin compressed mica cone B. A gas-tight joint was made between the cone and the plug by tightening the nut C. Ignition was effected by electrically fusing a thin platinum wire stretching between the insulated rod A and the body of the plug.

In designing the valve special precautions had to be taken to protect its seating from the corrosive action of the hot explosion products. The seating

Fig. 2.

was therefore made in the interior of the plug 4f inches away from the explosion cavity. As it was impossible to drill a hole tlirough this length of hard steel sufficiently small to prevent the access of hot gas to the seating, a f-inch diameter steel plug (D) on the side of which a fine V groove had been machined, was driven into the end of the plug and extended to within \ inch of the seating. The narrow gas passage thus produced admirably protected the seating, whilst at the pressures employed no difficulty was experienced in forcing the gas through it into the bomb. The valve spindle was f inch in diameter and was turned by a 3-foot tommy bar.

The Petavel Gauge carried by the other screwed end-fitting was similar in design to that employed in our former experiments.

The copper washers originally employed for the obturation of the inlet valve and Petavel gauge fittings proved unsuitable for explosions at initial pressures exceeding 500 atmospheres ; accordingly for use at such higher pressures the design had to be modified, a procedure which necessitated shorten




ing the length of the cylindrical explosion chamber from 3 inches to 2|- inches without altering its diameter.

The Hydraulic Intensijier used in Calibrating the Petavel Manometer.—In order to calibrate the Petavel gauge for the pressures generated during the explosions, it was necessary to produce and maintain hydraulically for some time in the explosion chamber static pressures up to 10,000 atmospheres. For this purpose a special “ intensifier ” (fig. 3) was designed. I t consisted essentially of a high pressure piston A of f-inch diameter closely fitting into a steel plug which could be screwed into the valve opening of the bomb.

In making the calibration, the explosion cavity of the bomb was completely filled with vaseline, and then the piston A was forced inwards by means of pressure applied hydraulically to the larger piston B, of 10 times the sectional area of A, abutting on its opposite end, the pressure so applied being measured by a standard Bourdon-tube gauge.

In order to ensure a liquid-tight-joint between the pistons and cylinder walls, each piston had a false-head (C and C') between which and the piston proper was a soft rubber packing ring. This made a self-tightening packing which proved perfectly satisfactory up to the highest pressure reached in the experiments.

The Filling System and Experimental Procedure.—In order tha t the experimental data may be rightly understood, some reference must be made to the “ filling system ” for mixing and introducing the gases into the bomb explosion- chamber and to the subsequent general experimental procedure. The filling system, shown diagrammatically in fig. 4 consisted essentially of the following items : (1) A series of high-pressure steel cylinders ( ., C) into which thehighly purified single gases had been separately compressed to pressures between 400 and 500 atmospheres ; (2) two standard Bourdon gauges, Gl5 G2, having pressure-ranges (a) 0-250, and (6) 0-2000 atmospheres respectively; (3) a glass-lined steel tube I), one-half filled with “ active ” coconut charcoal, for




the removal of any iron-carbonyl possibly present in the compressed carbonic oxide used, and the other half with specially purified and re-distilled phosphoric anhydride, to ensure a uniform degree of drying of the gases passing through i t ; (4) a compression cylinder, B, in which the gases were finally compressed hydraulically over clean, dry mercury, into the explosion bomb.

Fig. 4.

Passage of the gases was controlled by means of the standard three-way nickel-steel valves Y1? V2, V3, all connections being of drawn steel fine-bore tubing screwed into mild steel union nipples and rendered gas-tight by silver brazing.

Procedure.—In making an experiment, the compressed constituents of the particular explosive mixture were separately introduced in proper proportions, slowly through D, into the compression cylinder B and bomb chamber A, and from 12 to 24 hours allowed for mixing, after which the final compression to just above the pressure desired for the subsequent explosion was effected by means of the mercury hydraulic pump P. This being accomplished, a final mixing of the gases in the explosion chamber was effected by rotating the bomb on its bearings, the mixture was then sampled for analysis, and its pressure finally accurately adjusted to the desired point (Pt) after which it was fired in the usual manner with the Petavel manometer and recorder in action.

B.—Corrections of the Initial and Maximum Explosion Pressures (Pt- and Pm) for Deviations from the Gas Laws.

