Proceedings of the Symposium on Combustion最新文献

In this paper a preliminary attempt has been made to trace the relationships, where they exist, between the speeds of flame in mixtures of air with the constituents of the common industrial gases, hydrogen, carbon monoxide, methane (and other paraffin hydrocarbons), ethylene, and acetylene, inflamed under different conditions. It is hoped to extend these relationships as the results of work now in progress, and also to be able to examine systematically, and in somewhat greater detail, the exceptions to these relationship as they appear.

It is shown that the knock rating of the one fuel with respect to another may depend upon the carburetor setting at which the comparison is made. The influence of mixture strength is often so large that, unless careful attention is given to this factor during knock measurements, it is possible to obtain widely discordant results in spite of what may otherwise be the best of experimental technic.

If knock ratings of some fuels made by different laboratories are to be comparable, the different experimenters must agree upon some general specification as to the mixture ratio at which the measurements shall be made. Because it is both the point of highest intensity and one that can be located readily, it is proposed that knock measurements be made independently for each fuel at the mixture ratio giving its maximum degree of knock.

In general, flames may be divided into two classes: flames of the Bunsen type in which the combustible gas and air are premixed before ignition occurs and flames in which the combustible gas and air meet coincidently with the occurrence of combustion. To this second class of flames the authors have applied the term “diffusion flames.”

An analysis of this type of flame has been made which has led to a theory of its mechanism. A mathematical presentation of the theory is given and also the results of an extensive experimental investigation of the deductions therefrom. As a consequence of this work considerable light is shed on the physical characteristics, the mechanism, and the general properties of this very common class of flames.

In Mallard and Le Chatelier's treatment of flame propagation the problem is considered simply one of heat flow in which the unburnt gas is raised to its ignition temperature. Although crude, this treatment is able to explain a number of observations: limits of inflammability, effect of diluent gases on the latter and on rate of flame propagation, and near coincidence of maximum flame temperature mixture and maximum speed mixture. Later elaborations of Mallard and Le Chatelier's treatment have not advanced the problem appreciably, due to the indefiniteness of the term “ignition temperature”. Certain observations show the importance of diffusion in the treatment of flame propagation. A solution of the problem without the use of ignition temperature has been attempted for the propagation of ozone-oxygen flames, using simplifying assumptions concerning the reaction mechanism and the combined effects of heat flow and diffusion. Agreement in the order of magnitude is found between calculated flame speeds and experimental values. In the flame front there is a steep temperature gradient and also a high local concentration of active species. The width of the flame front is calculated to be of the order of 10⁻³ cm. Some consideration is given to the effect of activators and inhibitors on flame speed.

The catalytic partial oxidation of various mixtures of methane and ethane with oxygen has been studied by the dynamic method at atmospheric pressure within the temperature range 100° to 700°C. Some experiments have also been made with a natural gas under similar conditions.

For the production of alcoholic or aldehydic intermediates, catalysts of copper and silver, oxides of these metals, activated charcoal, platinum oxide, and barium peroxide proved unsatisfactory on the basis of hydrocarbon consumed and products obtained.

Small amounts of nitrogen dioxide, when added to hydrocarbon-oxygen mixtures and passed through heated capillary tubes, were found to promote the oxidation materially. Yields of oxygenated derivatives varying from 15 to 30 per cent by volume of the amount of hydrocarbon used were obtained. As much as 38 per cent of the hydrocarbon has been decomposed in a single pass through the catalytic chamber.

Auxiliary catalysts used in conjunction with nitrogen dioxide activated the decomposition of intermediate oxidation products without materially increasing the amount of hydrocarbon decomposed.

Methyl nitrite has been shown to exert a promoting action in partial oxidation reactions of hydrocarbons.

An explanation is offered of the effect of small amounts of nitrogen dioxide and methyl nitrite on the partial oxidation of aliphatic hydrocarbons.

The hydroxylation theory of the combustion of hydrocarbons has been further confirmed by thermodynamic considerations as well as by experimental evidence.

An abstract of a description, illustrated by lantern slides and autochromes, of unusual flame structures, the causes for which have not yet been investigated.

Quantitative calculations of the effects of flame propagation and of piston movement on the temperatures attained in the various parts of on Otto-cycle engine charge during combustion are made relatively simple by the use of a Mollier diagram of the properties of the combustion products of octane and air. The method is applied to a consideration of the effect of spark advance on the temperature attained ahead of the flame front, and it is concluded that the results are significant in studies of engine knock.