Carbon Monoxide-air Mixtures Research Articles

Detonations in hydrocarbon fuel blends

A study of detonations in high-molecular weight hydrocarbon fuels of interest to pulse detonation engine applications was performed in a 280-mm diameter, 7.3-m long facility. Detonation pressure, wave speed, and cell width measurements were made in JP-10 mixtures and in mixtures representative of the decomposition products of JP-10. Experiments were performed in vapor-phase JP-10 mixtures at 353 K over a range of equivalence ratios (0.7 ≤ φ ≤ 1.4), nitrogen dilutions (fuel-oxygen to fuel-air), and initial pressures (20–130 kPa). The cell widths of the JP-10 mixtures are found to be similar to those of propane mixtures. A fuel blend representative of thermally decomposed JP-10 was studied at 295 K. This blend consisted of hydrogen, carbon monoxide, methane, acetylene, ethylene, and hexane with varying fractions of oxygen and nitrogen. The measured cell width of the fuel blend-air mixture is about half that of JP-10-air. The addition of components of the fuel blend (acetylene, ethylene, and methane) to JP-10 in air at 353 K was characterized. Nitrogen diluted mixtures of stoichiometric hexane-oxygen were studied and the cell widths for hexane-air and JP-10-air are found to be comparable. The addition of lower molecular weight fuels (hydrogen, acetylene, ethylene, and carbon monoxide) to hexane-air was investigated. The measured cell width decreases, indicating increased sensitivity to detonation, with increasing fraction of hydrogen, acetylene, and ethylene, in order of effectiveness. The addition of a small fraction of carbon monoxide produces a small decrease in the cell width, but addition of more than about 75% (by fuel mass) carbon monoxide results in a significant increase in cell width. Carbon monoxide is a principal intermediate product of hydrocarbon combustion yet there are relatively little cell width data available. Cell width measurements were made in carbon monoxide-air mixtures with the addition of hydrogen or hydrocarbons (acetylene, ethylene, and hexane). A linear relationship is found between the cell width and the reaction zone length when it is defined as the location of the peak in hydroxyl mole fraction.

The maximum experimental safe gap: The effects of oxygen enrichment and the influence of reaction kinetics

Measurements of the Maximum Experimental Safe Gaps (MESGs) for several flammable gases with oxygen-enriched air are reported. The MESGs for mixtures in air of carbon monoxide and methane and carbon monoxide and water have been measured also. The 20-cm 3 apparatus was used throughout. The results demonstrate that oxygen enrichment has a marked effect on the value of the MESG, which decreases as the oxygen enrichment increases. At high levels of oxygen enrichment very low values of MESG are obtained when the flow of the jet of hot gases through the safe gap becomes sonic. The addition of water to carbon monoxide-air mixtures decreases the MESG rapidly, and the addition of methane to carbon monoxide-air mixtures can give MESGs with values less than those of methane-air and carbon monoxide-air. These results demonstrate the influence of reaction kinetics on the MESG.

Prediction of burning velocities of saturated carbon monoxide-air flames by application of mixing rules

The burning velocities of carbon monoxide-air mixtures containing various amounts of water have been determined using a flat-flame burner with heat extraction. The addition of water is then treated as being equivalent to that of molecular hydrogen and oxygen in order to obtain a binary fuel mixture of hydrogen and carbon monoxide to which existing mixing rules are applied. This treatment shows that the burning velocities of carbon monoxide-air flames containing water can be predicted with less than eight percent of error when the Spalding mixing rule is used. Calculations have shown that the heat release rates, corresponding to a homogeneous reaction, are identical if the same amount of hydrogen or water is added to the mixture, thus confirming the equivalence of these two compounds.

The influence of small quantities of hydrogen and hydrogen compounds on the burning velocity of carbon monoxide-air flames

The dependence of the burning velocity of carbon monoxide-air mixtures on small admixed quantities of hydrogen, hydrogen compounds and deuterium has been measured. It was found with carbon monoxidehydrogen mixtures that the square of burning velocity equals the sum of the square of the burning velocity of pure carbon monoxide and a term proportional to the hydrogen content. With added hydrogen compounds or deuterium a similar relation is valid.