(1) P t-.—At the higher initial pressures employed in these experiments, the deviations of the gaseous media from the gas-laws became considerable, and




in each case were directly determined beforehand in our compressibility apparatus by the method already described in detail on pp. 50 to 54 of our book ( q.v.). The relationships between the gauge-pressure (Pf) actually employed and the corresponding “ corrected ” pressures (Pi6) for each explosive medium at each of the various experimental explosion pressures were as follows.

Table I.

Explosivemedium.

Initial explosion pressure Pi as indicated by the gauge (atmospheres).

75 250 350 500 750 1000

Ascertained “ corrected ” pressure P#.

2H2 + 0 2 + 3-76N2 74-2 238 305 392 485 5602CO + 0 2 + 3-76N2 76-2 243-5 312-5 388-5 460 5202CO + 0 2 + 3-76CO 76-2 245 320 392 —

I t is thus seen how far a t such higher pressures the actual rate of increase in the density of each particular medium lagged behind the increase in its corresponding pressure as observed on the gauge. Thus, for example, a doubling of the latter from 500 to 1000 atmospheres increased the density of the theoretical hydrogen-air medium by 1*43 and of the theoretical CO-air medium by 1-34 only, and it is clear that beyond 1000 atmospheres a further large increment in the gauge-pressure would have had a disproportionately small effect upon the density of such media.

Pm.—A co-volume correction was applied to the observed maximum explosion pressure in each case on the assumption that the space occupied by a gas molecule is proportional to the third power of its effective molecular diameter and that the variation of the latter with the absolute temperature is in accordance with the mean values calculated (1) on the assumption that it is proportional to nearly the first power of the absolute temperature, and (2) according to Sutherland’s formula. The basis of such “ correction ” is discussed on pp. 252-254 of our book, and the so-corrected value will be referred to as Pwt).

The Pressure-Time Explosion Records and the “ Cooling Correction ” for P m•—It should always be remembered that the pressure-time records obtained in such explosions are influenced by the shape and capacity of the particular explosion chamber used, and especially by the ratio between its wall-surface




and total volume which largely determines the cooling factor. Therefore the explosion data actually observed with any given mixture at a particular initial pressure and temperature will vary with changes in the explosion chamber, and their significance in any case will be relative to the particular chamber used. Hence it follows that while the data from a series of explosions of a particular mixture over a wide range of different initial pressures in one and the same explosion vessel may be regarded as quite comparable amongst themselves, they are not so with the corresponding data from a similar series of explosions of that mixture in another chamber of different size and contour unless, what is always difficult, correlating factors between the two series can be deduced experimentally.

In comparing the data from these new experiments with those from our previous ones, it should be remembered that whereas formerly a spherical explosion chamber of circa 240 c.c. capacity with a surface/volume ratio circa 0-78 was employed, we were now using a cylindrical chamber of circa 116 c.c. capacity with a surface/volume ratio circa 1*17, the firing point in all cases being at one side or end so that the flame always had the same horizontal run to the head of the recording pressure gauge.

In our theoretical H 2-air explosions, where the explosion-times were so rapid that the pressure-rises on the pressure-time records were almost vertical, any direct estimation of the proper “ cooling-correction ” applicable to the Pmb values was impracticable, and therefore not attempted. In the slower CO-air, etc., explosions, such “ cooling corrections ” were deduced and applied as described on pp. 245-247 of our book ( .) and the fully-corrected maximum explosion pressures will be referred to as Pm6c.

Experimental Comparisons between New and Old Conditions.—In order to establish as far as possible a basis of correlation between the conditions of the old and new experiments, respectively, a preliminary series of theoretical H 2-air, CO-air and 2CO -f- 0 2 + 3-76/CO explosions was made a tP f = 75 atmospheres in the new cylindrical bomb (No. 5) for comparison with previous similar explosions at the same initial pressure in the old spherical bombs Nos. 2 and 3. It should, however, be noted that whereas the diluent in the latter was 4(N2or CO) in the former it was 3 ’76(N2 or CO).

The results, as detailed in Table II, showed that whereas with slow explosions in the new bomb the explosion time (tm), if anything, tended to be shorter, the cooling effect of the walls was so much greater that the observed maximum explosion pressures and temperatures were only about 0*86 those formerly obtained in the spherical bomb. In this, and all other tabulations :—



VOL. CXXXIX ►

Tabl

e II

.—Ex

plos

ions

at

P, —

75

Atm

osph

eres

in

Diff

eren

t B

ombs

.

