Proceedings of the Symposium on Combustion最新文献

An apparatus and method for determining the flame speed of hydrogen sulfide in air by horizontal flame propagation are described. The flame records were made by photographic method, the gas being inflamed in a 2.5-cm glass tube, open at one end and 1 meter long. The maximum flame speed was found to be 49.5 cm per second on burning 10.8 per cent hydrogen sulfide.

With a view to investigating the relative rates of combustion of the olefins, known mixtures of ethylene and propene and of ethylene and isobutene were exploded with oxygen, and the proportion of each olefin remaining unburned was found by analysis of the products. One slow combustion was also made of a mixture of ethylene and isobutene. In every case propene or isobutene burned faster than ethylene.

To test their relative ease of oxidation by potassium permanganate, known mixtures of ethylene and isobutene were dissolved in water and oxidized by a deficiency of permanganate. Then the proportion of each olefin unoxidized was found by boiling out the gases and analyzing them. Here again isobutene reacted faster than ethylene.

Calculations of the relative rates of reaction based on a formula developed by Francis, Hill, and Johnston are given.

The course of the gaseous explosive reaction at constant pressure is described and then followed experimentally by means of photographic time-volume records obtained by a simple device that is found to function as a transparent bomb of constant pressure. It is found that at constant pressure the uniform rate of propagation, s, of the zone of explosive reaction, when measured relative to the active gases, is proportional to the product of their concentrations (partial pressures): $s=k_1{\left[A\right]}^{n1}{[B]}^{n2}{\left[C\right]}^{n3}\cdots$.

In the light of this relationship studies have been made of the effect of inert gases and of composite fuels on the rate of the gaseous explosive transformation.

Researches into the combustion of complex hydrocarbons, designed to throw light on the problem of knock in internal-combustion engines, have revealed generally that the mechanisms involved are far from simple. Much new light has recently been thrown on the subject by systematic investigation of the influence of pressure on the spontaneous ignition points of these materials.

Inflammable mixtures with air of the paraffins containing three or more carbon atoms, while not spontaneously ignitible at low pressures below about 500°C, give rise abruptly to ignition at higher pressures in a temperature range between about 310° and 370°C, where normally only “cool flames” are initiated; and although neither methane-air nor ethane-air mixtures appear to develop cool flames, the latter are ultimately ignitible in a lower temperature system less complex than that characteristic of the higher members. There is general agreement between ease of ignition in the lower temperature range and the knock ratings of the materials concerned. This holds good for side-chain paraffins, olefins, naphthenes, and aromatic fuels.

All olefins higher than ethylene behave in a similar manner; they differ from the paraffins in that the cool flames are less intense and the preflame time-lags are not only greater but decrease less rapidly with increase of pressure.

The influence of higher aldehydes, nitrogen dioxide, and diethyl ether as promoters of ignition is also discussed.

In moist hydrogen-oxygen mixtures diluted with argon, helium, or excess hydrogen, explosion pressures are found that agree with the theoretical pressures calculated from band spectroscopic data. In dry mixtures the observed pressures are lower, possibly owing to heat loss by luminescence radiation. In moist mixtures diluted with nitrogen or excess oxygen the pressures are higher. This has been ascribed to the time-dependence of specific heats, called excitation lag. This excitation lag has been linked to gas vibrations which appear early in the explosion. The results with carbon monoxide-oxygen and with acetylene-oxygen mixtures can also be interpreted by heat loss and excitation lag. If a small amount of hydrogen is added to carbon monoxide-oxygen mixtures the heat loss appears to be reduced considerably, probably owing to the shorter duration of the explosion. Excellent agreement is found between experimental and theoretical explosion pressures in ozone-oxygen mixtures. An explanation of the absence of excitation lag in the latter is proposed. Measurements of expansion ratios in soap-bubble explosions of carbon monoxide-oxygen mixtures and flame temperatures by the line-reversal method of coal gas-air mixtures show a trend similar to explosion pressures in hydrogen-oxygen and carbon monoxide-oxygen mixtures.