Stability and Burning Velocities of Laminar Carbon Monoxide-Air Flames at Pressures up to 93 Atmospheres

Bunsen-burner flames of carbon monoxide-air mixtures were investigated at ambient pressures up to 93 atmos. The experiments show that the critical velocity gradients at the burner tube wall for flash-back increase with pressure whereas the burning velocities decrease when the pressure is raised. However, in a previous investigation it was found that the burning velocities of hydrogen-oxygen flames increase with pressure. It is concluded that the burning velocities of carbon monoxide-air flames decrease with rising pressure because the rate of diffusion of active particles into the unburned gas is reduced with pressure while no increase in heat transfer occurs. In hydrogen-oxygen flames the rate of heat transfer increases because the flame temperatures are higher at elevated pressures because of the reduction in the degree of dissociation.

Gaseous Combustion at High Pressure

AT the meeting of the Royal Society on November 10 when the Duke of York was admitted to the fellowship of the Society, Prof. W. A. Bone gave an account of Parts 14, 15 and 16 of his researches on gaseous combustion at high pressure. These record an exploration of the phenomena of explosion of hydrogen-air and carbon monoxide—air mixtures into regions of pressure much higher than those hitherto examined and the apparatus specially designed for the purpose was described. Hydrogen—air mixtures explode quite normally with initial pressures up to 500 atmospheres but at 750 atmospheres detonation occurs with violence sufficient to damage the apparatus. Carbon monoxide—air mixtures have been successfully exploded at initial pressures up to 1,000 atmospheres. As previously observed, the nitrogen is activated, absorbing during the early stages energy which is released during the later stages so as to retard the cooling of the products. This activated nitrogen reacts with excess oxygen, if present at the high temperature of explosion, giving oxides of nitrogen, the formation of which is favoured by increase of pressure. Nitric oxide dissociates readily during the process of cooling, so experiments were made in which the cooling is accelerated by causing the gas to expand suddenly at a predetermined instant after firing. Exploding mixtures of (2CO + 3O2 + 2N2) at an initial pressure of 70 atmospheres, the yield of nitric oxide is 5.4 per cent, and results at 88 atmospheres indicate a prdbable maximum of about six per cent. Such yields exceed those previously recorded but are probably insufficient to serve as a basis for the commercial fixation of nitrogen by explosive combustion. Experiments were shown to demonstrate how a rise of pressure increases the luminosity of carbon monoxide—air flames and leads to the formation of oxides of nitrogen.

Gaseous combustion at high pressures.—Part V. The explosion of hydrogen-air and carbon monoxide-air mixtures at varying initial pressures up to 175 atmospheres

Since publishing the last paper of this series, in which were recorded the results of our experiments upon the behaviour of hydrogen-air and carbon monoxide-air mixtures when exploded in our bomb apparatus at varying initial pressures between 3 and 75 atmospheres, we have been enabled, thanks to further substantial aid from the Society’s Government Grant Committee, to instal in the Fuel Research Laboratories of the Imperial College of Science and Technology, South Kensington, a new chrome-nickel steel bomb (No. 3), of similar design to the one (No. 2) previously employed by us, but capable of withstanding explosion pressures up to 2,000 atmospheres. This has enabled us to extend the research to still higher pressures than would have been safe with the old bomb, and the present paper embodies the results of our further experiments with the mixtures in question at varying initial pressures between 75 and 175 atmospheres. A review of these results, in conjunction with those already published in our previous paper ( q. v .), besides providing further strong evidence in support of our view of the activation of nitrogen in the explosion of carbon-monoxide—oxygen—nitrogen mixtures at high pressures, a subject which we have already fully dealt with, throws further light upon other important aspects of gaseous explosions which have always been keenly discussed by chemists and engineers.

Societies and Academies

Societies and Academies

Gaseous combustion at high pressures. Part II. — The explosion of hydrogen-air and carbon monoxide-air mixtures

In a previous paper upon the subject, the question was propounded whether or no there is any direct relation between the actual rate at which the potential energy of an explosive mixture is transferred on explosion as sensible heat to its products and the magnitude of the chemical affinity between its combining constituents. As the result of an experimental enquiry into the matter, it was proved:– ( a ) that, whereas the affinity for oxygen of methane is at least twenty to thirty times greater than that of hydrogen, the time required for the attainment of maximum pressure in the case of the primary methane-air mixture (CH 4 + O 2 + 4N 2 ) is at least some five to eight times as long as that required in the case of the primary hydrogen-air mixture (2H 2 + O 2 + 4N 2 );