Mix

ture

exp

lode

d:2H

2+0

2+4N

2.2H

2+0

2+3

* 76N

2.2C

0+02

+4N

2.2C

0+02

+3-

76N

2.2C

0+02

+4C

0.2C

0+02

+3-7

6C0.

No.

2N

o. 3

No.

5N

o. 2

No.

3N

o. 5

No.

2N

o. 3

No.

5In

bom

b of

cap

acity

sphe

rica

lsp

heri

cal

cylin

dric

alsp

heri

cal

sphe

rica

lcy

lindr

ical

sphe

rica

lsp

heri

cal

cylin

dric

alc.

c.:

240.

240.

116.

240.

240.

116.

240.

240.

116.

P(5, a

tmos

pher

es

......

.....

74-2

74-2

74-2

76-2

76-2

76-2

76-2

76-2

76-2

seco

nds .

......

......

......

...0

005

0-00

50-

005

0-30

0-32

0-24

0-01

50-

010-

01Pw

, atm

osph

eres

...

......

..63

562

554

563

563

555

072

072

065

0PT

O&, a

tmos

pher

es...

......

..60

859

751

860

560

552

368

368

361

1^m

bl^i

b ...

......

......

......

.....

8-19

8-05

6-98

7-94

7-94

6-86

8-96

8-96

8-02

P-fa

ll in

1 s

ec. a

fter

tm—

Atm

osph

eres

....

......

.....

320

385

415

125

130

230

223

310

370

Per

cent

.*

......

......

......

.54

6683

2223

47-5

3447

-564

T,„,

K°

......

......

......

......

..27

50°

2705

°23

45 °

2660

°26

60°

2305

°30

20°

3020

°27

25°

Tot i

n cy

lindr

ical

bom

b0-

860-

865

0-85

5T

m in

sph

eric

al

,,

* i.e

., th

e pe

rcen

tage

of|t

he t

otal

pos

sible

P-f

all b

etw

een

Tm

and

room

tem

pera

ture

.

a Co o 2 Co Q o o* 2 Co <>*. O § a s C

oC

o ss Co o> Oi

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Pf = observed initial pressure in atmospheres at the actual firing temperature.

P tb = ditto “ corrected ” for ascertained deviations from the gas laws.tm — time in seconds from commencement of pressure-rise to the attain

ment of maximum pressure (also referred to as the “ explosion time ” in the text).

Pm = observed maximum pressure in atmospheres.

Pto6 = ditto “ corrected ” for estimated deviation from Boyle’s Law (i.e., co-volume correction).

Pw6c = ditto also for cooling during tm.Tw = mean maximum temperature K° actually attained on explosion.

P f — observed final pressure in atmospheres of the cold explosion products at room temperature 0.

P/6 = ditto “ corrected ” for ascertained deviations from the gas laws.

The explosive mixtures were always fired a t room temperature, which varied between 15° and 17°. At all initial pressures up to and including 500 atmospheres several experiments were carried out with each particular mixture, with results which invariably agreed within about 2 per cent. ; at still higher initial pressures we were content with two well-agreeing experiments at each particular pressure. In the present publication, however, we have restricted ourselves to detailing the results of what we consider the best representative experiment with each mixture at each selected initial pressure.

D.—2Ha + 0 2 + 3*76N2 Explosions at Initial Pressures between 250 and 750Atmospheres.

In this series of experiments, theoretical hydrogen-air (2H2 -f- 0 2 -f-3*76N2) mixtures were fired in the cylindrical bomb at initial pressures of 250, 350, 500 and 750 atmospheres respectively. Up to Pt — 500 atmospheres the explosions were all well under control and went off normally without damaging the bomb, but a t P* = 750 atmospheres detonation was set up instantaneously and so violently as to lift both the Petavel manometer and the inlet valve from their respective seatings, whereby hot gaseous products got past them with consequential considerable damage to the screw threads adjacent to the bomb cavity, which in parts were completely melted. As this entailed undue risk to the operators, it was decided not to proceed to any higher pressure.




