Acknowledgment
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FUEL N-HEPTANE TEMPERATURE AT FUEL INJECTION 1100% PRESSURE 17 ATM,
DURATION OF FLAME GAS TEMPERATURE, MILLISECONDS Figure 7. For a given fuel, amount of nitrogen dioxide formed depends on the time interval for high temperature reaction
differences in ignition lag could be expected for various fuels (Figure 6). T h e long ignition delay for ethyl alcohol is noteworthy as well as the fact that a t temperatures before fuel injection higher than 1000” K . ignition lag tends to become the same for all the fuels studied. Ignition lag for 2-propanol is similar to ethyl alcohol but 1-propanol is between ethyl alcohol and iso-octane. For the apparatus used in this work, combustion of a liquid fuel spray with a somewhat shorter ignition lag-e.g., n-heptane-would provide high temperature gases for a maximum time of about 25 msec. before beginning of the quench period. IYith the time of injection and the quench time fixed, a liquid fuel spray with a long ignition lag such as 2-propanol would react and provide a high temperature interval of about 10 msec. when air temperature before fuel injection is 950” K . and air pressure is 17 atm. Ignition lag reduced the time interval a t high temperature during combustion. I t also provided more time for fuel-air mixing and therefore because over-all composition of the reacting mixture is lean, it may have lowered the maximum effective flame temperature after autoignition. Thus, another approach was tried for investigating the effect of exposure time a t high temperature on nitric oxide formation. By using a high air temperature before fuel injection (1100” K.) to ensure a short ignition lag and changing the time of fuel injection the duration of the combustion process could be controlled. As noted earlier, the quench time was fixed by the geometry of the shock tube. For a fixed quantity of fuel injected (54 mg. of n-heptane), the nitrogen dioxide yield increased as the time interval available for the high temperature combustion gas to form nitric oxide was increased (Figure 7). By applying the d a t a in Figure 3, these results suggest that a n effective temperature of 2100”
532
to 2200” K. !vas obtained in the combustion zone of the shock tube and that less than 2070 of the equilibrium nitric oxide concentration is formed in the time intervals used. Formation of nitric oxide in the diffusion flame resulting from the autoignition of a liquid fuel spray appears to depend on the reactions for oxidation of nitrogen a t high temperatures. Because of the exponential dependence of nitric oxide formation rate on temperature: the maximum temperature is probably the most important factor to be considered in studies of nitric oxide abatement. These results also apply to O t t o cycle engines.
.4. J. Nerad initiated the work reported here. Helpful discussions Jvith G. E. Moore, W. E. Kaskan, and C . P . Fenimore are gratefully acknowledged. literature Cited
(I) Elliott, M., Nebel, G., Pounds, F.,
J . Air Pollution Control Assoc. 5 , 103 (1955). (2) Fenimore, C. P., Jones, G. W., J . Phys. Chem. 61, 654 (1957).
(3;) Giffen, E., Muraszew, -4., “Atomization of Liquid Fuels,” p. 176, John M’iley, New York, 1953. (4) Glick, H., Squire, N., Hertzberg, A.: 5th Symp. on Combustion, pp. 393-402, Reinhold, New York, 1955. (5) Glock, H., Klein, J., Squire, S . , J . Chem. Phys. 27, 850-7 (1957). (6) Haagen-Smit, ‘4.J.: IND.ENG.CHEM. 44, 1342 (1952). (7) Jost, W., “Explosion and Combustion Processes, in Gases,” p. 589, McGrawHill, New York, 1946. (8) Mullaney, G. J., IND.ENG.CHEM.50, 53-8 (1958). (9) Zbid., 51, 779-82 (1959). (10) Powell, H., Schaffer, A., Suciu, S., “Properties of Combustion Gases. System, C,,H,,-Air,” McGraw-Hill, New York, 1956. (11) Saltzman, B., Anal. Chem. 26, 1949-55 (1954). \ - - ,
(12) Tawde, N., Laud, B., 6th Symp. on Combustion, p. 143, Reinhold, New York, 1957. (13) Zeldovich, J., Acta Physarochzm., L‘.R.S.S. 21, 577 (1946). RECEIVED for review November 2, 1959 ACCEPTED FEBRUARY 29, 1960 Division of Water and Wastes, Symposium on Air Pollution, 136th Meeting, ACS, Atlantic City, N. J., September 13-18, 1959.
CORRESPONDENCE
Basic Raw Materials in the Petrochemical Industry SIR: As p a r t of a Symposium on Plant Costs and Economics in the Chemical Process Industry you published a n article on “Basic R a w Materials in the Petrochemical Industry” by Oscar A. Colten of Shell Chemical Corp. [IND. ENG.CHEM.51, No. 9, 983 (1959)l. A discussion of the cost of acetylene included reference to both the Sachsse and SBA processes. T h e figures given were misleading as to the competitive position of the two processes. W e have discussed this matter with the author and find that 1. H e inadvertently compared the investment of a n 80-ton-per-day Sachsse unit with a 90-ton-per-day SBA unit. 2. H e used different costs for the oxygen unit, which in either case could be a ”purchased” unit as it is not a n integral
INDUSTRIAL AND ENGINEERING CHEMISTRY
part of either design. T h e cost of the oxygen unit as reported in the Kellogg article on the SBA process is SOYc more than the cost of the oxygen unit mentioned in the Forbath article on the Sachsse process. Because the oxygen units required are practically identical, a fairer comparison of the two acetylene processes would have assigned equal investment costs to the oxygen units. IVith one oxygen unit representing 35% of the total investment. a n error of nearly 15yofavoring the Sachsse process was therefore introduced in M r . Colten’s article in addition to the error resulting from the 12.5y0 difference in plant sizes.
J. L. PATTON M. \V. Kellogg Co. New York, N . Y .
