1464 PAYMAN THE PROPAGATION OF FLAME IN CXXXVI1.- l h e Propagation of Flame in Complex Gaseous 17Mixt w e s . Part 1II. The Uniform Movement of Flame in Mixtures of Air with Mixtares of Methane Hydrogen and Carbon Monoxide and with Indust?-ial Injlarnmable Gases. By WILLIAM PAYMAN. THE common industrial gases contain as their inflammable con-stituents methane hydrogen and carbon monoxide in various proportions. The speed of the uniform movement of flame in mixtures of methane and air in a tube 2.5 cm. in diameter was given in Part I1 of this series of papers. The speeds with hydrogen and air in a similar tube (over the major portioa of the range of inflammable mixtures) have been determined by Haward and Otagawa (T. 1916 109 83). The speeds in mixtures of carbon monoxide and air are recorded in the present paper.Mixtures of Carbon Monoxide a*nd Air.-It is well known that the rate of combustion of carbon monoxide is dependent on the amount of water vapour present. Dixon for example (Phil. Trans. 1893 184 97) has shown that the velocity of the detona-tion wave in a mixture of carbon monoxide and oxygen (2COt-0,) increases with the percentage saturation of water vapour. The present series of determinations of the speed of the uniform movement of flame in mixtures of carbon monoxide and air was carried out with mixtures saturated with water vapour a t the ordinary temperature and pressure. Since the room tempera-ture varied it was not surprising to find that the speed in a given mixture did not remain constant from day to day.Identical results were however obtained in experiments made within a few minutes of each other a t the same temperature and pressure. Table I illustrates the effect of change in the percentage saturation of water vapour on the speed of the uniform movement of flame in a mixture of carbon monoxide and air containing 50 per cent. of carbon monoxide. TABLE I . Speed of Uniform Movement of Flame in. a Mixture of Carbon Monoxide and Air (50 per cent. CO) in a Tube 2.5 cm. in Diameter . Temperature and pressure. 10" and 750 mm. ............ (1) 59.9 (2) 59-9 15" and 750 mm. ............ (1) 65.0 (2) 64-5 17' and 755 mm. ............ (1) 79.4 (2) 79-0 Cm. per sec COMPLEX GASEOUS MIXTURES. PART III. 1455 A series of determinations of speeds of flame over the whole range of inflammable mixtures was carried out during a period when the temperature of the laboratory did not alter appreciably (about 1 2 O ) .The values obtained are given in table 11. TABLE 11. Speed of Uniform Movement of Flame in Mixtures of Cu~bofi Monoxide and Air in a Tube 2.5 cm. in Iliameter at 1 2 O and 750 mm. Per cent. of carbon monoxide. 16-15 16.29 16.40 16-51 24-47 30.50 44.84 50.45 54-40 59-58 Cm. per sec. Tongue of flame only. 19.5 19.4 19.4 34.0 46-0 60-1 59.9 57.8 56.2 Per cent. of carbon monoxide. 59.81 65-55 65.84 67.10 67-57 69.00 70-63 70.68 71-19 71-31 Cm. per sec. 54.2 37.4 36.3 30-2 29.6 26-0 20.0 20.3 19.4 Trailing flame travelled 15 cm.These values are of interest in themselves apart from their con-nexion with the problem of the propagation of flame in complex gaseous mixtures inasmuch as they disclose the fact that the maximum speed of flame is obtained with mixtures containing from 45 to 50 per cent. of carbon monoxide. The mixture for complete combustion contains 29.5 per cent. carbon monoxide so that the ‘‘ displacement ” of the maximum-speed mixture is greater even than with hydrogen despite the fact t,hat the thermal conductivity of carbon monoxide is but little different from that of air. Industrial gas mixtures may contain varying proportions of water vapour. There may therefore be some uncertainty as to the correct values to use for the speed of flame in mixtures of carbon monoxide and air when attempting t o calculate