Satisfactorily complete records, as detailed in Table III, were obtained at all initial pressures up to and including 500 atmospheres, from which it will be seen that both the explosion time (tm), the Pw6/P i6 ratios (and consequently the Tw also), while tending to increase with the density of the medium, had become nearly constant after the latter exceeded that corresponding with P t- = 350 atmospheres. From the pressure-time records reproduced in fig. 5, a, b and c, it will be seen how sudden was the pressure rise on ignition and

Table III.—2Ha + 0 2 -f- 3-76N2 Explosions in Cylindrical Chamber7*5 X 3*75 cm .; capacity = 114 c.c.

Pi atmospheres ................... 250 350 500Pi5 atmospheres ................... 238 305 392tm seconds ........................... 0015 0 02 0 022POT atmospheres ................... 2130 2950 4100P mb atmospheres ........ 1810 2390 3075P ft,atmospheres ...........P fall in 1 second—

132 170 215

Atmospheres ............... 1450 1780 2100Per cent. ....................... 72-5 64 54

^mbl ib................................... 7-61 7-83 7-85K° ................................... 2560° 2630° 2640°

2000

£ 1000k 500 \ 250r%2500

.se 1500

rv._

-j Pi * 25tms:

S 350 •5$

3000

P i- 3 5 0 a t ms.

1000500 P i‘f300atrns:

20 40 60Tim e in '/tooth. Seconds.

Fig. 5.

SO 100

how abruptly the “ cooling ” period succeeded the attainment of the maximum pressure. In each case the rate of cooling followed Newton’s law throughout showing it to be uncomplicated by any exothermic effects ; and from calculations it would appear that the amoimt of H 20-dissociation at Tw was always less than 0*5 per cent., or a quite negligible amount so far as its possible effect on the cooling curves.




E.—2CO -f- 0 2 + 3-76N2 Explosions at Various Initial Pressures up to 1000Atmospheres.

In this series of experiments explosions of theoretical CO-air (2CO + 0 2 + 3-76N2) mixtures were successfully carried out at initial pressures of 250, 350, 500, 750 and 1000 atmospheres, respectively. Up to and including 500 atmospheres the original length of the cylindrical bomb cavity, namely, 7*5 cm., was used ; but a change in the copper washers, and the damage done to the end fittings by the H 2-air detonation at P f = 750 atmospheres, necessitated certain alterations before higher pressures were attempted, which reduced the length but not the diameter of the explosion chamber to 6-25 cm. Consequently the explosions at P* = 7 5 0 and 1000 atmospheres, respectively, were carried out in the so-reduced chamber; and in order to correlate the two sets of results, an explosion was carried out in it a t P* = 500 atmospheres also.

The experimental results, which are detailed in Table IV, entirely support the conclusions drawn from our previous experiments that absolutely the N2-activation effect in such explosions was rapidly approaching a maximum when the density of the medium exceeded that corresponding with P = 150 atmospheres. Thus the fact of there being neither any increased “ lag ” in the “ explosion time ” (tm) nor yet any further increase in the estimated exothermic effect during the first second of the “ cooling period,” after the initial pressure exceeded 350 atmospheres, may be regarded as conclusive evidence of there having been no further increase in the N2-activation after such point had been passed.

As might be expected, the Pm6/P i& ratios steadily increased from 7-89 to 9-00, corresponding with a rise of from 2650 to just under 3000° K. in the mean maximum “ explosion temperature,” as the initial pressure was increased from 250 to 1000 atmospheres ; and the calculated degree of C02-dissociation at the maximum temperature correspondingly increased from about 2*5 to 5*5 per cent.

I t should also be observed that at no time was there the slightest sign of any “ carbon deposition ” during any of the explosions, an important consideration especially in view of what was found during the next series of explosions with 2CO + 0 2 + 3-76CO media in which the nitrogen in the air had been replaced by its equivalent of carbonic oxide.

From the pressure-time records reproduced in fig. 6, a, b, c and d, it will be observed that (unlike similar records obtained when these mixtures were



Tabl

e IV

.—2C

0 +

02

-f- 3

-76N

2 Ex

plos

ions

.

PiPi

ttm

P»n

Pm&

P rri

bcP/

6

P-fa

ll in

1 s

ec.

afte

r tm

.^m

bl^i

bat

mos

.at

mos

.se

cs.

atm

os.

atm

os.

atm

os.

atm

os.

atm

os.

