Detonation characteristics of hydrogen‐oxygen mixtures

Abstract

E X P E R I M E N T A L WORKThe experimental equipment for the measurement of detonation velocities consisted of six different detonation tubes, a mixing and charging system, an ignition system, and a timing system.The characteristics of the detonation tubes are given in Table 1. The five round, straight tubes (A, B, C, D, and E ) were used to determine the effect of tube diameter on detonation velocity. Tube F was a 10-in. coil for convenience in temperature control for the high-and low-temperature experiments. The effect of coiling was evaluated by comparison of the velocities measured in tubes F and B. Rectangular tube G was used only to obtain schlieren photographs. All seven tubes were closed at both ends.The velocity of the detonation wave was measured with ionization probes. The probes were made by drilling a no. 76 drill through a Teflon insert in a stainless steel sleeve. The probes were threaded into the detonation tubes and adjusted so that the tip was flush with the wall. Each probe was connected as a shorting switch in the grid of an 884-thyratron tube. The grid bias of the thyratron tube was adjusted almost to the firing point to obtain maximum sensitivity. When the ionized gases behind the detonation front reached a probe, the resistance between the probe electrode (the drill) and ground (the tube wall) fell, and the thyratron fired. One probe and thyratron started a timer, and another probe and thyratron stopped it. The time interval was indicated to the nearest microsecond. The distances between the probes and the distance from the ignitor to the first probe are given in Table 1. The probe locations on tube F were on the outside of the coil and were determined before coiling. The distance between the probes was corrected for thermal expansion and contraction of the tube in computing the detonation velocity at nonambient temperatures. This correction was about 0.1% at the extreme temperatures. The starting distance for all the tubes was greater than the distance A.1.Ch.E. Journal indicated by LafEtte (14) and Greene (9) as necessary to attain stable detonation in hydrogen-oxygen mixtures. The probes required replacement after 20 to 30 runs.The high-temperature runs were made with the coiled tube in an oven, and the low-temperature runs with the coiled tube immersed in 5 gal. of normal propanol in an insulated tank. Dry ice was added to the propanol to cool to 200°K. and liquid nitrogen to reach lower temperatures. As the result of vigorous stirring, the temperature variation within the bath was held within rrfr2"K.The detonation tube was evacuated and then filled with premixed oxygen and hydrogen through a mapifold and switch system that kept the ignition circuit open while the filling valve was open. In the low-temperature runs the tube was evacuated at room temperature before cooling to avoid condensation. In both the highand low-temperature runs the mixture was not ignited until the pressure indicated on a manometer had remained constant for at least 5 min. Analyses of the hydrogen and oxygen o...

Detonation Properties of Heavy Knallgas.

“…In particular, measured and predicted detonation properties of heavy knallgas may differ significantly. Although detonation velocities in knallgas (2H2 + 02) agree well with theory (3,11,12,24,27), the slower reaction kinetics exhibited by deuterium-oxygen mixtures (4,8,16) suggest increased wave-front energy loss to the detonation tube. Resulting effects on the detonat'on velocity of heavy knallgas may thus be marked.…”

“…Brief note should be made that stable detonation properties, particularly the theoretical reflected pressures reported herein, do, in some cases, constitute adequate criteria for engineering design (26,27). However, situations exist during the detonation formation process wherein unstable detonation pressures are developed (1,2,15,31,32,33).…”

“…Detonation velocities were determined by measurement of the time interval required for an established wave to traverse a distance of 8.984 feet measured over the far end of the detonation tube length. Timing siginals were generated by two ionization-type (6,17,27) velocity probes mounted flush with the inner tube wall at each end of the distance traverse. Time intervals were recorded by a Berkeley Model 5120 time interval meter accurate to ± 1 (isec.…”

Detonation of hydrogen-oxygen at low temperature and high pressure

“…The results of detonation velocities for fully developed (Chapman-Jouguet) waves vs initial temperature of the mixtures for initial pressures of 1, 5, 10, 15 atm and 0 500, 0 667, 0 730, 0 800 mole-fraction of hydrogen are presented in Figs 1-4 The test results indicate that for a given initial pressure the detonation velocity increases at a slightly greater than linear rate as the initial temperature is lowered down to the saturation point of oxygen The results for stoichiometric H 2 -0 2 mixtures are compared with the theoretical results of Zeleznik and Gordon 4 and with the previous data of Moyle 2 In comparing theory with experiment it should be noted that the size of the detonation tube has a significant effect on the velocity so that the measured velocity is less than that predicted by the Chapman-Jouguet plane-wave theory Fay 5 has proposed that this velocity deficit is caused by a viscous boundary layer on the tube wall within the reaction zone On the basis of a two-dimensional analysis, Fay obtains the following expression for the velocity deficit AUii = 2l<r*/D where and where D = diameter of tube in centimeters a* = boundary-layer displacement thickness Ui = propagation velocity of the detonation wave t = thickness of reaction zone He = viscosity of the gas in the combustion zone at outer edge of boundary layer pi = initial (upstream) density For the stoichiometric hydrogen-oxygen reaction at 1 atm pressure and room temperature, Fay suggests the values t = 0 35 cm and /*« = 12 3 X 10~4 g-cm-^sec" 1 For application to this experiment we assume that the thickness of the reaction zone (t) is primarily determined by a recombination reaction so that t is inversely proportional to the square of the initial pressure Also, we assume that /*« does not vary significantly with initial pressure and temperature…”

Apparatus for Measuring Strength in Biaxial Compression

“…This is analogous to the fact that a gas is 50% ionized at temperatures far below those corresponding to the ionization energy. Some results are reported in 20 , who found that for a stoichiometric mixture H 2 O constituted barely 50% of the mole fraction of the product gas.…”