the speed of flame in the mixed industrial gas.Such gases however con-tain hydrogen as well as carbon monoxide and the presence of hydrogen affects the speed of flame in a similar degree to that of water vapour. With mixtures of gases containing fairly high pro-portions of hydrogen it is therefore not unlikely that the effect of variation in the moisture content would be inappreciable. It should therefore be sufficient for our purpose to know the values for the speed of flame in mixtures of air with a mixture of hydrogen and carbon monoxide. Or the “effective” speeds for mixtures of carbon monoxide and air could be calculat.ed from such values and these speeds used for further calculation 1456 PAYMAN THE PROPAGATION OF FUME IN In this connexion it is interesting to note that Berthelot (Ann.Ckim. Phys. 1881 [v] 28 289) found the rate of detonation in mixtures of carbon monoxide and oxygen to be about half the calculated value. For mixtures of oxygen with carbon monoxide plus hydrogen the calculated values were in good agreement with those found. Similarly in the present research the maximum speed of uniform movement of flame in mixtures of carbon mon-oxide and air is found to be about half the value calculated making use of the values determined for hydrogen-air and hydrogen-carbon monoxideair mixtures. Mixtures of Hydrogen and Air.-& with tubes of smaller diameter (this vol. p. 36) it was not found possible to determine accurately the speed of the uniform movement of flame in the upper-limit mixture of hydrogen and air in a tube 2.5 cm.in diameter. A mixture containing 71.4 per cent. of hydrogen was found to be the richest which would propagate flame under the experimental conditions. The flame was not hot enough t o melt “screen wires,” but its speed as measured by means of a tapping key in connexion with a chronograph was found to be approxim-ately 50 cm. per second. A characteristic of the lower-limit mixture and of mixtures near t o it is the formation on ignition of minute balls of flame which pass steadily from the open to the closed end of the tube. These flames are propagated mainly by the influence of convection currents and the speed-percentage curve a t the lower-limit region is not continuous but shows a definite break.Nevertheless no definite distinction at the point of break in the curve could be drawn between the normal and the balls of flame the latter increasing in size and gradually changing their form as the per-centage of hydrogen increased. The speeds of the flames in mixtures near the limits are given in table 111 which completes the table given by Haward and TABLE 111. Speed of the Uniform Movement of Flame in Mixtures of Hydrogen and A i r an a Tube 2.5 cm. in Diameter. Hydrogen. Speed, Per cent. em. per see. 6.10 No flame observed. 6-19 10 6.31 12 6-52 16 14-71 120 7 1.39 50 71.51 Flame to open end only COMPLEX GASEOUS MIXTURES. PART III. 1457 Otagawa (Zoc. cit. p. 89). In only one instance was the flame hot enough to melt (( screen wires,” namely with the mixture contain-ing 14-71 per cent.of hydrogen; the remaining speeds were deter-mined by means of a tapping key. Mixtures of Methane Hydrogen and Air.-The speed of the uniform movement of flame in a tube 2.5 cm. in diameter was determined over a range of mixtures of air with two mixtures of methane and hydrogen. The first mixture contained equal volumes of methane and hydrogen (CH,+H,) the second three volumes of methane to one volume of hydrogen (3CH + H,). The results are recorded in table IV. The lower-limit flames preserved the general character of the corresponding hydrogen flames and their speeds were found to be lower than the speed in the limit mixture of methane and air. TABLE IV. Speed of the Uniform Movement of Flame in Mixtures of Air with