Per

cent

.

P-eq

uiva

lent

Cal

cula

ted

T m

K°.

of e

xoth

erm

icC0

2-d

isso

ciat

edef

fect

inat

1 se

c. a

fter

tm.

per

cent

.

Expl

osio

n C

ham

ber,

7-5

X 3

-75

cm.

250

243-

50-

2822

9019

2322

1220

578

037

7-89

2650

°31

52-

435

031

2-5

0-33

3270

2583

3024

269

1060

358-

2627

60°

326

3-6

500

388-

50-

3345

0033

3038

1432

713

5032

-58-

5728

60°

5-0

Expl

osio

n C

ham

ber,

6-25

X 3

-75

cm.

500

388-

50-

2244

8033

2032

514

3034

-58-

5428

50°

____

5-0

750

460

0-22

5820

4070

—38

516

0030

8-85

2950

°—

5-5

1000

520

0-24

7100

4690

—43

419

9030

9-00

2995

°5-

5

<35 SOGaseous Combustion at High Pressures.

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exploded in our spherical bombs) there was always a well-marked “ hump ” in the rising pressure-curve indicative of some retardation of the flame when it first impinged upon the walls of the cylindrical cavity. This feature was more marked in these comparatively slow explosions than in the next series of more rapid 2CO + 0 2 -f 3*76CO explosions; and in the still more rapid H 2-air explosions (q.v.) it was untraceable. I t was due to purely “ environmental ” circumstances and had no chemical significance.

2500

1500

500250

5500

(a)

§250

-I%1500 o

£ 7)505000fg

/1 //

A__ —(b)

= r//

/r— Pi-350atms.

7000

5000

5000

1000

/ J t = :/ .1

/ r 1........y/ .

y — — — Pi-K OO ulms.20 40 60 80

T im e inSooth Seconds.F ig . 6.

100

B.—2CO + 0 2 -j- 3-76CO Explosions at Initial Pressures between 250 and 500Atmospheres.

Hitherto in these investigations we had always carried out explosions of 2CO + 0 2 + 4CO mixtures at initial pressures corresponding with those of our 2CO + 0 2 -j- 4N2 explosions in order to obtain data required for the measurement of the Na-activation and C02-dissociation effects during the last- named. And it may be recalled how the replacement of N2 by its equivalent of CO in such explosions not only made the “ explosion time ” as short as in corresponding 2H2 -f- 0 2 —j— 4N2 explosions, and eliminated the “ exothermic




effect ” exerted by the nitrogen during the “ cooling period,” but also suppressed C02-dissociation altogether. Moreover in none of such 2 C 0 + 0 2+4C 0 explosions at initial pressures up to 150 atmospheres was there even the slightest deposition of carbon.

Accordingly in these new experiments a t still higher initial pressures, we essayed for comparative purposes a corresponding series of 2CO 4- 0 2 + 3 • 76CO explosions at initial pressures of 250, 350, 500, etc., atmospheres. Unfortunately, however, for the strict validity of the comparison, it was found that a t all such higher initial pressures slight but unmistakable carbon-deposition occurred during the explosions, a feature which had never been observed at lower initial pressures. Nevertheless the observations were not without interest inasmuch as they showed very clearly how an increase in pressure affects equilibrium in a reversible CO-C-C02 system in the opposite direction to an increase in temperature. The experimental details are shown in Table V and the corresponding pressure-time records are reproduced in fig. 7, a, b, and c.

2500

1500

«5 500

| 250 %5500

§%2500

.§ 1500

b 5001 3502 5000

■Pi- 2 5 0 a im s : ’ -

$J 000

lOOO 1 500

Pi '5 5 0 aim s.

4 j — ----- — . ---

f---- !—

fPt -5 0 0 alms: -

20 40 60 80 Time in ‘/too th Seconds.

Fig. 7.

lOO

I t will be seen that, in conformity with our previous experience at lower pressures, the “ explosion-times ” were all considerably less, the mean maximum temperature considerably higher, and the rates of cooling after tm much faster than in the corresponding 2CO + 0 2 + 3-76N2 explosions, circumstances



<1 to

Tabl

e V

.—2C

0 -f

02 +

3-7

6CO

Exp

losi

ons

in C

ylin

dric

al C

ham

ber,

7-5

X 3-

75 c

m.

