Proceedings of the Symposium on Combustion最新文献

The thermodynamic approach to combustion and the rate of rise of pressure in the Otto cycle are fruitful in analyzing the effect of different conditions upon the operation of the cycle. It is suggested that the thermodynamic method is an important tool in explaining and analyzing known characteristics such as “engine knock”, roughness, and the effect of supercharging on the relative knock ratings of different types of fuels, and also a means of predicting characteristics of such combustion cycles as in the case of the critical initial temperature giving maximum rate of rise of pressure.

This investigation was undertaken in order to obtain experimental data concerning the relation between flame propagation and the pressure changes resulting therefrom. The apparatus used and its method of operation are described in detail and the experimental data are interpreted and discussed.

An apparatus has been devised and a method described for determining the effect of various inhibitors and accelerators of knock upon the slow oxidation of hydrocarbon fuels. Data are given to show the effect of various substances upon the slow oxidation of n-heptane and its normal oxygen derivatives, gasoline, and kerosene. A surprising similarity is shown between the action of lead tetraethyl and various compounds of sodium and potassium, and also a difference in the action of lead tetraethyl and these compounds of sodium and potassium upon the oxidation of hydrocarbons, in the gas or liquid phases.

In order to obtain some information as to the cause of the “pink” or knock of motor fuels, a photographic study has been made of the movement of flames, simultaneously with measurements of the development of pressure, during the explosion of the charge in an engine cylinder. Explosions of mixtures of pentane and air and benzene and air, at various temperatures and pressures, and of various blended mixtures of benzene and pentane, and of ethyl ether with pentane and air, have been studied. Suggestions are made for the suppression of pinking, and on the basis of these studies the differences between pinking and non-pinking explosions are pointed out.

The concept of temperature as applied to flames is discussed. A number of proposed methods for measuring the temperatures of flames are critically reviewed and the optical method of Kurlbaum-Fery is described and examined in detail. This method depends upon comparing the brightness temperature of a continuous radiator with the brightness of the radiation from the flame colored with an alkali-metal vapor at a given spectral line. From a consideration of the laws of radiation it is shown that the true flame temperature is equal to the brightness temperature of the comparison radiator, as read with an optical pyrometer, when the spectral line is just reversed as seen in a spectrometer.

Curves representing flame temperature as a function of air-gas ratio as measured by the line-reversal method are given for Pittsburgh natural gas, methane, propane, and carbon monoxide. These results are compared with measurements depending on the flame gases heating a solid radiator contained in the flame and with the calculated results for the maximum temperature attainable at complete combustion.

When energy is released by a local source such as an electric spark in a combustible gaseous mixture, it is assumed to heat instantaneously a small volume and also to create active particles, chain carriers, which diffuse through the gas and increase in number by chain-branching processes at a rate proportional to their concentration. The heat-producing reaction proceeds at a rate proportional to concentration of active particles. Taking as a criterion for ignition the requirement that the temperature at the point of ignition shall never decrease, the following condition for ignition is obtained: $A=\frac{4(T_1-T_0)k}{Q{n}_0{R}^2}$ must be less than or equal to a value depending on α, the relation being given in Fig. 1.

The significance and applicability of this result are discussed.

In the slow oxidation of propane at 270°–280°C it has been found that treating the Pyrex reaction bulb with potassium chloride greatly lengthens the induction period, thus indicating that the preliminary reaction occurs on the surface. Addition of small amounts of acetaldehyde shortens but does not eliminate the induction period, a fact which confirms previous conclusions that peracids (formed from aldehyde) are unimportant in the reaction scheme. Experiments after the potassium chloride treatment show that conditions favoring access to the walls diminish the rate of reaction markedly. This, together with the previously observed destructive action of the treated wall on peroxides, indicates that the latter play an essential role in the slow oxidation of the higher paraffins, whatever may be the case for methane and ethane.