Hydrogen Methane Mixtures in a Tube 2.5 em.in Diameter. Combustible gas. Per cent. 6-03 6.20 6.31 6-73 7.68 9-05 10.23 11.95 11-99 13-50 14-93 15.93 16.90 18.31 19.96 20.22 20.32 20.48 20.80 Speed, cm. per sec. 15.0 17.1 19.1 22.1 28.6 45-6 67.4 104.1 106.3 128.6 135.3 127.3 111.9 65.6 35.5 30.5 28.5 27.3 24-3 3CH + H2. Cornb&tible gas. Speed, Per cent. cm. per see. 6-09 18.0 6-22 19.9 6-50 21.0 6.80 27.7 7-84 39-6 9.06 58.3 9.93 78.7 11-35 84.9 12.26 82.2 13-25 66.7 14-20 45.7 14-99 27.8 15.50 22.6 The results are plotted as curves in Fig. 1 the calculated curves being shown in dotted line. The maximum speeds calculated by the method given in P a r t I1 are 150 and 99 cm.per second respectively for the mixtures CH + H and 3CH + H,. The values found were 135 and 85 cm. per second. Mixtures of Carbon Monoxide Hydrogen and Air.-Two mix-tures of carbon monoxide and hydrogen were employed of com-position CO + H2 and 3CO + H, corresponding with the methane-hydrogen mixtures. The results are given in table V and are plotted as curves in Fig. 2 PAYMAN THE PROPAGATION OF FLAME! IN FIG. 1. Combustible gas per cent. FIG. 2. ---I_ -/ __ Combustible g a s per cent COMPLEX GASEOUS MIXTUREF. PART III. 1459 From the values found for hydrogen and for the mixture 3CO+H, the speeds of the flames in midures of air with CO+H, were calculated. The results are shown in dotted line in Fig.2. The values for carbon monoxide and air were also calculated from these values and the curve is given in the diagram for comparison. It will be seen that the values calculated in this manner are much higher than those found by experiment. These '' effective " speeds have been used in subsequent calculations instead of khe values as determined which are dependent on the amount of water vapour present. TABLE V. Speed of Uniform Movement of 3'lam.e im Mixtures of Air with the Mixtures CO+H and 3CO+H i& a Tube 2.5 cm. in Diameter. CO + H,. Combustible gas. Per cent. 9-25 10.35 15-40 20.57 30.25 36.94 41.50 45-92 51-23 58.55 69.00 70.75 71.34 Speed, cm. per sec. 18.2 21.1 58.3 100.4 211.5 282.9 309.7 315.2 280.0 178.5 64-5 50-1 44.4 3CO + H,.Comb;stible gas. Per cent. 12.00 18.99 27.82 34-73 41.32 46.90 53-17 58-49 70.36 71.42 -. Speed, cm. per see. 19.2 67- l. 115.0 166-2 205-5 214.0 200.0 154.7 3 4 4 20.8 Mixtures of Methane and Carbon Monoxide and Mixtures of Methane Hydrogen and Carbon Monoxide with Air.-Table VL records the results obtained with a mixture containing equal volumes of methane and carbon monoxide and with one containing equal volumes of methane hydrogen and carbon monoxide. Methane or any gas into the composition of which hydrogen enters, acts towards mixtures of carbon monoxide and air in a manner comparable with that of hydrogen and water vapour. The maxi-mum speed of uniform movement of flame in mixtures of air with each of the mixtures CH + CO and CH + CO + H was found to be 91 and 150 cm.per second respectively whilst the correspond-ing calculated values are 78 and 145 cm. per second 1460 PAYMAN THE PROPAGATION OF FLAME IN CH + CO. c - Combustible gas. Speed, TABLE VI. Speed of Uniform Movement of Flame in Mixtures of Air with the Mixtures CH + CO and CH + H2+ CO in a Tube 2.5 cm. in Diameter. CH + H + CO. I . Combustible gas. Speed, 9.45 9.88 12.07 13.73 15-95 18.06 19.32 21.55 cm. per sec. 21-9 36.2 62-5 85-7 91.3 68.9 52.3 19.8 FIQ. 3. I I 5 10 20 30 7.70 10.01 14.01 15.80 18-92 20.42 22-43 25.05 27.57 21.2 36.5 83-3 109.4 150.0 148.7 118-5 57.8 21.8 60 70 1 50 Combustible gas per cent.The speed-percentage curves for the equimolecular mixtures CH,+H2 H,+CO CO+CH, and CH,+H,+CO are plotted in Fig. 3 the curves for the pure gases being included for comparison. Mixtures of Industrial Gases with Air.