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attributable to the total suppression of both N2-activation and C02-dissociation effects by the replacement of N2 by CO as the diluent.

In conclusion we wish to express our best thanks to Imperial Chemical Industries, Ltd., for generous grants out of which both the heavy capital, and running costs of the experiments have been defrayed.

Summary.

(1) Explosions of 2H2 -f- 0 2 + 3-76N2, 2C0 + 0 2 + 3-76CO, and2C0 -J- 0 2 -f- 3 • 76N2 mixtures have been successfully carried out in a cylindrical bomb chamber 7*5 cm. long by 3*75 cm. diameter, of 114 c.c. capacity at initial pressures up to 500 atmospheres in the first and second and up to 1000 atmospheres in the third case, and complete pressure-time records thereof have been obtained.

(2) Correlating experiments at P*• = 75 atmospheres have indicated that whereas the observed explosion times for quick explosions were much the same as, or for slow explosions a little less than, would have been observed had a spherical bomb chamber of 240 c.c. capacity been employed (as in our previous experiments) the mean maximum temperatures (abs.) were probably circa 0*86 those which would have resulted in the latter case.

(3) The effects of the considerable deviations of the explosive media concerned from the gas-laws at the high initial pressure over 250 atmospheres) employed are such as involve much smaller actual density increments from given gauge-pressure increments.

(4) With the 2H2 -f- 0 2 + 3*76N2 explosions there was a quite definite increase in the “ explosion times ” with density at initial pressures over 250 atmospheres ; but a t 750 atmospheres the detonation, instantaneously set up, was so violent that further work at any higher pressure was impracticable.

(5) In the 2CO -f- 0 2 -j- 3*76N2 explosions, the characteristic lag in the “ explosion time,” as well as the exothermic effects observed during the “ cooling period ” after tm—both of which had hitherto consistently increased with the density of the medium—reached their maxima at a density corresponding with P t- somewhere between 350 at 500 atmospheres, and afterwards remained constant. These circumstances are indicative of the N2-activation effect having reached a maximum at such a density of the medium.

(6) The C02-dissociation at the maximum temperature in the 2CO + 0 2 -)- 3*76N2 explosions at P t- = 500 to 1000 atmospheres was of the order of 5 to 6 per cent.



74 D. T. A. Townend and L. E. Outridge.

(7) In the 2CO + 0 2 + 3-76CO explosions, which were always very much more rapid than the corresponding 2CO -f- 0 2 + 3*76N2 explosions, the “ explosion times,” which up to then had been nearly constant, began definitely to increase with further increments in the density of the medium above Pj- = 250 atmospheres, and at about the same point slight carbon-deposition began to be manifested during the explosion, the two circumstances probably being connected. The rates of pressure-fall during the first second of the “ cooling periods ” immediately after tm were also always much faster than in the corresponding 2CO -f- 0 2 -f- 3*76N2 experiments.

Gaseous Combustion at High Pressures. Part XV.— The Formation of Nitric Oxide in Carbonic Oxide-Oxygen-Nitrogen Explosions.

By D onald T. A. Townend, D.Sc., and Lionel E. Outridge, B.Sc.

(Communicated by W. A. Bone, F.R.S.—Received August 19, 1932).

Introduction.

In previous papers of this series* it was shown that the secondary formation of nitric oxide in C 0 -0 2-N 2 explosions, when oxygen is present in excess of that required to burn all the carbonic oxide, rapidly increases with the density of the medium, the optimum composition of the medium for the purpose being 2CO + 302 + 2N2.

The former experiments were carried out, in bombs Nos. 2 and 3, the 7-5 cm. diameter spherical explosion chambers of which were each of 240 c.c. capacity with a surface/volume ratio 0*78, under conditions permitting of no acceleration in the normal rate of cooling down of the hot products from the maximum explosion temperature.

In such circumstances the amounts of N 0 2 surviving in the cold products of

* ‘ Proc. Roy. Soc.,’ A, vol. 105, p. 426 (1924); vol. 108, p. 415 (1925); and vol. 115, p. 45 (1927); also “ Gaseous Combustion at High Pressures,” chap. X II, pp. 174-190 (1929).



gaseous combustion at high pressures, part xiv....

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