-The equimolecular mix-ture of carbon monoxide and hydrogen correspond nearly with A coal-gas and a producer-gas were also examined, the compositions of these being : water-gas. COMPLEX GASEOUS MIXTURES. PART 111. 1461 Coal-gas. Producer-gas. Per cent. Per cent. - Benzene and higher olefines ......... 1.1 Carbon dioxide 0.3 5-0 Ethylene ................................. 2.6 Carbon monoxide ........................ 9.6 21.3 Hydrogen ................................. 49-2 12.6 Methane and higher paraffins ......33.9 3.1 Nitrogen (by difference) ............... 3.3 58.0 ........................... -The speeds of the uniform movement of flame in mixtures of air with each of these two gases are given in table VII. TABLE VII. Speed of Uniform Movement of Flame in Mixtures of Air with Coal-gas and with Producer-gns in a Tube 2.5 cm. in Diameter. Coal-gas. Per cent. 7.2 10-0 11.9 14.7 16.8 17.9 20-4 21.8 24.3 Speed, cm. per sec. 21.5 50.5 87.1 133.7 153.9 154.1 115-6 74.3 22-0 Producer-gas. Per cent. 24.7 38.9 46-0 49-0 54.3 58.8 61.6 Speed, cm. per sec. 20.0 47.4 62.7 72.2 69.7 43.5 24.0 The principal constituents of the coal-gas are hydrogen methane, and carbon monoxide.I f all the hydrocarbons be reckoned as methane the calculated maximum speed of uniform movement of flame in mixtures of air with this coal-gas is 164 cm. per second, with a mixture containing 18.4 per cent. of coal-gas. Since the content of inert gases (nitrogen and carbon dioxide) is low they may be neglected when making the calculations. Producer-gas on the other hand always contains a large pro-portion of inert gas; the sample used for these experiments con-tained only 37 per cent. of combustible gas. For this reason a value for the maximum speed of uniform movement of flame in a mixture of producer-gas and air calculated from the maximum speeds in mixtures of the pure gases with air would be too high. The speed of flame in mixtures of air with gas containing a large proportion of nitrogen can be calculated on the assumption that the cooling or retarding effect on the flame of excess of air or of nitrogen will be the same since their specific heats are the same.* A mixture of carbon monoxide hydrogen and methane in the pro-* This assumption is not quite correct since the presence of reactive gas slightly opposes the retarding effect of air 1462 WHITE AND PRICE THE IGNITION OF portions in which they are found in the sample of producer-gas used in these experiments will have as its “ fastest-speed ” mixture with air one containing 34.7 per cent.of combustible gases. I f nitrogen is added to this mixture so that the ratio of nitrogen to combustible gases is the same as in the producer-gas the result is a mixture containing 21.7 per cent. of combustible gases. (The carbon dioxide content being low it may be calculated as nitrogen.) The speed of flame in this mixture should on the assumption given above be but little different from the speed of flame in the same mixture of combustible gases with air. The latter speed is most easily determined by a graphical method and is found to be 85 cm. per second. The mixture of air and producer-gas with the fastest speed of uniform movement of flame contains slightly more inflammable gases than is required for complete combustion. A greater “dis-placement ” of the maximum-speed mixture might be expected for the reason that the chief inflammable constituents are hydrogen and carbon monoxide the individual displacements of which are con-siderable. The small displacement with producer-gas is due to the presence of inert gases as will be explained in the succeeding section of this series of researches. The effect in general of inert gases on the speed of the uniform movement of flame in gaseous mixtures will also be considered. ESKMEALS, CUMBERLAND. [Received October loth 1919.